Skeletal Muscle Deoxygenation Abnormalities in Early Post-Myocardial Infarction

Effect of High-Intensity With Short-Duration Re-Warm-Up on Subsequent Performance in a Cold Environment

ABSTRACT

Yamashita, Y and Umemura, Y. Effect of high-intensity with short-duration re-warm up on subsequent performance in a cold environment. J Strength Cond Res 38(6): e280-e287, 2024-The aim of this study was to investigate the effect of high-intensity, short-duration re-warm-up (RW) during half time (HT) on subsequent performance in a cold environment. Eleven male subjects (age, 21 ± 2 years; height, 172.4 ± 4.5 cm; body mass, 65.6 ± 7.1 kg; V̇ o2 max, 47.5 ± 4.8 ml·kg -1 ·min -1 ) performed 2 experimental trials comprising 40 minutes of intermittent cycling exercise, which consisted of 15-second rest, 25-second unloading cycling, 10-second high-intensity cycling, and 70-second moderate-intensity cycling as the first half. In the second half, a cycling intermittent-sprint protocol (CISP) was performed, separated by a 15-minute HT period in cold conditions (5 °C, 50% relative humidity). Two experimental trials were included in a random order: (a) approximately 1 minute of high-intensity, short-duration RW (3 sets of 3-second maximal pedaling [body weight × 0.075 kp]) trial high-intensity intermittent cycling trials (HII); (b) 15 minutes of seated rest trial (CON). Cycling intermittent-sprint protocol consisted of 10 sets of a 2-minute exercise protocol, and each set consisted of 10-second rest, 5-second maximal pedaling (body weight × 0.075 kp), and 105-second active recovery at 50% maximum oxygen uptake (V̇ o2 max). Peak power output of 5-second maximal pedaling during CISP was higher in HII trials than in CON trials (HII: 807 ± 81 W, CON: 791 ± 78 W, p < 0.05). There was no significant difference in rectal temperature between trial types ( p > 0.05). These results suggest that high-intensity, short-duration RW may be a useful HT strategy for improving subsequent performance in cold environments.

Evaluation of Muscle Oxygen Dynamics in Children's Gait and Its Relationship with the Physiological Cost Index

The response of muscle oxygen saturation, which is an index for the energy metabolism of muscles during walking in children, and its relationship to the physiological cost index, which indicates walking efficiency, are unknown. This study aimed to evaluate muscle oxygen saturation in lower extremity muscles during walking in children, its changes with age, and the relationship between the physiological cost index. The oxygen saturation was measured by the amount of change during a two-minute walk, and the physiological cost index was calculated from the change in heart rate before and after exercise and walking speed. Results were compared for each muscle, and the correlation between the two was examined. Changes in muscle oxygen saturation were greater in the lower leg muscles, significantly greater in the tibialis anterior at six to seven years, and in the gastrocnemius medial head at eight to ten years. The physiological cost index was significantly correlated with changes in muscle oxygen saturation in the tibialis anterior (r = 0.44, p < 0.001). The lower leg muscles were metabolically active in children’s gait, and their response varied with age. Moreover, the muscle oxygenation dynamics of the tibialis anterior may influence walking efficiency.

Skeletal Muscle Deoxygenation and Its Relationship to Aerobic Capacity During Early and Late Stages of Aging

The aim of this study was to compare muscle O₂ dynamics during exercise among elderly (n = 10, age: 73 ± 3 years), middle-aged (n = 9, age: 50 ± 6 years), and young (n = 10, age: 25 ± 3 years) adults. The subjects performed ramp bicycle exercise until exhaustion. Muscle O₂ saturation (SmO₂) and relative changes from rest in oxygenated hemoglobin/myoglobin (∆oxy-Hb/Mb), deoxygenated hemoglobin/myoglobin (∆deoxy-Hb/Mb), and total hemoglobin concentration (∆total-Hb) were monitored continuously at the vastus lateralis muscle by near-infrared spatial resolved spectroscopy. At given absolute workloads, SmO₂ and ∆oxy-Hb/Mb were significantly lower in elderly than the other groups, while ∆deoxy-Hb/Mb, ∆total-Hb, and pulmonary O₂ uptake (VO₂) were similar among the three groups. In contrast, there were no significant differences in muscle O₂ dynamics during submaximal exercise between middle-aged and young subjects. Muscle O₂ dynamics may be relatively preserved in early stages of aging, although muscle deoxygenation is enhanced in late stages of aging, probably due to reduced convective O₂ supply. Moreover, change in SmO₂ was significantly positively correlated with peak VO₂ in the elderly, while a significant negative relationship was observed in middle-aged and young subjects. In late stages of aging, diminished peak VO₂ may be caused by attenuated convective O₂ transport, while reduced peak VO₂ can be explained by lowered muscle O₂ extraction in early stages of aging.

Muscle deoxygenation and neuromuscular activation in synergistic muscles during intermittent exercise under hypoxic conditions

The purpose of this study was to elucidate the effects of hypoxia on deoxygenation and neuromuscular activation in synergistic quadriceps femoris (QF) muscles (i.e., the rectus femoris, vastus medialis, vastus intermedius, and vastus lateralis) during submaximal intermittent knee extension. Ten healthy men performed isometric intermittent knee extension exercises with the right leg at 50% of maximal voluntary contraction for 3 min while inhaling a normoxic [inspired oxygen (O₂) fraction = 0.21] or hypoxic (inspired O₂ fraction = 0.10–0.12) gas mixture. Muscle deoxygenation was measured by tissue O₂ saturation (StO₂), and neuromuscular activation by root mean square (RMS) of the surface electromyographic signals, from individual muscles of the QF using near-infrared spectroscopy and surface electromyography. StO₂ was decreased more in hypoxia than normoxia during the exercises, and there was a greater increase in RMS during intermittent knee extension in hypoxia than normoxia in individual muscles of the QF. There were no differences in the ratios of StO₂ and RMS in hypoxia compared with normoxia between individual muscles of the QF. These findings suggest that submaximal, isometric, and intermittent exercises in hypoxic conditions enhanced muscle oxygen consumption and muscle activity similarly for synergistic muscles.

High-intensity cycling re-warm up within a very short time-frame increases the subsequent intermittent sprint performance

This study investigated the effect of high-intensity cycling re-warm up (RW) within a very short time-frame on the subsequent intermittent sprint performance. Twelve active males completed three trials in random order: control (CON); 3-min RW at 30% of maximal oxygen uptake (VO_2max) (RW30); and 1-min RW at 90% of VO_2max (RW90). During the experimental trials, participants performed 40-min intermittent cycling exercise followed by 15-min rest. During the rest period, participants completed CON, RW30, or RW90. After the rest period, participants performed the Cycling Intermittent-Sprint Protocol (CISP), which consisted of 10-s rest, 5-s maximal sprint, and 105-s active recovery with the cycles repeated over 10 min. The mean work during sprint for the CISP was significantly higher in both RW trials than in the CON trial (mean±standard deviation; CON: 3539±698 J; RW30: 3724±720 J; RW90: 3739±736 J; p<0.05). The mean electromyogram amplitude during the sprint for the CISP was higher in the RW30 trial than in the CON trial; however, there was no significant difference between the two trials (p=0.06). The mean median frequency during sprint for the CISP was significantly higher in the RW90 trial than in the other trials (p<0.05). Rectal temperature did not differ among the three trials. Oxygenated haemoglobin during the initial 30 s of the CISP was significantly higher in the RW90 trial than in the CON trial (p<0.05). Compared with seated rest, RW, irrespective of whether it comprised 1-min at 90% of VO_2max or 3-min at 30% of VO_2max, increased the subsequent intermittent sprint performance.

Concentric and Eccentric Pedaling-Type Interval Exercise on a Soft Robot for Stable Coronary Artery Disease Patients: Toward a Personalized Protocol

BACKGROUND

Cardiovascular diseases are the leading causes of death worldwide, and coronary artery disease (CAD) is one of the most common causes of death in Europe. Leading cardiac societies recommend exercise as an integral part of cardiovascular rehabilitation because it reduces the morbidity and mortality of patients with CAD. Continuous low-intensity exercise using shortening muscle actions (concentric, CON) is a common training modality during cardiovascular rehabilitation. However, a growing clinical interest has been recently developed in high-intensity interval training (HIIT) for stable patients with CAD. Exercise performed with lengthening muscle actions (eccentric, ECC) could be tolerated better by patients with CAD as they can be performed with higher loads and lower metabolic cost than CON exercise.

OBJECTIVE

We developed a clinical protocol on a soft robot to compare cardiovascular and muscle effects of repeated and work-matched CON versus ECC pedaling-type interval exercise between patients with CAD during cardiovascular rehabilitation. This study aims to ascertain whether the developed training protocols affect peak oxygen uptake (VO_2peak), peak aerobic power output (P_peak), and parameters of muscle oxygen saturation (SmO₂) during exercise, and anaerobic muscle power.

METHODS

We will randomize 20-30 subjects to either the CON or ECC group. Both groups will perform a ramp test to exhaustion before and after the training period to measure cardiovascular parameters and SmO₂. Moreover, the aerobic skeletal muscle power (P_peak) is measured weekly during the 8-week training period using a simulated squat jump and a counter movement jump on the soft robot and used to adjust the training load. The pedaling-type interval exercise on the soft robot is performed involving either CON or ECC muscle actions. The soft robotic device being used is a closed kinetic chain, force-controlled interactive training, and testing device for the lower extremities, which consists of two independent pedals and free footplates that are operated by pneumatic artificial muscles.

RESULTS

The first patients with CAD, who completed the training, showed protocol-specific improvements, reflecting, in part, the lower aerobic training status of the patient completing the CON protocol. Rehabilitation under the CON protocol, more than under the ECC protocol, improved cardiovascular parameters, that is, VO_2peak (+26% vs -6%), and P_peak (+20% vs 0%), and exaggerated muscle deoxygenation during the ramp test (248% vs 49%). Conversely, markers of metabolic stress and recovery from the exhaustive ramp test improved more after the ECC than the CON protocol, that is, peak blood lactate (-9% vs +20%) and peak SmO₂ (+7% vs -7%). Anaerobic muscle power only improved after the CON protocol (+18% vs -15%).

CONCLUSIONS

This study indicates the potential of the implemented CON and ECC protocols of pedaling-type interval exercise to improve oxygen metabolism of exercised muscle groups while maintaining or even increasing the P_peak. The ECC training protocol seemingly provided a lower cardiovascular stimulus in patients with CAD while specifically enhancing the reoxygenation and blood lactate clearance in recruited muscle groups during recovery from exercise.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02845063; https://clinicaltrials.gov/ct2/show/NCT02845063.

Plasma asymmetric dimethylarginine concentrations are not related to differences in maximal oxygen uptake in endurance trained and untrained men

NEW FINDINGS

What is the central question of this study? Is there an association of plasma concentration of asymmetric dimethylarginine, which is related to exercise capacity in patients with cardiovascular diseases, with oxygen delivery and subsequently exercise capacity in healthy subjects in the absence of the potentially confounding influence of inflammation and oxidative stress? What is the main finding and its importance? Plasma asymmetric dimethylarginine concentrations are not related to exercise capacity in healthy subjects, while O₂ delivery in the working skeletal muscle during the maximal graded-exercise test is not associated with any of the l-arginine analogues. ADMA alone does not play a crucial role in local muscle perfusion and in maintaining exercise capacity.

ABSTRACT

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide (NO) synthesis that could limit oxygen (O₂ ) delivery in the working skeletal muscles by altering endothelium-dependent vasodilatation. Exercise capacity is associated with plasma ADMA concentrations in patients with cardiovascular diseases, but this issue has still not been investigated in healthy subjects. We aimed to determine whether plasma ADMA concentrations were negatively associated with exercise capacity in young healthy male subjects. Ten men with maximal oxygen uptake ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>max</mml:mi> </mml:mrow> </mml:msub> </mml:math> ) > 65 mL kg^-1  min^-1 were included in the high exercise capacity group (HI-FIT), and 10 men with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>max</mml:mi> </mml:mrow> </mml:msub> </mml:math>  < 45 mL kg^-1  min^-1 were included in the low exercise capacity group (LO-FIT). Plasma ADMA and other l-arginine analogue concentrations were measured before and after a maximal graded-exercise test by liquid chromatography-tandem mass spectrometry. Microvascular O₂ delivery during exercise was estimated through the pattern from the sigmoid model of muscle deoxygenation in the vastus lateralis measured by near infrared spectroscopy. <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>max</mml:mi> </mml:mrow> </mml:msub> </mml:math> was 60% higher in the HI-FIT group (median: 70.2 mL kg^-1  min^-1 ; IQR: 68.0-71.9 mL kg^-1  min^-1 ) than in the LO-FIT group (median: 43.8 mL kg^-1  min^-1 ; IQR: 34.8-45.3 mL kg^-1  min^-1 ). Plasma ADMA concentrations did not differ between the LO-FIT and HI-FIT groups before (0.50 ± 0.06 vs. 0.54 ± 0.07 μmol L^-1 , respectively) and after the maximal incremental exercise test (0.49 ± 0.08 vs. 0.55 ± 0.03 μmol L^-1 , respectively). There was no significant association of plasma ADMA concentrations with the pattern of local muscle deoxygenation and exercise capacity. Exercise capacity and microvascular O₂ delivery are not related to plasma ADMA concentrations in young healthy male subjects. Our findings show that ADMA does not play a crucial role in local muscle perfusion and in maintaining exercise capacity without pathological conditions.

Interval exercise training increases LIF expression and prevents myocardial infarction-induced skeletal muscle atrophy in rats

AIMS

Myocardial infarction (MI) is commonly associated with body weight loss and skeletal muscle atrophy. Studies have shown that exercise training could give beneficial effects on skeletal muscle growth. Leukemia inhibitory factor (LIF) is a key regulator of muscle growth and regeneration. The aim of this study was to investigate the effects of interval exercise training (IET) on the expression of LIF and the MI-induced skeletal muscle atrophy.

MAIN METHODS

Male Sprague-Dawley rats were used to establish the MI model by ligation of the left anterior descending coronary artery. Infarcted Rats were divided into two groups: sedentary MI group (MI) and MI with interval exercise group (ME), and compared to sham-operated group (Sham). Exercise-trained animals were subjected to eight weeks of IET. Cardiac function, collagen volume fraction, expression of LIF and its receptor LIFR, myofiber size, apoptosis and proliferation in gastrocnemius muscle were analyzed.

KEY FINDINGS

IET increased heart functional performance and was accompanied with reversing cardiac pathological remodeling. Moreover, IET increased the expression of LIF and LIFR, activated signal transducer and activator of transcription (STAT3), reduced apoptosis and promoted proliferation in gastrocnemius muscle compared with the MI group. In addition, there was a significant negative correlation between skeletal muscle atrophy and LIF expression which was stimulated by IET in infarcted rats.

SIGNIFICANCE

IET reverses MI-induced cardiac dysfunction and skeletal muscle atrophy. In addition, IET up-regulates the expression of muscle LIF/LIFR and activates the STAT3.

Multi-site Measurements of Muscle O2 Dynamics During Cycling Exercise in Early Post-myocardial Infarction

The aim of this study was to compare the muscle oxygen dynamics between early post-myocardial infarction (n = 12; MI) and age-matched elderly subjects without MI (n = 12; CON) in several leg muscles during ramp cycling exercise. Muscle oxygen saturation (SmO₂), deoxygenated-hemoglobin concentration (∆deoxy-Hb), and total-hemoglobin concentration (∆total-Hb) were monitored continuously at the distal site of vastus lateralis (VLd), proximal site of the vastus lateralis (VLp), rectus femoris (RF), vastus medialis (VM), gastrocnemius medialis (GM), and tibialis anterior (TA) muscles by near infrared spatial resolved spectroscopy. At given absolute workloads, higher SmO₂ was observed at VLd, VLp, RF, and VM in MI, compared to CON. Simultaneously, in MI, deoxy-Hb was lower at VLd, VLp, and VM than CON. In contrast to the thigh muscles, muscle oxygen dynamics were similar between groups in GM and TA. In total-Hb, no significant differences were found at any measurement sites. These results demonstrated that the absence of muscle deoxygenation was observed in MI muscles, especially in the thigh muscles, but not in the lower leg muscles.

Appropriateness of the metabolic equivalent (MET) as an estimate of exercise intensity for post-myocardial infarction patients

AIMS

To explore: (1) whether during exercise metabolic equivalents (METs) appropriately indicate the intensity and/or metabolic cost for post-myocardial infarction (MI) males and (2) whether post-exercise VO2 parameters provide insight into the intensity and/or metabolic cost of the prior exercise.

METHODS

15 male phase-IV post-MIs (64.4±6.5 years) and 16 apparently healthy males (63.0±6.4 years) participated. Participants performed a graded cycle ergometer test (CET) of 50, 75 and 100 W, followed by 10 min active recovery (at 50 W) and 22 min seated recovery. Participants' heart rate (HR, bpm), expired air parameters and ratings of perceived exertion (exercise only) were measured.

RESULTS

General linear model analysis showed throughout significantly lower HR values in post-MI participants that were related to β-blocker medication (F(2,5)=18.47, p<0.01), with significantly higher VCO2/VO2 (F(2,5)=11.25, p<0.001) and gross kcals/LO2/min (F(2,5)=11.25, p<0.001). Analysis comparing lines of regression showed, during the CET: post-MI participants worked at higher percentage of their anaerobic threshold (%AT)/MET than controls (F(2,90)=18.98, p<0.001), as well as during active recovery (100-50 W) (F(2,56)=20.81, p<0.001); during seated recovery: GLM analysis showed significantly higher values of VCO2/VO2 for post-MI participants compared with controls (F(2,3)=21.48, p=0.001) as well as gross kcals/LO2/min (F(2,3)=21.48, p=0.001).

CONCLUSION

Since METs take no consideration of any anaerobic component, they failed to reflect the significantly greater anaerobic contribution during exercise per MET for phase-IV post-MI patients. Given the anaerobic component will be greater for those with more severe forms of cardiac disease, current METs should be used with caution when determining exercise intensity in any patient with cardiac disease.

Low Volume Aerobic Training Heightens Muscle Deoxygenation in Early Post-Angina Pectoris Patients

The aim of this study was to investigate the effect of low volume aerobic exercise training on muscle O2 dynamics during exercise in early post-angina pectoris (AP) patients, as a pilot study. Seven AP patients (age: 72 ± 6 years) participated in aerobic exercise training for 12 weeks. Training consisted of continuous cycling exercise for 30 min at the individual's estimated lactate threshold, and the subjects trained for 15 ± 5 exercise sessions over 12 weeks. Before and after training, the subjects performed ramp cycling exercise until exhaustion. Muscle O2 saturation (SmO2) and relative changes from rest in deoxygenated hemoglobin concentration (∆Deoxy-Hb) and total hemoglobin concentration (∆Total-Hb) were monitored at the vastus lateralis by near infrared spatial resolved spectroscopy during exercise. The SmO2 was significantly lower and ∆Deoxy-Hb was significantly higher after training than before training, while there were no significant changes in ∆Total-Hb. These results indicated that muscle deoxygenation and muscle O2 extraction were potentially heightened by aerobic exercise training in AP patients, even though the exercise training volume was low.

Impaired Skeletal Muscle Oxygenation and Exercise Tolerance in Pulmonary Hypertension

BACKGROUND

Limb muscle dysfunction is documented in pulmonary arterial hypertension (PAH), but little is known regarding muscle oxygen (O2) supply and its possible effects on exercise tolerance in PAH.

METHODS

Ten patients with PAH and 10 matched controls underwent progressive maximal cardiopulmonary exercise test, voluntary and nonvolitional dominant quadriceps muscle strength measures, and nondominant quadriceps biopsy to assess maximal oxygen uptake, muscle function, and lower limb fiber type and capillarity, respectively. Both groups then performed normoxic and hyperoxic submaximal intensity exercise protocol at the same absolute workload during which muscle O2 supply was assessed by measuring changes in myoglobin-deoxyhemoglobin level (Δ[Mb-HHb]) and tissue oxygenation index in the dominant quadriceps using near-infrared spectroscopy. Changes in cardiac output, estimated systemic O2 delivery, and systemic O2 saturation were also assessed noninvasively throughout both submaximal exercises.

RESULTS

Patients with PAH displayed lower maximal oxygen uptake (P < 0.01), skeletal muscle strength (P < 0.05), and capillarity (P = 0.01). Throughout the normoxic submaximal exercise protocol, Δ[Mb-HHb] (P < 0.01) was higher whereas changes in tissue oxygenation index (P < 0.01) and systemic O2 saturation (P = 0.01) were lower in patients with PAH compared with those in controls. Conversely, changes in cardiac output and estimated systemic O2 delivery were similar between groups. Muscle oxygenation remained unchanged with O2 supplementation. Among variables known to influence tissue oxygenation, only quadriceps capillarity density correlated with Δ[Mb-HHb] (r = -0.66, P < 0.01), which in turn correlated with maximal oxygen uptake (r = -0.64, P < 0.01), 6-min walked distance (r = -0.74, P = 0.01), and both voluntary (r = -0.46, P = 0.04) and nonvolitional (r = -0.50, P = 0.02) quadriceps strength.

CONCLUSIONS

Capillary rarefaction within the skeletal muscle influences exercise tolerance and quadriceps strength at least partly through impaired muscle oxygen supply in PAH.

Influence of Adjuvant Therapy in Cancer Survivors on Endothelial Function and Skeletal Muscle Deoxygenation

The cardiotoxic effects of adjuvant cancer treatments (i.e., chemotherapy and radiation treatment) have been well documented, but the effects on peripheral cardiovascular function are still unclear. We hypothesized that cancer survivors i) would have decreased resting endothelial function; and ii) altered muscle deoxygenation response during moderate intensity cycling exercise compared to cancer-free controls. A total of 8 cancer survivors (~70 months post-treatment) and 9 healthy controls completed a brachial artery FMD test, an index of endothelial-dependent dilation, followed by an incremental exercise test up to the ventilatory threshold (VT) on a cycle ergometer during which pulmonary V˙O2 and changes in near-infrared spectroscopy (NIRS)-derived microvascular tissue oxygenation (TOI), total hemoglobin concentration ([Hb]_total), and muscle deoxygenation ([HHb] ≈ fractional O₂ extraction) were measured. There were no significant differences in age, height, weight, and resting blood pressure between cancer survivors and control participants. Brachial artery FMD was similar between groups (P = 0.98). During exercise at the VT, TOI was similar between groups, but [Hb]_total and [HHb] were significantly decreased in cancer survivors compared to controls (P < 0.01) The rate of change for TOI (ΔTOIΔ/V˙O2) and [HHb] (Δ[HHb]/ΔV˙O2) relative to ΔV˙O2 were decreased in cancer survivors compared to controls (P = 0.02 and P = 0.03 respectively). In cancer survivors, a decreased skeletal muscle microvascular function was observed during moderate intensity cycling exercise. These data suggest that adjuvant cancer therapies have an effect on the integrated relationship between O₂ extraction, V˙O2 and O₂ delivery during exercise.

Effects of Low Volume Aerobic Training on Muscle Desaturation During Exercise in Elderly Subjects

Aging enhances muscle desaturation responses due to reduced O2 supply. Even though aerobic training enhances muscle desaturation responses in young subjects, it is unclear whether the same is true in elderly subjects. Ten elderly women (age: 62±4 years) participated in 12-weeks of cycling exercise training. Training consisted of 30 min cycling exercise at the lactate threshold. The subjects exercised 15±6 sessions during training. Before and after endurance training, the subjects performed ramp cycling exercise. Muscle O2 saturation (SmO2) was measured at the vastus lateralis by near infrared spectroscopy during the exercise. There were no significant differences in SmO2 between before and after training. Nevertheless, changes in peak pulmonary O2 uptake were significantly negatively related to changes in SmO2 (r=-0.67, p<0.05) after training. Muscle desaturation was not enhanced by low volume aerobic training in this study, possibly because the training volume was too low. However, our findings suggest that aerobic training may potentially enhance muscle desaturation at peak exercise in elderly subjects.

Aerobic training enhances muscle deoxygenation in early post-myocardial infarction

Purpose

Exercise-induced skeletal muscle deoxygenation is startling by its absence in early post-myocardial infarction (MI) patients. Exercise training early post-MI is associated with reduced cardiovascular risk and increased aerobic capacity. We therefore investigated whether aerobic training could enhance the muscle deoxygenation in early post-MI patients.

Methods

21 ± 8 days after the first MI patients (n = 16) were divided into 12-week aerobic training (TR, n = 10) or non-training (CON, n = 6) groups. Before and after intervention, patients performed ramp bicycle exercise until exhaustion. Muscle deoxygenation was measured at vastus lateralis by near-infrared spectroscopy during exercise.

Results

Aerobic training significantly increased peak oxygen uptake (VO₂) (18.1 ± 3.0 vs. 22.9 ± 2.8 mL/kg/min), decreased the change in muscle oxygen saturation from rest to submaximal and peak exercise (∆SmO₂; 2.4 ± 5.7 vs. −7.0 ± 3.4 %), and increased the relative change in deoxygenated hemoglobin/myoglobin concentration from rest to submaximal (−1.5 ± 2.3 vs. 3.0 ± 3.6 μmol/L) and peak exercise (1.1 ± 4.5 vs. 8.2 ± 3.5 μmol/L). Change in total hemoglobin/myoglobin concentration in muscle was not significantly affected by training. In CON, no significant alterations were found after 12 weeks in either muscle deoxygenation or peak VO₂ (18.6 ± 3.8 vs. 18.9 ± 4.6 mL/kg/min). An increase in peak VO₂ was significantly negatively correlated with change in ∆SmO₂ (r = −0.65) and positively associated with change in ∆deoxy-Hb/Mb at peak exercise (r = 0.64) in TR.

Conclusions

In early post-MI patients, aerobic training enhanced skeletal muscle deoxygenation, and the enhancement was related to increased aerobic capacity.

Muscle Oxygen Dynamics During Cycling Exercise in Angina Pectoris Patients

Muscle O2 dynamics during ramp cycling exercise were compared between angina pectoris patients (AP; n = 7, age: 73 ± 6 years) after coronary artery bypass grafting and age-, height-, and body weight-matched elderly control subjects (CON; n = 7, age: 74 ± 8 years). Muscle O2 saturation (SmO2) and relative change in deoxygenated (∆deoxy-Hb) and total hemoglobin concentration (∆total-Hb) were measured continuously during exercise in the vastus lateralis (VL) by near infrared spatial resolved spectroscopy. Pulmonary O2 uptake (VO2) was also monitored throughout exercise to determine peak VO2. In AP, SmO2 was significantly higher, and ∆deoxy-Hb was significantly lower during exercise, compared to CON. In all subjects, ∆SmO2 (values at peak exercise minus values at resting) was negatively correlated to peak VO2 (r = -0.52, p < 0.05), and ∆deoxy-Hb at peak exercise tended to be negatively associated with peak VO2 (r = 0.48, p = 0.07). Blunted skeletal muscle deoxygenation response was observed in AP patients, which may be related to lower aerobic capacity in AP patients.