A Comparison of Heat Treatment-Induced Skeletal Muscle Adaptations Relative to Exercise Training

ABSTRACT In vitro and animal studies indicate that the response to heat stress is associated with beneficial adaptations that promote cell health and survival. Few studies to date have examined this finding in human subjects, and it is unclear how the adaptation compares in magnitude to exercise training. PURPOSE: To investigate the skeletal muscle adaptations (namely mitochondrial biogenesis and capillarization) of 6 weeks of deep-muscle heat treatment relative to exercise training. We hypothesized that heat treatment (HT), applied through pulsed shortwave diathermy (2 hr, 3 days/week) over a 6-week intervention period would lead to increased mitochondrial content and capillarity within skeletal muscle, though to a lesser extent than single-leg knee extension exercise training (EX; 40 min, 3 days/week). METHODS: We randomized 28 sedentary but otherwise healthy, young adults (ages 18–36; n = 13 female, n = 15 male) to receive either HT, EX, or sham heating sessions (CON; 2 hr, 3 days/week) over 6 weeks. Diathermy increased muscle temperature by 3.2 ± 0.33 °C (P \u3c 0.0001) within 20 minutes. Muscle biopsies were taken from the vastus lateralis at baseline, after 3 weeks of intervention and again after 6 weeks of intervention. RESULTS: Following 3 and 6 weeks of heat treatment, we did not observe significant changes in mitochondrial biogenesis or capillarization. However, exercise training was sufficient to elicit an increase in individual capillary-to-fiber ratio (P = 0.0003), capillary density (P = 0.0428), and the Capillary to Fiber Perimeter Exchange Index (P = 0.0089). Significant increases in the expression of mitochondrial protein Complexes I (P = 0.0073) and IV (P = 0.0015), were observed in the exercise group, but not the heat or control groups. CONCLUSIONS: 6 weeks of localized HT, when applied to young healthy individuals, is insufficient to induce mitochondrial biogenesis or capillarization in skeletal muscle. Additionally, our findings provide support for the extensive body of literature that connects exercise training to beneficial skeletal muscle adaptations

The Effect of Heat Therapy on Skeletal Muscle Satellite Cell Content

Satellite cells are essential for proper muscle repair and adaptation. Studies have shown that exercise can lead to an increase in satellite cell content within muscle tissue. However, it is unknown whether other environmental stressors, such as heat, are also capable of augmenting the satellite cell pool. PURPOSE: The purpose of this study was to quantify changes in satellite cell content before and after 6-weeks (3x/wk) of skeletal muscle heat therapy (HT) or single leg knee extension exercise training (EX). Additionally, a sham heat treatment was used as a control. We hypothesized that HT would result in an increase in satellite cell content, though to a lesser extent than the EX group. METHODS: We randomized 28 sedentary but otherwise healthy, young adults (ages 18-36; n = 13 female, n = 15 male) to receive either HT (2 hr, 3 days/wk, 6-week period), EX (40 min, 3 days/wk, 6-week period), or sham heating sessions (CON; 2hr, 3 days/wk, 6-week period). The HT was administered through pulsed, shortwave diathermy. Muscle biopsies were taken from the vastus lateralis at baseline, after 3 weeks of intervention, and again after 6 weeks of intervention. RESULTS: For the Control Group, satellite cell count per mm2 at baseline = 8.107 (± 0.4799), at 3 weeks = 10.27 (± 0.911), at 6 weeks = 9.84 (± 0.675). For the EX Group, satellite cell count per mm2 at baseline = 9.705 (± 1.27), at 3 weeks = 10.87 (± 1.12), and at 6 weeks = 10.47 (±0.7997). For the HT Group, satellite cell count per mm2 at baseline = 8.535 (± 0.582), at 3 weeks = 11.54 (± 1.43), and at 6 weeks = 10.202 (± 0.940). Statistical analysis indicated a significant main effect of time (p=0.0125), but no significant effect of group (p=0.5504) or the group x time interaction (p=0.8412). CONCLUSION: Our findings suggest that 6 weeks of HT is insufficient to affect the satellite cell content within muscle fibers. This study provides additional insight in the literature about the effects of HT on human subjects

The Effect of Heat Therapy on Skeletal Muscle Satellite Cell Content

Satellite cells are essential for proper muscle repair and adaptation. Studies have shown that exercise can lead to an increase in satellite cell content within muscle tissue. However, it is unknown whether other environmental stressors, such as heat, are also capable of augmenting the satellite cell pool. PURPOSE: The purpose of this study was to quantify changes in satellite cell content before and after 6-weeks (3x/wk) of skeletal muscle heat therapy (HT) or single leg knee extension exercise training (EX). Additionally, a sham heat treatment was used as a control. We hypothesized that HT would result in an increase in satellite cell content, though to a lesser extent than the EX group. METHODS: We randomized 28 sedentary but otherwise healthy, young adults (ages 18-36; n = 13 female, n = 15 male) to receive either HT (2 hr, 3 days/wk, 6-week period), EX (40 min, 3 days/wk, 6-week period), or sham heating sessions (CON; 2hr, 3 days/wk, 6-week period). The HT was administered through pulsed, shortwave diathermy. Muscle biopsies were taken from the vastus lateralis at baseline, after 3 weeks of intervention, and again after 6 weeks of intervention. RESULTS: For the Control Group, satellite cell count per mm2 at baseline = 8.107 (± 0.4799), at 3 weeks = 10.27 (± 0.911), at 6 weeks = 9.84 (± 0.675). For the EX Group, satellite cell count per mm2 at baseline = 9.705 (± 1.27), at 3 weeks = 10.87 (± 1.12), and at 6 weeks = 10.47 (±0.7997). For the HT Group, satellite cell count per mm2 at baseline = 8.535 (± 0.582), at 3 weeks = 11.54 (± 1.43), and at 6 weeks = 10.202 (± 0.940). Statistical analysis indicated a significant main effect of time (p=0.0125), but no significant effect of group (p=0.5504) or the group x time interaction (p=0.8412). CONCLUSION: Our findings suggest that 6 weeks of HT is insufficient to affect the satellite cell content within muscle fibers. This study provides additional insight in the literature about the effects of HT on human subjects

Localized Heat Therapy Improves Mitochondrial Respiratory Capacity but Not Fatty Acid Oxidation

AIM: Mild heat stress can improve mitochondrial respiratory capacity in skeletal muscle. However, long-term heat interventions are scarce, and the effects of heat therapy need to be understood in the context of the adaptations which follow the more complex combination of stimuli from exercise training. The purpose of this work was to compare the effects of 6 weeks of localized heat therapy on human skeletal muscle mitochondria to single-leg interval training. METHODS: Thirty-five subjects were assigned to receive sham therapy, short-wave diathermy heat therapy, or single-leg interval exercise training, localized to the quadriceps muscles of the right leg. All interventions took place 3 times per week. Muscle biopsies were performed at baseline, and after 3 and 6 weeks of intervention. Mitochondrial respiratory capacity was assessed on permeabilized muscle fibers via high-resolution respirometry. RESULTS: The primary finding of this work was that heat therapy and exercise training significantly improved mitochondrial respiratory capacity by 24.8 ± 6.2% and 27.9 ± 8.7%, respectively (p < 0.05). Fatty acid oxidation and citrate synthase activity were also increased following exercise training by 29.5 ± 6.8% and 19.0 ± 7.4%, respectively (p < 0.05). However, contrary to our hypothesis, heat therapy did not increase fatty acid oxidation or citrate synthase activity. CONCLUSION: Six weeks of muscle-localized heat therapy significantly improves mitochondrial respiratory capacity, comparable to exercise training. However, unlike exercise, heat does not improve fatty acid oxidation capacity