Understanding near infrared spectroscopy and its application to skeletal muscle research

Integrative Field-Based Health and Performance Research: A Narrative Review on Experimental Methods and Logistics to Conduct Competition and Training Camp Studies in Athletes

Field-based sport research involves studies that collect data from athletes and/or teams during competition and/or their daily training environments. Over the last decade, sport-specific field-based research projects have significantly increased in number and complexity, partially owing to the further development of more portable measurement equipment (e.g., indirect calorimetry, desktop blood/gas analyzers, portable laboratories, etc.) and/or wearable or consumable technologies (e.g., smart watches, sensors, core temp pills, etc.). However, given these rapid advances and novelty, challenges remain in the validity and applicability of these devices. Unfortunately, there are no global ethical or best-practice standards for the use of portable devices and/or wearables in sport; however, this review will outline various opportunities and challenges. Many decision trade-offs are required when designing field-based research studies to balance gold-standard scientific rigor and strict research control with highly applied, but less-controlled, "real-world" conditions. To our knowledge, there are no narrative reviews that take a wholistic view of the logistical and methodological considerations of field-based research in athletes. Accordingly, this review takes a multi-disciplinary methodological approach (physiological, nutritional/energetic, biomechanical, musculoskeletal, cognitive, and psychosocial factors), along with the logistical considerations involved in project planning, research design, and ethics of field-based research with elite athletes and/or teams. We also provide practical guidance for characterizing the extreme demands of elite training and competition to support research that ultimately catalyzes improved understanding of the limits of human capacity. We hope this review can serve as a practical guide for researchers undertaking elite athlete field-based research.

The Use of Near-Infrared Spectroscopy for the Measurement of Abdominal Wall Tissue Oxygenation During Pneumoperitoneum in Laparoscopic Cholecystectomy

Background: Near-infrared spectroscopy (NIRS) has been developed to monitor cerebral oxygenation. Various studies have investigated its utility in measuring somatic tissue oxygenation and in noncardiac surgeries. Aims: The aim of this study was to determine the effect of pneumoperitoneum on the abdominal wall. Study Design: A prospective, case-control study. Methods: This study included 70 patients who had elective laparoscopic cholecystectomy. A regional oximetry sensor was placed on the anterior abdominal wall in all patients. Primary outcome measures included preoperative regional tissue saturation (rSO2) values. For secondary outcome measures, we recorded visual analogue scale (VAS) scores and tramadol usage at postoperative hours 2, 6, 12, and 24: intraoperative end-tidal CO2 values; peripheral oxygen saturation (spo2); and abdominal subcutaneous fat tissue thickness. Results: The initial rSO2 value (T1: 75.6 ± 6.64) was significantly higher than those measured at the predetermined time intervals during pneumoperitoneum (T4: 73.4 ± 6.3, T5: 68 ± 8.9, T6: 68 ± 8.9, T7: 66.6 ± 9.4, T8: 65.81 ± 10.2, T9: 65.6 ± 8.8) (P < .05). The mean change in rSO2 between preoperative measurements (T1) and mid-pneumoperitoneum measurements (T8) was -12.9 ± 11%. This change was found to be negatively correlated with postoperative VAS scores and 24-hour tramadol consumption amounts. Conclusion: The results of the present study show that changes in abdominal wall tissue oxygenation during pneumoperitoneum can be measured with NIRS.

Oxidative and O2 diffusive function in triceps brachii of recreational to world class swimmers

This study aimed to evaluate in vivo oxidative capacity and relative resistance to O2 diffusion using near-infrared spectroscopy (NIRS) in the m. triceps brachii of recreational to world class swimmers and evaluate their relationships with swimming performance. Twenty-eight swimmers were enrolled and assigned into three subgroups according to their level: 'recreational/trained' (Tier 1/2; n = 8), 'national' (Tier 3; n = 12) and 'international/world class' (Tier 4/5; n = 8). Performance was evaluated by 100 m freestyle trials. Training volume was measured by self-reported distance (km/week). Them V ̇ O 2 ${\mathrm{m}}{{\dot{V}}_{{{{\mathrm{O}}}_{\mathrm{2}}}}}$ recovery k of m. triceps brachii was non-invasively estimated by NIRS through repeated intermittent occlusions under two conditions: well-oxygenated (kHIGH) and low O2 availability (kLOW). The difference between kHIGH and kLOW (Δk) was calculated as an index of relative resistance to O2 diffusion. FINA points and 100 m performance differed among all groups. Training volume was greater in Tier 4/5 (34.0 ± 5.5 km week-1) and Tier 3 (35.5 ± 11.6 km week-1) than in Tier 1/2 (6.4 ± 1.8 km week-1). kHIGH was greater in Tier 4/5 and Tier 3 (3.18 ± 0.41 and 2.79 ± 0.40 min-1) versus Tier 1/2 (2.10 ± 0.36 min-1; all P < 0.002). kHIGH correlated with FINA points, 100 m performance and training volume. ∆k was not different among tiers and was not associated with training volume or performance. M. triceps brachii oxidative capacity (kHIGH) was positively associated with performance and training volume in swimmers. ∆k, which reflects relative resistance to O2 diffusion, was not different among athletes. These data suggest that m. triceps brachii oxidative capacity is associated with swimming performance and that muscle O2 diffusing capacity exerts a similar relative resistance to O2 diffusive flow across swimmers.

Skeletal Muscle Resaturation Relates to Aerobic Fitness in Adults Participating in Strength and Aerobic Exercises

Purpose: This study examined differences in metrics of skeletal muscle re-saturation between strength and aerobically oriented individuals and potential relations between re-saturation and aerobic fitness. Methods: Forty-nine healthy young adult men and women completed body composition analysis, a maximal lower-body strength assessment, a maximal aerobic fitness (V . O 2 max ) test, and a near-infrared spectroscopy vascular occlusion test (NIRS+VOT). Skeletal muscle tissue oxygenation (StO2), oxygenated hemoglobin (O2Hb), and deoxygenated (HHb) hemoglobin were collected from a NIRS device attached to the vastus lateralis. Re-saturation measures (e.g. upslope, re-saturation max, and hypersaturation area under the curve (AUC)) were derived from the reperfusion phase of the NIRS+VOT. Results: All O2Hb and StO2 re-saturation metrics, particularly upslope (r = 0.622 and r = -.613, respectively), were significantly (p < .05) related to V . O 2 max . In the strength group, O2Hb and HHb upslope (r = 0.584; p < .001; r = -.550; p = .001, respectively) and re-saturation max (r = 0.372; p = .036; r = .562, p < .001, respectively) were significantly related to V . O 2 max . For the aerobic group, O2Hb upslope (r = .486; p = .048), re-saturation max (r = 0.535; p = .027), and hypersaturation AUC (r = 0.564; p = .018) were significantly related to V . O 2 max . The aerobic group had significantly (p = .011; BF10 = 8.043) greater O2Hb upslope (1.6 ± .789 vs. 1.1 ± .474 A.U.s-1) and (p = .027; BF10 = 2.929) hypersaturation AUC (1158.3 ± 545.02 vs. 860.4 ± 365.35 A.U.s-1) than the strength group. Conclusion: Upslope was the most related to V . O 2 max in strength and aerobically oriented adults. Interestingly, O2Hb re-saturation max may not be sensitive to differences between routine strength and aerobic exercise and may reflect shared underlying physiological mechanisms of the predominant fitness orientation.

The influence of cuff location on the oxygenation and reperfusion of the foot during ischemic preconditioning: A reliability study

Ischemic preconditioning (IPC) involves the application of occlusion cycles, typically prior to exercise. IPC is commonly applied at the arm or thigh for improving exercise performance, which can be combined with near-infrared spectroscopy (NIRS) to assess the microcirculation and tissue oxygenation. Despite the use of NIRS during IPC, few studies have investigated the reliability of NIRS during lower limb IPC with no relevant publications investigating IPC at the ankle. Therefore, the purpose of this study was to investigate the intra-session reliability in the NIRS measurements during repeated IPC at the thigh, ankle and arm. Eighteen participants volunteered. IPC was applied at the thigh (220 mmHg), ankle (individualized arterial occlusion pressure: 212 ± 24 mmHg) and arm (220 mmHg) in a randomized order involving 3 repeated cycles of 5-min occlusion and reperfusion, within a session. NIRS recorded tissue oxygen saturation (SO2), oxygenated (O2Hb) and deoxygenated hemoglobin (HHb) at the abductor hallucis muscle. Reliability was assessed using intraclass correlation coefficients. For all NIRS measurements assessed, there was excellent reliability (All ICC > 0.94) for the average, minimum and maximum values. The results indicate that IPC can successfully be applied at the ankle, offering reliable measures between three repeated occlusions within a session.

The impact of skinfold thickness and exercise intensity on the reliability of NIRS in the vastus lateralis

PURPOSE

The aims of this study were (1) to assess the test-retest reliability of the primary near infrared spectroscopy (NIRS) variables (i.e., StO2, T[Hb], [HbO2] and [HHb]) during cycling and (2) to investigate potential influences of exercise intensity and adipose tissue thickness (ATT) on this reliability.

METHODS

21 men and 20 women completed twelve constant work rate tests (6 min) at six different exercise intensities with each intensity performed twice. NIRS variables were measured at the vastus lateralis. The coefficient of variance (CV%), the intraclass correlation coefficient (ICC), mean bias and limits of agreement (LoA) were determined for reliability purposes.

RESULTS

The reliability of baseline values were acceptable to very good (CV% range: 5.83 - 21.96%). The reliability of end-values (CV% range: 0.02 - 25.02%, ICC range: 0.0 - 0.935) and amplitudes (CV% range: 0.46 - 5099%, ICC range: 0.0 - 0.887) were more variable. In general, the mean biases of end-values and amplitudes showed wide limits of agreement. A homogeneous influence of exercise intensity on reliability could not be established but reliability measures appeared to be lower in people with a lower skinfold thickness. Moreover, the NIRS signals decreased with increasing ATT but stabilized upon reaching a cut-off of 8 mm ATT. In addition, ATT did have a significant influence on [HHb] amplitude. In participants with ATT < 8 mm, higher amplitudes were observed with increasing intensity whereas in participants with ATT > 8 mm, there were no differences between the intensities.

CONCLUSION

The study reveals variable results with regards to reliability and there was no consistent influence of exercise intensity on reliability. Participants with a lower skinfold thickness showed stronger reliability. Moreover, NIRS signals decrease when ATT exceeds 8 mm. Careful consideration is necessary when interpreting NIRS signals in such cases.

Time-continuous analysis of muscle and cerebral oxygenation during repeated treadmill sprints under heat stress: a statistical parametric mapping study

PURPOSE

We examined how heat exposure affects muscle and cerebral oxygenation kinetics using statistical parametric mapping (SPM) during repeated treadmill sprints.

METHODS

Eleven recreationally active males performed three sets of five 5-s sprints with 25 s of recovery and 3 min between sets in hot (38 °C) and temperate (25 °C) conditions. Continuous measurements of muscle (vastus lateralis) and cerebral (prefrontal cortex) tissue oxygenation were obtained using near-infrared spectroscopy. One-way ANOVA SPM{F} statistics were applied to pooled sprint data, with each condition including 15 time-series (three sets of five sprints) combined. Each time-series included the sprint and subsequent recovery phases.

RESULTS

Muscle tissue saturation index further decreased in hot compared to temperate condition, from the middle of the 5-s sprint phase (~ 2.9 s) until the end of the recovery period (p < 0.001), while total hemoglobin concentration was significantly higher in the early phase of recovery (from 5.1 to 11.8 s, p = 0.003). Cerebral tissue saturation index decreased from 0.7 s to 13.0 s (p < 0.001) in the heat. Total hemoglobin concentration was lower in hot condition during both the sprint phase and the initial third of the recovery (from 0 to 11.7 s, p < 0.001), as well as during the recovery (from 20.5 to 24.8 s, p = 0.007).

CONCLUSION

Adding heat stress to repeating treadmill sprints further lowered muscle oxygenation levels during both the sprint and recovery phases, and limited cerebral tissue perfusion during the sprint and the initial recovery phases. The use of SPM for continuous analysis of near-infrared spectroscopy data provides new insights beyond summary statistics.

Boys vs men differences in muscular fatigue, muscle and cerebral oxygenation during maximal effort isometric contractions: the effect of muscle blood flow restriction

PURPOSE

To examine whether the children's superiority, over adults, to resist fatigue during repeated maximal-efforts depends on their often-cited oxidative advantage, attributed to greater muscle blood flow and O2-delivery. We also investigated the mechanisms underlying child-adult differences in muscle-oxygenation (due to O2-supply or O2-utilization) and examined if there are age-differences in cerebral-oxygenation response (a brain-activation index).

METHODS

Eleven men (23.3 ± 1.8yrs) and eleven boys (11.6 ± 1.1 yrs) performed 15 maximal-effort handgrips (3-s contraction/3-s rest) under two conditions: free-flow circulation (FF) and arterial-occlusion (OCC). Force, muscle-oxygenation (TSImuscle) and cerebral-oxygenation (oxyhemoglobin-O2Hbcerebral; total hemoglobin-tHbcerebral; deoxyhemoglobin-HHbcerebral) were assessed.

RESULTS

In boys, force declined less (- 26.3 ± 2.6 vs. - 34.4 ± 2.4%) and at slower rate (- 1.56 ± 0.16 vs. - 2.24 ± 0.17%·rep-1) vs. men in FF (p < 0.01-0.05; d = 0.60-1.24). However, in OCC there were no age-differences in the magnitude (- 38.3 ± 3.0 vs. - 37.8 ± 3.0%) and rate (- 2.44 ± 0.26 vs. - 2.54 ± 0.26%·rep-1) of force decline. Boys compared to men, exhibited less TSImuscle decline in both protocols, and lower muscle VO2 (p < 0.05). Boys, also, presented a smaller O2Hbcerebral and tHbcerebral rise than men in FF; exercising with OCC increased the O2Hbcerebral and tHbcerebral response in boys. Using MVIC as a covariate in FF condition, abolished boys-men differences in force and TSImuscle decline and O2Hbcerebral rise.

CONCLUSION

During repeated maximal-efforts: (i) blood flow is a significant contributor to children's superiority over adults to resist fatigue; (ii) age-difference in muscle hypoxia/deoxygenation is rather attributed to men's greater metabolic demand than to lower muscle-perfusion; and (iii) cerebral oxygenation/blood volume increase more in men than boys under free circulation, implying greater brain activation.

Effects of acute selective cyclooxygenase-2 inhibition on skeletal muscle microvascular oxygenation and exercise tolerance

The cyclooxygenase (COX) pathway regulates vascular tone and, therefore, local O2 delivery-utilization matching. The two main isoforms, COX-1 and COX-2, may promote opposing effects on contracting muscle O2 transport in health by inducing vasoconstriction and vasodilatation, respectively. Whether COX-2 and its main vasodilatory product (prostacyclin, PGI2) modulate microvascular O2 transport to skeletal muscle and thus exercise tolerance is unknown. We tested the hypothesis that acute selective COX-2 inhibition (SC2I) would impair cardiorespiratory and skeletal muscle microvascular responses from rest to exercise, thereby reducing exercise tolerance in healthy adults. Twelve individuals participated in a randomized, double-blind, crossover study to receive SC2I (200 mg celecoxib) or placebo (control, CON). Moderate and severe intensity cycling were performed with measurements of heart rate, arterial blood pressure, pulmonary oxygen uptake (V ̇ O 2 ${\dot V_{{{\mathrm{O}}_2}}}$ ), leg muscle microvascular oxygenation (S t O 2 ${S_{{\mathrm{t}}{{\mathrm{O}}_2}}}$ ; near-infrared spectroscopy) and time to exhaustion. Leg muscleS t O 2 ${S_{{\mathrm{t}}{{\mathrm{O}}_2}}}$ was also assessed during cuff occlusion protocols. SC2I decreased the plasma concentration of the stable PGI2 metabolite 6-keto prostaglandin F1α (CON: 203 (54) pg/mL; SC2I: 108 (54) pg/mL; P = 0.002). There was no difference in exercise tolerance (CON: 278 (55) s; SC2I: 298 (75) s), arterial blood pressure, heart rate, pulmonaryV ̇ O 2 ${\dot V_{{{\mathrm{O}}_2}}}$ or leg muscleS t O 2 ${S_{{\mathrm{t}}{{\mathrm{O}}_2}}}$ from rest to moderate or severe exercise between conditions (P > 0.05 for all). Moreover, there was no significant difference inS t O 2 ${S_{{\mathrm{t}}{{\mathrm{O}}_2}}}$ during cuff occlusion protocols between conditions. Contrary to our hypothesis, these data indicate that COX-2 is not obligatory for the regulation of skeletal muscle microvascular oxygenation at rest or during moderate or severe intensity exercise, and therefore does not modulate exercise tolerance in healthy adults.

Effect of Inspiratory Muscle-Loaded Exercise Training on Ventilatory Response and Intercostal Muscle Deoxygenation During Incremental Cycling Exercise

Purpose: This study evaluated the effects of exercise training (ET) and inspiratory muscle-loaded exercise training (IMLET) on ventilatory response and intercostal muscle deoxygenation levels during incremental cycling exercise. Methods: Twenty-one male participants were randomly divided into IMLET (n = 10) or ET (n = 11) groups. All participants underwent a 4-week cycling exercise training at 60% peak oxygen uptake. IMLET loaded 50% of maximal inspiratory pressure (PImax). Respiratory muscle strength test, respiratory muscle endurance test (RMET), resting hypoxic ventilatory responsiveness (HVR) test, and incremental cycling test were performed pre- and post-training. Results: The extent of improvement in the PImax was significantly greater in the IMLET group (24%) than in the ET group (8%) (p = .018), and an extended RMET time was observed in the IMLET group (p < .001). Minute ventilation (V ˙ E ) during exercise was unchanged in both groups before and after training, but tidal volume during exercise increased in the IMLET group. The increase in the exercise intensity threshold for muscle deoxygenation was similar in both groups (p < .001). HVR remained unchanged in both groups post-training. The exercise duration for the incremental exercise until reaching fatigue increased by 7.9% after ET and 6.9% after IMLET (p < .001). Conclusion: The 4-week IMLET improved respiratory muscle strength and endurance but did not alter HVR. Respiratory muscle deoxygenation was alleviated by exercise training, with a limited impact of inspiratory load training.

Combined effect of sprint interval training and post-exercise blood flow restriction on muscle deoxygenation responses during ramp incremental cycling

PURPOSE

This study investigated the effect of sprint-interval training combined with post-exercise blood flow restriction (i.e., SIT + BFR) on pulmonary gas exchange and microvascular deoxygenation responses during ramp incremental (RI) cycling.

METHODS

Nineteen healthy, untrained males (mean ± SD age: 24 ± 5 years; height: 178 ± 6 cm; body mass: 77.0 ± 10.7 kg) were assigned to receive 4 weeks of SIT or SIT + BFR. Before and after the intervention period, each participant completed a RI cycling test for determination of peak oxygen uptake (V ˙ O 2peak ) and the gas exchange threshold (GET) with deoxygenated heme (Δdeoxy[heme]) and tissue oxygenation index (TOI) measured by near-infrared spectroscopy (NIRS) in vastus lateralis (VL) muscle.

RESULTS

RelativeV ˙ O 2peak increased by 7% following both interventions (P ≤ 0.03). SIT + BFR increased peak Δdeoxy[heme] when normalized relative to leg arterial occlusion (PRE: 57.3 ± 13.0 vs. POST: 62.0 ± 13.2%; P = 0.009) whereas there was no significant difference following SIT (PRE: 64.9 ± 14.3 vs. POST: 71.4 ± 11.7%; P = 0.17). Likewise, TOI nadir decreased at exhaustion following SIT + BFR (PRE: 56.9 ± 9.1 vs. POST: 51.4 ± 9.2%; P = 0.002) but not after SIT (PRE: 58.5 ± 7.1 vs. POST: 56.3 ± 8.2%; P = 0.29). The absolute cycling power at the GET increased following SIT + BFR (PRE: 108 ± 13 vs. POST: 125 ± 17 W, P = 0.001) but was not significantly different following SIT (PRE: 112 ± 7 VS. POST: 116 ± 11 W, P = 0.54).

CONCLUSION

The addition of post-exercise BFR to SIT alters the mechanism underlying the enhancement inV ˙ O 2peak by increasing the peak rate of muscle fractional O2 extraction in previously untrained males.

Monitoring skeletal muscle oxygen saturation kinetics during graded exercise testing in NCAA division I female rowers

Purpose

The purpose of this study was to analyze changes in skeletal muscle oxygen saturation (SmO2) kinetics during exercise in female rowers both acutely and longitudinally in relation to blood lactate (BLa). We also aimed to determine the agreement and statistical equivalence between physiological thresholds derived from SmO2 and BLa kinetics.

Methods

Twenty-three female NCAA Division I rowers were tested throughout the 2023-2024 academic year. Of these, 11 athletes completed at least two near-infrared spectroscopy (NIRS)-equipped GXTs, with physiological data analyzed for longitudinal changes. A 7x4-min discontinuous GXT protocol was performed by all athletes. First and second SmO2 breakpoints (SmO2BP1 and SmO2BP2) were estimated via piecewise linear regression modeling, and BLa thresholds (LT1 and LT2) were calculated using ADAPT software. Paired-samples t-tests assessed differences, and equivalence was tested using two one-sided tests (TOST). Agreement was determined using Bland-Altman analysis yielding mean differences (MD) and 95% limits of agreement (LoA). Intraclass correlation coefficients (ICC2,1) were also calculated.

Results

No difference was found between SmO2BP2 and LT2 (MD = -5.76W [95% LoA = -38.52 to 22.25W], p = 0.134), moderate-to-good levels of agreement (ICC2,1 = 0.67 [95% CI: 0.36-0.85], p < 0.001), and no statistical equivalence (p = 0.117). This was not the case for SmO2BP1 and LT1, with NIRS significantly underestimating LT1 (MD = -8.14W [95% LoA = -38.90 to 27.37W], p = 0.026), poor-to-moderate agreement (ICC2,1 = 0.24 [95% CI: -0.13-0.58], p = 0.10), and no statistical equivalence (p = 0.487). Additionally, SmO2 recovery kinetics (SmO2resat) during 1-min rest intervals increased in response to graded increases in exercise intensity (p < 0.001, η2 p = 0.71), with higher intensities appearing to blunt this effect (step 6 - step 7: MD = -0.16%⋅s-1, p = 0.69). No statistically significant changes were observed in LT's or SmO2BP's throughout the 2023-2024 season.

Conclusion

In female collegiate rowers, NIRS may be a tool that compliments BLa testing when determining the second lactate threshold (i.e., LT2). However, significant inter-individual variablility exists between SmO2BP2 and LT2 paired with a lack of statistical equivalence suggest the two are not interchangeable. While not a standalone replacement, if used in combination with traditional BLa testing methods NIRS may be a complimentary tool that helps inform individual athlete training zone prescription.

Sex-Based Effects on Muscle Oxygenation During Repeated Maximal Intermittent Handgrip Exercise

BACKGROUND

This investigation aimed to examine sex-based differences in deoxy[heme] (HHb), tissue saturation (StO2), and force-deoxygenation ratio (FD) of the forearm flexor muscles during a maximal-effort intermittent fatiguing handgrip protocol.

METHODS

Thirty-three healthy males (n = 15) and females (n = 18) completed a fatiguing handgrip protocol consisting of 60 4 s contractions separated by a 1 s rest. Near-infrared spectroscopy was used to measure muscle oxygenation before, during, and after the protocol.

RESULTS

Sex differences in HHb (p = 0.033) and StO2 (p = 0.021) were observed with significantly greater values for females (HHb: 110.204 ± 12.626% of baseline; StO2: 72.091 ± 5.812%) in comparison to males (HHb: 101.153 ± 12.847% of baseline; StO2: 66.978 ± 7.799%). Females (0.199 ± 0.081 AU) also demonstrated significantly (p = 0.001) lower FD in comparison to males (0.216 ± 0.094 AU). However, males (b = -0.023 ± 0.008 AU) demonstrated a significantly (p < 0.001) greater rate of decline in FD in comparison to females (b = -0.017 ± 0.006 AU).

CONCLUSIONS

Prior to, during, and after a maximal-effort intermittent fatiguing handgrip fatiguing protocol, males demonstrate significantly lower StO2 than females and a faster rate of decline in FD. Moreover, females demonstrate greater HHb values than males when assessed relative to a resting baseline.

Muscle microvascular oxygen delivery limitations during the contraction phase of intermittent maximal effort contractions

PURPOSE

The end-test torque (ETT) during intermittent maximal effort contractions reflects the highest contraction intensity at which a muscle metabolic steady-state can be attained. This study determined if ETT is the highest intensity at which the contraction phase of intermittent exercise does not limit the matching of microvascular oxygen delivery to muscle oxygen demand.

METHODS

Microvascular oxygenation characteristics of the biceps brachii muscle were measured in sixteen young, healthy individuals (8M/8F, 22 ± 3 years, 80.9 ± 20.3 kg) by near-infrared spectroscopy during maximal effort elbow flexion under control conditions (CON) and with complete circulatory occlusion (OCC).

RESULTS

Increases in total-[heme] were blunted during OCC compared to CON (225 ± 87 vs. 264 ± 88 μM, p < 0.001) but OCC did not elicit a compensatory increase in deoxygenated-[heme] at any timepoint (108 ± 62 vs. 101 ± 61 μM, p > 0.05). Deoxygenated-[heme] was significantly elevated during contraction, relative to relaxation, above ETT (107 ± 60 vs. 98.8 ± 60.5 μM, p < 0.001), but not at ETT (91.7 ± 54.1 vs. 98.4 ± 62.2 μM, p = 0.174). Total-[heme] was significantly reduced during contraction, relative to relaxation, at all contraction intensities during CON (p < 0.05) and OCC (p < 0.05).

CONCLUSION

These data suggest that ETT may reflect the highest contraction intensity at which contraction-induced increases in intramuscular pressures do not limit muscle perfusion to a degree that requires further increases in fractional oxygen extraction (i.e., deoxygenated-[heme]) despite limited microvascular diffusive conductance (i.e., total-[heme]).

Sex differences in the maximal metabolic steady state of fitness-matched women and men

We tested the hypothesis that power at maximal metabolic steady state is similar between fitness-matched men and women. Eighteen participants (9 men and 9 women) performed a cycling graded exercise test for maximal oxygen consumption (V̇o2max). Men and women were matched for V̇o2max normalized to fat-free mass (FFM), which was 50.4 ± 4.7 mL·min-1·kg·FFM-1 and 52.1 ± 8.2 mL·min-1·kg·FFM-1, respectively (P = 0.62). Participants completed a muscle oxygenation (%SmO2) zero-slope prediction trial and a 3-min all-out trial (3MT). The %SmO2 zero-slope trials included three, 5-min cycling bouts (30-s rest) spanning intensity domains. Linear regression of trial work rate and %SmO2 slope over the final 3 min established the work rate occurring at the predicted zero slope in %SmO2. The 3MT required cycling all-out until the word "stop" without providing time elapsed. End test power (ETP) was calculated as the mean power output over the last 30 s and work above end test power (WEP) as the power-time integral above ETP. Independent of method, means ± SD absolute power at the maximal metabolic steady state was similar between fitness-matched women and men (P = 0.72), yet became higher in women when expressed relative to FFM (P = 0.02). Furthermore, V̇o2 at the power associated with %SmO2 zero-slope represented a significantly higher fraction of V̇o2max for women compared with men (P = 0.03). Normalized WEP (W/kg·FFM) remained higher in men (P < 0.01). Although highly correlated (r = 0.88, P < 0.01), ETP was ∼8% higher than %SmO2 zero-slope power (P = 0.03). Compared with fitness-matched men, women displayed higher FFM normalized power associated with the heavy-severe exercise domain boundary. When matched for fitness, women have a higher power associated with the heavy-severe domain boundary compared with men, when expressed relative to FFM. This exercise intensity also represents a higher fraction of maximal oxygen uptake for women; suggesting women can sustain a higher relative V̇o2 compared with men. Power at the heavy-severe domain boundary, in both sexes, was lower using muscle oxygenation-derived slope methods compared with 3-min all-out determinations.NEW & NOTEWORTHY When matched for fitness, women have a higher power associated with the heavy-severe domain boundary compared with men, when expressed relative to FFM. This exercise intensity also represents a higher fraction of maximal oxygen uptake for women; suggesting women can sustain a higher relative V̇o2 compared with men. Power at the heavy-severe domain boundary, in both sexes, was lower using muscle oxygenation derived slope methods compared with 3-min all-out determinations.

Challenging the skin pigmentation bias in tissue oximetry via time-domain near-infrared spectroscopy

Recently, skin pigmentation has been shown to affect the performance of pulse oximeters and other light-based techniques like photo-acoustic imaging, tissue oximetry, and continuous wave near-infrared spectroscopy. Evaluating the robustness to changes in skin pigmentation is therefore essential for the proper use of optical technologies in the clinical scenario. We conducted systematic time-domain near-infrared spectroscopy measurements on calibrated tissue phantoms and in vivo on volunteers during static and dynamic (i.e., arterial occlusion) measurements. To simulate varying melanosome volume fractions in the skin, we inserted, between the target sample and the measurement probe, thin tissue phantoms made of silicone and nigrosine (skin phantoms). Additionally, we conducted an extensive measurement campaign on a large cohort of pediatric subjects, covering the full spectrum of skin pigmentation. Our findings consistently demonstrate that skin pigmentation has a negligible effect on time-domain near-infrared spectroscopy results, underscoring the reliability and potential of this emerging technology in diverse clinical settings.

Physiological and perceptual response to critical power anchored HIIT: a sex comparison study

PURPOSE

The aim of this study was to test the hypothesis that using threshold-based high intensity interval training (HIITTHR) prescribed at an intensity above critical power (CP) in males and females matched for maximal oxygen uptake ( V ˙ O2max) (mL/kg lean mass/min) will yield no sex differences in time to fatigue.

METHODS

Thirteen males (mean ± SD: 22.0 ± 2.48 years, 181 ± 8.36 cm, 78.8 ± 11.4 kg) and eleven females (mean ± SD: 22.4 ± 2.69 years, 170 ± 5.73 cm, 65.2 ± 7.66 kg) initially undertook an incremental test to exhaustion to determine V ˙ O2max, and a CP test. Then, one HIIT session (4 min on, 2 min off) was performed to exhaustion at the work rate associated with 105%CP. Acute physiological and cardiovascular responses were recorded.

RESULTS

No sex differences were recorded in time to fatigue [Female vs. Male (min): 36.0 ± 18.5 vs. 39.3 ± 16.3], heart rate, rate of perceived exertion, or %oxygenated [haem]. Females displayed lower %deoxygenated [haem] at the end of interval 1, 2, 3, and 4 [Female vs. Male (%): 89.4 ± 21.2 vs. 110 ± 27.3, 92.0 ± 21.5 vs. 115 ± 27.6, 87.1 ± 23.7 vs. 112 ± 22.8, 88.9 ± 26.3 vs. 113 ± 23.5]. Large interindividual variability in performance, and physiological and perceptual response were present despite the use of threshold-based prescription.

CONCLUSION

The present study suggests that threshold-based prescription may help standardize the mean response exercise across sexes but does not eliminate physiological or perceptual variability. Furthermore, the lack of sex differences in TTF was accompanied by greater %deoxy[haem] in males, indicating tissue oxygenation is an unlikely determinant of HIIT performance. This study has been retrospectively registered at Trial Registration https://doi.org/10.17605/OSF.IO/KZVGC January 17th, 2023, following data collection but prior to data analyses.

A Muscle Physiology-Based Framework for Quantifying Training Load in Resistance Exercises

BACKGROUND

Objective training load (TL) indexes used in resistance training lack physiological significance. This study was aimed to provide a muscle physiology-based approach for quantifying TL in resistance exercises (REs).

METHODS

Following individual torque-velocity profiling, fifteen participants (11 healthy males, stature: 178.36 ± 3.95 cm, and body mass (BM): 77.48 ± 7.74 kg; 4 healthy females, stature: 169.25 ± 5.03 cm, and body mass: 60.62 ± 3.91 kg) performed isokinetic leg extension exercise sessions at low, moderate, and high intensities (LI, MI, and HI, respectively). Systemic and local physiological responses were measured, and sessions were volume-equated according to the "volume-load" (VL) method.

RESULTS

Significant differences were found between sessions in terms of mechanical work (p<0.05 and p<0.001, for LI-MI and MI-HI, respectively), averaged normalised torque (p<0.001), mechanical impulse (p<0.001), and rate of force development (RFD, p<0.001 for LI-MI). RFD was mainly impacted by the accumulation of repetitions. Muscle function impairments mainly occurred at low intensities-long series, and high intensities, supported by greater RFD rate decay and changes in electromyographic activity. Therefore, accounting for muscle fatigue kinetics within objective TL indexes and using dimension reduction methods better described physiological responses to RE.

CONCLUSIONS

A generic equation of muscle fatigue rise could add value to TL quantification in RE. Considering other training-related information and TL indexes stands essential, applicable to field situations and supports the multidimensional facet of physiological responses to RE.

Insights Into Retinal Pathologies in Neurological Disorders: A Focus on Parkinson's Disease, Multiple Sclerosis, Amyotrophic Lateral Sclerosis, and Alzheimer's Disease

Neurological diseases are central nervous system (CNS) disorders affecting the whole body. Early diagnosis of the diseases is difficult due to the lack of disease-specific tests. Adding new biomarkers external to the CNS facilitates the diagnosis of neurological diseases. In this respect, the retina has a common embryologic origin with the CNS. Retinal imaging technologies including optical coherence tomography (OCT) can be used in the understanding and processual monitoring of neurological diseases. Retinal imaging has been recently recognized as a potential source of biomarkers for neurological diseases, increasing the number of studies in this direction. In this review, the association of retinal abnormalities with Parkinson's disease (PD), multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), and Alzheimer's disease (AD) is explained. Structural and functional abnormalities in retina as a predictive marker may facilitate early diagnosis of diseases. Although not all retinal abnormalities are predictive of neurologic diseases, changes in the retinal layers including retinal pigment epithelium and plexiform layers should suggest the risk of PD, MS, ALS, and AD.

The effects of sex and contraction intensity on fatigability and muscle oxygenation in trained individuals

Fatigability varies depending on sex and contraction intensity during sustained exercise. This study examined the responses of time to task failure (TTF), performance fatigability (PF), and muscle oxygenation (SmO2) in males and females during isometric handgrip holds to failure (HTF) at 30% and 60% maximum voluntary isometric contraction (MVIC). Males (n = 12) and females (n = 12) performed a pre-MVIC, handgrip HTF at randomly ordered percentages of MVIC (either 30% or 60%), followed by a post-MVIC on the dominant arm. During the HTF testing, the TTF and SmO2 responses were recorded, and PF was determined from the pre- to post-MVICs. TTF for 30% MVIC HTF was greater than 60% MVIC HTF (p < 0.001), but was not different between males and females (p = 0.117). PF exhibited an inverse relationship with intensity for each sex, while males demonstrated greater PF than females for both 30% and 60% MVIC HTF. For the 60% MVIC HTF, males demonstrated greater desaturation than females (CI95% = [-28.1, -2.6%], p = 0.021, d = 0.621), but not for the 30% MVIC HTF (CI95% = [-12.2, 7.9%], p = 0.315, d = 0.621). Sex differences in PF and SmO2 may be attributed to the differences in muscle mass, absolute strength, contractile properties, and muscle metabolism between males and females. However, these proposed differences between males and females may not fully inform exercise performance (e.g., TTF). Sex-specific fatigue responses may be affected by complex physio-psychological mechanisms, and therefore, additional investigations under diverse exercise conditions are required to better prescribe exercise for both males and females.

When sng meets acupuncture -- a paradigm-shift biomarker for translational research

The sensation of sng (pronounced/səŋ/, the Romanization form of or soreness in Taiwanese Southern Min) associated with de qi, a composite of unique sensations, is a novel phenotype for acupoint stimulation. It is perceived by test participants but also by experienced practitioners as a sensation of "taking the bait" (by fish when fishing), a characteristic heavy and tight sensation from the needle. Here, we propose that sng is a powerful biomarker for de qi associated with successful manual acupuncture. Sngception (sng-ception), a specific somatosensory function of acid-sensation or tether-mode mechano-sensation, may serve as the ideal molecular and physiological link between sng perception and needle manipulation (e.g., lifting, thrusting, and twisting). To explain how manual acupuncture can induce de qi, we constructed a hypothetical model of manual needling-driven sngception. In acupoints (e.g., ST36), an acupuncture needle can easily stick to extracellular matrix (ECM) proteins (e.g., fibronectin and laminin). While the acupuncture needle is manually twisted, it mingles with ECM and delivers a pulling force to ECM-tethered mechanically sensitive ion channels (e.g., acid-sensing ion channels) on somatosensory nerves to induce sngception. The concept of sng and sngception represents an emerging field for research into the peripheral mechanisms of acupuncture.

Evaluation of leg symmetry in muscle oxygen saturation during submaximal to maximal cycling exercise

It is unclear whether physiological responses, such as muscle oxygen saturation (SmO2), can be considered symmetrical during cycling. This knowledge has important practical implications for both training and performance assessment. The aim of this study was to determine whether oxygenation profiles in the three active muscles of both legs were symmetrical during cycling at different intensities. Twenty-six trained cyclists and triathletes completed a graded exercise test (GXT) and an 8-min functional threshold power estimation test (8MTT) on a cycle ergometer over two nonconsecutive days. SmO2 was bilaterally assessed using NIRS technology in the vastus lateralis, gastrocnemius medialis, and tibialis anterior. Symmetry was compared between legs in both tests, and reliability and agreement between the measurements were quantified. The main results were that SmO2 in the three muscles assessed did not differ between legs during the GXT and 8MTT (p > 0.05). Reliability of the measures was poor to good in the vastus lateralis (ICC = 0.83-0.37), moderate to excellent in the tibialis anterior (ICC = 0.92-0.73), and poor to good for the gastrocnemius medialis (ICC = 0.80-0.24). Overall, the group variability in SmO2 showed a narrower distribution at lower intensities, with data dispersion increasing at higher intensities. In conclusion, the SmO2 was similar and showed symmetrical responses in both the preferred and nonpreferred limb in different muscles assessed during cycling at different intensities within a range of 10%-20%. Although individual physiological differences that might be relevant in some clinical/performance settings should not be disregarded, these findings indicate that measuring a single lower limb provides an accurate approximation of the responses in both lower limbs.

Diagnosis, Pathophysiology and Management of Microvascular Dysfunction in Diabetes Mellitus

Microcirculation is an essential system that regulates oxygen and nutrients to cells and tissues in response to various environmental stimuli and pathophysiological conditions. Diabetes mellitus can cause microvascular complications including nephropathy, neuropathy, and retinopathy. The pathogenesis of microvascular dysfunction in diabetes is associated with hyperglycemia and the result of an interplay of various factors. Research studies have demonstrated that functional microvascular dysfunction appears much earlier than structural alterations in vasculature in diabetes. This finding of the progression from microvascular dysfunction to macrovascular disease establishes a foundation for the screening and early diagnosis of diabetes by assessing the microvascular function. This comprehensive review discusses technologies (laser Doppler, transcutaneous oximetry, infrared thermography and near-infrared spectroscopy) with computational methods (linear (time and frequency domains), nonlinear and machine learning approaches) for diagnosing microvascular dysfunction in diabetes. Pathophysiological changes of microvascular dysfunction leading to impaired vasomotion and blood flow oscillations in diabetes are reviewed. Recent findings in managing microvascular dysfunction using lifestyle modifications and force-based modulations are evaluated. A consensus endorsed by the American Diabetes Association has been reached that an effective exercise program would greatly slow down the progression of microvascular dysfunction and its impact on diabetic foot ulcers, muscle fatigue and weakness and peripheral neuropathy. However, it is imperative to determine the dose-response relationship of exercise and microvascular responses in patients with diabetes. Research studies have demonstrated that local vibration and whole-body vibration can improve microcirculation in various pathological conditions, including diabetes. Due to the complex nature of microvascular regulation, various computational methods have been developed to shed light on the influence of diabetes on microvascular dysfunction. This comprehensive review will contribute to the diagnosis and management of microvascular dysfunction in diabetes.

Optimizing active recovery strategies for finger flexor fatigue

Introduction

Active recovery (AR) is used during exercise training; however, it is unclear whether the AR should involve the whole body, only the upper extremities, or only the lower extremities when aiming to maintain localized upper body performance. Therefore, this study aimed to evaluate the impact of different AR strategies on repeated intermittent finger flexor performance leading to exhaustion.

Methods

A crossover trial involving a familiarization session and three laboratory visits, each including three exhaustive intermittent isometric tests at 60% of finger flexor maximal voluntary contraction separated by 22 min of randomly assigned AR: walking, intermittent hanging, and climbing.

Results

The impulse (Nꞏs) significantly decreased from the first to third trials after walking (-18.4%, P = 0.002, d = 0.78), climbing (-29.5%, P < 0.001, d = 1.48), and hanging (-27.2%, P < 0.001, d = 1.22). In the third trial, the impulse from the intermittent test was significantly higher after walking (21,253 ± 5,650 Nꞏs) than after hanging (18,618 ± 5,174 Nꞏs, P = 0.013, d = 0.49) and after climbing (18,508 ± 4,435 Nꞏs, P = 0.009, d = 0.54).

Conclusions

The results show that easy climbing or intermittent isolated forearm contractions should not be used as AR strategies to maintain subsequent performance in comparison to walking, indicating that using the same muscle group for AR should be avoided between exhaustive isometric contractions.

Contributions to forearm desaturation during transient ischemia in healthy adult males and females across the lifespan

This study investigated skeletal muscle tissue oxygenation (StO2) desaturation in males and females across the adult lifespan. One hundred-two individuals (51 females) of 41 young, 34 midlife, and 27 older adults completed a vascular occlusion test with near-infrared spectroscopy (NIRS + VOT). This included five minutes of arterial occlusion, inducing transient ischemia in the forearm flexor muscle group while recording StO2. The magnitude of desaturation (StO2mag) was quantified as the difference between baseline StO2 and the minimum StO2 value observed during ischemia. The rate of desaturation was also examined. Forearm adipose tissue thickness (ATT), forearm lean mass, and handgrip muscular strength were measured. A p ≤ 0.05 was considered significant. Two-way between factor Analysis of variance (ANOVAs) indicated that males exhibited significantly (p < 0.001) less ATT than females (collapsed across age) and that forearm lean mass (p < 0.001) and muscular strength (p < 0.001) decreased across the lifespan independent of sex. Bivariate analyses revealed significant (p < 0.05) associations for sex, age, ATT, forearm lean mass, and muscular strength with the desaturation metrics. The ATT values demonstrated the strongest relations with StO2mag and desaturation rate (r = -0.620 and 0.618). Using a model comparison approach, ATT plus age offered the best predictive power for StO2mag and desaturation rate (R2 = 0.456 and 0.438) such that the inclusion of sex did not improve the models. These findings suggested differences in desaturation were primarily explained by variations in ATT and, to a lesser extent, age, but biological sex had no meaningful effect. Future studies must determine what other factors influence desaturation during ischemia.

Effects of coffee intake on skeletal muscle microvascular reactivity at rest and oxygen extraction during exercise: a randomized cross-over trial

PURPOSE

The effects of coffee ingestion on skeletal muscle microvascular function are not well understood. This study aimed to investigate the acute effects of coffee intake with varying levels of caffeine on skeletal muscle microvascular reactivity at rest and oxygen extraction during maximal incremental exercise in physically active individuals.

METHODS

Twenty healthy young male participants were administered coffee with low caffeine (3 mg/kg body weight; LC), high caffeine (6 mg/kg body weight; HC), and placebo (decaf) in different sessions. Skeletal muscle reactivity indexes, including tissue saturation index 10s slope (TSI10) and TSI half time recovery (TSI ½) following 5-minute ischemia were measured at rest and were measured at baseline and post-coffee consumption using near-infrared spectroscopy (NIRS). Post-coffee intake, NIRS was also used to measure microvascular oxygen extraction during exercise via maximal incremental exercise. Peak oxygen consumption and peak power output (Wpeak) were simultaneously evaluated.

RESULTS

Post-coffee consumption, TSI10 was significantly higher in the LC condition compared to placebo (p = 0.001) and significantly higher in the HC condition compared to placebo (p < 0.001). However, no difference was detected between LC and HC conditions (p = 0.527). HC condition also showed significant less TSI ½ compared to placebo (p = 0.005). However, no difference was detected for microvascular oxygen extraction during exercise, despite the greater Wpeak found for HC condition (p < 0.001) compared to placebo.

CONCLUSION

Coffee ingestion with high caffeine level (6 mg/kg body weight) significantly enhanced skeletal muscle reactivity at rest. However, the improvement of exercise performance with coffee intake is not accompanied by alterations in muscle oxygen extraction.

A short review of application of near-infrared spectroscopy (NIRS) for the assessment of microvascular post-occlusive reactive hyperaemia (PORH) in skeletal muscle

Near-infrared spectroscopy (NIRS) is an optical technique that can be used to non-invasively interrogate haemodynamic changes within skeletal muscle. It can be combined with a short (3-5 min) arterial cuff-occlusion to quantify post-occlusive reactive hyperaemia (PORH). This technique has utility in tracking changes in vascular health in relation to exercise, disease progression or treatment efficacy. However, methods for assessing PORH vary widely and there is little consensus on methodological approaches such as sampling frequency, correction for adipose tissue or the analysis endpoints. The purpose of this review was to: (1) summarise recent advances; (2) compare different methodological approaches and (3) identify current knowledge gaps and future objectives for use of NIRS for vascular assessment. We propose key areas for future work, including optimising occlusion duration and comparing methods of correction for the ischemic stimulus, standardising methods for adjustment of adipose tissue thickness, cross-device comparisons and establishing a standard for minimum sampling rate. Comparisons with alternative methods of capturing PORH or upstream vasodilatory responses would be valuable. Addressing these methodological considerations will aid our understanding of this useful, non-invasive tool for characterising PORH within skeletal muscle and facilitate interpretation of results across studies.

Study of Physiological Adaptations in Vertical Kilometer Runners: Focus on Cardiorespiratory and Local Muscle Demands

Background: Research into key performance factors in trail running, particularly in vertical kilometer (VK) races, is crucial for effective training and periodization. However, recent studies on metabolic and cardiorespiratory responses during VK races, especially using field tests, are limited. Objectives: Therefore, the aim of this study is to evaluate the metabolic and cardiorespiratory responses during a VK field test, identifying differences based on sex and performance level, as well as key performance factors and their deterioration due to fatigue. Fifteen trained trail runners (ten males and five females, 19 to 38 years old) perform a VK race. Methods: The global physiological response is evaluated using the portable gas analyzer Cosmed K5 and the local response using near-infrared spectroscopy technology. Results: In gender comparisons, the ANCOVA test shows significant differences (p < 0.05) in the ventilation, tidal volume, expiratory time-to-inspiratory time ratio, inspiratory flow rate, end-tidal CO2 partial pressure, heart rate, oxygen pulse, and total hemoglobin. Additionally, the performance comparison reveals significant differences in the variables' velocity, oxygen consumption, carbon dioxide production, ventilation, dead space-to-tidal volume ratio, total time of the breathing cycle, expiratory time-to-inspiratory time ratio, inspiratory duty cycle, expiratory fractions of CO2, quadriceps saturation index, and VE/VCO2 ratio. Finally, the correlation analysis shows oxygen consumption (r = -0.80 mean; r = -0.72 peak), carbon dioxide production (r = -0.91 mean; r = -0.75 peak), expiratory time-to-inspiratory time ratio (r = 0.68 peak), ventilation (r = -0.58 mean), and quadriceps saturation index (r = 0.54 mean; r = -0.76 coefficient of variation) as the key performance factors in the VK race. Conclusions: Overall, the physiological analysis indicates the importance of local muscular adaptations and respiratory system capacity in this type of short-duration race.

Induced blood flow oscillations at 0.1 Hz protects oxygenation of severely ischemic tissue in humans

Generating 10-s (∼0.1 Hz) fluctuations or "oscillations" in arterial pressure and blood flow blunts reductions in cerebral tissue oxygenation in response to 15%-20% reductions in cerebral blood flow. To examine the effect of 0.1 Hz hemodynamic oscillations on tissue oxygenation during severe ischemia, we developed a partial limb ischemia protocol targeting a 70%-80% reduction in blood flow. We hypothesized that 0.1 Hz hemodynamic oscillations would attenuate reductions in tissue oxygenation during severe ischemia. Thirteen healthy humans (6 M and 7 F; 27.3 ± 4.2 yr) completed two experimental protocols separated by ≥48 h. In both conditions, an upper arm cuff was used to decrease brachial artery (BA) blood velocity by ∼70%-80% from baseline. In the oscillation condition (0.1 Hz), 0.1 Hz hemodynamic oscillations were induced by intermittently inflating and deflating bilateral thigh cuffs every 5 s during forearm ischemia. In the control condition (0 Hz), the thigh cuffs were inactive. BA blood flow, forearm tissue oxygenation (SmO2), and arterial pressure were measured continuously. The initial reduction in BA blood velocity was tightly matched between protocols (0 Hz: -76.9 ± 7.9% vs. 0.1 Hz: -75.5 ± 7.4%, P = 0.49). Although 0.1 Hz oscillations during forearm ischemia had no effect on the reduction in BA velocity (0 Hz: -73.0 ± 9.9% vs. 0.1 Hz: -73.3 ± 8.2%, P = 0.91), the reduction in SmO2 was attenuated (0 Hz: -35.7 ± 8.6% vs. 0.1 Hz: -27.2 ± 8.9%, P = 0.01). These data provide further evidence for the use of 0.1 Hz hemodynamic oscillations as a potential therapeutic intervention for conditions associated with severe tissue ischemia (e.g., hemorrhage and stroke).NEW & NOTEWORTHY We investigated the effects of induced 10-s (0.1 Hz) oscillations in blood flow on forearm tissue oxygenation during severe ischemia. Intermittent inflation of bilateral thigh cuffs was used as a clinically applicable method to drive blood flow oscillations. In support of our hypothesis, 0.1 Hz oscillations in blood flow blunted reductions in forearm tissue oxygenation. These results further support the potential use of oscillatory hemodynamics as a therapeutic intervention for ischemic conditions.

Exercise intolerance and oxygen dynamics in nontuberculous mycobacteria with bronchiectasis

BACKGROUND

Nontuberculous mycobacterial pulmonary disease (NTM-PD) patients often have exercise intolerance. Pulmonary rehabilitation (PR) to improve such patients' conditions is often not based on its exercise pathophysiology. We have reported that the oxygen consumption (ΔFO2) by expiratory gas analysis, i.e., the inspired-expired-expiratory mean oxygen concentration difference, is related to the minute ventilation-carbon dioxide output (V'E-V'CO2)-slope and oxygen uptake (V'O2) independent of the V'E. The aim of this study was to investigate how ΔFO2 is related to dynamic ventilatory variables, chest computed tomography (CT), and echocardiography findings in NTM-PD patients to understand their pathophysiological conditions.

METHODS

Clinical data of NTM-PD patients with exertional dyspnea (n = 29) who underwent incremental exercise testing, chest CT, and echocardiography at the same time were compared with those of control participants (n = 12).

RESULTS

In the NTM-PD group, 1) peak V'O2 decreased (NTM-PD: 17.6 vs. controls: 28.7 mL⋅min-1⋅kg-1), and 2) ΔFO2 at peak exercise was negatively correlated with respiratory frequency at peak exercise (correlation coefficient: r = -0.80, p < 0.0001), V'E-V'CO2-slope (r = -0.75, p < 0.0001), bronchiectasis CT score (r = -0.52, p = 0.0042), and the trans-tricuspid pressure gradient (r = -0.39, p = 0.0417), and positively correlated with peak V'O2 (r = 0.71, p < 0.0001) and the body mass index (r = 0.42, p = 0.0217), but it was not correlated with V'E at peak exercise and the cavity CT score.

CONCLUSIONS

Exertional oxygen consumption, independent of ventilatory ability, is associated with exercise tolerance and ventilatory efficiency, while being related to tachypnea and bronchiectasis rather than cavitation in NTM-PD patients. These findings may be useful in considering exercise physiology-based PR for NTM-PD patients with exertional dyspnea.

Reliability of near-infrared spectroscopy in measuring muscle oxygenation during squat exercise

Monitoring of changes in skeletal muscle oxygenation during exercise has increased in recent years. Tissue oxygenation, which is related to fatigue and muscle hypertrophy, is often measured using near-infrared spectroscopy (NIRS).

OBJECTIVES

This study aimed to determine the test-retest reliability of a non-portable NIRS (NIRO200Nx) during the full-squat exercise and recovery in young healthy men.

DESIGN

Twenty-five male participants (21.8 ± 2.6 years) were recruited for this original research. Each participant completed an 8-repetition test with a load that elicited a velocity of 1 m·s-1. The test was conducted twice, with a 48-hour washout period between sessions.

METHODS

The NIRS measured the changes of oxygenated-Hemoglobin (O2Hb), deoxygenated-Hemoglobin (HHb) and Tissue Oxygenation Index (TOI) in both Vastus Lateralis and Vastus Medialis during rest, exercise, and recovery. Coefficient of Variation (CV), Standard Error Measurement (SEM) and Intraclass Correlation Coefficient (ICC) were used to evaluate the reliability of the data. Significance was set at p < 0.05.

RESULTS

The results indicated that TOI had good to acceptable absolute reliability (CVTOI = 2.7-10.2 %). A good relative relativity for the overall test was found for Vastus Medialis O2Hb (ICC = 0.851), HHb (ICC = 0.852), and TOI (ICC = 0.864), and Vastus Lateralis O2Hb (ICC = 0.898), HHb (ICC = 0.899), and TOI (ICC = 0.897).

CONCLUSIONS

We conclude that NIRO200Nx is a reliable instrument for measuring muscle oxygen saturation through the TOI parameter in not-to-failure dynamic resistance exercises (1 set of 8 reps against ∼40 % 1 repetition maximum). Tissue oxygenation assessment could be a new way of individualizing exercise through dynamic resistance exercises.

The effects of six sprint interval training sessions on muscle oxygenation and swimming performance in untrained swimmers

The current study examined the changes in muscle oxygenation values and swimming performance after six sessions of sprint interval training during a three-week period in untrained swimmers. Twelve swimmers of both genders (age: 23.5 ± 5.6yrs) executed the twice-weekly experimental training protocol (EXP, n = 12), consisting of a 4 × 50 m front-crawl swimming (repeated sprint training-RST) with maximal intensity, and 2 min of passive recovery in between, after a short in-water warm-up. The control group (CON, n = 9) performed a continuous swimming set (200 m) at 120 b pm-1, with the same weekly frequency. Performance times in two maximum swim trials (400 m: T400 and 50 m: T50), muscle oxygenation of the deltoid muscle (SmO2) immediately after T400 and T50, 1-min heart rate recovery (HRR1) after T400, T50, and swim strokes during both swim trials (S/T400, S/T50) were assessed. For the EXP group, T400 improved by 2.4 (p = 0.011). In contrast, T50 presented no significant improvement (1%, p > 0.05). SmO2 decreased at T400 (5.5%, p = 0.017) and increased at T50 (3.7%, p = 0.030). HRR1 improved after T400 (7.9%, p = 0.002), T50 (4.6%, p = 0.005) and RST (9.6%, p = 0.002). S/T400 and S/T50 remained relatively unchanged (p > 0.05). The CON group presented no significant changes in any of the variables examined. In conclusion, six sprint interval training sessions can improve aerobic capacity over a 3-week training period, as indicated by the enhanced T400 performance and the reduced HRR1 values, in previously trained swimmers. Finally, the sensitivity of the near-infrared spectroscopy method to detect short-term training-induced changes is highlighted.

The effects of endurance training on muscle oxygen desaturation during incremental exercise tests: a systematic review and meta-analysis

Objective

Minimum muscle oxygen saturation (SmO2min) measured via near-infrared spectroscopy (NIRS) is a common measure during incremental exercise testing (IET). Our objective was to determine the effects of pre-to-post endurance training on SmO2min (ΔSmO2min) during an IET, using a meta-analysis.

Data sources

MEDLINE, EMBASE, and SPORTDiscus.

Study selection

Studies including healthy individuals had to meet the following criteria: (1) endurance training intervention; (2) peripheral muscle NIRS; (3) incremental exercise test pre/post training; (4) SmO2 or analogous saturation parameter measured.

Analysis

A PEDro scale was used for risk of bias analysis. A random effect meta-analysis model was used to synthesize the effect of training on ΔSmO2min in individual studies. Statistical heterogeneity was quantified using I2 statistic. A meta-regression was used to estimate the effect of training on the relationship between peak cycling power output (Wpeak), peak pulmonary oxygen uptake (V˙O2peak), and ΔSmO2min. A mixed-effect model was used to estimate categorical variables.

Results

Five studies met the inclusion criteria. No difference in SmO2min was detected following training pre- and post-intervention IETs. A trend for an effect of training on the relationship between Wpeak and ΔSmO2min was observed (p = 0.06).

Conclusion

This meta-analysis showed no effects of endurance training on SmO2min during an IET. Our results showed a trend for an effect of training on the relationship between Wpeak and ΔSmO2min, with no effect for V˙O2peak and ΔSmO2min. It is possible that SmO2min is not affected by endurance training, and may be used as a physiological marker for improvements in submaximal performance rather than at peak.

Best practices for simultaneous measurement of NIRS-based cerebral and muscle oximetry during exercise

•NIRS-based oximetry is a valuable tool for exercise physiology. •NIRS-based oximetry measurements are influenced by the device used. •NIRS-based oximetry measurements must be interpreted carefully.

Oxygenation Kinetics of Three Quadriceps Muscles During Squatting Exercise in Trained Men

This study aimed to monitor the oxygenation and blood supply in three quadriceps muscles [the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF)] during squatting exercise to exhaustion. Eighteen young resistance-trained males performed five sets of 15 back squats in a Smith machine, with two warm-up sets [at 14% and 45% of the 15-repetition maximum (15RM)] and three main sets at 100% of the 15RM. Three near-infrared spectroscopy devices were attached to the VL, VM, and RF to record the muscle oxygen saturation (SmO2) and total hemoglobin (tHb, an index of muscle blood supply). The blood lactate concentration was measured after each set with a portable analyzer. The SmO2 and tHb data were analyzed by repeated-measures two-way ANOVA (muscle × set). Lactate data were analyzed by repeated-measures one-way ANOVA. The statistical significance was set at α = 0.05. The SmO2 dropped during each set (hitting zero in many instances) and was reinstated during recovery. The three main sets caused severe deoxygenation in the VL and VM, as opposed to moderate deoxygenation in the RF. From one set to the next, the initial value and the drop in the SmO2 increased, whereas the final SmO2 value decreased. The tHb increased in the VL, did not change considerably in the VM, and decreased in the RF during each set. The blood lactate concentration increased gradually from one set to the next, reaching about 10 mmol/L. These findings show pronounced differences in the physiological and metabolic responses of three quadriceps muscles to squatting exercise, thus highlighting the importance of studying such responses at multiple sites.

Acute psycho-physiological responses to submaximal constant-load cycling under intermittent hypoxia-hyperoxia vs. hypoxia-normoxia in young males

Background

Hypoxia and hyperoxia can affect the acute psycho-physiological response to exercise. Recording various perceptual responses to exercise is of particular importance for investigating behavioral changes to physical activity, given that the perception of exercise-induced pain, discomfort or unpleasure, and a low level of exercise enjoyment are commonly associated with a low adherence to physical activity. Therefore, this study aimed to compare the acute perceptual and physiological responses to aerobic exercise under intermittent hypoxia-hyperoxia (IHHT), hypoxia-normoxia (IHT), and sustained normoxia (NOR) in young, recreational active, healthy males.

Methods

Using a randomized, single-blinded, crossover design, 15 males (age: 24.5 ± 4.2 yrs) performed 40 min of submaximal constant-load cycling (at 60% peak oxygen uptake, 80 rpm) under IHHT (5 × 4 min hypoxia and hyperoxia), IHT (5 × 4 min hypoxia and normoxia), and NOR. Inspiratory fraction of oxygen during hypoxia and hyperoxia was set to 14% and 30%, respectively. Heart rate (HR), total hemoglobin (tHb) and muscle oxygen saturation (SmO2) of the right vastus lateralis muscle were continuously recorded during cycling. Participants' peripheral oxygen saturation (SpO2) and perceptual responses (i.e., perceived motor fatigue, effort perception, perceived physical strain, affective valence, arousal, motivation to exercise, and conflict to continue exercise) were surveyed prior, during (every 4 min), and after cycling. Prior to and after exercise, peripheral blood lactate concentration (BLC) was determined. Exercise enjoyment was ascertained after cycling. For statistical analysis, repeated measures analyses of variance were conducted.

Results

No differences in the acute perceptual responses were found between conditions (p ≥ 0.059, ηp 2 ≤ 0.18), while the physiological responses differed. Accordingly, SpO2 was higher during the hyperoxic periods during the IHHT compared to the normoxic periods during the IHT (p < 0.001, ηp 2 = 0.91). Moreover, HR (p = 0.005, ηp 2 = 0.33) and BLC (p = 0.033, ηp 2 = 0.28) were higher during IHT compared to NOR. No differences between conditions were found for changes in tHb (p = 0.684, ηp 2 = 0.03) and SmO2 (p = 0.093, ηp 2 = 0.16).

Conclusion

IHT was associated with a higher physiological response and metabolic stress, while IHHT did not lead to an increase in HR and BLC compared to NOR. In addition, compared to IHT, IHHT seems to improve reoxygenation indicated by a higher SpO2 during the hyperoxic periods. However, there were no differences in perceptual responses and ratings of exercise enjoyment between conditions. These results suggest that replacing normoxic by hyperoxic reoxygenation-periods during submaximal constant-load cycling under intermittent hypoxia reduced the exercise-related physiological stress but had no effect on perceptual responses and perceived exercise enjoyment in young recreational active healthy males.

Impact of foam rolling with and without vibration on muscle oxidative metabolism and microvascular reactivity

Background and Purpose

There is a growing interest in use vibration foam rolling as a warm up and recovery tool. However, whether vibration foam rolling offers additional benefits to traditional foam rolling is unclear. The current study aims to compare the effects of acute foam rolling, with and without vibration, on skeletal muscle metabolism and microvascular reactivity.

Methods

Fifteen physically active young males were tested on two different days, with gastrocnemius muscle microvascular function assessed using near-infrared spectroscopy coupled with the post-occlusive reactive hyperemia technique, before and after foam rolling, performed with or without vibration. The slope of tissue saturation index (TSI) decrease during occlusion between 120 s to 150 s (TSI occlusion slope) was assessed for muscle metabolic rate. Three commonly used microvascular function indexes, including the first10s TSI slope after occlusion (TSI10), time for TSI to reach half of peak magnitude (TSI1/2), and TSI peak reactive hyperemia, were also assessed.

Results

None of the measured indexes showed significance for interaction or method (all p > 0.05). However, there was a main effect for time for TSI occlusion slope, TSI1/2, and TSI peak reactive hyperemia (p = 0.005, 0.034 and 0.046, respectively). No main effect for time for TSI10 was detected (p = 0.963).

Conclusions

The application of foam rolling can decrease muscle metabolism, and may improve some aspects of muscle microvascular function. However, vibration foam rolling does not seem to offer any additional benefits compared to traditional foam rolling alone.

Microvascular Reactivity Is Greater Following Blood Flow Restriction Resistance Exercise Compared with Traditional Resistance Exercise

ABSTRACT

Perlet, MR, Hosick, PA, Licameli, N, and Matthews, EL. Microvascular reactivity is greater following blood flow restriction resistance exercise compared with traditional resistance exercise. J Strength Cond Res 38(10): e553-e562, 2024-Chronic blood flow restriction (BFR) resistance exercise can improve muscular strength, hypertrophy, and microvasculature function, but the acute microvascular effects are unknown. We aimed to test the effects of acute BFR resistance exercise on postexercise microvascular reactivity in an exercising muscle and nonexercising muscle compared with traditional resistance exercise (TRE). Twenty-five adults (men = 14, women = 11, age: 22 ± 3 years, body mass: 71.69 ± 14.49 kg, height: 170 ± 10 cm) completed barbell back squat 1-repetition maximum (1RM) testing followed by 2 randomized and counterbalanced resistance exercise visits separated by ≥48 hours. The 2 visits involved either BFR (4 sets of 30-15-15-15 repetitions at 30% 1RM, with 60-second rest intervals) or TRE (4 sets of 10 repetitions at 70% 1RM, 60-second rest intervals). During each exercise visit, a pre- and postbarbell back squat vascular occlusion test was performed using near-infrared spectroscopy to measure skeletal muscle oxygen (SmO 2 ) in the vastus lateralis (VL) and flexor carpi radialis (FCR). Two-way repeated-measures ANOVA found an interaction effect ( p = 0.020) for SmO 2 reactivity in the VL. Post hoc analysis found greater reactive hyperemia postexercise in the VL for the BFR condition ( p < 0.001) but not the TRE condition ( p ≥ 0.05). There were no time, condition, or interaction effects (all p > 0.05) for the same analysis in the FCR. This analysis suggests that BFR, but not TRE, lead to acutely improved microvasculature function. Moreover, it suggests that the effects of BFR resistance exercise are local to the exercised or occluded limb and not systemic.

Early EEG and NIRS measurements in preterm babies: a systematic review

Preterm birth represents a public health problem, with prematurity being the leading cause of infant mortality. An objective brain maturation and oxygenation measurement are necessary. The objective has been To test the feasibility of EEG and NIRS combination in the assessment of physiological brain maturation and oxygenation in preterm and non-preterm babies. A systematic review in Pubmed, Web of Science, MEDLINE, Cochrane, Dialnet, CINAHL, Scopus, Lilacs and PEDro databases until December 2022 was developed. 598 registers were found, finally 5 of them reached the inclusion criteria. Two independent reviewers analyzed data and a third reviewer were available for discrepancies. All articles combined EEG and NIRS to assess brain oxygenation and maturation in healthy new-born babies. There is an agreement on the electrode's placement for EEG at P3 and P4; besides, these regions have been shown to be a development predictive area, as well as the frontoparietal region for the NIRS region and comparison between regions. There is little evidence about the physiological brain electrical activity and oxygenation without stimuli.Conclusion: EEG and NIRS have been useful to assess brain electrical activity and oxygenation in preterm and non-preterm. The combined measurement of these instruments could be essential in neurological disorders diagnosis or their sequels. Unfortunately, the heterogeneity of the results found prevents a consensus on which variables are the most appropriate for the assessment of this population. What is Known • Brain assessment could help clinicians to prevent sequels. • There is an agreement for EEG electrodes placement at P3 and P4 region. What is New • EEG and NIRS assessment are effective measurements for preterm babies. • P3 and P4 regions have shown to be a predictive area of development, as well as the frontoparietal region for NIRS assessment.

Side differences and reproducibility of the Moxy muscle oximeter during cycling in trained men

PURPOSE

Portable near-infrared spectroscopy devices allow measurements of muscle oxygen saturation (SmO2) in real time and non-invasively. To use NIRS for typical applications including intensity control and load monitoring, the day-to-day variability needs to be known to interpret changes confidently. This study investigates the absolute and relative test-retest reliability of the Moxy Monitor and investigates side differences of SmO2 at the vastus lateralis muscle of both legs in cyclists.

METHODS

Twelve trained cyclists and triathletes completed 3 incremental step tests with 5 min step duration starting at 1.0 W/kg with an increase of 0.5 W/kg separated by 2-7 days. SmO2 was averaged over the last minute of each stage. For all power outputs, the intra-class coefficient (ICC), the standard error of measurement (SEM) and the minimal detectable change (MDC) were calculated. Dominant and non-dominant leg SmO2 were compared using a three-factor ANOVA and limits of agreement (LoA).

RESULTS

ANOVA showed no significant systematic differences between trials and side. For both legs and all intensities, the ICC ranged from 0.79 to 0.92, the SEM from 5 to 9% SmO2 and the MDC from 14 to 18% SmO2. The bias and LoA between both legs were -2.0% ± 19.9% SmO2.

CONCLUSION

Relative reliability of SmO2 was numerically good to excellent according to current standards. However, it depends on the specific analytical goal whether the test-retest reliability is deemed sufficient. Wide LoA indicate side differences in muscle oxygenation during exercise unexplained by leg dominance.

Comparison of analysis strategies to assess sex differences in microvascular reperfusion using near-infrared spectroscopy

The near-infrared spectroscopy (NIRS) vascular occlusion test (VOT) assesses microvascular reperfusion. Two strategies have been used to quantify reperfusion following reactive hyperemia, but it is unclear whether both yield similar results when comparing biological sex. This study aimed to determine whether sex differences in NIRS-based microvascular reperfusion are similarly apparent using the 10-s reactive hyperemia slope of the tissue saturation index (StO2) signal (slope 2) and the halftime to maximal reperfusion (T ½). Healthy, recreationally active males (n = 31) and females (n = 31) between 18 and 82 years took part in this study. A NIRS VOT was performed on the tibialis anterior muscle, and reperfusion was quantified using slope 2 (% s-1) and T ½ (s). Adipose tissue thickness (ATT) was higher in females (P = 0.009), which was associated with a lower StO2 (P = 0.001) and oxygenated hemoglobin (O2Hb) (P = 0.05) signal range. The StO2 slope 2 was significantly steeper in males versus females (P = 0.001) but not after correcting for ATT (P = 0.295). There were no sex differences in StO2 T ½ (P = 0.067) or O2Hb T ½ (P = 0.197). In a subset of males (n = 26) and females (n = 21) with similar ATT, there were no sex differences in StO2 slope 2 (P = 0.068), StO2 T ½ (P = 0.491), or O2Hb T ½ (P = 0.899). An ATT-corrected StO2 slope 2 or the T ½ approach is recommended for analysis of NIRS-based microvascular reperfusion when differences in ATT are present between sexes.NEW & NOTEWORTHY Sex differences in near-infrared spectroscopy (NIRS)-based microvascular reperfusion have been previously reported. We found that greater adipose tissue thickness in females reduces kinetic measures of NIRS-based microvascular reperfusion. Sex differences are eliminated when performing an adipose tissue thickness correction, when the NIRS signal range is accounted for, or when adipose tissue thickness is similar between sexes. This highlights the importance of considering factors that affect NIRS signals, such as adipose tissue thickness, when drawing comparisons between groups.

Acute impact of inorganic nitrate supplementation after ischemia and during small muscle mass exercise in postmenopausal females: A pilot study

Menopause is associated with reduced endothelial-dependent vasodilation and increased cardiovascular disease (CVD) risk. Dietary nitrate, a non-pharmacological approach, may increase vasodilatory capacity consequentially reducing CVD risk. We investigated macro- and microvascular function after acute nitrate supplementation in postmenopausal females (PMF). Vascular function was studied with flow-mediated vasodilation (FMD) and near-infrared post occlusive reactive hyperemia (PORH). Incremental handgrip exercise was performed to investigate blood flow and tissue oxygenation. We hypothesized acute dietary nitrate would not impact resting endothelial measures but would increase post ischemic vasodilation and incremental exercise blood flow. Late-phase PMF (n = 12) participated in a randomized crossover design with 140 mL of nitrate-rich (NR) beetroot juice or nitrate-poor black currant juice. Testing included a 5-min FMD, a 3-min ischemic exercise FMD, and incremental exercise at 10%, 15%, and 20% maximal voluntary contraction to measure blood flow and pressure responses. A p ≤ 0.05 was considered significant. One-way ANOVA indicated lower resting pressures, but no change to FMD, or PORH in either protocol. Two-way repeated measures ANOVA indicated NR supplementation significantly reduced mean arterial pressure at rest and during incremental exercise at all intensities without changes to blood flow. Acute nitrate is effective for resting and exercising blood pressure management in PMF.

Effects of occlusion pressure on hemodynamic responses recorded by near-infrared spectroscopy across two visits

Ischemic Preconditioning (IPC) has emerged as a promising approach to mitigate the impact of hypoxia on physiological functions. However, the heterogeneity of occlusion pressures for inducing arterial occlusion has led to inconsistent hemodynamic outcomes across studies. This study aims to evaluate the peripheral hemodynamic responses to partial and total blood-flow occlusions on the left arm at rest, using absolute or individualized pressures, on two occasions. Thirty-five young males volunteered to participate in this study. IPC procedure (3 × 7-min) was performed on the left upper arm with cuff pressures at 50 mmHg (G1), 50 mmHg over the systolic blood pressure (SBP + 50 mmHg) (G2) or 250 mmHg (G3). NIRS-derived parameters were assessed for each occlusion and reperfusion phase in the brachioradialis. Results showed a significantly lower magnitude of deoxygenation (TSIAUC) for G1 compared to G2 (-1959.2 ± 1417.4 vs. -10908.1 ± 1607.5, P < 0.001) and G3 -1959.2 ± 1417.4 vs. -11079.3 ± 1828.1, P < 0.001), without differences between G2 and G3. However, G3 showed a significantly faster reoxygenation only for tissue saturation index (TSIslope) compared to G2 (1.3 ± 0.1 vs. 1.0 ± 0.2, P = 0.010), but without differences in the speed of recovery of deoxyhemoglobin [(HHb) slope], or in the magnitude of post-occlusive hyperemia (PORH). Besides TSI reoxygenation speed, G2 and G3 elicit comparable resting hemodynamic responses measured by NIRS. Thus, this study highlights the practicality and effectiveness of using relative occlusion pressures based on systolic blood pressure (SBP) rather than relying on excessively high absolute pressures.

A personalized clinical assessment: multi-sensor approach for understanding musculoskeletal health in the frail population

BACKGROUND

Sarcopenia is a muscle disorder causing a progressive reduction of muscle mass and strength, but the mechanism of its manifestation is still partially unknown. The three main parameters to assess are: muscle strength, muscle volume or quality and low physical performance. There is not a definitive approach to assess the musculoskeletal condition of frail population and often the available tests to be performed in those clinical bedridden patients is reduced because of physical impairments. In this paper, we propose a novel instrumental multi-domain and non-invasive approach during a well-defined protocol of measurements for overcoming these limitations. A group of 28 bedridden elder people, subjected to surgery after hip fracture, was asked to perform voluntary isometric contractions at the 80% of their maximum voluntary contraction with the non-injured leg. The sensor employed before and/or during the exercise were: ultrasound to determine the muscle architecture (vastus lateralis); force acquisition with a load cell placed on the chair, giving an indication of the muscle strength; surface electromyography (EMG) for monitoring muscular electrical activity; time-domain (TD) near-infrared spectroscopy (NIRS) for evaluating muscle oxidative metabolism.

RESULTS

A personalized "report card" for each subject was created. It includes: the force diagram (both instantaneous and cumulative, expected and measured); the EMG-force diagram for a comparison between EMG derived median frequency and measured force; two graphs related to the hemodynamic parameters for muscle oxidative metabolism evaluation, i.e., oxy-, deoxy-, total-hemoglobin and tissue oxygen saturation for the whole exercise period. A table with the absolute values of the previous hemodynamic parameters during the rest and the ultrasound related parameters are also included.

CONCLUSIONS

In this work, we present the union of protocols, multi-domain sensors and parameters for the evaluation of the musculoskeletal condition. The novelties are the use of sensors of different nature, i.e., force, electrical and optical, together with a new way to visualize and combine the results, by means of a concise, exhaustive and personalized medical report card for each patient. This assessment, totally non-invasive, is focused on a bedridden population, but can be extended to the monitoring of rehabilitation progresses or of the training of athletes.

Dynamic Peripheral Hemoperfusion Distribution Monitoring Based on Janus Flexible Sensor System

OBJECTIVE

Peripheral vascular disease is a worldwide leading health concern. Real-time peripheral hemoperfusion monitoring during treatment is essential to plan treatment strategies to improve circulatory enhancement effects.

METHODS

The present work establishes a Janus flexible perfusion (JFP) sensor system for dynamic peripheral hemoperfusion monitoring. We develop a Janus structure with different Young's modulus to improve the mechanical properties for motion artifacts suppression. Besides, we propose a peripheral perfusion index (PPI) based on an optical perfusion model that is experimentally verified using an in-vitro model. The effectiveness of the system is assessed in three experimental scenarios, including motion artifact-robust test, induced vascular occlusion, and peripheral hemoperfusion monitoring with the intermittent pneumatic compression treatment.

RESULTS

The noise level of the traditional rigid sensor is five times that of the JFP sensor within the effective signal frequency domain when there is movement. The PPI can effectively discriminate between different peripheral hemoperfusion states and has a correlation coefficient of 0.92 with the Laser Doppler flowmetry (LDF) mean values. The kappa statistic between the JFP sensor and LDF is 0.78, indicating substantial agreement to estimate the peripheral hemoperfusion improvements.

CONCLUSION

The sensor system we proposed can monitor peripheral hemoperfusion variation in real-time and is insensitive to motion artifacts.

SIGNIFICANCE

The proposed sensing system provides a functional module for real-time estimation of peripheral hemoperfusion during clinical interventions.

Reproducibility and sex differences in muscle oxygenation during brachial artery occlusion in healthy participants

SIGNIFICANCE

Near-infrared spectroscopy (NIRS) measurement is a widely used technique to measure muscle oxygenation. A knowledge of the reproducibility of NIRS measurements is essential for the correct interpretation of data.

AIM

Our aim was to test the reproducibility and sex differences of NIRS measurements during brachial artery occlusion in healthy participants.

APPROACH

An NIRS device was used to measure muscle oxygenation and microvascular function during a 5 min brachial occlusion. Muscle oxygen consumption (mVO2) and tissue saturation index (TSI%) were used. The occlusion test was performed three times on separate days for males (n = 13, 28 ± 8 years) and females (n = 13, 29 ± 7 years).

RESULTS

During the occlusion phase, the reproducibility of mVO2 was excellent (intraclass correlation; ICC = 0.90). During the reperfusion phase, the maximal change in TSI% revealed the best reproducibility (ICC = 0.77). There were no sex differences in reproducibility. Male participants had higher muscle oxygenation during occlusion (mVO2, 0.054 ± 0.010 vs. 0.038 ± 0.012 mLO2/min/100 g, p = 0.001, male and female, respectively). There were no sex differences during the reperfusion phase.

CONCLUSION

The reproducibility of NIRS to measure muscle oxygenation and microvascular function during circulation occlusion and reperfusion is good to excellent. Muscle oxygen capacity measured during occlusion is higher in males compared to females, and there are no sex differences in microvascular function during the reperfusion phase.

Reference Ranges for Regional Cerebral Oxygen Saturation with Masimo O3 after Birth and Differences with Other Devices

OBJECTIVE

 Cerebral oximetry using near-infrared spectroscopy (NIRS) is a noninvasive optical technology widely used in neonatology. The present study aimed to define reference ranges for cerebral tissue oxygen saturation (crSO2) with a new four-wavelength NIRS device, Masimo O3 oximeter, during immediate transition after birth and compare values with those obtained previously with NIRO 200NX®.

STUDY DESIGN

 This was a prospective observational study using Masimo O3 device to measure crSO2 and regional cerebral fractional tissue oxygen extraction (cFTOE) in healthy term newborns delivered by primary cesarean section, during the 15 minutes after cord clamping. The neonates who required any medical support were excluded. The NIRS sensor was placed on the right forehead. Peripheral oxygen saturation and heart rate were continuously measured by pulse oximetry. Previous studies which established centiles for crSO2 with NIRO 200NX were used for comparison.

RESULTS

 A total of 44 newborns were included. The median crSO2 and cFTOE (interquartile range) at 2, 5, and 7 minutes was 54% (49-54), 71% (64-86), and 79% (73-84) and 0,25 (0,18-0,33), 0,19 (0,15-0,23), and 0,16 (0,12-0,21), respectively, with no further changes afterwards. The crSO2 measurements were significantly higher with Masimo O3 compared with NIRO-200NX.

CONCLUSION

 The present observational study presented reference ranges for crSO2 and cFTOE measured with Masimo O3 oximeter during the immediate neonatal transition. Values obtained with O3 were higher than those obtained with other oximeters. For this reason, crSO2 is device-specific so there must be known reference values for each oximeter to define therapeutic interventions based on crSO2 and assess cerebral oxygenation in clinical studies.

KEY POINTS

· Masimo O3 uses four wavelengths to measure regional oxygen saturation value.. · O3 values of crSO2 and cFTOE differ with other neonatal oximeters at birth.. · Knowledge of reference range of O3 at birth is essential to guide resuscitation..

Muscle reoxygenation is slower after higher cycling intensity, and is faster and more reliable in locomotor than in accessory muscle sites

Introduction

Wearable near-infrared spectroscopy (NIRS) can be used during dynamic exercise to reflect the balance of muscle oxygen delivery and uptake. This study describes the behaviour and reliability of postexercise reoxygenation with NIRS as a function of exercise intensity at four muscle sites during an incremental cycling test. We discuss physiological components of faster and slower reoxygenation kinetics in the context of sport science and clinical applications. We hypothesised that reoxygenation would be slower at higher intensity, and that locomotor muscles would be faster than accessory muscles. We quantified test-retest reliability and agreement for each site.

Methods

Twenty-one trained cyclists performed two trials of an incremental cycling protocol with 5-min work stages and 1-min rest between stages. NIRS was recorded from the locomotor vastus lateralis and rectus femoris muscles, and accessory lumbar paraspinal and lateral deltoid muscles. Reoxygenation time course was analysed as the half-recovery time (HRT) from the end of work to half of the peak reoxygenation amplitude during rest. Coefficient of variability (CV) between participants, standard error of the measurement (SEM) within participants, and intraclass correlation coefficient (ICC) for test-retest reliability were evaluated at 50%, 75%, and 100% peak workloads. A linear mixed-effects model was used to compare differences between workloads and muscle sites.

Results

HRT was slower with increasing workload in the VL, RF, and PS, but not DL. VL had the fastest reoxygenation (lowest HRT) across muscle sites at all workloads (HRT = 8, 12, 17 s at 50%, 75%, 100% workload, respectively). VL also had the greatest reliability and agreement. HRT was sequentially slower between muscle sites in the order of VL < RF < PS < DL, and reliability was lower than for the VL.

Discussion

This study highlights the potential for using wearable NIRS on multiple muscle sites during exercise. Reoxygenation kinetics differ between local muscle sites with increasing intensity. Moderate-to-good reliability in the VL support its increasing use in sport science and clinical applications. Lower reliability in other muscle sites suggest they are not appropriate to be used alone, but may add information when combined to better reflect systemic intensity and fatigue during exercise at different intensities.

Comparison of Force, Neuromuscular, and Metabolic Responses During Sustained, Isometric Handgrip Holds to Failure Anchored to Low and High Perceptual Intensities in Men: An Exploratory Study

ABSTRACT

Kwak, M, Succi, PJ, Benitez, B, Mitchinson, C, Samaan, MA, Abel, MG, and Bergstrom, HC. Comparison of force, neuromuscular, and metabolic responses during sustained, isometric handgrip holds to failure anchored to low and high perceptual intensities in men: An exploratory study. J Strength Cond Res 38(8): e405-e416, 2024-This study examined the responses of force alterations, relative to critical force (CF), neuromuscular parameters, and muscle oxygenation (SmO2) for isometric handgrip holds to failure (HTF) anchored to ratings of perceived exertion (RPE) of 3 and 7. Twelve men completed pre-maximal voluntary isometric contractions (pre-MVIC), submaximal HTF at 4 percentages of pre-MVIC, HTF at RPE = 3 and 7, and post-MVIC. Mechanomyograpic (MMG) signals and SmO2 were recorded during the RPE HTF. Analyses included paired-samples t-tests and repeated-measures ANOVAs at an alpha level of p ≤ 0.05. Time to task failure was not different between RPE 3 (478.7 ± 196.6 s) and RPE 7 (495.8 ± 173.8 s). Performance fatigability (PF) and MMG amplitude (AMP) were greater for RPE 7 (PF: 37.9 ± 12.9%; MMG AMP: 15.7 ± 7.4% MVIC) than RPE 3 (PF: 30.0 ± 14.5%; MMG AMP: 10.2 ± 6.5% MVIC), but MMG mean power frequency (MPF) was greater for RPE 3 (146.2 ± 31.1% MVIC) than RPE 7 (128.8 ± 23.0% MVIC). There were RPE-dependent decreases in force (p ≤ 0.01) across 3 discernable phases during the HTF. There were decreases in MMG AMP across time for both RPEs, but there were no significant changes in MMG MPF or SmO2. There were overall similar motor unit control strategies and local metabolic demand between RPEs. The majority of the HTF performed below CF at RPE 3 and 7 indicated CF did not reflect the highest sustainable force. When prescribing isometric exercise anchored to RPE, practitioners should be aware of the magnitude of force loss and relative intensity of the task to be sure desired training loads are met.