Impact of heat therapy on recovery after eccentric exercise in humans

The effect of a 4-week, remotely administered, post-exercise passive leg heating intervention on determinants of endurance performance

PURPOSE

Post-exercise passive heating has been reported to augment adaptations associated with endurance training. The current study evaluated the effect of a 4-week remotely administered, post-exercise passive leg heating protocol, using an electrically heated layering ensemble, on determinants of endurance performance.

METHODS

Thirty recreationally trained participants were randomly allocated to either a post-exercise passive leg heating (PAH, n = 16) or unsupervised training only control group (CON, n = 14). The PAH group wore the passive heating ensemble for 90-120 min/day, completing a total of 20 (16 post-exercise and 4 stand-alone leg heating) sessions across 4 weeks. Whole-body (peak oxygen uptake, gas exchange threshold, gross efficiency and pulmonary oxygen uptake kinetics), single-leg exercise (critical torque and NIRS-derived muscle oxygenation), resting vascular characteristics (flow-mediated dilation) and angiogenic blood measures (nitrate, vascular endothelial growth factor and hypoxia inducible factor 1-α) were recorded to characterize the endurance phenotype. All measures were assessed before (PRE), at 2 weeks (MID) and after (POST) the intervention.

RESULTS

There was no effect of the intervention on test of whole-body endurance capacity, vascular function or blood markers (p > 0.05). However, oxygen kinetics were adversely affected by PAH, denoted by a slowing of the phase II time constant; τ (p = 0.02). Furthermore, critical torque-deoxygenation ratio was improved in CON relative to PAH (p = 0.03).

CONCLUSION

We have demonstrated that PAH had no ergogenic benefit but instead elicited some unfavourable effects on sub-maximal exercise characteristics in recreationally trained individuals.

Six weeks of localized passive heat therapy elicits some exercise-like improvements in resistance artery function

The purpose of this study was to examine the effects of 6 weeks of localized, muscle-focused (quadriceps femoris) passive heat therapy (PHT) on resistance artery function, exercise haemodynamics and exercise performance relative to knee extension (KE) exercise training (EX). We randomized 34 healthy adults (ages 18-36; n = 17 female, 17 male) to receive either PHT or sham heating sessions (120 min, 3 days/week), or EX (40 min, 3 days/week) over 6 weeks. Blood flow was assessed with Doppler ultrasound of the femoral artery during both passive leg movement (PLM) and a KE graded exercise test. Muscle biopsies were taken from the vastus lateralis at baseline and after 6 weeks. Peak blood flow during PLM increased to the same extent in both the EX (∼10.5% increase, P = 0.009) and PHT groups (∼8.5% increase, P = 0.044). Peak flow during knee extension exercise increased in EX (∼19%, P = 0.005), but did not change in PHT (P = 0.523) and decreased in SHAM (∼7%, P = 0.020). Peak vascular conductance during KE increased by ∼25% in EX (P = 0.030) and PHT (P = 0.012). KE peak power increased in EX by ∼27% (P = 0.001) but did not significantly change in PHT and SHAM groups. Expression of endothelial nitric oxide synthase increased significantly in both EX (P = 0.028) and PHT (P = 0.0095), but only EX resulted in increased angiogenesis. In conclusion, 6 weeks of localized PHT improved resistance artery function at rest and during exercise to the same extent as exercise training but did not yield significant improvements in performance. KEY POINTS: Many for whom exercise would be most beneficial are either unable to exercise or have a very low exercise tolerance. In these cases, an alternative treatment to combat declines in resistance artery function is needed. We tested the hypothesis that passive heat therapy (PHT) would increase resistance artery function, improve exercise haemodynamics and enhance exercise performance compared to a sham treatment, but less than aerobic exercise training. This report shows that 6 weeks of localized PHT improved resistance artery function at rest and during exercise to the same extent as exercise training but did not improve exercise performance. Additionally, muscle biopsy analyses revealed that endothelial nitric oxide synthase expression increased in both PHT and exercise training groups, but only exercise resulted in increased angiogenesis. Our data demonstrate the efficacy of applying passive heat as an alternative treatment to improve resistance artery function for those unable to receive the benefits of regular exercise.

Acute Recovery after a Fatigue Protocol Using a Recovery Sports Legging: An Experimental Study

Enhancing recovery is a fundamental component of high-performance sports training since it enables practitioners to potentiate physical performance and minimise the risk of injuries. Using a new sports legging embedded with an intelligent system for electrostimulation, localised heating and compression (completely embodied into the textile structures), we aimed to analyse acute recovery following a fatigue protocol. Surface electromyography- and torque-related variables were recorded on eight recreational athletes. A fatigue protocol conducted in an isokinetic dynamometer allowed us to examine isometric torque and consequent post-exercise acute recovery after using the sports legging. Regarding peak torque, no differences were found between post-fatigue and post-recovery assessments in any variable; however, pre-fatigue registered a 16% greater peak torque when compared with post-fatigue for localised heating and compression recovery methods. Our data are supported by recent meta-analyses indicating that individual recovery methods, such as localised heating, electrostimulation and compression, are not effective to recover from a fatiguing exercise. In fact, none of the recovery methods available through the sports legging tested was effective in acutely recovering the torque values produced isometrically.

Skeletal muscle oxidative adaptations following localized heat therapy

Repeated heat treatment has been shown to induce oxidative adaptations in cell cultures and rodents, but similar work within human models is scarce. This study investigated the effects of 6 weeks of localized heat therapy on near-infrared spectroscopy-(NIRS) derived indices of muscle oxidative and microvascular function. Twelve physically active participants (8 males and 4 females, age: 34.9 ± 5.9 years, stature: 175 ± 7 cm, body mass: 76.7 ± 13.3 kg) undertook a 6-week intervention, where adhesive heat pads were applied for 8 h/day, 5 days/week, on one calf of each participant, while the contralateral leg acted as control. Prior to and following the intervention, the microvascular function was assessed using NIRS-based methods, where 5 min of popliteal artery occlusion was applied, and the reperfusion (i.e., re-saturation rate, re-saturation amplitude, and hyperemic response) was monitored for 2 min upon release. Participants also performed a 1-min isometric contraction of the plantar flexors (30% maximal voluntary contraction), following which a further 2 min interval was undertaken for the assessment of recovery kinetics. A 20-min time interval was allowed before the assessment protocol was repeated on the contralateral leg. Repeated localized heating of the gastrocnemius did not influence any of the NIRS-derive indices of microvascular or oxidative function (p > 0.05) following 6 weeks of treatment. Our findings indicate that localized heating via the use of adhesive heat pads may not be a potent stimulus for muscle adaptations in physically active humans.

Skeletal muscle angiogenic, regulatory, and heat shock protein responses to prolonged passive hyperthermia of the human lower limb

Passive hyperthermia induces a range of physiological responses including augmenting skeletal muscle mRNA expression. This experiment aimed to examine gene and protein responses to prolonged passive leg hyperthermia. Seven young participants underwent 3 h of resting unilateral leg heating (HEAT) followed by a further 3 h of rest, with the contralateral leg serving as an unheated control (CONT). Muscle biopsies were taken at baseline (0 h), and at 1.5, 3, 4, and 6 h in HEAT and 0 and 6 h in CONT to assess changes in selected mRNA expression via qRT-PCR, and HSP72 and VEGFα concentration via ELISA. Muscle temperature (T_m) increased in HEAT plateauing from 1.5 to 3 h (+3.5 ± 1.5°C from 34.2 ± 1.2°C baseline value; P < 0.001), returning to baseline at 6 h. No change occurred in CONT. Endothelial nitric oxide synthase (eNOS), Forkhead box O1 (FOXO-1), Hsp72, and VEGFα mRNA increased in HEAT (P < 0.05); however, post hoc analysis identified that only Hsp72 mRNA statistically increased (at 4 h vs. baseline). When peak change during HEAT was calculated angiopoietin 2 (ANGPT-2) decreased (-0.4 ± 0.2-fold), and C-C motif chemokine ligand 2 (CCL2) (+2.9 ± 1.6-fold), FOXO-1 (+6.2 ± 4.4-fold), Hsp27 (+2.9 ± 1.7-fold), Hsp72 (+8.5 ± 3.5-fold), Hsp90α (+4.6 ± 3.7-fold), and VEGFα (+5.9 ± 3.1-fold) increased from baseline (all P < 0.05). At 6 h T_m were not different between limbs (P = 0.582; CONT = 32.5 ± 1.6°C, HEAT = 34.3 ± 1.2°C), and only ANGPT-2 (P = 0.031; -1.3 ± 1.4-fold) and VEGFα (P = 0.030; 1.1 ± 1.2-fold) differed between HEAT and CONT. No change in VEGFα or HSP72 protein concentration were observed over time; however, peak change in VEGFα did increase (P < 0.05) in HEAT (+140 ± 184 pg·mL^-1) versus CONT (+7 ± 86 pg·mL^-1). Passive hyperthermia transiently augmented ANGPT-2, CCL2, eNOS, FOXO-1, Hsp27, Hsp72, Hsp90α and VEGFα mRNA, and VEGFα protein.

Role of macrophages during skeletal muscle regeneration and hypertrophy-Implications for immunomodulatory strategies

Skeletal muscle is a plastic tissue that regenerates ad integrum after injury and adapts to raise mechanical loading/contractile activity by increasing its mass and/or myofiber size, a phenomenon commonly refers to as skeletal muscle hypertrophy. Both muscle regeneration and hypertrophy rely on the interactions between muscle stem cells and their neighborhood, which include inflammatory cells, and particularly macrophages. This review first summarizes the role of macrophages in muscle regeneration in various animal models of injury and in response to exercise-induced muscle damage in humans. Then, the potential contribution of macrophages to skeletal muscle hypertrophy is discussed on the basis of both animal and human experiments. We also present a brief comparative analysis of the role of macrophages during muscle regeneration versus hypertrophy. Finally, we summarize the current knowledge on the impact of different immunomodulatory strategies, such as heat therapy, cooling, massage, nonsteroidal anti-inflammatory drugs and resolvins, on skeletal muscle regeneration and their potential impact on muscle hypertrophy.

Effects of home-based leg heat therapy on walking performance in patients with symptomatic peripheral artery disease: a pilot randomized trial

Few noninvasive therapies currently exist to improve functional capacity in people with lower extremity peripheral artery disease (PAD). The goal of the present study was to test the hypothesis that unsupervised, home-based leg heat therapy (HT) using water-circulating trousers perfused with warm water would improve walking performance in patients with PAD. Patients with symptomatic PAD were randomized into either leg HT (n = 18) or a sham treatment (n = 16). Patients were provided with water-circulating trousers and a portable pump and were asked to apply the therapy daily (7 days/wk, 90 min/session) for 8 wk. The primary study outcome was the change from baseline in 6-min walk distance at 8-wk follow-up. Secondary outcomes included the claudication onset-time, peak walking time, peak pulmonary oxygen consumption and peak blood pressure during a graded treadmill test, resting blood pressure, the ankle-brachial index, postocclusive reactive hyperemia in the calf, cutaneous microvascular reactivity, and perceived quality of life. Of the 34 participants randomized, 29 completed the 8-wk follow-up. The change in 6-min walk distance at the 8-wk follow-up was significantly higher (P = 0.029) in the group exposed to HT than in the sham-treated group (Sham: median: -0.9; 25%, 75% percentiles: -5.8, 14.3; HT: median: 21.3; 25%, 75% percentiles: 10.1, 42.4, P = 0.029). There were no significant differences in secondary outcomes between the HT and sham group at 8-wk follow-up. The results of this pilot study indicate that unsupervised, home-based leg HT is safe, well-tolerated, and elicits a clinically meaningful improvement in walking tolerance in patients with symptomatic PAD.NEW & NOTEWORTHY This is the first sham-controlled trial to examine the effects of home-based leg heat therapy (HT) on walking performance in patients with peripheral artery disease (PAD). We demonstrate that unsupervised HT using water-circulating trousers is safe, well-tolerated, and elicits meaningful changes in walking ability in patients with symptomatic PAD. This home-based treatment option is practical, painless, and may be a feasible adjunctive therapy to counteract the decline in lower extremity physical function in patients with PAD.

The Effects on Knee Swelling, Range of Motion and Pain using a Commercially Available Hot/Cold Contrast Device in a Rehabilitation and Sports Medicine Setting

Background and Purpose

Contrast therapy consists of alternating thermotherapy and cryotherapy repeatedly to assist in the management of acute, subacute, and chronic musculoskeletal conditions. This has been utilized for several decades with good to excellent subjective and objective results reported for patients with swelling (acute to chronic), pain, and loss of motion. Typically, the intervention is performed by either the use of a hot and cold whirlpool or by applying hot and cold packs which can be very time consuming and labor intensive. The purpose of this study was to determine the efficacy of a single treatment of the Hyperice X system in reducing knee joint pain, swelling and stiffness in active patients and young injured athletes. A secondary purpose was to measure patient satisfaction with the use of the device.

Subjects

Fifty subjects (34 males and 16 females) with a mean age of 22.2 +/- 4.9 yrs (ranging from 17 to 45 yrs of age) were recruited. Subjects presented with various types of knee pain, both non-operative and operative, secondary to ligamentous, tendinous, cartilage, muscle, and/or meniscus pathology. The subjects were in various stages of rehabilitation with six in the acute stage, 24 in subacute stage, and 20 in the chronic stage. The subjects participated in a variety of different sports at various levels of competition ranging from recreational to professional.

Methods

Subjects were recruited from one of two centers: an athletic training room or an outpatient sports medicine rehabilitation center. They were evaluated for baseline pain using the visual analog scale (VAS),verbal patient satisfaction on a scale of 1-10, verbal assessment of knee tightness, knee circumference, and knee flexion range of motion. The Hyperice X was applied to the knee utilizing the contrast setting for a total of 18 minutes with three six-minute cycles, each consisting of three minutes of heat therapy and three minutes of cold therapy. The contrast therapy was applied at the initiation of the physical therapy session and all subjective and objective measures were repeated immediately post contrast treatment.

Results

The VAS scores significantly improved following the treatment session with the mean score pretreatment of 2.59 and following the treatment of 1.68. Knee circumference improved for mid patella and 5 cm below mid patella, but no significant improvement was noted at the 5 cm above the patella region. Knee flexion improved from 130 degrees pre-treatment to 134 degrees post treatment. Knee extension improved from 2.72 degrees of hyperextension to 3.44 degrees, both of which were statistically significant(p<.001).

Conclusion

Contrast therapy utilizing the Hyperice X device demonstrated effectiveness in affecting pain reduction, swelling, and knee ROM. A commercially available device providing contrast therapy, may enhance outcomes in athletes after even a single treatment. In addition, the device was found to be easy to use, clinically practical, and demonstrated very high subjective patient satisfaction.

Level of Evidence

Level 3.

Eccentric Exercise Causes Specific Adjustment in Pyruvate Oxidation by Mitochondria

INTRODUCTION

The impact of eccentric exercise on mitochondrial function has only been poorly investigated and remains unclear. This study aimed to identify the changes in skeletal muscle mitochondrial respiration, specifically triggered by a single bout of eccentric treadmill exercise.

METHODS

Male adult mice were randomly divided into eccentric (ECC; downhill running), concentric (CON; uphill running), and unexercised control groups ( n = 5/group). Running groups performed 18 bouts of 5 min at 20 cm·s -1 on an inclined treadmill (±15° to 20°). Mice were sacrificed 48 h after exercise for blood and quadriceps muscles collection. Deep proximal (red) and superficial distal (white) muscle portions were used for high-resolution respirometric measurements.

RESULTS

Plasma creatine kinase activity was significantly higher in the ECC compared with CON group, reflecting exercise-induced muscle damage ( P < 0.01). The ECC exercise induced a significant decrease in oxidative phosphorylation capacity in both quadriceps femoris parts ( P = 0.032 in proximal portion, P = 0.010 in distal portion) in comparison with the CON group. This observation was only made for the nicotinamide adenine dinucleotide (NADH) pathway using pyruvate + malate as substrates. When expressed as a flux control ratio, indicating a change related to mitochondrial quality rather than quantity, this change seemed more prominent in distal compared with proximal portion of quadriceps muscle. No significant difference between groups was found for the NADH pathway with glutamate or glutamate + malate as substrates, for the succinate pathway or for fatty acid oxidation.

CONCLUSIONS

Our data suggest that ECC exercise specifically affects pyruvate mitochondrial transport and/or oxidation 48 h after exercise, and this alteration mainly concerns the distal white muscle portion. This study provides new perspectives to improve our understanding of the mitochondrial adaptation associated with ECC exercise.

Self-assisted wound healing using piezoelectric and triboelectric nanogenerators

The complex process of wound healing depends on the coordinated interaction between various immunological and biological systems, which can be aided by technology. This present review provides a broad overview of the medical applications of piezoelectric and triboelectric nanogenerators, focusing on their role in the development of wound healing technology. Based on the finding that the damaged epithelial layer of the wound generates an endogenous bioelectric field to regulate the wound healing process, development of technological device for providing an exogenous electric field has therefore been paid attention. Authors of this review focus on the design and application of piezoelectric and triboelectric materials to manufacture self-powered nanogenerators, and conclude with an outlook on the current challenges and future potential in meeting medical needs and commercialization.

Effect of heat pre-conditioning on recovery following exercise-induced muscle damage

This study investigated the influence of heat pre-conditioning on the recovery of muscle torque, microvascular function, movement economy and stride mechanics following exercise-induced muscle damage (EIMD). Twenty male participants were equally assigned to a control (CON) and an experimental group (HEAT), and performed a 30-min downhill run (DHR) to elicit EIMD. HEAT group received three consecutive days of heat exposure (45.1 ​± ​3.2 ​min of hot water immersion at 42 ​°C) prior to DHR. Microvascular function (near-infrared spectroscopy), maximal voluntary contraction (MVC) torque of the knee extensors, as well as two treadmill-based steady-state runs performed below (SSR-1) and above (SSR-2) the first ventilatory threshold were assessed prior to DHR and repeated for four consecutive days post-DHR (D1-POST to D4-POST). The decline in MVC torque following EIMD was attenuated in HEAT compared with CON at D1-POST (p ​= ​0.037), D3-POST (p ​= ​0.002) and D4-POST (p ​= ​0.022). Muscle soreness increased in both CON and HEAT, but was significantly attenuated in HEAT compared with CON at D2-POST (p ​= ​0.024) and D3-POST (p ​= ​0.013). Microvascular function decreased in CON from D1-POST to D3-POST (p ​= ​0.009 to 0.018), and was lower compared with HEAT throughout D1-POST to D3-POST (p ​= ​0.003 to 0.017). Pre-heat treatment decreased the magnitude of strength loss and muscle soreness, as well as attenuated the decline in microvascular function following EIMD. Heat treatment appears a promising pre-conditioning strategy when embarking on intensified training periods or competition.

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Three days of heat pre-conditioning decreases the extent of strength loss, soreness and microvascular function after EIMD.

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Pre heat treatment might be a promising preconditioning tool prior to intensified training periods or competition.

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Heat tretament may positively impact activities of daily living, training quality and adherence to training programs.

Neither Peristaltic Pulse Dynamic Compressions nor Heat Therapy Accelerate Glycogen Resynthesis after Intermittent Running

PURPOSE

To investigate the effects of a single session of either peristaltic pulse dynamic leg compressions (PPDC) or local heat therapy (HT) after prolonged intermittent shuttle running on skeletal muscle glycogen content, muscle function, and the expression of factors involved in skeletal muscle remodeling.

METHODS

Twenty-six trained individuals were randomly allocated to either a PPDC (n = 13) or a HT (n = 13) group. After completing a 90-min session of intermittent shuttle running, participants consumed 0.3 g·kg-1 protein plus 1.0 g·kg-1 carbohydrate and received either PPDC or HT for 60 min in one randomly selected leg, while the opposite leg served as control. Muscle biopsies from both legs were obtained before and after exposure to the treatments. Muscle function and soreness were also evaluated before, immediately after, and 24 h after the exercise bout.

RESULTS

The changes in glycogen content were similar (P > 0.05) between the thigh exposed to PPDC and the control thigh ~90 min (Control: 14.9 ± 34.3 vs PPDC: 29.6 ± 34 mmol·kg-1 wet wt) and ~210 min (Control: 45.8 ± 40.7 vs PPDC: 52 ± 25.3 mmol·kg-1 wet wt) after the treatment. There were also no differences in the change in glycogen content between thighs ~90 min (Control: 35.9 ± 26.1 vs HT: 38.7 ± 21.3 mmol·kg-1 wet wt) and ~210 min (Control: 61.4 ± 50.6 vs HT: 63.4 ± 17.5 mmol·kg-1 wet wt) after local HT. The changes in peak torque and fatigue resistance of the knee extensors, muscle soreness, and the mRNA expression and protein abundance of select factors were also similar (P > 0.05) in both thighs, irrespective of the treatment.

CONCLUSIONS

A single 1-h session of either PPDC or local HT does not accelerate glycogen resynthesis and the recovery of muscle function after prolonged intermittent shuttle running.

SCIENTIFIC PHYSICAL EXERCISE TO PREVENT MUSCLE INJURY IN COMPETITIVE SPORTS

ABSTRACT Introduction: Various factors cause many sports traumas in groups engaged in mass sports activities, amateur sports training, and professional sports training in China that must be called to our attention. Objective: Scientific Sports Therapy is a scientific and reasonable systemic sports training program formulated for competitive athletes based on their physical and disease characteristics. Methods: This article conducted scientific sports therapy interventions on tennis elbow patients and analyzed multiple physiological indicators such as muscle endurance before and after the intervention. Results: There are significant differences in the athletes’ muscle strength and muscle endurance data after physical exercise therapy. Conclusion: We analyzed the causes of muscle damage and adopted scientific and practical sports therapy. In this way, coaches and athletes can find effective ways to prevent and manage muscle injuries, thereby improving competitive sports training. Level of evidence II; Therapeutic studies - investigation of treatment results.

Local Heat Therapy to Accelerate Recovery After Exercise-Induced Muscle Damage

The prolonged impairment in muscle strength, power, and fatigue resistance after eccentric exercise has been ascribed to a plethora of mechanisms, including delayed muscle refueling and microvascular and mitochondrial dysfunction. This review explores the hypothesis that local heat therapy hastens functional recovery after strenuous eccentric exercise by facilitating glycogen resynthesis, reversing vascular derangements, augmenting mitochondrial function, and stimulating muscle protein synthesis.

Skeletal muscle adaptations to heat therapy

The therapeutic effects of heat have been harnessed for centuries to treat skeletal muscle disorders and other pathologies. However, the fundamental mechanisms underlying the well-documented clinical benefits associated with heat therapy (HT) remain poorly defined. Foundational studies in cultured skeletal muscle and endothelial cells, as well as in rodents, revealed that episodic exposure to heat stress activates a number of intracellular signaling networks and promotes skeletal muscle remodeling. Renewed interest in the physiology of HT in recent years has provided greater understanding of the signals and molecular players involved in the skeletal muscle adaptations to episodic exposures to HT. It is increasingly clear that heat stress promotes signaling mechanisms involved in angiogenesis, muscle hypertrophy, mitochondrial biogenesis, and glucose metabolism through not only elevations in tissue temperature but also other perturbations, including increased intramyocellular calcium and enhanced energy turnover. The few available translational studies seem to indicate that the earlier observations in rodents also apply to human skeletal muscle. Indeed, recent findings revealed that both local and whole-body HT may promote capillary growth, enhance mitochondrial content and function, improve insulin sensitivity and attenuate disuse-induced muscle wasting. This accumulating body of work implies that HT may be a practical treatment to combat skeletal abnormalities in individuals with chronic disease who are unwilling or cannot participate in traditional exercise-training regimens.

Effects of repeated local heat therapy on skeletal muscle structure and function in humans

The purpose of the present study was to examine the effects of repeated exposure to local heat therapy (HT) on skeletal muscle function, myofiber morphology, capillarization, and mitochondrial content in humans. Twelve young adults (23.6 ± 4.8 yr, body mass index 24.9 ± 3.0 kg/m²) had one randomly selected thigh treated with HT (garment perfused with water at ~52°C) for 8 consecutive weeks (90 min, 5 days/wk) while the opposite thigh served as a control. Biopsies were obtained from the vastus lateralis muscle before and after 4 and 8 wk of treatment. Knee extensor strength and fatigue resistance were also assessed using isokinetic dynamometry. The changes in peak isokinetic torque were higher (P = 0.007) in the thigh exposed to HT than in the control thigh at weeks 4 (control 4.2 ± 13.1 Nm vs. HT 9.1 ± 16.1 Nm) and 8 (control 1.8 ± 9.7 Nm vs. HT 7.8 ± 10.2 Nm). Exposure to HT averted a temporal decline in capillarization around type II fibers (P < 0.05), but had no effect on capillarization indexes in type I fibers. The content of endothelial nitric oxide synthase was ~18% and 35% higher in the thigh exposed to HT at 4 and 8 wk, respectively (P = 0.003). Similarly, HT increased the content of small heat shock proteins HSPB5 (P = 0.007) and HSPB1 (P = 0.009). There were no differences between thighs for the changes in fiber cross-sectional area and mitochondrial content. These results indicate that exposure to local HT for 8 wk promotes a proangiogenic environment and enhances muscle strength but does not affect mitochondrial content in humans.NEW & NOTEWORTHY We demonstrate that repeated application of heat therapy to the thigh with a garment perfused with warm water enhances the strength of knee extensors and influences muscle capillarization in parallel with increases in the content of endothelial nitric oxide synthase and small heat shock proteins. This practical method of passive heat stress may be a feasible tool to treat conditions associated with capillary rarefaction and muscle weakness.

Accelerating Recovery from Exercise-Induced Muscle Injuries in Triathletes: Considerations for Olympic Distance Races

The triathlon is one of the fastest developing sports in the world due to expanding participation and media attention. The fundamental change in Olympic triathlon races from a single to a multistart event is highly demanding in terms of recovery from and prevention of exercise-induced muscle injures. In elite and competitive sports, ultrastructural muscle injuries, including delayed onset muscle soreness (DOMS), are responsible for impaired muscle performance capacities. Prevention and treatment of these conditions have become key in regaining muscular performance levels and to guarantee performance and economy of motion in swimming, cycling and running. The aim of this review is to provide an overview of the current findings on the pathophysiology, as well as treatment and prevention of, these conditions in compliance with clinical implications for elite triathletes. In the context of DOMS, the majority of recovery interventions have focused on different protocols of compression, cold or heat therapy, active regeneration, nutritional interventions, or sleep. The authors agree that there is a compelling need for further studies, including high-quality randomized trials, to completely evaluate the effectiveness of existing therapeutic approaches, particularly in triathletes. The given recommendations must be updated and adjusted, as further evidence emerges.

Heat therapy improves soleus muscle force in a model of ischemia-induced muscle damage

Leg muscle ischemia in patients with peripheral artery disease (PAD) leads to alterations in skeletal muscle morphology and reduced leg strength. We tested the hypothesis that exposure to heat therapy (HT) would improve skeletal muscle function in a mouse model of ischemia-induced muscle damage. Male 42-wk-old C57Bl/6 mice underwent ligation of the femoral artery and were randomly assigned to receive HT (immersion in a water bath at 37°C, 39°C, or 41°C for 30 min) or a control intervention for 3 wk. At the end of the treatment, the animals were anesthetized and the soleus and extensor digitorum longus (EDL) muscles were harvested for the assessment of contractile function and examination of muscle morphology. A subset of animals was used to examine the impact of a single HT session on the expression of genes involved in myogenesis and the regulation of muscle mass. Relative soleus muscle mass was significantly higher in animals exposed to HT at 39°C compared with the control group (control: 0.36 ± 0.01 mg/g versus 39°C: 0.40 ± 0.01 mg/g, P = 0.024). Maximal absolute force of the soleus was also significantly higher in animals treated with HT at 37°C and 39°C (control: 274.7 ± 6.6 mN; 37°C: 300.1 ± 7.7 mN; 39°C: 299.5 ± 10 mN, P < 0.05). In the soleus, but not the EDL muscle, a single session of HT enhanced the mRNA expression of myogenic factors as well as of both positive and negative regulators of muscle mass. These findings suggest that the beneficial effects of HT are muscle specific and dependent on the treatment temperature in a model of PAD. NEW & NOTEWORTHY This is the first study to comprehensively examine the impact of temperature and muscle fiber type composition on the adaptations to repeated heat stress in a model of ischemia-induced muscle damage. Exposure to heat therapy (HT) at 37°C and 39°C, but not at 41°C, improved force development of the isolated soleus muscle. These results suggest that HT may be a practical therapeutic tool to restore muscle mass and strength in patients with peripheral artery disease.