Daily heat treatment maintains mitochondrial function and attenuates atrophy in human skeletal muscle subjected to immobilization

Abstract

Skeletal muscle immobilization leads to atrophy, decreased metabolic health, and substantial losses in function. Animal models suggest that heat stress can provide protection against atrophy in skeletal muscle. This study investigated the effects of daily heat therapy on human skeletal muscle subjected to 10 days of immobilization. Muscle biopsies were collected, and MRIs were analyzed from the vastus lateralis of 23 healthy volunteers (11 women, 12 men) before and after either 10 days of immobilization with a daily sham treatment (Imm) or with a targeted, daily 2-h heat treatment using pulsed shortwave diathermy (Imm + H). Diathermy increased intramuscular temperature 4.2 ± 0.29°C ( P < 0.0001), with no change during sham treatment. As a result, heat shock protein (HSP)70 and HSP90 increased ( P < 0.05) following Imm + H (25 ± 6.6 and 20 ± 7.4%, respectively) but were unaltered with Imm only. Heat treatment prevented the immobilization-induced loss of coupled (−27 ± 5.2% vs. −8 ± 6.0%, P = 0.0041) and uncoupled (−25 ± 7.0% vs. −10 ± 3.9%, P = 0.0302) myofiber respiratory capacity. Likewise, heat treatment prevented the immobilization-induced loss of proteins associated with all five mitochondrial respiratory complexes ( P < 0.05). Furthermore, decreases in muscle cross-sectional area following Imm were greater than Imm + H at both the level of the whole muscle (−7.6 ± 0.96% vs. −4.5 ± 1.09%, P = 0.0374) and myofiber (−10.8 ± 1.52% vs. −5.8 ± 1.49%, P = 0.0322). Our findings demonstrate that daily heat treatments, applied during 10 days of immobilization, prevent the loss of mitochondrial function and attenuate atrophy in human skeletal muscle. NEW & NOTEWORTHY Limb immobilization results in substantial decreases in skeletal muscle size, function, and metabolic capacity. To date, there are few, if any, interventions to prevent the deleterious effects of limb immobilization on skeletal muscle health. Heat stress has been shown to elicit a stress response, resulting in increased heat shock protein expression and improved mitochondrial function. We show that during 10 days of lower-limb immobilization in humans, daily exposure to heat stress maintains mitochondrial respiratory capacity and attenuates atrophy in skeletal muscle. Our findings suggest that heat stress may serve as an effective therapeutic strategy to attenuate the decreases of muscle mass and metabolic function that accompany periods of disuse.

Preventing endothelial cell‐mediated muscle satellite cell dysfunction: a new hot topic?

“…; Hafen et al . ). Much more research is needed to determine whether heat therapy would improve/preserve muscle mass and function with ageing and/or with diseases associated with sarcopenia in humans; however, the study by Kargl et al .…”

“…Moreover, recent studies have reported beneficial effects of heat therapy on skeletal muscle function. Specifically, heat therapy attenuates reductions in muscle strength and accelerates muscle regeneration and recovery following muscle-damaging exercise or injury (McGorm et al 2018) and attenuates muscle atrophy associated with limb immobilization (McGorm et al 2018;Hafen et al 2019). Much more research is needed to determine whether heat therapy would improve/preserve muscle mass and function with ageing and/or with diseases associated with sarcopenia in humans; however, the study by Kargl et al (2019), when combined with the studies of heat therapy presented here, provides compelling support for this hypothesis, and that these beneficial effects may occur via the EC secretome.…”

Integrating Heat Training in the Rehabilitation Toolbox for the Injured Athlete

“…The potential for heat-based interventions to be an integrative part of a rehabilitation strategy has, therefore, gathered considerable enthusiasm lately. This surge in interest is in-part due to recent studies in humans demonstrating improved muscle contractile function (Racinais et al, 2017b) or attenuated loss of muscle mass during immobilization (Hafen et al, 2019) following short-term heat exposure. Specifically, Racinais et al (2017b) showed that 11 days of passive whole body heat exposure (60 min @ 48-50 • C, 50% RH) resulted in an increased peak twitch amplitude, improved maximal voluntary torque, as well as the relative torque/electromyographic relationship.…”

“…Specifically, Racinais et al (2017b) showed that 11 days of passive whole body heat exposure (60 min @ 48-50 • C, 50% RH) resulted in an increased peak twitch amplitude, improved maximal voluntary torque, as well as the relative torque/electromyographic relationship. Additionally, more recent data by Hafen et al (2019) showed that the decline in muscle mass following 10 days of lower limb immobilization was in-part attenuated when 120 min of localized heating of the vastus lateralis was administered daily. The preserved muscle mass following heat treatment coincided with the protein abundance of the transcriptional co-activator PGC-1α, HSP 70, and HSP 90, as well as minimized loss of mitochondrial respiratory chain protein content and mitochondrial respiratory function (Hafen et al, 2019).…”

“…Here we propose that an athlete's rehabilitation program may be optimized by incorporating repeated heat exposures or heat acclimation, given the evidence in support of this modality to minimize skeletal muscle and cardiovascular de-conditioning during periods of disuse and reduced physical activity. For example, there is emerging evidence demonstrating remarkable benefits of heat stress on the regulation of muscle mass (Selsby and Dodd, 2005;Selsby et al, 2007;Ihsan et al, 2014;Hafen et al, 2019). Moreover, training in the heat allows for maintaining a lower absolute work load for a given relative exercise intensity, reducing the mechanical demands of the rehabilitating athlete.…”