Speeding of VO2 kinetics with endurance training in old and young men is associated with improved matching of local O2 delivery to muscle O2 utilization

Long-Term Alterations in Pulmonary V˙O2 and Muscle Deoxygenation On-Kinetics During Heavy-Intensity Exercise in Competitive Youth Cyclists: A Cohort Study

PURPOSE

The aim of this investigation was to assess alterations of pulmonary oxygen uptake (V˙O2) and muscle deoxygenation on-kinetics during heavy-intensity cycling in youth cyclists over a period of 15 months.

METHODS

Eleven cyclists (initial age, 14.3 [1.6] y; peak V˙O2, 62.2 [4.5] mL·min-1·kg-1) visited the laboratory twice on 3 occasions within 15 months. Participants performed an incremental ramp exercise test and a constant workrate test within the heavy-intensity domain during the first visit and second visit, respectively. Subsequently, parameter estimates of the V˙O2 and muscle deoxygenation on-kinetics were determined with mono-exponential models.

RESULTS

The V˙O2 phase II time constant decreased from occasion 1 (34 [4] s) to occasion 2 (30 [4] s, P = .005) and 3 (28 [4] s, P = .010). However, no significant alteration was observed between occasions 2 and 3 (P = .565). The V˙O2 slow component amplitude either expressed in absolute values (ie, L·min-1) or relative to end exercise V˙O2 (ie, %) showed no significant changes throughout the study (P = .972 and .996). Furthermore, the muscle deoxygenation on-kinetic mean response time showed no significant changes throughout the study (18 [8], 18 [3], and 16 [5] s for occasions 1, 2, and 3, respectively; P = .279).

CONCLUSION

These results indicate proportional enhancements of local muscle oxygen distribution and utilization, which both contributed to the speeding of the V˙O2 on-kinetics herein.

Leg cycling efficiency is unaltered in healthy aging regardless of sex or training status

Muscular efficiency during exercise has been used to interrogate aspects of human muscle energetics, including mitochondrial coupling and biomechanical efficiencies. Typically, assessments of muscular efficiency have involved graded exercises. Results of previous studies have been interpreted to indicate a decline in exercise efficiency with aging owing to decreased mitochondrial function. However, discrepancies in variables such as exercise stage duration, cycling cadence, and treadmill walking mechanics may have affected interpretations of results. Furthermore, recent data from our lab examining the ATP to oxygen ratio (P:O) in mitochondrial preparations isolated from NIA mouse skeletal muscle showed no change with aging. Thus, we hypothesized that delta efficiency (Δ€) during steady-rate cycling exercise would not be altered in older healthy subjects compared with young counterparts regardless of biological sex or training status. Young (21-35 yr) and older (60-80 yr) men (n = 21) and women (n = 20) underwent continual, progressive leg cycle ergometer tests pedaling at 60 RPM for three stages (35, 60, 85 W) lasting 4 min. Δ€was calculated as: (Δ work accomplished/Δ energy expended). Overall, cycling efficiencies were not significantly different in older compared with young subjects. Similarly, trained subjects did not exhibit significantly different exercise efficiencies compared to untrained. Moreover, there were no differences between men and women. Hence, our results obtained on healthy young and older subjects are interpreted to mean that previous reports of decreased efficiency in older individuals were attributable to metabolic or biomechanical comorbidities, not aging per se.NEW & NOTEWORTHY Muscular power is reduced, but the efficiency of movement is unaltered in healthy aging.

No sex differences in oxygen uptake or extraction kinetics in the moderate or heavy exercise intensity domains

The integrative response to exercise differs between sexes, with oxidative energy contribution purported as a potential mechanism. The present study investigated whether this difference was evident in the kinetics of oxygen uptake (V̇o2) and extraction (HHb + Mb) during exercise. Sixteen adults (8 males, 8 females, age: 27 ± 5 yr) completed three experimental visits. Incremental exercise testing was performed to obtain lactate threshold and V̇o2peak. Subsequent visits involved three 6-min cycling bouts at 80% of lactate threshold and one 30-min bout at a work rate of 30% between the lactate threshold and power at V̇o2peak. Pulmonary gas exchange and near-infrared spectroscopy of the vastus lateralis were used to continuously sample V̇o2 and HHb + Mb, respectively. The phase II V̇o2 kinetics were quantified using monoexponential curves during moderate and heavy exercise. Slow component amplitudes were also quantified for the heavy-intensity domain. Relative V̇o2peak values were not different between sexes (P = 0.111). Males achieved ∼30% greater power outputs (P = 0.002). In the moderate- and heavy-intensity domains, the relative amplitude of the phase II transition was not different between sexes for V̇o2 (∼24 and ∼40% V̇o2peak, P ≥ 0.179) and HHb + Mb (∼20 and ∼32% ischemia, P ≥ 0.193). Similarly, there were no sex differences in the time constants for V̇o2 (∼28 s, P ≥ 0.385) or HHb + Mb (∼10 s, P ≥ 0.274). In the heavy-intensity domain, neither V̇o2 (P ≥ 0.686) or HHb + Mb (P ≥ 0.432) slow component amplitudes were different between sexes. The oxidative response to moderate- and heavy-intensity exercises did not differ between males and females, suggesting similar dynamic responses of oxidative metabolism during intensity-matched exercise.NEW & NOTEWORTHY This study demonstrated no sex differences in the oxidative response to moderate- and heavy-intensity cycling exercise. The change in oxygen uptake and deoxyhemoglobin were modeled with monoexponential curve fitting, which revealed no differences in the rate of oxidative energy provision between sexes. This provides insight into previously reported sex differences in the integrative response to exercise.

Acute Oxygen Consumption Response to Fast Start High-Intensity Intermittent Exercise

The current investigation compared the acute oxygen consumption (VO2) response of two high-intensity interval exercises (HIIE), fast start (FSHIIE), and steady power (SPHIIE), which matched w prime (W') depletion. Eight cyclists completed an incremental max test and a three-minute all-out test (3MT) to determine maximal oxygen consumption (VO2max), critical power (CP), and W'. HIIE sessions consisted of 3 X 4 min intervals interspersed by 3 min of active recovery, with W' depleted by 60% (W'target) within each working interval. SPHIIE depleted the W'target consistently throughout the 3 min intervals, while FSHIIE depleted the W'target by 50% within the first minute, with the remaining 50% depleted evenly across the remainder of the interval. The paired samples t-test revealed no differences in the percentage of training time spent above 90% of VO2max (PT ≥ 90% VO2max) between SPHIIE and FSHIIE with an average of 25.20% and 26.07%, respectively. Pairwise comparisons indicated a difference between minute 1 peak VO2, minute 2, and minute 3, while no differences were present between minutes 2 and 3. The results suggest that when HIIE formats are matched based on W' expenditure, there are no differences in PT ≥ 90% VO2max or peak VO2 during each interval.

Aerobic capacity and [Formula: see text] kinetics adaptive responses to short-term high-intensity interval training and detraining in untrained females

PURPOSE

This study investigated the physical fitness and oxygen uptake kinetics (τ[Formula: see text]) along with the O2 delivery and utilization (heart rate kinetics, τHR; deoxyhemoglobin/[Formula: see text] ratio, ∆[HHb]/[Formula: see text]) adaptations of untrained female participants responding to 4 weeks of high-intensity interval training (HIIT) and 2 weeks of detraining.

METHODS

Participants were randomly assigned to HIIT (n = 11, 4 × 4 protocol) or nonexercising control (n = 9) groups. Exercising group engaged 4 weeks of treadmill HIIT followed by 2 weeks of detraining while maintaining daily activity level. Ramp-incremental (RI) tests and step-transitions to moderate-intensity exercise were performed. Aerobic capacity and performance (maximal oxygen uptake, [Formula: see text]; gas-exchange threshold, GET; power output, PO), body composition (skeletal muscle mass, SMM; body fat percentage, BF%), muscle oxygenation status (∆[HHb]), [Formula: see text], and HR kinetics were assessed.

RESULTS

HIIT elicited improvements in aerobic capacity ([Formula: see text], + 0.17 ± 0.04 L/min; GET, + 0.18 ± 0.05 L/min, P < 0.01; PO-[Formula: see text], ± 23.36 ± 8.37 W; PO-GET, + 17.18 ± 3.07 W, P < 0.05), body composition (SMM, + 0.92 ± 0.17 kg; BF%, - 3.08% ± 0.58%, P < 0.001), and speed up the τ[Formula: see text] (- 8.04 ± 1.57 s, P < 0.001) significantly, extending to better ∆[HHb]/[Formula: see text] ratio (1.18 ± 0.08 to 1.05 ± 0.14). After a period of detraining, the adaptation in body composition and aerobic capacity, as well as the accelerated τ[Formula: see text] were maintained in the HIIT group, but the PO-[Formula: see text] and PO-GET declined below the post-training level (P < 0.05), whereas no changes were reported in controls (P > 0.05). Four weeks of HIIT induced widespread physiological adaptations in females, and the majority of improvements were preserved after 2 weeks of detraining except for power output corresponding to [Formula: see text] and GET.

How Priming Exercise Affects Oxygen Uptake Kinetics: From Underpinning Mechanisms to Endurance Performance

The observation that prior heavy or severe-intensity exercise speeds overall oxygen uptake ([Formula: see text]O₂) kinetics, termed the "priming effect", has garnered significant research attention and its underpinning mechanisms have been hotly debated. In the first part of this review, the evidence for and against (1) lactic acidosis, (2) increased muscle temperature, (3) O₂ delivery, (4) altered motor unit recruitment patterns and (5) enhanced intracellular O₂ utilisation in underpinning the priming effect is discussed. Lactic acidosis and increased muscle temperature are most likely not key determinants of the priming effect. Whilst priming increases muscle O₂ delivery, many studies have demonstrated that an increased muscle O₂ delivery is not a prerequisite for the priming effect. Motor unit recruitment patterns are altered by prior exercise, and these alterations are consistent with some of the observed changes in [Formula: see text]O₂ kinetics in humans. Enhancements in intracellular O₂ utilisation likely play a central role in mediating the priming effect, probably related to elevated mitochondrial calcium levels and parallel activation of mitochondrial enzymes at the onset of the second bout. In the latter portion of the review, the implications of priming on the parameters of the power-duration relationship are discussed. The effect of priming on subsequent endurance performance depends critically upon which phases of the [Formula: see text]O₂ response are altered. A reduced [Formula: see text]O₂ slow component or increased fundamental phase amplitude tend to increase the work performable above critical power (i.e. W´), whereas a reduction in the fundamental phase time constant following priming results in an increased critical power.

Walking Endurance and Oxygen Uptake On-Kinetics in Individuals With Parkinson Disease Following Overground Locomotor Training

BACKGROUND AND PURPOSE

Poor walking endurance in Parkinson disease (PD) may be attributable to both bioenergetic and biomechanical factors, but locomotor training methods addressing both these factors simultaneously are understudied. Our objective was to examine the effects of overground locomotor training (OLT) on walking endurance in individuals with mild-to-moderate PD, and to further explore potential cardiorespiratory contributions.

METHODS

A single-arm, longitudinal design was used to examine the effects of 24 biweekly sessions of OLT in people with mild-to-moderate PD (n = 12). Walking endurance was measured as total distance walked during a 10-minute walk test (10minWT). Oxygen uptake (V˙ o2 ) on-kinetic profiles were determined using a monoexponential function. Perceived fatigability was assessed following the 10minWT using a self-report scale. Magnitude of change in primary outcomes was assessed using Cohen's d and adjusted for sample size (Cohen's d(unbiased) ).

RESULTS

Participants executed 3036 (297) steps and maintained 65.5% (8%) age-predicted heart rate maximum in a typical session lasting 56.9 (2.5) minutes. Medium effects in total distance walked-885.9 (157.2) versus 969.5 (140.9); Cohen's d(unbiased) = 0.54-and phase II time constant of the V˙ o2 on-kinetic profile-33.7 (12.3) versus 25.9 (15.3); Cohen's d(unbiased) = 0.54-were observed alongside trivial effects for perceived fatigability-4.7 (1.4) versus 4.8 (1.5); Cohen's d(unbiased) = 0.11-following OLT.

DISCUSSION AND CONCLUSIONS

These preliminary findings may demonstrate the potential for moderate-intensity OLT to improve walking endurance and enhance cardiorespiratory adjustments to walking activity in adults with mild-to-moderate PD.Video Abstract available for more insights from the authors (see the Video, Supplemental Digital Content 1, http://links.lww.com/JNPT/A407 ).

Adaptations to 4 weeks of high-intensity interval training in healthy adults with different training backgrounds

PURPOSE

This study investigated the physical fitness and oxygen uptake kinetics ([Formula: see text]) along with the exercise-onset O₂ delivery (heart rate kinetics, τHR; changes in normalized deoxyhemoglobin/[Formula: see text] ratio, Δ[HHb]/[Formula: see text]) adaptations of individuals with different physical activity (PA) backgrounds responding to 4 weeks of high-intensity interval training (HIIT), and the possible effects of skeletal muscle mass (SMM) on training-induced adaptations.

METHODS

Twenty subjects (10 high-PA level, HIIT-H; 10 moderate-PA level, HIIT-M) engaged in 4 weeks of treadmill HIIT. Ramp-incremental (RI) test and step-transitions to moderate-intensity exercise were performed. Cardiorespiratory fitness, body composition, muscle oxygenation status, VO₂ and HR kinetics were assessed at baseline and post-training.

RESULTS

HIIT improved fitness status for HIIT-H ([Formula: see text], + 0.26 ± 0.07 L/min; SMM, + 0.66 ± 0.70 kg; body fat, - 1.52 ± 1.93 kg; [Formula: see text], - 7.11 ± 1.05 s, p < 0.05) and HIIT-M ([Formula: see text], 0.24 ± 0.07 L/min, SMM, + 0.58 ± 0.61 kg; body fat, - 1.64 ± 1.37 kg; [Formula: see text], - 5.48 ± 1.05 s, p < 0.05) except for visceral fat area (p = 0.293) without between-group differences (p > 0.05). Oxygenated and deoxygenated hemoglobin amplitude during the RI test increased for both groups (p < 0.05) except for total hemoglobin (p = 0.179). The Δ[HHb]/[Formula: see text] overshoot was attenuated for both groups (p < 0.05) but only eliminated in HIIT-H (1.05 ± 0.14 to 0.92 ± 0.11), and no change was observed in τHR (p = 0.144). Linear mixed-effect models presented positive effects of SMM on absolute [Formula: see text] (p < 0.001) and ΔHHb (p = 0.034).

CONCLUSION

Four weeks of HIIT promoted positive adaptations in physical fitness and [Formula: see text] kinetics, with the peripheral adaptations attributing to the observed improvements. The training effects are similar between groups suggesting that HIIT is effective for reaching higher physical fitness levels.

Longitudinal alterations of pulmonary V.O2 on-kinetics during moderate-intensity exercise in competitive youth cyclists are related to alterations in the balance between microvascular O2 distribution and muscular O2 utilization

Purpose

The main purpose of the current study was to investigate the dynamic adjustment of pulmonary oxygen uptake (V.O2) in response to moderate-intensity cycling on three occasions within 15 months in competitive youth cyclists. Furthermore, the muscle Δdeoxy[heme] on-kinetics and the Δdeoxy[heme]-to-V.O2 ratio were modeled to examine possible mechanistic basis regulating pulmonary V.O2 on-kinetics.

Methods

Eleven cyclists (initial age, 14.3 ± 1.6 y; peak V.O2, 62.2 ± 4.5 mL.min−1.kg−1) with a training history of 2–5 years and a training volume of ~10 h per week participated in this investigation. V.O2 and Δdeoxy[heme] responses during workrate-transitions to moderate-intensity cycling were measured with breath-by-breath spirometry and near-infrared spectroscopy, respectively, and subsequently modeled with mono-exponential models to derive parameter estimates. Additionally, a normalized Δdeoxy[heme]-to-V.O2 ratio was calculated for each participant. One-way repeated-measures ANOVA was used to assess effects of time on the dependent variables of the responses.

Results

The V.O2 time constant remained unchanged between the first (~24 s) and second visit (~22 s, P &gt; 0.05), whereas it was significantly improved through the third visit (~13 s, P = 0.006–0.013). No significant effects of time were revealed for the parameter estimates of the Δdeoxy[heme] response (P &gt; 0.05). A significant Δdeoxy[heme]-to-V.O2 ratio “overshoot” was evident on the first (1.09 ± 0.10, P = 0.006) and second (1.05 ± 0.09, P = 0.047), though not the third (0.97 ± 0.10, P &gt; 0.05), occasion. These “overshoots” showed strong positive relationships with the V.O2 time constant during the first (r = 0.66, P = 0.028) and second visit (r = 0.76, P = 0.007). Further, strong positive relationships have been observed between the individual changes of the fundamental phase τp and the Δdeoxy[heme]-to-V.O2 ratio “overshoot” from occasion one to two (r = 0.70, P = 0.017), and two to three (r = 0.74, P = 0.009).

Conclusion

This suggests that improvements in muscle oxygen provision and utilization capacity both occurred, and each may have contributed to enhancing the dynamic adjustment of the oxidative “machinery” in competitive youth cyclists. Furthermore, it indicates a strong link between an oxygen maldistribution within the tissue of interrogation and the V.O2 time constant.

Repeated Ischemic Preconditioning Effects on Physiological Responses to Hypoxic Exercise

INTRODUCTION: Repeated ischemic preconditioning (IPC) can improve muscle and pulmonary oxygen on-kinetics, blood flow, and exercise efficiency, but these effects have not been investigated in severe hypoxia. The aim of the current study was to evaluate the effects of 7 d of IPC on resting and exercising muscle and cardio-pulmonary responses to severe hypoxia.METHODS: A total of 14 subjects received either: 1) 7 d of repeated lower-limb occlusion (4 × 5 min, 217 ± 30 mmHg) at limb occlusive pressure (IPC) or SHAM (4 × 5 min, 20 mmHg). Subjects were tested for resting limb blood flow, relative microvascular deoxyhemoglobin concentration ([HHB]), and pulmonary oxygen (Vo_2p) responses to steady state and incremental exercise to exhaustion in hypoxia (fractional inspired O₂ = 0.103), which was followed by 7 d of IPC or SHAM and retesting 72 h post-intervention.RESULTS: There were no effects of IPC on maximal oxygen consumption, time to exhaustion during the incremental test, or minute ventilation and arterial oxygen saturation. However, the IPC group had higher delta efficiency based on pooled results and lower steady state Δ[HHB] (IPC ∼24% vs. SHAM ∼6% pre to post), as well as slowing the [HHB] time constant (IPC ∼26% vs. SHAM ∼3% pre to post) and reducing the overshoot in [HHB]: Vo₂ ratio during exercise onset.CONCLUSIONS: Collectively, these results demonstrate that muscle O₂ efficiency and microvascular O₂ distribution can be improved by repeated IPC, but there are no effects on maximal exercise capacity in severe hypoxia.Chopra K, Jeffries O, Tallent J, Heffernan S, Kilduff L, Gray A, Waldron M. Repeated ischemic preconditioning effects on physiological responses to hypoxic exercise. Aerosp Med Hum Perform. 2022; 93(1):13-21.

Central and Peripheral Oxygen Distribution in Two Different Modes of Interval Training

In high-intensity interval training the interval duration can be adjusted to optimize training results in oxygen uptake, cardiac output, and local oxygen supply. This study aimed to compare these variables in two interval trainings (long intervals HIIT3m: 3 min work, 3 min active rest vs. short intervals HIIT30s: 30 s work, 30 s active rest) at the same overall work rate and training duration. 24 participants accomplished both protocols, (work: 80% power output at VO₂peak, relief: 85% power output at gas exchange threshold) in randomized order. Spirometry, impedance cardiography, and near-infrared spectroscopy were used to analyze the physiological stress of the cardiopulmonary system and muscle tissue. Although times above gas exchange threshold were shorter in HIIT3m (HIIT3m 1669.9 ± 310.9 s vs. HIIT30s 1769.5 ± 189.0 s, p = 0.034), both protocols evoked similar average fractional utilization of VO₂peak (HIIT3m 65.23 ± 4.68% VO₂peak vs. HIIT30s 64.39 ± 6.78% VO₂peak, p = 0.261). However, HIIT3m resulted in higher cardiovascular responses during the loaded phases (VO₂p < 0.001, cardiac output p < 0.001). Local hemodynamics were not different between both protocols. Average physiological responses were not different in both protocols owning to incomplete rests in HIIT30s and large response amplitudes in HIIT3m. Despite lower acute cardiovascular stress in HIIT30s, short submaximal intervals may also trigger microvascular and metabolic adaptions similar to HIIT3m. Therefore, the adaption of interval duration is an important tool to adjust the goals of interval training to the needs of the athlete or patient.

Key role of left ventricular untwisting in endurance cyclists at onset of exercise

The rise in oxygen consumption during the transition from rest to exercise is faster in those who are endurance-trained than those who have sedentary lifestyles, partly due to a more efficient cardiac response. However, data regarding this acute cardiac response in trained individuals are limited to heart rate (HR), stroke volume, and cardiac output. Considering this, we compared cardiac kinetics, including left ventricular (LV) strains and twist/untwist mechanics, between endurance-trained cyclists and their sedentary counterparts. Twenty young, male, trained cyclists and 23 untrained participants aged 18-25 yr performed five similar constant workload exercises on a cyclo-ergometer (target HR: 130 beats/min). During each session, LV myocardial diastolic and systolic linear strains, as well as torsional mechanics, were assessed using speckle-tracking echocardiography. Cardiac function was evaluated every 15 s during the first minute and every 30 s thereafter, until 240 s. Stroke volume increased during the first 30-45 s in both groups but to a significantly greater extent in trained cyclists (31% vs. 24%). Systolic parameters were similar in both groups. Transmitral peak filling velocity and peak filling rate responded faster to exercise and with greater amplitude in trained cyclists. Left ventricular filling pressure was lower in the former, whereas LV relaxation was greater but only at the base of the left ventricle. Basal rotation and peak untwisting rate responded faster and to a greater extent in the cyclists. This study provides new mechanical insights into the key role of LV untwisting in the more efficient acute cardiac response of endurance-trained athletes at onset of exercise.NEW & NOTEWORTHY Our study assessed for the first time, to our knowledge, the kinetics of left ventricular function during the transition from rest to constant-load exercise in endurance-trained subjects. We observed a faster cardiac response in cyclists characterized by a faster response of cardiac output, left ventricular transmitral filling, basal rotation, and untwisting. This study highlighted the key role of left ventricular twisting mechanics in the more efficient acute cardiac response of endurance-trained athletes at onset of exercise.

Cardiorespiratory responses to exercise related to post-stroke fatigue severity

Physical deconditioning after stroke may induce post-stroke fatigue. However, research on this association is limited. Our primary objective was to investigate the associations of post-stroke fatigue severity with oxygen uptake ([Formula: see text]O₂) at peak exercise and the time constant of [Formula: see text]O₂ kinetics (τ[Formula: see text]O₂) at exercise onset. The secondary objective was to examine the associations between fatigue and cardiorespiratory variables potentially affecting [Formula: see text]O₂ during exercise. Twenty-three inpatients from a subacute rehabilitation ward were enrolled in this study. The median (interquartile range) Fatigue Severity Scale (FSS) score, as a measure of fatigue, was 32 (range 27-42) points. The FSS score was not associated with [Formula: see text]O₂ at peak exercise during a symptom-limited graded exercise test (rho = - 0.264; p = 0.224), whereas it was significantly associated with τ[Formula: see text]O₂ during a submaximal constant-load exercise test (rho = 0.530; p = 0.009). A higher FSS score also significantly correlated with a longer time constant of cardiac output (CO) kinetics (rho = 0.476; p = 0.022). Our findings suggest that severe post-stroke fatigue is associated with delayed increases in [Formula: see text]O₂ and CO at the onset of exercise. Our findings can contribute to the development of an appropriate rehabilitation programme for individuals with post-stroke fatigue.

Cocoa-flavanols enhance moderate-intensity pulmonary [Formula: see text] kinetics but not exercise tolerance in sedentary middle-aged adults

INTRODUCTION

Cocoa flavanols (CF) may exert health benefits through their potent vasodilatory effects, which are perpetuated by elevations in nitric oxide (NO) bioavailability. These vasodilatory effects may contribute to improved delivery of blood and oxygen (O₂) to exercising muscle.

PURPOSE

Therefore, the objective of this study was to examine how CF supplementation impacts pulmonary O₂ uptake ([Formula: see text]) kinetics and exercise tolerance in sedentary middle-aged adults.

METHODS

We employed a double-blind cross-over, placebo-controlled design whereby 17 participants (11 male, 6 female; mean ± SD, 45 ± 6 years) randomly received either 7 days of daily CF (400 mg) or placebo (PL) supplementation. On day 7, participants completed a series of 'step' moderate- and severe-intensity exercise tests for the determination of [Formula: see text] kinetics.

RESULTS

During moderate-intensity exercise, the time constant of the phase II [Formula: see text] kinetics ([Formula: see text]) was decreased by 15% in CF as compared to PL (mean ± SD; PL 40 ± 12 s vs. CF 34 ± 9 s, P = 0.019), with no differences in the amplitude of [Formula: see text] (A[Formula: see text]; PL 0.77 ± 0.32 l min^-1 vs. CF 0.79 ± 0.34 l min^-1, P = 0.263). However, during severe-intensity exercise, [Formula: see text], the amplitude of the slow component ([Formula: see text]) and exercise tolerance (PL 435 ± 58 s vs. CF 424 ± 47 s, P = 0.480) were unchanged between conditions.

CONCLUSION

Our data show that acute CF supplementation enhanced [Formula: see text] kinetics during moderate-, but not severe-intensity exercise in middle-aged participants. These novel effects of CFs, in this demographic, may contribute to improved tolerance of moderate-activity physical activities, which appear commonly present in daily life.

TRIAL REGISTRATION

Registered under ClinicalTrials.gov Identifier no. NCT04370353, 30/04/20 retrospectively registered.

Time-course of V̇o2 kinetics responses during moderate-intensity exercise subsequent to HIIT versus moderate-intensity continuous training in type 2 diabetes

We assessed the time-course of changes in oxygen uptake (V̇o₂) and muscle deoxygenation (i.e., deoxygenated hemoglobin and myoglobin, [HHb + Mb]) kinetics during transitions to moderate-intensity cycling following 12 wk of low-volume high-intensity interval training (HIIT) vs. moderate-intensity continuous training (MICT) in adults with type 2 diabetes (T2D). Participants were randomly assigned to MICT (n = 10, 50 min of moderate-intensity cycling), HIIT (n = 9, 10 × 1 min at ∼90% maximal heart rate), or nonexercising control (n = 9) groups. Exercising groups trained three times per week, and measurements were taken every 3 wk. [HHb + Mb] kinetics were measured by near-infrared spectroscopy at the vastus lateralis muscle. The local matching of O₂ delivery to O₂ utilization was assessed by the Δ[HHb + Mb]/ΔV̇o₂ ratio. The pretraining time constant of the primary phase of V̇o₂ (τV̇o_2p) decreased (P < 0.05) at wk 3 of training in both MICT (from 44 ± 12 to 32 ± 5 s) and HIIT (from 42 ± 8 to 32 ± 4 s) with no further changes thereafter, whereas no changes were reported in controls. The pretraining overall dynamic response of muscle deoxygenation (τ'[HHb + Mb]) was faster than τV̇o_2p in all groups, resulting in Δ[HHb + Mb]/V̇o_2p showing a transient "overshoot" relative to the subsequent steady-state level. After 3 wk, the Δ[HHb + Mb]/V̇o_2p overshoot was eliminated only in the training groups, so that τ'[HHb + Mb] was not different to τV̇o_2p in MICT and HIIT. The enhanced V̇o₂ kinetics response consequent to both MICT and HIIT in T2D was likely attributed to a training-induced improvement in matching of O₂ delivery to utilization.NEW & NOTEWORTHY High-intensity interval training and moderate-intensity continuous training elicited faster pulmonary oxygen uptake (V̇o₂) kinetics during moderate-intensity cycling within 3 wk of training with no further changes thereafter in individuals with type 2 diabetes. These adaptations were accompanied by unaltered near-infrared spectroscopy-derived muscle deoxygenation (i.e. deoxygenated hemoglobin and myoglobin concentration, [HHb+Mb]) kinetics and transiently reduced Δ[HHb+Mb]-to-ΔV̇o₂ ratio, suggesting an enhanced blood flow distribution within the active muscles subsequent to both training interventions.

Association between [Formula: see text]O2 kinetics and [Formula: see text]O2max in groups differing in fitness status

PURPOSE

This study evaluated (i) the relationship between oxygen uptake ([Formula: see text]O₂) kinetics and maximal [Formula: see text]O₂ ([Formula: see text]O_2max) within groups differing in fitness status, and (ii) the adjustment of [Formula: see text]O₂ kinetics compared to that of central [cardiac output (Q̇), heart rate (HR)] and peripheral (deoxyhemoglobin over [Formula: see text]O₂ ratio ([HHb]/[Formula: see text]O₂)] O₂ delivery, during step-transitions to moderate-intensity exercise.

METHODS

Thirty-six young healthy male participants (18 untrained; 18 trained) performed a ramp-incremental test to exhaustion and 3 step-transitions to moderate-intensity exercise. Q̇ and HR kinetics were measured in 18 participants (9 untrained; 9 trained).

RESULTS

No significant correlation between τ̇[Formula: see text]O₂ and [Formula: see text]O_2max was found in trained participants (r = 0.29; p > 0.05) whereas a significant negative correlation was found in untrained (r = - 0.58; p < 0.05) and all participants (r = - 0.82; p < 0.05). τQ̇ (18.8 ± 5.5 s) and τHR (20.1 ± 6.2 s) were significantly greater than τ[Formula: see text]O₂ (13.9 ± 2.7 s) for trained (p < 0.05). No differences were found between τQ̇ (22.8 ± 8.45 s), τHR (21.2 ± 8.3 s) and τ[Formula: see text]O₂ (28.9 ± 5.7 s) for untrained (p > 0.05). τQ̇ demonstrated a significant strong positive correlation with τHR in trained (r = 0.76; p < 0.05) but not untrained (r = 0.61; p > 0.05). A significant overshoot in the [HHb]/[Formula: see text]O₂ ratio was found in the untrained groups (p < 0.05) but not in the trained groups (p > 0.05) CONCLUSION: The results indicated that when comparing participants of different fitness status (i) there is a point at which greater V̇O_2max values are not accompanied by faster [Formula: see text]O₂ kinetics; (ii) central delivery of O₂ does not seem to limit the kinetics of [Formula: see text]O₂; and (iii) O₂ delivery within the active tissues might contribute to the slower [Formula: see text]O₂ kinetics response in untrained participants.

The role of vascular function on exercise capacity in health and disease

Three sentinel parameters of aerobic performance are the maximal oxygen uptake ( V ̇ O 2 max ), critical power (CP) and speed of the V ̇ O 2 kinetics following exercise onset. Of these, the latter is, perhaps, the cardinal test of integrated function along the O2 transport pathway from lungs to skeletal muscle mitochondria. Fast V ̇ O 2 kinetics demands that the cardiovascular system distributes exercise-induced blood flow elevations among and within those vascular beds subserving the contracting muscle(s). Ideally, this process must occur at least as rapidly as mitochondrial metabolism elevates V ̇ O 2 . Chronic disease and ageing create an O2 delivery (i.e. blood flow × arterial [O2 ], Q ̇ O 2 ) dependency that slows V ̇ O 2 kinetics, decreasing CP and V ̇ O 2 max , increasing the O2 deficit and sowing the seeds of exercise intolerance. Exercise training, in contrast, does the opposite. Within the context of these three parameters (see Graphical Abstract), this brief review examines the training-induced plasticity of key elements in the O2 transport pathway. It asks how structural and functional vascular adaptations accelerate and redistribute muscle Q ̇ O 2 and thus defend microvascular O2 partial pressures and capillary blood-myocyte O2 diffusion across a ∼100-fold range of muscle V ̇ O 2 values. Recent discoveries, especially in the muscle microcirculation and Q ̇ O 2 -to- V ̇ O 2 heterogeneity, are integrated with the O2 transport pathway to appreciate how local and systemic vascular control helps defend V ̇ O 2 kinetics and determine CP and V ̇ O 2 max in health and how vascular dysfunction in disease predicates exercise intolerance. Finally, the latest evidence that nitrate supplementation improves vascular and therefore aerobic function in health and disease is presented.

The Relationship Between Repeated-Sprint Ability, Aerobic Capacity, and Oxygen Uptake Recovery Kinetics in Female Soccer Athletes

This study investigated the relationship between repeated-sprint ability, aerobic capacity, and oxygen uptake kinetics during the transition between exercise and recovery (off-transient) in female athletes of an intermittent sport modality. Eighteen professional soccer players completed three tests: 1) a maximal incremental exercise test; 2) a constant speed time-to-exhaustion test; and 3) a repeated-sprint ability test consisting of six 40-m sprints with 20 s of passive recovery in-between. Correlations between time-to-exhaustion, repeated-sprint ability, and oxygen uptake kinetics were calculated afterwards. The level of significance was set at p < 0.05. A performance decrement during repeated-sprint ability was found to be related to: 1) time-to-exhaustion (e.g., exercise tolerance; r = -0.773, p < 0.001); 2) oxygen uptake recovery time (r = 0.601, p = 0.008); and 3) oxygen uptake mean response time of recovery (r = 0.722, p < 0.001). Moreover, the best sprint time (r = -0.601, p = 0.008) and the mean sprint time (r = -0.608, p = 0.007) were found to be related to maximal oxygen uptake. Collectively, these results reinforce the relation between oxygen uptake kinetics and the ability to maintain sprint performance in female athletes. These results may contribute to coaches and training staff of female soccer teams to focus on training and improve their athletes’ aerobic capacity and recovery capacity to improve intermittent exercise performance.

Training-induced changes in muscle contraction patterns enhance exercise performance after short-term neuromuscular electrical stimulation

BACKGROUND: Neuromuscular electrical stimulation (NMES) is a complementary tool for therapeutic exercise for muscle strengthening and may potentially enhance exercise performance. OBJECTIVE: To determine whether high-intensity interval training (HIIT) and continuous aerobic training (CA) coupled with NMES enhance the changes in the eccentric/concentric muscle contraction patterns of hamstring and quadriceps. METHODS: Forty-five healthy sedentary male participants performed cycling training 3 times per week for 8 weeks combined with/without NMES performed at a load equivalent to 65% and 120% of IVO2max (intensity associated with the achievement of maximal oxygen uptake). Anthropometrics, blood lactate measurements, IVO2max, TLimVO2max (time-to-exhaustion) and isokinetic strength parameters were measured at baseline and post-training using a randomized controlled trial. RESULTS: The conventional hamstring-to-quadriceps-ratio (HQR: Hcon/Qcon) at 60∘/s and the Dynamic Control Ratio (DCR: Hecc/Qcon) at 180∘/s significantly increased both in the dominant (D) and non-dominant (ND) limb in the HIIT + NMES group (p< 0.05). There was a positive significant correlation between the individual changes in D HQR at 60∘/s and IVO2max (r= 0.94, p= 0.005) and the DCR at 180∘/s and TLimVO2max (r= 0.90, p= 0.015), respectively. CONCLUSIONS: The increases in the eccentric muscle contraction and DCR following HIIT + NMES seem to improve fatigue tolerance, cause less fatigue and oxidative stress on the lower limb during pedaling at high intensities.

Cardiopulmonary exercise testing in patients with non-small cell lung cancer: trust the V˙ O2peak?

Background

Maximal oxygen consumption (V^˙ O_2max) is the most frequently used variable to determine postoperative risk in patients with non-small cell lung cancer (NSCLC), however patients frequently cannot provide the necessary maximum effort to ensure the validity of the V^˙ O₂ measurements. The aim of this observational study was to assess exercise-limiting factors and the rate of achievement of the currently recommended maximality criteria in patients with NSCLC who had been routinely referred for cardiopulmonary exercise testing (CPET) to assess their postoperative risk.

Methods

Patient data, including peak exercise variables and markers used to designate the exercise test as maximal, were retrospectively analysed from 203 preoperative CPET assessments that were performed at Rouen University Hospital from January 2014 until July 2019.

Results

Ventilatory limitation was the most common physiological cause of exercise cessation. A total of 62 patients (or 30.5%) achieved either one, or no, markers of maximality. The mean duration of the incremental phase (after the 3-minute warm-up) was 5.1±2 minutes.

Conclusions

About 30% of the patients in this study did not generate maximum effort during CPET. As a result, it is likely that their V^˙ O_2peak was underestimated and that their post-operative risk was overestimated. It is therefore important to incorporate strategies to verify V^˙ O_2peak results for patients with _values close to the risk threshold.

A Comparison of V̇O , and Muscle and Prefrontal Cortex Tissue Oxygen Extraction between Short and Long-term Aerobically Trained Men Aged 40 - 60 Years

This study was designed to compare systemic O2 utilization (V̇O2), and changes in tissue O2 extraction [deoxyhemoglobin (ΔHHb)] in the vastus lateralis (VL), gastrocnemius (GAST) and pre-frontal cortex (PFC) tissue; between aerobically short-term trained (STT) and long-term trained (LTT) older men (40 - 60 yr) who were matched for current training load. On separate occasions, 14 STT and 14 LTT participants completed ramp incremental (RI) and square-wave constant load (SWCL) tests on a cycle ergometer. In LTT compared to STT; (i) V̇O2 was higher during the RI (p > 0.001) and SWCL (p > 0.001) tests, (ii) ΔHHb in the GAST was greater in SWCL (p = 0.011); and (iii) ΔHHb in the PFC was greater at 90% GET during SWCL (p = 0.011). The additional years of training in LTT compared to STT (LTT 17.50yr ± 6.94yr vs STT 1.68yr ± 0.31yr) were associated with higher V̇O2peak, and sub-GET V̇O2, and ΔHHb in the GAST and PFC at sub-GET exercise, despite there being no difference in current training volume.

Test-retest reliability of pulmonary oxygen uptake and muscle deoxygenation during moderate- and heavy-intensity cycling in youth elite-cyclists

To establish the test-retest reliability of pulmonary oxygen uptake (V̇O₂), muscle deoxygenation (deoxy[haem]) and tissue oxygen saturation (StO₂) kinetics in youth elite-cyclists. From baseline pedalling, 15 youth cyclists completed 6-min step transitions to a moderate- and heavy-intensity work rate separated by 8 min of baseline cycling. The protocol was repeated after 1 h of passive rest. V̇O₂ was measured breath-by-breath alongside deoxy[haem] and StO₂ of the vastus lateralis by near-infrared spectroscopy. Reliability was assessed using 95% limits of agreement (LoA), the typical error (TE) and the intraclass correlation coefficient (ICC). During moderate- and heavy-intensity step cycling, TEs for the amplitude, time delay and time constant ranged between 3.5-21.9% and 3.9-12.1% for V̇O₂ and between 6.6-13.7% and 3.5-10.4% for deoxy[haem], respectively. The 95% confidence interval for estimating the kinetic parameters significantly improved for ensemble-averaged transitions of V̇O₂ (p < 0.01) but not for deoxy[haem]. For StO₂, the TEs for the baseline, end-exercise and the rate of deoxygenation were 1.0-42.5% and 1.1-5.5% during moderate- and heavy-intensity exercise, respectively. The ICC ranged from 0.81 to 0.99 for all measures. Test-retest reliability data provide limits within which changes in V̇O₂, deoxy[haem] and StO₂ kinetics may be interpreted with confidence in youth athletes.

Benefits of a four-week functional restoration program in chronic low back pain patients and three-month follow-up: focus on paraspinal muscle aerobic metabolism responses to exercise

BACKGROUND

Chronic low back pain (CLBP) is a major health concern characterized by paraspinal muscle fatigability. This can be improved following a functional restoration program. Muscle fatigability can be related to impairment in aerobic metabolism responses. In this study, we investigated paraspinal muscles aerobic metabolism in CLBP patients before and after a functional restoration program, in order to determine if the enhancement in patients' condition following the program is associated to changes in metabolism responses.

METHODS

Twenty-two CLBP patients (11 women, 11 men; 41.6±1.8 years; 73.7±3.1 kg; 1.74±0.02 m) were evaluated before and after a 4-week functional restoration program, with exercise therapy as the main component. Three months later, 12 patients were seen for a follow-up visit. During each testing session, patients performed a five-minute isokinetic trunk extension exercise in measuring pulmonary gas exchanges and paraspinal muscle oxygenation. Mechanical efficiency and onset V̇O<inf>2</inf> kinetics were also calculated, in addition to usual questionnaires and exercises designed to evaluate psychosocial and physical factors.

RESULTS

At the end of the program, paraspinal muscle oxygenation, mechanical efficiency, and the V̇O<inf>2</inf> onset kinetics were improved (P<0.05). All measures remained stable during the three-month follow-up except for paraspinal muscle oxygenation, which deteriorated (P<0.05). Return-to-work was associated with the level of workday physical activities and to a decrease in fear-avoidance beliefs.

CONCLUSIONS

At the end of the program, aerobic metabolism responses were improved in paraspinal muscles in patients. These improvements were not associated with return-to-work, which was primarily influenced by socio-psychological factors.

The effect of age and training status on oxygen uptake kinetics in women

We examined the effect of age and training status on the oxygen uptake (V˙ O₂) kinetics of untrained and recreationally trained women. Young (20-35yr), middle-age (40-55yr) and older (58-71yr) recreationally trained (YTR, n = 10; MTR, n = 12; OTR, n = 9) and untrained (YUT, n = 12; MUT, n = 10; OUT, n = 9) women participated in this crossectional study. Breath-by-breath V˙ O₂ and near-infrared-spectroscopy-derived (NIRS) muscle deoxygenation [HHb] were monitored continuously during increasing and constant walking exercises. On-transition V˙ O₂ and [HHb] responses to moderate intensity walking were modeled as mono-exponential. The data were normalized for each subject (0%-100 %), and [HHb]/ V˙ O₂ ratio was calculated as the average [HHb]/ V˙ O₂ during the 20- to 120-s period after the onset of moderate intensity walking exercise. The time constant of V˙ O₂ (τ V˙ O₂) was longer in OUT(23.8 ± 2.4), MUT(25.4 ± 5.1), YUT(23.1 ± 3.4) than in YTR(16.2 ± 2.0), MTR(16.7 ± 3.9), OTR(16.3 ± 2.8) women (p < 0.05). The [HHb]/ V˙ O₂ ratio in OUT (1.31 ± 0.18) was higher than in YTR(1.08 ± 0.05), MTR(1.13 ± 0.09), YUT(1.12 ± 0.09) (p < 0.05). It is concluded that recreationally trained women had faster V˙ O₂ kinetics along with better matching of O₂ delivery and utilization at the site of gas exchange in the exercising muscles.

Effect of a 3-Weeks Training Camp on Muscle Oxygenation, V ˙ O2 and Performance in Elite Sprint Kayakers

Purpose: Peripheral adaptations, as assessed via near-infrared spectroscopy (NIRS) derived changes in muscle oxygenation (SmO2), are good predictors of sprint kayak performance. Therefore, the goal of the present study was to assess changes in SmO2 andV ˙ O2 following a training camp in elite sprint kayakers to evaluate if the training prescribed elicits peripheral adaptations, and to assess associations between training-induced changes in physiological responses and performance. Methods: Eight male elite sprint kayakers, members of the Canadian National Team, performed a 200-m and 1,000-m on-water time trial (TT) before and after a 3-weeks winter training camp. Change in performance,V ˙ O2 and SmO2 of the biceps brachii were assessed in relation to training load. Results: Training load and intensity were increased by ~20% over the course of the training camp, which resulted in a 3.7 ± 1.7% (ES 1.2) and 2.8 ± 2.4% (ES 1.3) improvement in 200-m and 1,000-m performance, respectively. Performance improvement in the 200-m was concomitant to a reduced SmO2, an increasedV ˙ O2 peak and an increased reoxygenation rate after the TT. The 1,000-m TT performance improvement was concurrent with a reduced SmO2 in the last half of the TT and an increasedV ˙ O2 in the first minute of the TT. Conclusion: Our results strongly suggest that peripheral skeletal muscle adaptations occurred in these athletes with the proposed training plan. This further attests the benefit of using portable NIRS as a monitoring tool to track training-induced adaptations in muscle oxygen extraction in elite athletes.

Speeding of oxygen uptake kinetics is not different following low-intensity blood-flow-restricted and high-intensity interval training

NEW FINDINGS

What is the central question of this study? Can interval blood-flow-restricted (BFR) cycling training, undertaken at a low intensity, promote a similar adaptation to oxygen uptake ( V ̇ O 2 ) kinetics to high-intensity interval training? What is the main finding and its importance? Speeding of pulmonary V ̇ O 2 on-kinetics in healthy young subjects was not different between low-intensity interval BFR training and traditional high-intensity interval training. Given that very low workloads are well tolerated during BFR cycle training and speed V ̇ O 2 on-kinetics, this training method could be used when high mechanical loads are contraindicated.

ABSTRACT

Low-intensity blood-flow-restricted (BFR) endurance training is effective to increase aerobic capacity. Whether it speeds pulmonary oxygen uptake ( V ̇ O 2 p ), CO₂ output ( V ̇ C O 2 p ) and ventilatory ( V ̇ Ep ) kinetics has not been examined. We hypothesized that low-intensity BFR training would reduce the phase 2 time constant (τ_p ) of V ̇ O 2 p , V ̇ C O 2 p and V ̇ Ep by a similar magnitude to traditional high-intensity interval training (HIT). Low-intensity interval training with BFR served as a control. Twenty-four participants (25 ± 6 years old; maximal V ̇ O 2 46 ± 6 ml kg^-1  min^-1 ) were assigned to one of the following: low-intensity BFR interval training (BFR; n = 8); low-intensity interval training without BFR (LOW; n = 7); or high-intensity interval training without BFR (HIT; n = 9). Training was 12 sessions of two sets of five to eight × 2 min cycling and 1 min resting intervals. LOW and BFR were conducted at 30% of peak incremental power (P_peak ), and HIT was at ∼103% P_peak . For BFR, cuffs were inflated on both thighs (140-200 mmHg) during exercise and deflated during rest intervals. Six moderate-intensity step transitions (30% P_peak ) were averaged for analysis of pulmonary on-kinetics. Both BFR (pre- versus post-training τ_p  = 18.3 ± 3.2 versus 14.5 ± 3.4 s; effect size = 1.14) and HIT (τ_p  = 20.3 ± 4.0 versus 13.1 ± 2.9 s; effect size = 1.75) reduced the V ̇ O 2 p τ_p (P < 0.05). As expected, there was no change in LOW ( V ̇ O 2 p τ_p  = 17.9 ± 6.2 versus 17.7 ± 4.3 s; P = 0.9). The kinetics of V ̇ C O 2 p and V ̇ Ep were speeded only after HIT (38.5 ± 10.6%, P < 0.001 and 31.2 ± 24.7%, P = 0.004, respectively). Both HIT and low-intensity BFR training were effective in speeding moderate-intensity V ̇ O 2 p kinetics. These data support the findings of others that low-intensity cycling training with BFR increases muscle oxidative capacity.

Influence of priming exercise on oxygen uptake and muscle deoxygenation kinetics during moderate-intensity cycling in type 2 diabetes

The pulmonary oxygen uptake (V̇o2) kinetics during the transition to moderate-intensity exercise is slowed in individuals with type 2 diabetes (T2D), at least in part because of limitations in O2 delivery. The present study tested the hypothesis that a prior heavy-intensity warm-up or “priming” exercise (PE) bout would accelerate V̇o2 kinetics in T2D, because of a better matching of O2 delivery to utilization. Twelve middle-aged individuals with T2D and 12 healthy controls (ND) completed moderate-intensity constant-load cycling bouts either without (Mod A) or with (Mod B) prior PE. The rates of muscle deoxygenation (i.e., deoxygenated hemoglobin and myoglobin concentration, [HHb+Mb]) and oxygenation (i.e., tissue oxygenation index) were continuously measured by near-infrared spectroscopy at the vastus lateralis muscle. The local matching of O2 delivery to O2 utilization was assessed by the Δ[HHb+Mb]-to-ΔV̇o2 ratio. Both groups demonstrated an accelerated V̇O2 kinetics response during Mod B compared with Mod A (T2D, 32 ± 9 vs. 42 ± 12 s; ND, 28 ± 9 vs. 34 ± 8 s; means ± SD) and an elevated muscle oxygenation throughout Mod B, whereas the [HHb+Mb] amplitude was greater during Mod B only in individuals with T2D. The [HHb+Mb] kinetics remained unchanged in both groups. In T2D, Mod B was associated with a decrease in the “overshoot” relative to steady state in the Δ[HHb+Mb]-to-ΔV̇o2 ratio (1.17 ± 0.17 vs. 1.05 ± 0.15), whereas no overshoot was observed in the control group before (1.04 ± 0.12) or after (1.01 ± 0.12) PE. Our findings support a favorable priming-induced acceleration of the V̇o2 kinetics response in middle-aged individuals with uncomplicated T2D attributed to an enhanced matching of microvascular O2 delivery to utilization.

NEW & NOTEWORTHY Heavy-intensity “priming” exercise (PE) elicited faster pulmonary oxygen uptake (V̇o2) kinetics during moderate-intensity cycling exercise in middle-aged individuals with type 2 diabetes (T2D). This was accompanied by greater near-infrared spectroscopy-derived muscle deoxygenation (i.e., deoxygenated hemoglobin and myoglobin concentration, [HHb+Mb]) responses and a reduced Δ[HHb+Mb]-to-ΔV̇o2 ratio. This suggests that the PE-induced acceleration in oxidative metabolism in T2D is a result of greater O2 extraction and better matching between O2 delivery and utilization.

Relationship between (non)linear phase II pulmonary oxygen uptake kinetics with skeletal muscle oxygenation and age in 11-15 year olds

NEW FINDINGS

What is the central question of this study? Do the phase II parameters of pulmonary oxygen uptake ( V ̇ O 2 ) kinetics display linear, first-order behaviour in association with alterations in skeletal muscle oxygenation during step cycling of different intensities or when exercise is initiated from an elevated work rate in youths. What is the main finding and its importance? Both linear and non-linear features of phase II V ̇ O 2 kinetics may be determined by alterations in the dynamic balance between microvascular O₂ delivery and utilization in 11-15 year olds. The recruitment of higher-order (i.e. type II) muscle fibres during 'work-to-work' cycling might be responsible for modulating V ̇ O 2 kinetics with chronological age.

ABSTRACT

This study investigated in 19 male youths (mean age: 13.6 ± 1.1 years, range: 11.7-15.7 years) the relationship between pulmonary oxygen uptake ( V ̇ O 2 ) and muscle deoxygenation kinetics during moderate- and very heavy-intensity 'step' cycling initiated from unloaded pedalling (i.e. U → M and U → VH) and moderate to very heavy-intensity step cycling (i.e. M → VH). Pulmonary V ̇ O 2 was measured breath-by-breath along with the tissue oxygenation index (TOI) of the vastus lateralis using near-infrared spectroscopy. There were no significant differences in the phase II time constant ( τ V ̇ O 2 p ) between U → M and U → VH (23 ± 6 vs. 25 ± 7 s; P = 0.36); however, the τ V ̇ O 2 p was slower during M → VH (42 ± 16 s) compared to other conditions (P < 0.001). Quadriceps TOI decreased with a faster (P < 0.01) mean response time (MRT; i.e. time delay + τ) during U → VH (14 ± 2 s) compared to U → M (22 ± 4 s) and M → VH (20 ± 6 s). The difference (Δ) between the τ V ̇ O 2 p and MRT-TOI was greater during U → VH compared to U → M (12 ± 7 vs. 2 ± 7 s, P < 0.001) and during M → VH (23 ± 15 s) compared to other conditions (P < 0.02), suggesting an increased proportional speeding of fractional O₂ extraction. The slowing of the τ V ̇ O 2 p during M → VH relative to U → M and U → VH correlated positively with chronological age (r = 0.68 and 0.57, respectively, P < 0.01). In youths, 'work-to-work' transitions slowed microvascular O₂ delivery-to-O₂ utilization with alterations in phase II V ̇ O 2 dynamics accentuated between the ages of 11 and 15 years.

Edward F. Adolph Distinguished Lecture. Contemporary model of muscle microcirculation: gateway to function and dysfunction

This review strikes at the very heart of how the microcirculation functions to facilitate blood-tissue oxygen, substrate, and metabolite fluxes in skeletal muscle. Contemporary evidence, marshalled from animals and humans using the latest techniques, challenges iconic perspectives that have changed little over the past century. Those perspectives include the following: the presence of contractile or collapsible capillaries in muscle, unitary control by precapillary sphincters, capillary recruitment at the onset of contractions, and the notion of capillary-to-mitochondrial diffusion distances as limiting O₂ delivery. Today a wealth of physiological, morphological, and intravital microscopy evidence presents a completely different picture of microcirculatory control. Specifically, capillary red blood cell (RBC) and plasma flux is controlled primarily at the arteriolar level with most capillaries, in healthy muscle, supporting at least some flow at rest. In healthy skeletal muscle, this permits substrate access (whether carried in RBCs or plasma) to a prodigious total capillary surface area. Pathologies such as heart failure or diabetes decrease access to that exchange surface by reducing the proportion of flowing capillaries at rest and during exercise. Capillary morphology and function vary disparately among tissues. The contemporary model of capillary function explains how, following the onset of exercise, muscle O₂ uptake kinetics can be extremely fast in health but slowed in heart failure and diabetes impairing contractile function and exercise tolerance. It is argued that adoption of this model is fundamental for understanding microvascular function and dysfunction and, as such, to the design and evaluation of effective therapeutic strategies to improve exercise tolerance and decrease morbidity and mortality in disease.

The effect of minimally invasive surgical aortic valve replacement on postoperative pulmonary and skeletal muscle function

NEW FINDINGS

What is the central question of this study? How does surgical aortic valve replacement affect cardiopulmonary and muscle function during exercise? What is the main finding and its importance? Early after the surgical replacement of the aortic valve a significant decline in pulmonary function was observed, which was followed by a decline in skeletal muscle function in the subsequent weeks of recovery. These date reiterate, despite restoration of aortic valve function, the need for a tailored rehabilitation programme for the respiratory and peripheral muscular system.

ABSTRACT

Suboptimal post-operative improvements in functional capacity are often observed after minimally invasive aortic valve replacement (mini-AVR). It remains to be studied how AVR affects the cardiopulmonary and skeletal muscle function during exercise to explain these clinical observations and to provide a basis for improved/tailored post-operative rehabilitation. Twenty-two patients with severe aortic stenosis (AS) (aortic valve area (AVA) <1.0 cm²) were pre-operatively compared to 22 healthy controls during submaximal constant-workload endurance-type exercise for oxygen uptake ( V ̇ O 2 ), carbon dioxide output ( V ̇ C O 2 ), respiratory gas exchange ratio, expiratory volume ( V ̇ E ), ventilatory equivalents for O₂ ( V ̇ E / V ̇ O 2 ) and CO₂ ( V ̇ E / V ̇ C O 2 ), respiratory rate (RR), tidal volume (V_t ), heart rate (HR), oxygen pulse ( V ̇ O 2 /HR), blood lactate, Borg ratings of perceived exertion (RPE) and exercise-onset V ̇ O 2 kinetics. These exercise tests were repeated at 5 and 21 days after AVR surgery (n = 14), along with echocardiographic examinations. Respiratory exchange ratio and ventilatory equivalents ( V ̇ E / V ̇ O 2 and V ̇ E / V ̇ C O 2 ) were significantly elevated, V ̇ O 2 and V ̇ O 2 /HR were significantly lowered, and exercise-onset V ̇ O 2 kinetics were significantly slower in AS patients vs. healthy controls (P < 0.05). Although the AVA was restored by mini-AVR in AS patients, V ̇ E / V ̇ O 2 and V ̇ E / V ̇ C O 2 further worsened significantly within 5 days after surgery, accompanied by elevations in Borg RPE, V ̇ E and RR, and lowered V_t . At 21 days after mini-AVR, exercise-onset V ̇ O 2 kinetics further slowed significantly (P < 0.05). A decline in pulmonary function was observed early after mini-AVR surgery, which was followed by a decline in skeletal muscle function in the subsequent weeks of recovery. Therefore, a tailored rehabilitation programme should include training modalities for the respiratory and peripheral muscular system.

Understanding near infrared spectroscopy and its application to skeletal muscle research

Near infrared spectroscopy (NIRS) is a powerful noninvasive tool with which to study the matching of oxygen delivery to oxygen utilization and the number of new publications utilizing this technique has increased exponentially in the last 20 yr. By measuring the state of oxygenation of the primary heme compounds in skeletal muscle (hemoglobin and myoglobin), greater understanding of the underlying control mechanisms that couple perfusive and diffusive oxygen delivery to oxidative metabolism can be gained from the laboratory to the athletic field to the intensive care unit or emergency room. However, the field of NIRS has been complicated by the diversity of instrumentation, the inherent limitations of some of these technologies, the associated diversity of terminology, and a general lack of standardization of protocols. This Cores of Reproducibility in Physiology (CORP) will describe in basic but important detail the most common methodologies of NIRS, their strengths and limitations, and discuss some of the potential confounding factors that can affect the quality and reproducibility of NIRS data. Recommendations are provided to reduce the variability and errors in data collection, analysis, and interpretation. The goal of this CORP is to provide readers with a greater understanding of the methodology, limitations, and best practices so as to improve the reproducibility of NIRS research in skeletal muscle.

Oxygen Availability in Respiratory Muscles During Exercise in Children Following Fontan Operation

Introduction: As survival of previously considered as lethal congenital heart disease forms is the case in our days, issues regarding quality of life including sport and daily activities emerge. In patients with Fontan circulation, there is no pump to propel blood into the pulmonary arteries since the systemic veins are directly connected to the pulmonary arteries. The complex hemodynamics of Fontan circulation include atrial function, peripheral muscle pump, integrity of the atrioventricular valve, absence of restrictive, or obstructive pulmonary lung function. Therefore, thoracic mechanics are of particular importance within the complex hemodynamics of Fontan circulation. Methods: To understand the physiology of respiratory muscles, the aim of this study was to examine the matching of auxiliary respiratory muscle oxygen delivery and utilization during incremental exercise in young male Fontan patients (n = 22, age = 12.04 ± 2.51) and healthy Controls (n = 10, age = 14.90 ± 2.23). All subjects underwent a cardiopulmonary exercise test (CPET) to exhaustion whereas respiratory muscle oxygenation was measured non-invasively using a near-infrared spectrometer (NIRS). Results: CPET revealed significantly lower peak power output, oxygen uptake and breath activity in Fontan patients. The onset of respiratory muscle deoxygenation was significantly earlier. The matching of local muscle perfusion to oxygen demand was significantly worse in Fontans between 50 and 90% V . O 2 peak . Findings: The results indicate that (a) there is high strain on respiratory muscles during incremental cycling exercise and (b) auxiliary respiratory muscles are worse perfused in patients who underwent a Fontan procedure compared to healthy Controls. This might be indicative of a more general skeletal muscle strain and worse perfusion in Fontan patients rather than a localized-limited to thoracic muscles phenomenon.

Effect of Endurance and Strength Training on the Slow Component of O 2 Kinetics in Elderly Humans

We compared the effects of 8 weeks of high intensity, aerobic interval training (HIT) and isoinertial resistance training (IRT) on: (i) O₂ kinetics during heavy (HiEx) intensity exercise and; (ii) work economy during moderate (ModEx) intensity exercise in 12 healthy elderly men (69.3 ± 4.2 years). Breath-by-breath O₂ and muscle deoxygenation ([HHb] by means of NIRS) were measured in HiEx and ModEx at identical workloads before and after trainings. In HiEx, O₂ and HHb responses were modeled as tri-exponential and mono-exponential increasing functions, respectively. A two-way ANOVA for repeated measures analysis was made; Effect size (η²) was also evaluated. After HIT the amplitude and the time delay of the slow component of O₂ uptake (O_2sc) during HiEx were smaller (−32%; P = 0.045) and longer (+19.5%; P = 0.001), respectively. At Post IRT: (i) during ModEx, gain was lower (−5%; P = 0.050); (ii) during HiEx, τ₂ (+14.4%; P = 0.050), d₃ (+8.6%; P = 0.050), and τ₃ (+17.2%; P = 0.050) were longer than at Pre IRT. After HIT, the decrease of the O_2sc amplitude was likely induced by the beneficial effects of training on a more responsive O₂ delivery and consumption cascade leading to a better muscle metabolic stability. IRT training was able to increase exercise economy during ModEx and to reduce the amplitude and delay the onset of O_2sc during HiEx. These effects should be due to the reduction and the delayed recruitment of Type II muscle fibers. The better exercise economy and the delayed appearance of O_2sc induced by IRT suggests that strength training might be included in endurance training programs to improve exercise economy and resistance to fatigue in this population of old subjects.

Impact of venous return on pulmonary oxygen uptake kinetics during dynamic exercise: in silico time series analyses from muscles to lungs

The aim of the present study was to investigate whether a single-compartment (SCM) and a multi-compartment (MCM) venous return model will produce significantly different time-delaying and distortive effects on pulmonary oxygen uptake (V̇o2pulm) responses with equal cardiac outputs (Q̇) and muscle oxygen uptake (V̇o2musc) inputs. For each model, 64 data sets were simulated with alternating Q̇ and V̇o2musc kinetics—time constants (τ) ranging from 10 to 80 s—as responses to pseudorandom binary sequence work rate (WR) changes. Kinetic analyses were performed by using cross-correlation functions (CCFs) between WR with V̇o2pulm and V̇o2musc. Higher maxima of the CCF courses indicate faster system responses—equal to smaller τ values of the variables of interest (e.g., τV̇o2musc). The models demonstrated a highly significant relationship for the resulting V̇o2pulm responses ( r = 0.976, P < 0.001, n = 64). Both models showed significant differences between V̇o2pulm and V̇o2musc kinetics for τV̇o2musc ranging from 10 to 30 s ( P < 0.05 each). In addition, a significant difference in V̇o2pulm kinetics ( P < 0.05) between the models was observed for very fast V̇o2musc kinetics (τ = 10 s). The combinations of fast Q̇ dynamics and slow V̇o2musc kinetics yield distinct deviations in the resultant V̇o2pulm responses compared with V̇o2musc kinetics. Therefore, the venous return models should be used with care and caution if the aim is to infer V̇o2musc by means of V̇o2pulm kinetics. Finally, the resultant V̇o2pulm responses seem to be complex and most likely unpredictable if no cardiodynamic measurements are available in vivo.

NEW & NOTEWORTHY A single-compartment and a multi-compartment venous return model were tested to see whether they result in different pulmonary oxygen uptake (V̇o2pulm) kinetics from equal cardiac output and muscle oxygen uptake (V̇o2musc) kinetics. To infer V̇o2musc kinetics by means of V̇o2pulm kinetics, both models should only be used for V̇o2musc time constants ranging from 40 to 80 s. The resultant V̇o2pulm responses seem to be complex and most likely unpredictable if no cardiodynamic measurements are available.

Habitual exercise training in older adults offsets the age-related prolongation in leg vasodilator kinetics during single-limb lower body exercise

We tested the hypothesis that aging is associated with prolonged leg vasodilator kinetics and habitual exercise training in older adults improves these responses relative to untrained older adults. Additionally, we examined the relationship between contraction-induced rapid onset vasodilation (ROV) and vasodilator kinetics. Young ( n = 10), older untrained ( n = 13), and older trained ( n = 14) adults performed single and rhythmic knee-extension contractions at 20% and 40% work-rate maximum (WR_max). Femoral artery diameter and mean blood velocity were measured by Doppler ultrasound. Vascular conductance (VC; ml·min^-1·mmHg^-1) was calculated using blood flow (ml/min) and mean arterial pressure (mmHg). The primary outcome was the kinetic response (mean response time; MRT), modeled using an exponential model, expressed as the number of duty cycles to change 63% of the steady-state amplitude. There were no age- or training-related differences in VC MRT between the groups at 20% WR_max. Older untrained adults exhibited prolonged VC MRT at 40% WR_max relative to young (37 ± 16 vs. 24 ± 10 duty-cycles; P < 0.05) and older trained adults (37 ± 16 vs. 23 ± 14 duty-cycles; P < 0.05). There were no differences in VC MRT between young and older trained adults at 40% WR_max ( P = 0.96). There were no associations between peak ROV and VC MRT at 20% or 40% WR_max ( r = -0.08 and 0.22; P = 0.67 and 0.20, respectively) in the group as a whole. Our data suggest 1) advancing age prolongs leg vasodilator kinetics; 2) habitual exercise training in older adults offsets this age-related prolongation; and 3) contraction-induced ROV is not related to vasodilator kinetics within a group of young and older adults. NEW & NOTEWORTHY Aging is associated with reductions in exercise hyperemia and vasodilation at the onset of exercise, as well as during steady-state exercise. Habitual endurance exercise training offsets these age-related reductions. We found that aging prolongs vasodilator kinetics in the leg of older untrained but not older trained adults. Finally, our results demonstrate that contraction-induced rapid vasodilation is not associated with vasodilator kinetics within the leg of young and older adults.

Changes in pulmonary oxygen uptake and muscle deoxygenation kinetics during cycling exercise in older women performing walking training for 12 weeks

PURPOSE

This study examined the hypothesis that walking training (WT) could accelerate the slowed time constant (τ) of phase II in pulmonary oxygen uptake ([Formula: see text]O₂) on-kinetics in older women. Also, we aimed to demonstrate that O₂ delivery and O₂ utilization were better matched at the site of gas exchange in exercising muscles when τ[Formula: see text]O₂ was shortened.

METHODS

20 recreationally active older women underwent WT sessions of approximately 60 min, 3-4 times a week for 12 weeks. We assessed [Formula: see text]O₂, heart rate (HR) and deoxygenated-hemoglobin concentration ([HHb]) kinetics during a constant-load exercise test before training (0 week-Pre), and at 6 and 12 weeks (6 weeks-Mid, 12 weeks-Post) throughout the training period.

RESULTS

Maximal oxygen uptake ([Formula: see text]O_2max) was unchanged throughout the training program. τHR tended to decline at Mid (58.6 ± 22.0 s), and was significantly shorter at Post (51.7 ± 21.7 s, p = 0.01) compared to Pre (67.1 ± 23.8 s). τ[Formula: see text]O₂ significantly decreased from 38.9 ± 8.6 s for Pre, to 31.5 ± 7.9 s for Mid (p = 0.02), and 32.3 ± 10.5 s for Post (p = 0.03). The normalized [HHb] to [Formula: see text]O₂ ratio (Δ[HHb]/Δ[Formula: see text]O₂) at Pre (1.32 ± 0.93) gradually approached the perfectly matched value (= 1.0) at Mid (1.15 ± 0.61) and Post (1.07 ± 0.52).

CONCLUSIONS

The restoration to baseline (≒ 30 s) of the slower τ[Formula: see text]O₂ due to WT, which may reflect better matching of O₂ delivery and O₂ utilization at the site of gas exchange, suggests that a longer period of WT could be a useful tool for improving exercise tolerance in older individuals.

Oxygen uptake on-kinetics before and after aerobic exercise training in individuals with traumatic brain injury

Objective: The high prevalence of fatigue among persons with traumatic brain injury (TBI) may be related to poor cardiorespiratory fitness observed in this population. Oxygen uptake on-kinetics is a method of assessing cardiorespiratory fitness and may be used to examine performance fatigability (decline in performance during a given activity) in persons with TBI.Purpose: To examine the effect of aerobic exercise training on oxygen uptake on-kinetics during treadmill walking in individuals with TBI.Methods: Seven ambulatory adults with chronic non-penetrating TBI performed short moderate-intensity (3-6 metabolic equivalents) walking bouts on a treadmill, prior to and following an aerobic exercise training program (clinicaltrials.gov: NCT01294332). The 12-week training program consisted of vigorous-intensity exercise on a treadmill for 30 min, 3 times a week. Breath-by-breath pulmonary gas exchange was measured throughout the bouts, and oxygen uptake on-kinetics described the time taken to achieve a steady-state response.Results: Faster oxygen uptake on-kinetics was observed after exercise training, for both the absolute and relative intensity as pre-training.Conclusions: Faster oxygen uptake on-kinetics following aerobic exercise training suggests an attenuated decline in physical performance during a standardized walking bout and improved performance fatigability in these individuals with TBI.Implications for rehabilitationSevere fatigue is a common complaint among persons with traumatic brain injury (TBI).Oxygen uptake on-kinetics may be used as an objective physiological measure of performance fatigability in persons with TBI.Faster oxygen uptake on-kinetics following aerobic exercise training suggests improved performance fatigability in these individuals with TBI.Aerobic exercise training appeared beneficial for reducing performance fatigability and may be considered as part of the rehabilitative strategy for those living with TBI.

Temporal dissociation between muscle and pulmonary oxygen uptake kinetics: influences of perfusion dynamics and arteriovenous oxygen concentration differences in muscles and lungs

PURPOSE

The aim of the study was to test whether or not the arteriovenous oxygen concentration difference (avDO₂) kinetics at the pulmonary (avDO₂pulm) and muscle (avDO₂musc) levels is significantly different during dynamic exercise.

METHODS

A re-analysis involving six publications dealing with kinetic analysis was utilized with an overall sample size of 69 participants. All studies comprised an identical pseudorandom binary sequence work rate (WR) protocol-WR changes between 30 and 80 W-to analyze the kinetic responses of pulmonary ([Formula: see text]) and muscle ([Formula: see text]) oxygen uptake kinetics as well as those of avDO₂pulm and avDO₂musc.

RESULTS

A significant difference between [Formula: see text] (0.395 ± 0.079) and [Formula: see text] kinetics (0.330 ± 0.078) was observed (p < 0.001), where the variables showed a significant relationship (r_SP = 0.744, p < 0.001). There were no significant differences between avDO₂musc (0.446 ± 0.077) and avDO₂pulm kinetics (0.451 ± 0.075), which are highly correlated (r = 0.929, p < 0.001).

CONCLUSION

It is suggested that neither avDO₂pulm nor avDO₂musc kinetic responses seem to be responsible for the differences between estimated [Formula: see text] and measured [Formula: see text] kinetics. Obviously, the conflation of avDO₂ and perfusion ([Formula: see text] ) at different points in time and at different physiological levels drive potential differences in [Formula: see text] and [Formula: see text] kinetics. Therefore, [Formula: see text] should, in general, be considered whenever oxygen uptake kinetics are analyzed or discussed.

Does postexercise modelled capillary blood flow accurately reflect cardiovascular effects by different exercise intensities?

Blood flow (BF) in exercising muscles is an important factor for exercise capacity. Recently, a non-invasive method to estimate capillary BF (Q_cap ) was introduced. Using this method, the Fick principle is re-arranged by using relative differences in deoxygenated haemoglobin (ΔHHb) as a surrogate for arteriovenous O₂ difference and pulmonary oxygen uptake (VO₂ ) instead of muscular oxygen uptake. The aim of this study was to examine (I) the relationship between Q_cap and exercise intensity during and following exercise, and (II) to critically reflect the Q_cap approach. Seventeen male subjects completed six bouts of cycling exercise with different exercise intensities (40-90% peak oxygen uptake, VO_2peak ) in randomized order. VO₂ and ΔHHb were monitored continuously during the trail. Q_cap was modelled bi-exponentially, and mean response time (MRT) was calculated during recovery as well as the dissociation of modelled VO₂ and Q_cap recovery kinetics (MRT/τVO₂ ). End-exercise Q_cap increased continuously with exercise intensity. This also applied to MRT. Postexercise MRT/τVO₂ increased from 40 to 60% VO_2peak but remained stable thereafter. The results show that Q_cap response to exercise is linearly related to exercise intensity. This is presumably due to vasoactive factors like shear-stress or endothelial-mediated vasodilation. MRT/τVO₂ shows that postexercise Q_cap is elevated for a longer period than VO₂ , which is representative for metabolic demand following exercise ≥70% VO_2peak . This is a hint for prolonged local vasodilation. According to previous studies, Q_cap could not be modelled properly in some cases, which is a limitation to the method and therefore has to be interpreted with caution.

Effects of aging and exercise training on leg hemodynamics and oxidative metabolism in the transition from rest to steady-state exercise: role of cGMP signaling

Aging is associated with slower skeletal muscle O₂ uptake (V̇o₂) kinetics; however, the mechanisms underlying this effect of age are unclear. Also, the effects of exercise training in elderly on the initial vascular and metabolic response to exercise remain to be elucidated. We measured leg hemodynamics and oxidative metabolism in the transition from rest to steady-state exercise engaging the knee-extensor muscles in young ( n = 15, 25 ± 1 yr) and older ( n = 15, 72 ± 1 yr) subjects before and after a period of aerobic high-intensity exercise training. To enhance cGMP signaling, pharmacological inhibition of phosphodiesterase 5 (PDE5) was performed. Before training, the older group had a slower ( P <0.05) increase in femoral arterial blood flow and leg vascular conductance in the transition from rest to steady-state exercise at low- and moderate-intensity compared with the young group. The rate of increase in leg V̇o₂ was, however, similar in the two groups as a result of higher ( P < 0.05) arteriovenous O₂ difference in the older group. Potentiation of cGMP signaling did not affect the rate of increase in blood flow or V̇o₂ in either group. Exercise training augmented ( P < 0.05) the increase in leg vascular conductance and blood flow during the onset of moderate-intensity exercise in both groups without altering V̇o₂. These findings suggest that an age-related reduction in the initial vascular response to low- and moderate-intensity knee-extensor exercise is not limiting for V̇o₂ in older individuals. A lower blood flow response in aging does not appear to be a result of reduced cGMP signaling.

Fitness Level and Not Aging per se, Determines the Oxygen Uptake Kinetics Response

Although aging has been associated to slower V˙O₂ kinetics, some evidence indicates that fitness status and not aging per se might modulate this response. The main goal of this study was to examine the V˙O₂, deoxygenated hemoglobin+myoglobin (deoxy-[Hb+Mb]) kinetics, and the NIRS-derived vascular reperfusion responses in older compared to young men of different training levels (i.e., inactive, recreationally active, and endurance trained). Ten young inactive [YI; 26 ± 5 yrs.; peak V˙O₂ (V˙O_2peak), 2.96 ± 0.55 L·min⁻¹], 10 young recreationally active (YR; 26 ± 6 yrs.; 3.92 ± 0.33 L·min⁻¹), 10 young endurance trained (YT; 30 ± 4 yrs.; 4.42 ± 0.32 L·min⁻¹), 7 older inactive (OI; 69 ± 4 yrs.; 2.50 ± 0.31 L·min⁻¹), 10 older recreationally active (OR; 69 ± 5 yrs.; 2.71 ± 0.42 L·min⁻¹), and 10 older endurance trained (OT; 66 ± 3 yrs.; 3.20 ± 0.35 L·min⁻¹) men completed transitions of moderate intensity cycling exercise (MODS) to determine V˙O₂ and deoxy-[Hb+Mb] kinetics, and the deoxy-[Hb+Mb]/V˙O₂ ratio. The time constant of V˙O₂ (τV˙O₂) was greater in YI (38.8 ± 10.4 s) and OI (44.1 ± 10.8 s) compared with YR (26.8 ± 7.5 s) and OR (26.6 ± 6.5 s), as well as compared to YT (14.8 ± 3.4 s), and OT (17.7 ± 2.7 s) (p < 0.05). τV˙O₂ was greater in YR and OR compared with YT and OT (p < 0.05). The deoxy-[Hb+Mb]/V˙O₂ ratio was greater in YI (1.23 ± 0.05) and OI (1.29 ± 0.08) compared with YR (1.11 ± 0.03) and OR (1.13 ± 0.06), as well as compared to YT (1.01 ± 0.03), and OT (1.06 ± 0.03) (p < 0.05). Similarly, the deoxy-[Hb+Mb]/ V˙O₂ ratio was greater in YR and OR compared with YT and OT (p < 0.05). There was a main effect of training (p = 0.033), whereby inactive (p = 0.018) and recreationally active men (p = 0.031) had significantly poorer vascular reperfusion than endurance trained men regardless of age. This study demonstrated not only that age-related slowing of V˙O₂ kinetics can be eliminated in endurance trained individuals, but also that inactive lifestyle negatively impacts the V˙O₂ kinetics response of young healthy individuals.

Lack of age-specific influence on leg blood flow during incremental calf plantar-flexion exercise in men and women

PURPOSE

Age-related exercising leg blood flow (LBF) responses during dynamic knee-extension exercise and forearm blood flow responses during handgrip exercise are preserved in normally active men but attenuated in activity-matched women. We explored whether these age- and sex-specific effects are also apparent during isometric calf plantar-flexion incremental exercise.

METHODS

Normally active young men (YM, n = 15, 24 ± 2 years), young women (YW, n = 8, 22 ± 1 years), older men (OM, n = 13, 70 ± 7 years) and older women (OW, n = 10, 64 ± 7 years) were tested. LBF was measured between contractions using venous occlusion plethysmography.

RESULTS

Peak force obtained was higher (P < 0.05) in men compared with women and in young compared with older individuals. However, peak LBF (YM; 971 ± 328 ml min^-1, OM; 985 ± 504 ml min^-1, YW; 844 ± 366 ml min^-1, OW; 960 ± 244 ml min^-1) and peak leg vascular conductance [LVC = LBF/(MAP + hydrostatic pressure)] responses (YM; 6.0 ± 1.8 ml min^-1 mmHg^-1, OM; 5.5 ± 2.8 ml min^-1 mmHg^-1, YW; 5.3 ± 2.1 ml min^-1 mmHg^-1, OW; 5.5 ± 1.6 ml min^-1 mmHg^-1) were similar among the four groups. Furthermore, the hyperaemic (YM; 8.8 ± 3.7 ml min^-1 %F_peak^-1 OM; 8.3 ± 5.4 ml min^-1 %F_peak^-1, YW; 8.2 ± 3.5 ml min^-1 %F_peak^-1, OW; 9.6 ± 2.2 ml min^-1 %F_peak^-1) and vasodilatory responses (YM; 0.053 ± 0.020 ml min^-1 mmHg^-1 %F_peak^-1, OM; 0.048 ± 0.028 ml min^-1 mmHg^-1 %F_peak^-1, YW; 0.051 ± 0.019 ml min^-1 mmHg^-1 %F_peak^-1, OW; 0.055 ± 0.014 ml min^-1 mmHg^-1 %F_peak^-1) were not different among the four groups. These results were accompanied by similar resting LBF responses among groups and were not affected when data were normalised to estimated leg muscle mass.

CONCLUSIONS

Our results demonstrate that exercising LBF responses during isometric incremental calf muscle exercise are preserved in older men and women, suggesting that the previously observed age-related attenuations in leg and forearm hyperaemia among women may be muscle-group specific.

Cycling efficiency and energy cost of walking in young and older adults

To determine whether age affects cycling efficiency and the energy cost of walking (Cw), 190 healthy adults, ages 18-81 yr, cycled on an ergometer at 50 W and walked on a treadmill at 1.34 m/s. Ventilation and gas exchange at rest and during exercise were used to calculate net Cw and net efficiency of cycling. Compared with the 18-40 yr age group (2.17 ± 0.33 J·kg^-1·m^-1), net Cw was not different in the 60-64 yr (2.20 ± 0.40 J·kg^-1·m^-1) and 65-69 yr (2.20 ± 0.28 J·kg^-1·m^-1) age groups, but was significantly ( P < 0.03) higher in the ≥70 yr (2.37 ± 0.33 J·kg^-1·m^-1) age group. For subjects >60 yr, net Cw was significantly correlated with age ( R² = 0.123; P = 0.002). Cycling net efficiency was not different between 18-40 yr (23.5 ± 2.9%), 60-64 yr (24.5 ± 3.6%), 65-69 yr (23.3 ± 3.6%) and ≥70 yr (24.7 ± 2.7%) age groups. Repeat tests on a subset of subjects (walking, n = 43; cycling, n = 37) demonstrated high test-retest reliability [intraclass correlation coefficients (ICC), 0.74-0.86] for all energy outcome measures except cycling net energy expenditure (ICC = 0.54) and net efficiency (ICC = 0.50). Coefficients of variation for all variables ranged from 3.1 to 7.7%. Considerable individual variation in Cw and efficiency was evident, with a ~2-fold difference between the least and most economical/efficient subjects. We conclude that, between 18 and 81 yr, net Cw was only higher for ages ≥70 yr, and that cycling net efficiency was not different across age groups. NEW & NOTEWORTHY This study illustrates that the higher energy cost of walking in older adults is only evident for ages ≥70 yr. For older adults ages 60-69 yr, the energy cost of walking is similar to that of young adults. Cycling efficiency, by contrast, is not different across age groups. Considerable individual variation (∼2-fold) in cycling efficiency and energy cost of walking is observed in young and older adults.

Muscle Strength, But Not Muscle Oxidative Capacity, Varies Between the Morning and the Afternoon in Patients with Multiple Sclerosis: A Pilot Study

Despite frequent muscle strength or muscle oxidative capacity (based on exercise-onset oxygen uptake [VO2] kinetics) assessments in patients with multiple sclerosis, the impact of time of day on these parameters is often not taken into account. Based on observations in healthy subjects, it remains to be studied whether muscle strength, and/or exercise-onset VO2 kinetics, varies between the morning and the afternoon in patients with multiple sclerosis. In this prospective observational pilot study, walking capacity, exercise-onset VO2 kinetics, isometric knee extension/flexion strength (dynamometry), and self-reported fatigue were measured in 11 patients with multiple sclerosis (age, 51.8 ± 9.3 yrs; body mass index, 24.7 ± 5.1 kg/m; Expanded Disability Status Scale, 3.5 ± 1.4; 3 men) in the morning and 5 hrs later (afternoon). In the afternoon, self-reported fatigue (1.9 ± 0.9 cm) and muscle strength (knee extension peak torque at 45 degrees, 84 ± 26 Nm) were significantly different (P < 0.05), than in the morning (self-reported fatigue, 1.2 ± 0.9 cm; knee extension peak torque at 45 degrees, 93 ± 32 Nm), but walking capacity and exercise-onset VO2 kinetics were similar at these two time points (P > 0.05). Consistent with observations in healthy subjects, muscle strength varies between the morning and the afternoon in patients with multiple sclerosis, under the conditions of the present study. These findings suggest that muscle strength assessments should be conducted at similar or nearly similar times of the day to minimize diurnal variation in these measures and hence insure correct interpretation.