Heat stress enhances mTOR signaling after resistance exercise in human skeletal muscle

Effect of glucose supplementation on protein biosynthesis in chickens reared under thermoneutral or heat stress environment

Heat stress (HS) impacts broilers by reducing feed intake which impairs nutrient availability and energy levels, subsequently affecting protein biosynthesis. We hypothesize that an exogenous supply of glucose could provide extra energy resources that enhance protein biosynthesis in broilers reared under HS. Our experimental design involved two levels of temperature (25 °C [thermoneutral, TN]); 35 °C (8.00 AM to 8.00 PM, [Heat Stress, HS]), and two glucose levels (0 % and 6 %). We randomly assigned a total of 456 four-week-old Cobb500 broilers to four different treatment groups (TN0, TN6, HS0, and HS6), respectively. After 7 days post-HS, we observed an inverse relationship between the avian target of rapamycin (avTOR) and autophagy-related genes. The phosphorylation of mTOR and S6K1 at Ser2448 and Thr421/Ser424 respectively was higher (p < 0.05) in the TN0 group than in the HS groups. Additionally, the phosphorylation of Foxo3a at Ser253 was higher (p < 0.05) in the HS0 group than in the HS6 groups, indicating an adaptive response to HS. Thus, the combined effect of HS and glucose could influence the phosphorylation status of key signaling genes in the mTOR pathway. The expression levels of mRNA genes in the mTOR pathway were more pronounced (p < 0.05) in HS6 birds than in HS0 birds except for avTOR, Akt1, and S6K1.

Effects of thermal interventions on skeletal muscle adaptations and regeneration: perspectives on epigenetics: a narrative review

Recovery methods, such as thermal interventions, have been developed to promote optimal recovery and maximize long-term training adaptations. However, the beneficial effects of these recovery strategies remain a source of controversy. This narrative review aims to provide a detailed understanding of how cold and heat interventions impact long-term training adaptations. Emphasis is placed on skeletal muscle adaptations, particularly the involvement of signaling pathways regulating protein turnover, ribosome and mitochondrial biogenesis, as well as the critical role of satellite cells in promoting myofiber regeneration following atrophy. The current literature suggests that cold interventions can blunt molecular adaptations (e.g., protein synthesis and satellite cell activation) and oxi-inflammatory responses after resistance exercise, resulting in diminished exercise-induced hypertrophy and lower gains in isometric strength during training protocols. Conversely, heat interventions appear promising for mitigating skeletal muscle degradation during immobilization and atrophy. Indeed, heat treatments (e.g., passive interventions such as sauna-bathing or diathermy) can enhance protein turnover and improve the maintenance of muscle mass in atrophic conditions, although their effects on uninjured skeletal muscles in both humans and rodents remain controversial. Nonetheless, heat treatment may serve as an important tool for attenuating atrophy and preserving mitochondrial function in immobilized or injured athletes. Finally, the potential interplay between exercise, thermal interventions and epigenetics is discussed. Future studies must be encouraged to clarify how repeated thermal interventions (heat and cold) affect long-term exercise training adaptations and to determine the optimal modalities (i.e., method of application, temperature, duration, relative humidity, and timing).

Passive heating in sport: context-specific benefits, detriments, and considerations

Exercise and passive heating share some acute physiological responses. These include increases in body temperature, sweat rate, blood flow, heart rate, and redistribution of plasma and blood volume. These responses can vary depending on the heating modality or dose (e.g., temperature, duration, body coverage) and are beneficial to athletes in specific scenarios. These scenarios include being applied to increase muscle or force production, induce rapid weight loss, stimulate thermoregulatory or cardiovascular adaptation, or to accelerate recovery. The rationale being to tailor the specific passive heating protocol to target the desired physiological response. However, some acute responses to passive heating may also be detrimental to sporting outcomes, such as exercising in the heat, having unintended residual negative effects on performance or perceptions of fatigue, or even resulting in hospitalisation if implemented inappropriately. Accordingly, the effects of passive heating should be carefully considered prior to implementation by athletes, coaches, and support staff. Therefore, the purpose of this review is to evaluate the physiological responses to different modes and doses of passive heating and explore the various sport contexts where these effects may either benefit or hinder athletes. Understanding these responses can aid the implementation of passive heating in sport and identify potential recommended heating protocols in each given scenario.

Novel Applicator Utilizing HIFES and Enhanced Synchronized Radiofrequency+ for Subcutaneous Fat Reduction: Porcine Model Study

OBJECTIVES

Submental fullness has been associated with being perceived as unattractive. Technology combining radiofrequency and muscle stimulation offers submental contouring through fat reduction, muscle stimulation, and skin tightening. This study aims to demonstrate the effectiveness and safety of fat reduction aspect with a novel submentum applicator delivering HIFES and synchronized radiofrequency+ (RF+) energies.

MATERIALS AND METHODS

Six white pigs (sus scrofa domesticus, n = 6, 60-80 kg) were recruited for this study, five in the active group (n = 5) received four treatments on the abdominal area, one sow served as a control (n = 1). Ultrasound, histological, and RT-qPCR methods were used as evaluation methods.

RESULTS

Fat thickness decreased at 1 month by -17.35% and at 2 month by 31.40%. Proapoptotic caspase-9 gene expression increased (at 1 h, 6 h, 24 h to +43.45%, +21.22%, -8.36%), as well as caspase-3 (+15.28%, +21.77%, -6.71%), while bcl2l1 activity decreased (-11.46% at 1 h, -17.02% at 6 h, -3.9% at 24 h). While the AI in the control animal had minimal change (at 1 h -0.08%, at 6 h -0.09%, and at 24 h -0.025%), the active group's AI increased from the baseline of 9.14 to 44.85 at 1 h (+391%), peaked at 6 h to 53.50 (+485%), and at 24 h to 38.17 (+318%).

CONCLUSION

The study results indicate the efficacy and safety of subcutaneous fat reduction following the novel technology combining HIFES and RF+ energies, designed to target small localized areas.

The combined influences of local heat application and resistance exercise on the acute mRNA response of skeletal muscle

Introduction

The development and maintenance of the skeletal muscle is crucial for the support of daily function. Heat, when applied locally, has shown substantial promise in the maintenance of the muscle. The purpose of this study was to determine the combined effects of local heat application and acute resistance exercise on gene expression associated with the human muscle growth program.

Materials and methods

Participants (n = 12, 26 ± 7 years, 1.77 ± 0.07 m, 79.6 ± 15.4 kg, and 16.1 ± 11.6 %BF) completed an acute bilateral bout of resistance exercise consisting of leg press (11 ± 2 reps; 170 ± 37 kg) and leg extension (11 ± 1 reps; 58 ± 18 kg). Participants wore a thermal wrap containing circulating fluid (40°C, exercise + heat; EX + HT) during the entire experimental period and 4 h post-exercise, while the other leg served as an exercise-only (EX) control. Biopsies of the vastus lateralis were collected (Pre, Post, and 4hPost) for gene expression analyses.

Results

Intramuscular temperatures increased (Post, +2.2°C ± 0.7°C, and p < 0.001; 4hPost, +2.5°C ± 0.6°C, and p < 0.001) and were greater in the EX + HT leg post-exercise (+0.35°C ± 0.3°C, and p = 0.005) and after 4hPost (+2.1°C ± 0.8°C and p < 0.001). MYO-D1 mRNA was greater in the EX + HT leg vs. the EX (fold change = 2.74 ± 0.42 vs. 1.70 ± 0.28, p = 0.037). No other genes demonstrated temperature sensitivity when comparing both legs (p > 0.05). mRNA associated with the negative regulator, myostatin (MSTN), decreased post-exercise (p = 0.001) and after 4 h (p = 0.001). mRNA associated with proteolysis decreased post-exercise (FBXO32, p = 0.001; FOXO3a, p = 0.001) and after 4 h (FBXO32, p = 0.001; FOXO3a, p = 0.027).

Conclusion

The elevated transcription of the myogenic differentiation factor 1 (MYO-D1) after exercise in the heated condition may provide a mechanism by which muscle growth could be enhanced.

A Novel Approach to Shaping the Lateral Abdomen: Simultaneous Application of High-Intensity Focused Electromagnetic (HIFEM) Therapy and Synchronized Radiofrequency at the Flanks: A Multicenter MRI Study

BACKGROUND

An accumulation of adipose tissue on the lateral abdomen (flanks) coupled with muscle deconditioning negatively affects core stability, muscular balance, and the intrinsic strength essential for maintaining optimal body mechanics and posture. This lateral fat accumulation and diminution of muscle result in an unfavorable abdominal profile and present challenges in finding appropriately fitting attire.

OBJECTIVES

The aim of this study was to explore the effectiveness and safety of the simultaneous application of high-intensity focused electromagnetic (HIFEM) therapy and synchronized radiofrequency for sculpting the lateral abdomen.

METHODS

All patients were scheduled to undergo four 30-minute treatments at approximately weekly intervals and then subsequent follow-up visits at 1 month and 3 months after the last treatment. The primary evaluation assessed changes in the oblique muscles, adipose tissue thickness, and cross-sectional area (CSA) by MRI performed at baseline and follow-ups. The secondary outcomes included digital photographs of the treated areas, a Subject Satisfaction Questionnaire, and a Therapy Comfort Questionnaire. Adverse events and side effects were monitored throughout the study duration.

RESULTS

The muscle tissue showed a substantial increase in thickness (+27.2%) and CSA (+29.0%). The adipose tissue measurements showed a decrease of -30.5% in CSA and -28.8% in thickness. As secondary outcomes, 81.8% of patients reported feeling more toned, and 84.9% of patients found the treatment comfortable and reported less than mild pain.

CONCLUSIONS

Based on the evaluation, the study suggests that the simultaneous application of HIFEM and synchronized radiofrequency is safe and effective for reducing adipose tissue and strengthening muscle in the area of the lateral abdomen.

Endocrine Responses to Heated Resistance Exercise in Men and Women

ABSTRACT

Pryor, JL, Sweet, DK, Rosbrook, P, Qiao, J, Looney, DP, Mahmood, S, and Rideout, T. Endocrine responses to heated resistance exercise in men and women. J Strength Cond Res 38(7): 1248-1255, 2024-We examined the endocrine responses of 16 (female = 8) resistance trained volunteers to a single bout of whole-body high-volume load resistance exercise in hot (HOT; 40° C) and temperate (TEMP; 20° C) environmental conditions. Thermoregulatory and heart rate (HR) data were recorded, and venous blood was acquired before and after resistance exercise to assess serum anabolic and catabolic hormones. In men, testosterone increased after resistance exercise in HOT and TEMP ( p < 0.01), but postexercise testosterone was not different between condition ( p = 0.51). In women, human growth hormone was different between condition at pre-exercise ( p = 0.02) and postexercise ( p = 0.03). After controlling for pre-exercise values, the between-condition postexercise difference was abolished ( p = 0.16). There were no differences in insulin-like growth factor-1 for either sex ( p ≥ 0.06). In women, cortisol increased from pre-exercise to postexercise in HOT ( p = 0.04) but not TEMP ( p = 0.19), generating a between-condition difference at postexercise ( p < 0.01). In men, cortisol increased from pre-exercise to postexercise in HOT only ( p < 0.01). Rectal temperature increased to a greater extent in HOT compared with TEMP in both men ( p = 0.01) and women ( p = 0.02). Heart rate increased after exercise under both conditions in men and women ( p = 0.01), but only women experience greater postexercise HR in HOT vs. TEMP ( p = 0.04). The addition of heat stress to resistance exercise session did not overtly shift the endocrine response toward an anabolic or catabolic response. When acute program variables are prescribed to increase postresistance exercise anabolic hormones, adding heat stress is not synergistic but does increase physiologic strain (i.e., elevated HR and rectal temperature).

Resistance Training in the Heat: Mechanisms of Hypertrophy and Performance Enhancement

ABSTRACT

Pryor, JL, Sweet, D, Rosbrook, P, Qiao, J, Hess, HW, and Looney, DP. Resistance training in the heat: Mechanisms of hypertrophy and performance enhancement. J Strength Cond Res 38(7): 1350-1357, 2024-The addition of heat stress to resistance exercise or heated resistance exercise (HRE) is growing in popularity as emerging evidence indicates altered neuromuscular function and an amplification of several mechanistic targets of protein synthesis. Studies demonstrating increased protein synthesis activity have shown temperature-dependent mammalian target of rapamycin phosphorylation, supplemental calcium release, augmented heat shock protein expression, and altered immune and hormone activity. These intriguing observations have largely stemmed from myotube, isolated muscle fiber, or rodent models using passive heating alone or in combination with immobilization or injury models. A growing number of translational studies in humans show comparable results employing local tissue or whole-body heat with and without resistance exercise. While few, these translational studies are immensely valuable as they are most applicable to sport and exercise. As such, this brief narrative review aims to discuss evidence primarily from human HRE studies detailing the neuromuscular, hormonal, and molecular responses to HRE and subsequent strength and hypertrophy adaptations. Much remains unknown in this exciting new area of inquiry from both a mechanistic and functional perspective warranting continued research.

Hsf1 and the molecular chaperone Hsp90 support a 'rewiring stress response' leading to an adaptive cell size increase in chronic stress

Cells are exposed to a wide variety of internal and external stresses. Although many studies have focused on cellular responses to acute and severe stresses, little is known about how cellular systems adapt to sublethal chronic stresses. Using mammalian cells in culture, we discovered that they adapt to chronic mild stresses of up to two weeks, notably proteotoxic stresses such as heat, by increasing their size and translation, thereby scaling the amount of total protein. These adaptations render them more resilient to persistent and subsequent stresses. We demonstrate that Hsf1, well known for its role in acute stress responses, is required for the cell size increase, and that the molecular chaperone Hsp90 is essential for coupling the cell size increase to augmented translation. We term this translational reprogramming the 'rewiring stress response', and propose that this protective process of chronic stress adaptation contributes to the increase in size as cells get older, and that its failure promotes aging.

Holistic Approach for Noninvasive Facial Rejuvenation by Simultaneous Use of High Intensity Focused Electrical Stimulation and Synchronized Radiofrequency: A Review of Treatment Effects Underlined by Understanding of Facial Anatomy

Understanding facial anatomy is a key aspect for successful treatment of age-related changes manifested to facial tissues. Namely, changes to the facial muscles and their connective tissue framework result in an increased soft tissue laxity, leading to wrinkling, sagging, and altered texture. This review elaborates on the use of novel high intensity focused electrical stimulation (HIFES) and Synchronized RF technology to improve facial muscle tone and skin structure, focusing on the technology background and clinical aspects.

Exploring the impact of temporal heat stress on skeletal muscle hypertrophy in bovine myocytes

The primary aim of this investigation was to explore the impact of different temporal stress conditions on the regulators associated with skeletal muscle hypertrophy in bovine myocytes. Bovine satellite cells (BSCs) were extracted from three-month-old Holstein bull calves and subjected to myogenic differentiation under three thermal treatments: 38 °C (control; CON), 39.5 °C (moderate heat stress; MHS), and 41 °C (extreme heat stress; EHS) for a duration of 3 or 48 h. Exposure to EHS resulted in elevated (P < 0.01) expression levels of heat shock protein (HSP)20, HSP27, HSP70, and HSP90, along with increased (P < 0.01) protein levels. Moreover, cells exposed to MHS and EHS exhibited enhanced (P < 0.01) gene expression of myoblast determination protein 1 (MyoD), while myogenin (MyoG) was overexpressed (P < 0.01) in cells exposed to EHS. These findings suggest that heat exposure can potentially induce myogenic differentiation through the modulation of myogenic regulatory factors. Furthermore, our investigations revealed that exposure to EHS upregulated (P < 0.01) myosin heavy chain (MHC) I expression, whereas MHC IIA (P < 0.01) and IIX (P < 0.01) expression were increased; P < 0.01) under MHS conditions. These observations suggest that the temperature of the muscle may alter the proportion of muscle fiber types. Additionally, our data indicated that EHS activated (P < 0.01) the expression of insulin-like growth factor 1 (IGF-1) and triggered the activation of the Akt/mTOR/S6KB1 pathway, a known anabolic pathway associated with cellular protein synthesis. Consequently, these altered signaling pathways contributed to enhanced protein synthesis and increased myotube size. Overall, the results obtained from our current study revealed that extreme heat exposure (41 °C) may promote skeletal muscle hypertrophy by regulating myogenic regulatory factors and IGF-1-mediated mTOR pathway in bovine myocytes.

Effect of hot water immersion on acute physiological responses following resistance exercise

Purpose: Hot water immersion (HWI) is a strategy theorised to enhance exercise recovery. However, the acute physiological responses to HWI following resistance exercise are yet to be determined. Methods: The effect of HWI on intramuscular temperature (IMT), muscle function, muscle soreness and blood markers of muscle cell disruption and inflammatory processes after resistance exercise was assessed. Sixteen resistance trained males performed resistance exercise, followed by either 10 min HWI at 40°C or 10 min passive recovery (PAS). Results: Post-intervention, the increase in IMT at all depths was greater for HWI compared to PAS, however this difference had disappeared by 1 h post at depths of 1 and 2 cm, and by 2 h post at a depth of 3 cm. There were no differences between groups for muscle function, muscle soreness or any blood markers. Conclusion: These results suggest that HWI is a viable means of heat therapy to support a greater IMT following resistance exercise. Recovery of muscle function and muscle soreness is independent of acute changes in IMT associated with HWI.

The independent effects of local heat application on muscle growth program associated mRNA and protein phosphorylation

The development and maintenance of skeletal muscle is crucial for the support of daily function. Recent evidence suggests that genes coded for proteins associated with the human muscle growth program (myogenic and proteolytic genes) are sensitive to local heat application. Therefore, the purpose of this investigation was to determine the effect of 4 h of local heat application to the vastus lateralis at rest on acute phosphorylation (mTORSer2448, p70-S6K1Thr389, and 4E-BP1Thr47/36) and gene expression changes for proteins associated with the muscle growth program. Intramuscular temperature of the HOT limb was 1.2 ± 0.2 °C higher than CON limb after 4 h of local heating. However, this local heat stimulus did not influence transcription of genes associated with myogenesis (MSTN, p = 0.321; MYF5, p = 0.445; MYF6, p = 0.895; MEF2a, p = 0.809; MYO-G, p = 0.766; MYO-D1, p = 0.118; RPS3, p = 0.321; and RPL-3L, p = 0.577), proteolysis (Atrogin-1, p = 0.573; FOXO3a, p = 0.452; MURF-1, p = 0.284), nor protein phosphorylation (mTORSer2448, p = 0.981; P70-S6K1Thr389, p = 0.583; 4E-BP1Thr37/46, p = 0.238) associated with the muscle growth program. These findings suggest little to no association between the local application of heat, at rest, and the activation of the observed muscle growth program-related markers.

Active recovery vs hot- or cold-water immersion for repeated sprint ability after a strenuous exercise training session in elite skaters

This study compared the acute effects of three recovery methods: active recovery (AR), hot- and cold-water immersion (HWI and CWI, respectively), used between two training sessions in elite athletes. Twelve national-team skaters (7 males, 5 females) completed three trials according to a randomized cross-over study. Fifteen minutes after an exhaustive ice-skating training session, participants underwent 20 min of HWI (41.1 ± 0.5°C), 15 min of CWI (12.1 ± 0.7°C) or 15 min of active recovery (AR). After 1 h 30 min of the first exercise, they performed a repeated-sprint cycling session. Average power output was slightly but significantly higher for AR (767 ± 179 W) and HWI (766 ± 170 W) compared to CWI (738 ± 156 W) (p = 0.026, d = 0.18). No statistical difference was observed between the conditions for both lactatemia and rating of perceived exertion. Furthermore, no significant effect of recovery was observed on the fatigue index calculated from the repeated sprint cycling exercises (p > 0.05). Finally, a positive correlation was found between the average muscle temperature measured during the recoveries and the maximal power output obtained during cycling exercises. In conclusion, the use of CWI in between high-intensity training sessions could slightly impair the performance outcomes compared to AR and HWI. However, studies with larger samples are needed to confirm these results, especially in less trained athletes.

Temperature Fluctuations Modulate Molecular Mechanisms in Skeletal Muscle and Influence Growth Potential in Beef Steers

Our investigation elucidated the effects of severe temperature fluctuations on cellular and physiological responses in beef cattle. Eighteen Red Angus beef steers with an average body weight of 351 ± 24.5 kg were divided into three treatment groups: 1) Control (CON), exposed to a temperature-humidity index (THI) of 42 for 6 h without any temperature changes; 2) Transport (TP), subjected to a one-mile trailer trip with a THI of 42 for 6 h; and 3) Temperature swing (TS), exposed to a one-mile trailer trip with a THI shift from 42 to 72-75 for 3 h. Our findings indicate that TS can induce thermal stress in cattle, regardless of whether the overall temperature level is excessively high or not. Behavioral indications of extreme heat stress in the cattle were observed, including extended tongue protrusion, reduced appetite, excessive salivation, and increased respiratory rate. Furthermore, we observed a pronounced overexpression (P < 0.05) of heat shock proteins (HSPs) 20, 27, and 90 in response to the TS treatment in the longissimus muscle (LM). Alterations in signaling pathways associated with skeletal muscle growth were noted, including the upregulation (P < 0.01) of Pax7, Myf5, and myosin heavy chain (MHC) isoforms. In addition, an increase (P < 0.05) in transcription factors associated with adipogenesis was detected (P < 0.05), such as PPARγ, C/EBPα, FAS, and SCD in the TS group, suggesting the potential for adipose tissue accumulation due to temperature fluctuations. Our data illustrated the potential impacts of these temperature fluctuations on the growth of skeletal muscle and adipose tissue in beef cattle.

Genome-Wide Association Study Identifies CDKN1A as a Novel Locus Associated with Muscle Fiber Composition

Muscle fiber composition is associated with physical performance, with endurance athletes having a high proportion of slow-twitch muscle fibers compared to power athletes. Approximately 45% of muscle fiber composition is heritable, however, single nucleotide polymorphisms (SNP) underlying inter-individual differences in muscle fiber types remain largely unknown. Based on three whole genome SNP datasets, we have shown that the rs236448 A allele located near the cyclin-dependent kinase inhibitor 1A (CDKN1A) gene was associated with an increased proportion of slow-twitch muscle fibers in Russian (n = 151; p = 0.039), Finnish (n = 287; p = 0.03), and Japanese (n = 207; p = 0.008) cohorts (meta-analysis: p = 7.9 × 10−5. Furthermore, the frequency of the rs236448 A allele was significantly higher in Russian (p = 0.045) and Japanese (p = 0.038) elite endurance athletes compared to ethnically matched power athletes. On the contrary, the C allele was associated with a greater proportion of fast-twitch muscle fibers and a predisposition to power sports. CDKN1A participates in cell cycle regulation and is suppressed by the miR-208b, which has a prominent role in the activation of the slow myofiber gene program. Bioinformatic analysis revealed that the rs236448 C allele was associated with increased CDKN1A expression in whole blood (p = 8.5 × 10−15) and with greater appendicular lean mass (p = 1.2 × 10−5), whereas the A allele was associated with longer durations of exercise (p = 0.044) reported amongst the UK Biobank cohort. Furthermore, the expression of CDKN1A increased in response to strength (p < 0.0001) or sprint (p = 0.00035) training. Accordingly, we found that CDKN1A expression is significantly (p = 0.002) higher in the m. vastus lateralis of strength athletes compared to endurance athletes and is positively correlated with the percentage of fast-twitch muscle fibers (p = 0.018). In conclusion, our data suggest that the CDKN1A rs236448 SNP may be implicated in the determination of muscle fiber composition and may affect athletic performance.

Acute Effect of Exposure to Extreme Heat (100 ± 3 °C) on Lower Limb Maximal Resistance Strength

The aim of this study was to evaluate the acute effect of a single dry sauna bath lasting twelve minutes on the indirect determination of the one maximum repetition (1RM) leg press among trained and untrained participants. Thirty young men participated in the study, a trained group (TG; n = 15; age: 20.97 ± 0.44 years) and an untrained group (UG; n = 15; age: 21.03 ± 0.11 years). Subjects in the TG had performed resistance training for at least two years before the beginning of the experiment. All participants performed two indirect tests of their one maximum repetition leg press on two different days, with a rest period of three weeks between tests. Additionally, anthropometric, body composition, blood pressure, body temperature, and rated perceived exertion were evaluated. On the second testing day, all of the participants took a dry sauna bath lasting 12 min immediately before performing the leg press test. In the second evaluation (pre-heating in the sauna), the UG experienced increases in absolute RM (178.48 ± 56.66 to 217.60 ± 59.18 kg; p < 0.05; R = 0.798), relative RM (2.65 ± 0.61 to 3.24 ± 0.58 kg·g body mass^-1; p < 0.05; R = 0.798), and muscular RM (5.64 ± 1.20 to 6.77 ± 1.14 kg·kg muscle mass^-1; p < 0.05; R = 0.797). The TG also increased their values on the second day in absolute RM (284.96 ± 62.41 to 314.92 ± 1.04 kg; p < 0.01; R = 0.886), in relative RM (3.61 ± 0.88 to 3.99 ± 1.85 kg*kg body mass^-1; p < 0.01; R = 0.886), and muscular RM (7.83 ± 1.69 to 8.69 ± 1.85 kg·kg muscle mass^-1; p < 0.01; R = 0.854). A passive, extreme-heat sauna bath lasting 12 min taken immediately before a relative maximum repetition test seems to provoke clear positive responses for the development of strength.

High-throughput muscle fiber typing from RNA sequencing data

Background

Skeletal muscle fiber type distribution has implications for human health, muscle function, and performance. This knowledge has been gathered using labor-intensive and costly methodology that limited these studies. Here, we present a method based on muscle tissue RNA sequencing data (totRNAseq) to estimate the distribution of skeletal muscle fiber types from frozen human samples, allowing for a larger number of individuals to be tested.

Methods

By using single-nuclei RNA sequencing (snRNAseq) data as a reference, cluster expression signatures were produced by averaging gene expression of cluster gene markers and then applying these to totRNAseq data and inferring muscle fiber nuclei type via linear matrix decomposition. This estimate was then compared with fiber type distribution measured by ATPase staining or myosin heavy chain protein isoform distribution of 62 muscle samples in two independent cohorts (n = 39 and 22).

Results

The correlation between the sequencing-based method and the other two were r_ATPas = 0.44 [0.13–0.67], [95% CI], and r_myosin = 0.83 [0.61–0.93], with p = 5.70 × 10^–3 and 2.00 × 10^–6, respectively. The deconvolution inference of fiber type composition was accurate even for very low totRNAseq sequencing depths, i.e., down to an average of ~ 10,000 paired-end reads.

Conclusions

This new method (https://github.com/OlaHanssonLab/PredictFiberType) consequently allows for measurement of fiber type distribution of a larger number of samples using totRNAseq in a cost and labor-efficient way. It is now feasible to study the association between fiber type distribution and e.g. health outcomes in large well-powered studies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13395-022-00299-4.

The Heat Shock Connection: Skeletal Muscle Hypertrophy and Atrophy

Skeletal muscle is an integral tissue system that plays a crucial role in the physical function of all vertebrates and is a key target for maintaining or improving health and performance across the lifespan. Based largely on cellular and animal models, there is some evidence that various forms of heat stress with or without resistance exercise may enhance skeletal muscle growth or reduce its loss. It is not clear whether these stimuli are similarly effective in humans or meaningful in comparison to exercise alone across various heating methodologies. Furthermore, the magnitude by which heat stress may influence whole body thermoregulatory responses and the connection to skeletal muscle adaptation remains ambiguous. Finally, the underlying mechanisms, which may include interaction between relevant heat shock proteins and intracellular hypertrophy and atrophy related factors, remain unclear. In this narrative mini-review we examine the relevant literature regarding heat stress alone or in combination with resistance exercise emphasizing skeletal muscle hypertrophy and atrophy across cellular and animal models, as well as human investigations. Additionally, we present working mechanistic theories for heat shock protein mediated signaling effects regarding hypertrophy and atrophy related signaling processes. Importantly, continued research is necessary to determine the practical effects and mechanisms of heat stress with and without resistance exercise on skeletal muscle function via growth and maintenance.

Radiofrequency Heating and High-Intensity Focused Electromagnetic Treatment Delivered Simultaneously: The First Sham-Controlled Randomized Trial

Background:

Radiofrequency-based and high-intensity focused electromagnetic (HIFEM)-based devices have proved effective and safe for abdominal body shaping. Radiofrequency is known to reduce adipose tissue, whereas HIFEM treatment is effective for muscle definition. The authors investigated the efficacy of a novel device delivering synchronized radiofrequency and HIFEM treatment simultaneously for abdominal toning and fat reduction.

Methods:

Seventy-two patients were enrolled and randomly divided into active (n = 48; age, 45.5 ± 13.0 years) and sham groups (n = 24; age, 44.6 ± 12.3 years). Both groups received three treatments on the abdomen once a week. The intensity in the active group was set to maximum tolerable level; in the sham group, the intensities were set to 5 percent. Ultrasound images were taken before treatment and at 1, 3, and 6 months after treatment to examine changes in subcutaneous fat and rectus abdominis muscle thickness. Digital photographs were taken, and satisfaction and therapy comfort were assessed.

Results:

Ultrasound images of the active group at 1 month showed significant (p < 0.05) reduction in adipose tissue thickness by 20.5 percent (4.8 ± 2.6 mm), whereas rectus abdominis muscle thickness increased by 21.5 percent (2.0 ± 0.8 mm). Results at 3 months improved to 28.3 percent (7.6 ± 3.7 mm) and 24.2 percent (2.3 ± 0.9 mm), respectively. Improvements were maintained at 6 months after treatment in the active group, whereas the sham group showed no significant changes. Treatments were found to be comfortable. The active group showed higher satisfaction with outcomes.

Conclusion:

Active treatment utilizing simultaneous application of radiofrequency and HIFEM therapy resulted in a significant increase in rectus abdominis thickness and subcutaneous fat reduction, exceeding previously published results for separate HIFEM and radiofrequency treatments.

CLINICAL QUESTION/LEVEL OF EVIDENCE:

Therapeutic, II.

Genotype Score for Iron Status Is Associated with Muscle Fiber Composition in Women

Human muscle fiber composition is heterogeneous and mainly determined by genetic factors. A previous study reported that experimentally induced iron deficiency in rats increases the proportion of fast-twitch muscle fibers. Iron status has been reported to be affected by genetic factors. As the TMPRSS6 rs855791 T/C and HFE rs1799945 C/G polymorphisms are strongly associated with iron status in humans, we hypothesized that the genotype score (GS) based on these polymorphisms could be associated with the muscle fiber composition in humans. Herein, we examined 214 Japanese individuals, comprising of 107 men and 107 women, for possible associations of the GS for iron status with the proportion of myosin heavy chain (MHC) isoforms (I, IIa, and IIx) as markers of muscle fiber composition. No statistically significant correlations were found between the GS for iron status and the proportion of MHC isoforms in all participants. When the participants were stratified based on sex, women showed positive and negative correlations of the GS with MHC-IIa (age-adjusted p = 0.020) and MHC-IIx (age-adjusted p = 0.011), respectively. In contrast, no correlation was found in men. In women, a 1-point increase in the GS was associated with 2.42% higher MHC-IIa level and 2.72% lower MHC-IIx level. Our results suggest that the GS based on the TMPRSS6 rs855791 T/C and HFE rs1799945 C/G polymorphisms for iron status is associated with muscle fiber composition in women.

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.

Activation of Skeletal Muscle Satellite Cells by a Device Simultaneously Applying High-Intensity Focused Electromagnetic Technology and Novel RF Technology: Fluorescent Microscopy Facilitated Detection of NCAM/CD56

Background

Myosatellite cells are myogenic stem cells that can transform to provide nuclei for existing muscles or generate new muscle fibers as documented after extended exercise programs.

Objectives

The authors investigated whether the simultaneous application of High-Intensity Focused Electromagnetic (HIFEM) and Synchrode radiofrequency (RF) affects the levels of satellite cells similarly as the prolonged exercise does to achieve muscle growth.

Methods

Three 30-minute simultaneous HIFEM and Synchrode RF treatments (once a week) were administered over the abdominal area of 5 Large White swine aged approximately 6 months. All animals were anesthetized during the treatments and biopsy acquisition. Biopsies of muscle tissue were collected at baseline, 4 days, 2 weeks, and 1 month post-treatment. After binding the specific antibodies, the NCAM/CD56 levels, a marker of activated satellite cells, were quantified employing the immunofluorescence microscopy technique with a UV lamp.

Results

Examined slices showed a continuous increase in satellite cell levels throughout the study. Four days after the treatment, we observed a 26.1% increase in satellite cells, which increased to 30.2% at 2-week follow-up. Additional histological analysis revealed an increase in the cross-sectional area of muscle fibers and the signs of newly formed fibers of small diameters at 2 weeks after the treatment. No damage to muscle tissue and no adverse effects related to the treatment were observed.

Conclusions

The findings indicate that the simultaneous application of HIFEM and novel Synchrode RF treatment can initiate differentiation of satellite cells to support the growth of existing muscles and, presumably, even the formation of new myofibers.

Effect of Handgrip Training in Extreme Heat on the Development of Handgrip Maximal Isometric Strength among Young Males

The aim of this study was to evaluate the acute and adaptive effects of passive extreme heat (100 ± 3 °C) exposition in combination with a strength training protocol on maximal isometric handgrip strength. Fifty-four untrained male university students participated in this investigation. Twenty-nine formed the control group (NG) and 25 the heat-exposed group (HG). All the participants performed a 3-week isotonic handgrip strength training program twice a week with a training volume of 10 series of 10 repetitions with 45-s rest between series, per session. All the subjects only trained their right hand, leaving their left hand untrained. HG performed the same training protocol in hot (100 ± 3 °C) conditions in a dry sauna. Maximal isometric handgrip strength was evaluated each training day before and after the session. NG participants did not experience any modifications in either hand by the end of the study while HG increased maximal strength values in both hands (p < 0.05), decreased the difference between hands (p < 0.05), and recorded higher values than the controls in the trained (p < 0.05) and untrained (p < 0.01) hands after the intervention period. These changes were not accompanied by any modification in body composition in either group. The performance of a unilateral isotonic handgrip strength program in hot conditions during the three weeks induced an increase in maximal isometric handgrip strength in both hands without modifications to bodyweight or absolute body composition.

Effects of Twelve Sessions of High-Temperature Sauna Baths on Body Composition in Healthy Young Men

The health benefits of sauna baths are attracting ever-increasing interest. Therefore, the purpose of this study was to evaluate the effects of 12 high-temperature (100 °C) sauna baths on body composition of 23 healthy young men, divided into a control group (CG) and a sauna group (SG). Both groups were initially evaluated by dual-energy X-ray absorptiometry (DXA), after which the SG experienced 12 sessions of sauna baths at high temperatures (100 °C). Initial measurements were carried out after the sauna sessions and after two weeks of decay in both groups. The muscle mass of the right leg (pre vs. decay: 9.50 (5.59) vs. 10.52 (5.15); p < 0.05; Δ 1.07%), bone mineral density (pre vs. post: 1.221 (0.35) vs. 1.315 (0.45); p < 0.05; Δ 7.7%) and bone mineral content (pre vs. post: 0.470 (0.21) vs. 0.499 (0.22); p < 0.05; Δ 6.17%) of the left leg increased in the SG after the sauna baths. It seems that exposure to heat at high temperatures could produce improvements in bone and muscle mass.

Influence of post-exercise hot-water therapy on adaptations to training over 4 weeks in elite short-track speed skaters

This study aimed to investigate the effects of regular hot water bathing (HWB), undertaken 10 min after the last training session of the day, on chronic adaptations to training in elite athletes. Six short-track (ST) speed skaters completed four weeks of post-training HWB and four weeks of post-training passive recovery (PR) according to a randomized cross-over study. During HWB, participants sat in a jacuzzi (40 °C; 20 min). According to linear mixed models, maximal isometric strength of knee extensor muscles was significantly increased for training with HWB (p < 0.0001; d = 0.41) and a tendency (p = 0.0529) was observed concerning V˙O2max. No significant effect of training with PR or HWB was observed for several variables (p > 0.05), including aerobic peak power output, the decline rate of jump height during 1 min-continuous maximal countermovement jumps (i.e. anaerobic capacity index), and the force-velocity relationship. Regarding specific tasks on ice, a small effect of training was found on both half-lap time and total time during a 1.5-lap all-out exercise (p = 0.0487; d = 0.23 and p = 0.0332; d = 0.21, respectively) but no additional effect of HWB was observed. In summary, the regular HWB protocol used in this study can induce additional effects on maximal isometric strength without compromising aerobic and anaerobic adaptations or field performance in these athletes.

Ursolic acid has no additional effect on muscle strength and mass in active men undergoing a high-protein diet and resistance training: A double-blind and placebo-controlled trial

BACKGROUND

Ursolic acid (UA) is thought to have an anabolic effect on muscle mass in humans. This study sought to compare the effects of UA and a placebo on muscle strength and mass in young men undergoing resistance training (RT) and consuming a high-protein diet.

METHODS

A clinical, double-blind, placebo-controlled trial was conducted for 8 weeks. The Control + RT group (CON n = 12) received 400 mg/d of placebo, and the UA + RT group (UA n = 10) received 400 mg/d of UA. Both groups ingested ~1.6 g/kg of protein and performed the same RT program. Pre- and post-intervention, both groups were evaluated for anthropometric measures, body composition, food intake and muscle strength.

RESULTS

Food intake remained unchanged throughout the study. Both groups showed significant increases in body weight (CON Δ: 2.12 ± 0.47 kg, p = 0.001 vs. UA Δ: 2.24 ± 0.67 kg, p = 0.009), body mass index (BMI) (CON Δ: 0.69 ± 0.15 kg/m2, p = 0.001 vs. UA Δ: 0.75 ± 0.23, p = 0.011) and thigh circumference (CON Δ: 1.50 ± 0.36, p = 0.002 vs. UA Δ: 2.46 ± 0.50 cm, p = 0.003 vs. UA 1.84 ± 0.82 cm, p = 0.001), with differences between them. There was no difference in the arm, waist and hip circumferences. Both groups showed increases in muscle mass (CON Δ: 1.12 ± 0.26, p = 0.001 vs. UA Δ: 1.08 ± 0.28 kg, p = 0.004), but there was no significant difference between them. Additionally, there were significant increases in the one repetition maximum test in the bench press and in the 10-repetition maximum test in the knee extension (CON Δ: 5.00 ± 2.09, p = 0.036 vs. UA Δ: 7.8 ± 1.87, p = 0.340 and CON Δ: 3.58 ± 1.15, p = 0.010 vs. UA Δ: 1.20 ± 0.72, p = 0.133), respectively, with no difference between them.

CONCLUSIONS

Ursolic acid had no synergic effect on muscle strength and mass in response to RT in physically active men consuming a high-protein diet.

BRAZILIAN CLINICAL TRIALS REGISTRY (REBEC)

RBR-76tbqs.

Six weeks of localized heat therapy does not affect muscle mass, strength and contractile properties in healthy active humans

PURPOSE

Animal and human studies have shown that repeated heating may induce skeletal muscle adaptations, increasing muscle strength. The aim of this study is to investigate the effect of 6 weeks of localized heating on skeletal muscle strength, volume and contractile properties in healthy humans.

METHODS

Fifteen active participants (8 males/7 females, 35 ± 6 years, 70 ± 14 kg, 173 ± 7 cm, average training of 87 min per week) were subjected to 6 weeks of single-leg heat therapy. Heat pads were applied for 8 h/day, 5 days/week, on one randomly selected calf of each participant, while the contralateral leg acted as control. The heat pads increased muscle temperature by 4.6 ± 1.2 °C (p < 0.001). Every 2 weeks, participants were tested for morphological (MRI), architectural (ultrasound), contractile (electrically evoked twitch), and force (isometric and isokinetic) adaptations.

RESULTS

Repeated localized heating did not affect the cross-sectional area (p = 0.873) or pennation angle (p = 0.345) of the gastrocnemius muscles; did not change the evoked peak twitch amplitude (p = 0.574) or rate of torque development (p = 0.770) of the plantar flexors; and did not change maximal voluntary isometric (p = 0.214) or isokinetic (p = 0.973) plantar flexor torque.

CONCLUSION

Whereas previous studies have observed improved skeletal muscle function following whole-body and localized heating in active and immobilized humans, respectively, the current data suggested that localized heating may not be a potent stimulus for muscle adaptations in active humans.

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.

Resistance Exercise in a Hot Environment Alters Serum Markers in Untrained Males

Purpose: We examined the effects of moderate resistance exercise (RE) on serum cortisol, testosterone, extracellular heat shock protein (HSP70), and interleukin (IL)-6 and IL-15 concentrations in untrained males in a hot environment.

Methods: Ten untrained young males (26 ± 3 years; 75.8 ± 6 kg; 177.4 ± 5.3 cm) performed two series of full body RE [3 sets of 8 to 10 repetitions, 30–60 s recovery between series with 70% of one maximal repetition (1-RM), with a rest period of 1 to 3 min between exercises] carried out in a random order in both heated (∼35°C) and thermoneutral (22°C) conditions. Serum concentrations of testosterone, cortisol, HSP70, and IL-6 and IL-15 were measured before, at the end, and 1 h after RE sessions. Participants in both groups consumed 4 ml of water/kg body mass every 15 min.

Results: There were time-related changes in testosterone, HSP70, and IL-6 (P < 0.001), and cortisol and IL-15 (P < 0.05). Levels of cortisol, HSP70, and IL-6 increased immediately for RE at 35°C, and testosterone and IL-15 levels were decreased. Changes in serum testosterone, HSP70, cortisol, and IL-15 and IL-6 levels were reversed after 1 h. A significant time × condition interaction was observed for IL-15 and HSP70 (P < 0.001), cortisol and IL-6 (P < 0.05), but not for testosterone (P > 0.05).

Conclusion: RE in a heated environment may not be appropriate for achieving muscle adaptations due to acute changes of hormonal and inflammatory markers.

Combining cooling or heating applications with exercise training to enhance performance and muscle adaptations

Athletes use cold water immersion, cryotherapy chambers, or icing in the belief that these strategies improve postexercise recovery and promote greater adaptations to training. A number of studies have systematically investigated how regular cold water immersion influences long-term performance and muscle adaptations. The effects of regular cold water immersion after endurance or high-intensity interval training on aerobic capacity, lactate threshold, power output, and time trial performance are equivocal. Evidence for changes in angiogenesis and mitochondrial biogenesis in muscle in response to regular cold water immersion is also mixed. More consistent evidence is available that regular cold water immersion after strength training attenuates gains in muscle mass and strength. These effects are attributable to reduced activation of satellite cells, ribosomal biogenesis, anabolic signaling, and muscle protein synthesis. Athletes use passive heating to warm up before competition or improve postexercise recovery. Emerging evidence indicates that regular exposure to ambient heat, wearing garments perfused with hot water, or microwave diathermy can mimic the effects of endurance training by stimulating angiogenesis and mitochondrial biogenesis in muscle. Some passive heating applications may also mitigate muscle atrophy through their effects on mitochondrial biogenesis and muscle fiber hypertrophy. More research is needed to consolidate these findings, however. Future research in this field should focus on 1) the optimal modality, temperature, duration, and frequency of cooling and heating to enhance long-term performance and muscle adaptations and 2) whether molecular and morphological changes in muscle in response to cooling and heating applications translate to improvements in exercise performance.

Identification of Genomic Characteristics and Selective Signals in a Du'an Goat Flock

The Du'an goat is one of the most important farm animals in the Guangxi Autonomous Region of China, but the genetic basis underlying its adaptive traits has still not been investigated. Firstly, in this study, the genomes of 15 Du'an goats from a breeding farm were sequenced (mean depth: 9.50X) to analyze the patterns of genetic variation. A comparable diversity (17.3 million single nucleotide polymorphisms and 2.1 million indels) was observed to be associated with a lower runs of homozygosity-based inbreeding coefficient and smaller effective population size in comparison with other breeds. From selective sweep and gene set enrichment analyses, we revealed selective signals related to adaptive traits, including immune resistance (serpin cluster, INFGR1, TLR2, and immune-related pathways), body size (HMGA2, LCOR, ESR1, and cancer-related pathways) and heat tolerance (MTOR, ABCG2, PDE10A, and purine metabolism pathway). Our findings uncovered the unique diversity at the genomic level and will provide the opportunities for improvement of productivity in the Du'an goat.

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.

Hot-water immersion does not increase postprandial muscle protein synthesis rates during recovery from resistance-type exercise in healthy, young males

The purpose of this study was to assess the impact of postexercise hot-water immersion on postprandial myofibrillar protein synthesis rates during recovery from a single bout of resistance-type exercise in healthy, young men. Twelve healthy, adult men (age: 23 ± 1 y) performed a single bout of resistance-type exercise followed by 20 min of water immersion of both legs. One leg was immersed in hot water [46°C: hot-water immersion (HWI)], while the other leg was immersed in thermoneutral water (30°C: CON). After water immersion, a beverage was ingested containing 20 g intrinsically L-[1-¹³C]-phenylalanine and L-[1-¹³C]-leucine labeled milk protein with 45 g of carbohydrates. In addition, primed continuous L-[ring-²H₅]-phenylalanine and L-[1-¹³C]-leucine infusions were applied, with frequent collection of blood and muscle samples to assess myofibrillar protein synthesis rates in vivo over a 5-h recovery period. Muscle temperature immediately after water immersion was higher in the HWI compared with the CON leg (37.5 ± 0.1 vs. 35.2 ± 0.2°C; P < 0.001). Incorporation of dietary protein-derived L-[1-¹³C]-phenylalanine into myofibrillar protein did not differ between the HWI and CON leg during the 5-h recovery period (0.025 ± 0.003 vs. 0.024 ± 0.002 MPE; P = 0.953). Postexercise myofibrillar protein synthesis rates did not differ between the HWI and CON leg based upon L-[1-¹³C]-leucine (0.050 ± 0.005 vs. 0.049 ± 0.002%/h; P = 0.815) and L-[ring-²H₅]-phenylalanine (0.048 ± 0.002 vs. 0.047 ± 0.003%/h; P = 0.877), respectively. Hot-water immersion during recovery from resistance-type exercise does not increase the postprandial rise in myofibrillar protein synthesis rates. In addition, postexercise hot-water immersion does not increase the capacity of the muscle to incorporate dietary protein-derived amino acids in muscle tissue protein during subsequent recovery.NEW & NOTEWORTHY This is the first study to assess the effect of postexercise hot-water immersion on postprandial myofibrillar protein synthesis rates and the incorporation of dietary protein-derived amino acids into muscle protein. We observed that hot-water immersion during recovery from a single bout of resistance-type exercise does not further increase myofibrillar protein synthesis rates or augment the postprandial incorporation of dietary protein-derived amino acids in muscle throughout 5 h of postexercise recovery.

The complex genetics and biology of human temperament: a review of traditional concepts in relation to new molecular findings

Recent genome-wide association studies (GWAS) have shown that temperament is strongly influenced by more than 700 genes that modulate associative conditioning by molecular processes for synaptic plasticity and long-term learning and memory. The results were replicated in three independent samples despite variable cultures and environments. The identified genes were enriched in pathways activated by behavioral conditioning in animals, including the two major molecular pathways for response to extracellular stimuli, the Ras-MEK-ERK and the PI3K-AKT-mTOR cascades. These pathways are activated by a wide variety of physiological and psychosocial stimuli that vary in positive and negative valence and in consequences for health and survival. Changes in these pathways are orchestrated to maintain cellular homeostasis despite changing conditions by modulating temperament and its circadian and seasonal rhythms. In this review we first consider traditional concepts of temperament in relation to the new genetic findings by examining the partial overlap of alternative measures of temperament. Then we propose a definition of temperament as the disposition of a person to learn how to behave, react emotionally, and form attachments automatically by associative conditioning. This definition provides necessary and sufficient criteria to distinguish temperament from other aspects of personality that become integrated with it across the life span. We describe the effects of specific stimuli on the molecular processes underlying temperament from functional, developmental, and evolutionary perspectives. Our new knowledge can improve communication among investigators, increase the power and efficacy of clinical trials, and improve the effectiveness of treatment of personality and its disorders.

Molecular regulation of human skeletal muscle protein synthesis in response to exercise and nutrients: a compass for overcoming age-related anabolic resistance

Skeletal muscle mass, a strong predictor of longevity and health in humans, is determined by the balance of two cellular processes, muscle protein synthesis (MPS) and muscle protein breakdown. MPS seems to be particularly sensitive to changes in mechanical load and/or nutritional status; therefore, much research has focused on understanding the molecular mechanisms that underpin this cellular process. Furthermore, older individuals display an attenuated MPS response to anabolic stimuli, termed anabolic resistance, which has a negative impact on muscle mass and function, as well as quality of life. Therefore, an understanding of which, if any, molecular mechanisms contribute to anabolic resistance of MPS is of vital importance in formulation of therapeutic interventions for such populations. This review summarizes the current knowledge of the mechanisms that underpin MPS, which are broadly divided into mechanistic target of rapamycin complex 1 (mTORC1)-dependent, mTORC1-independent, and ribosomal biogenesis-related, and describes the evidence that shows how they are regulated by anabolic stimuli (exercise and/or nutrition) in healthy human skeletal muscle. This review also summarizes evidence regarding which of these mechanisms may be implicated in age-related skeletal muscle anabolic resistance and provides recommendations for future avenues of research that can expand our knowledge of this area.

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.

Heat stress decreased hair follicle population in rex rabbits

The aim of this study was conducted to investigate the effect of heat stress on the hair follicle population and related signalling pathways in rex rabbits. Forty-eight rabbits were randomly divided into two groups: one group in a high ambient environment (32 ± 2°C, heat stress) and the other group with normal temperature (20 ± 2°C, control). The results show that heat stress decreased the body weight gain and feed conversion rate, rabbit hair length and hair follicle density (p < 0.05). Besides, heat stress suppressed the gene expression of noggin, insulin-like growth factor 1 (IGF-1) and IGF-1 receptor and protein expression of phosphorylated mechanistic target of rapamycin (mTOR) in rabbit skin (p < 0.05), while stimulated significantly the gene expression of bone morphogenetic protein 2 (BMP2) and BMP4 (p < 0.05). Heat exposure did not alter significantly the gene expression of alkaline phosphatase, versican and hepatocyte growth factor compared with the control (p > 0.05). In conclusion, noggin-BMP, IGF-1 and mTOR signalling pathways may be associated with the process of heat stress-repressing hair follicle development.

Turning Up the Heat: An Evaluation of the Evidence for Heating to Promote Exercise Recovery, Muscle Rehabilitation and Adaptation

Historically, heat has been used in various clinical and sports rehabilitation settings to treat soft tissue injuries. More recently, interest has emerged in using heat to pre-condition muscle against injury. The aim of this narrative review was to collate information on different types of heat therapy, explain the physiological rationale for heat therapy, and to summarise and evaluate the effects of heat therapy before, during and after muscle injury, immobilisation and strength training. Studies on skeletal muscle cells demonstrate that heat attenuates cellular damage and protein degradation (following in vitro challenges/insults to the cells). Heat also increases the expression of heat shock proteins (HSPs) and upregulates the expression of genes involved in muscle growth and differentiation. In rats, applying heat before and after muscle injury or immobilisation typically reduces cellular damage and muscle atrophy, and promotes more rapid muscle growth/regeneration. In humans, some research has demonstrated benefits of microwave diathermy (and, to a lesser extent, hot water immersion) before exercise for restricting muscle soreness and restoring muscle function after exercise. By contrast, the benefits of applying heat to muscle after exercise are more variable. Animal studies reveal that applying heat during limb immobilisation attenuates muscle atrophy and oxidative stress. Heating muscle may also enhance the benefits of strength training for improving muscle mass in humans. Further research is needed to identify the most effective forms of heat therapy and to investigate the benefits of heat therapy for restricting muscle wasting in the elderly and those individuals recovering from serious injury or illness.

From Lab to Real World: Heat Acclimation Considerations for Elite Athletes

As major sporting events are often held in hot environments, increased interest in ways of optimally heat acclimating athletes to maximise performance has emerged. Heat acclimation involves repeated exercise sessions in hot conditions that induce physiological and thermoregulatory adaptations that attenuate heat-induced performance impairments. Current evidence-based guidelines for heat acclimation are clear, but the application of these recommendations is not always aligned with the time commitments and training priorities of elite athletes. Alternative forms of heat acclimation investigated include hot water immersion and sauna bathing, yet uncertainty remains around the efficacy of these methods for reducing heat-induced performance impairments, as well as how this form of heat stress may add to an athlete's overall training load. An understanding of how to optimally prescribe and periodise heat acclimation based on the performance determinants of a given event is limited, as is knowledge of how heat acclimation may affect the quality of concurrent training sessions. Finally, differences in individual athlete responses to heat acclimation need to be considered. This article addresses alternative methods of heat acclimation and heat exposure, explores gaps in literature around understanding the real world application of heat acclimation for athletes, and highlights specific athlete considerations for practitioners.

The effects of heat stress on morphological properties and intracellular signaling of denervated and intact soleus muscles in rats

The effects of heat stress on the morphological properties and intracellular signaling of innervated and denervated soleus muscles were investigated. Heat stress was applied to rats by immersing their hindlimbs in a warm water bath (42°C, 30 min/day, every other day following unilateral denervation) under anesthesia. During 14 days of experimental period, heat stress for a total of seven times promoted growth‐related hypertrophy in sham‐operated muscles and attenuated atrophy in denervated muscles. In denervated muscles, the transcription of ubiquitin ligase, atrogin‐1/muscle atrophy F‐box (Atrogin‐1), and muscle RING‐finger protein‐1 (MuRF‐1), genes was upregulated and ubiquitination of proteins was also increased. Intermittent heat stress inhibited the upregulation of Atrogin‐1, but not MuRF‐1 transcription. And the denervation‐caused reduction in phosphorylated protein kinase B (Akt), 70‐kDa heat‐shock protein (HSP70), and peroxisome proliferator‐activated receptor γ coactivator‐1α (PGC‐1α), which are negative regulators of Atrogin‐1 and MuRF‐1 transcription, was mitigated. In sham‐operated muscles, repeated application of heat stress did not affect Atrogin‐1 and MuRF‐1 transcription, but increased the level of phosphorylated Akt and HSP70, but not PGC‐1α. Furthermore, the phosphorylation of Akt and ribosomal protein S6, which is known to stimulate protein synthesis, was increased immediately after a single heat stress particularly in the sham‐operated muscles. The effect of a heat stress was suppressed in denervated muscles. These results indicated that the beneficial effects of heat stress on the morphological properties of muscles were brought regardless of innervation. However, the responses of intracellular signaling to heat stress were distinct between the innervated and denervated muscles.

Effects of training intensity in electromyostimulation on human skeletal muscle

PURPOSE

High-intensity neuromuscular electrical stimulation (NMES) training can induce muscle hypertrophy at the whole muscle and muscle fiber levels. However, whether low-intensity NMES training has a similar result is unknown. This study aimed to investigate whether low-intensity NMES training could elicit muscle hypertrophy at the whole muscle and muscle fiber levels in the human skeletal muscle.

METHODS

Eight untrained young males were subjected to 18 min of unilateral NMES training for 8 weeks. One leg received NMES at maximal tolerable intensity (HIGH); the other leg received NMES at an intensity half of that in the HIGH condition (LOW). Quadriceps muscle thickness (MT), muscle fiber cross-sectional area (CSA), and knee extension strength were measured before and after the training period.

RESULTS

The average training intensity throughout the intervention period in the HIGH and LOW conditions were 62.5 ± 4.6% maximal voluntary contraction (MVC) and 32.6 ± 2.6% MVC, respectively. MT, CSA, and muscle strength increased in both exercise conditions (p < 0.05); however, training effects in the LOW condition were lower than those in the HIGH condition (p < 0.05). The average training intensity showed a positive correlation with percent changes in muscle strength (r = 0.797, p = 0.001), MT (r = 0.876, p = 0.001), type I fiber CSA (r = 0.730, p = 0.01), and type II fiber CSA (r = 0.899, p = 0.001).

CONCLUSIONS

Low-intensity NMES could increase MT, muscle fiber CSA, and muscle strength in healthy human skeletal muscles. However, the magnitude of increase is lower in low-intensity than in high-intensity NMES training.

No clear benefit of muscle heating on hypertrophy and strength with resistance training

Heat is a major stressor during exercise, though its value in driving adaptation is not well understood. Muscle heating can upregulate pathways facilitating protein synthesis and could thereby enhance effects of exercise training, however, few studies have investigated this possibility. We examined whether heating active muscle during resistance training differentially affected physical and functional adaptations. Within a randomised contralateral-limb control study, ten healthy, resistance-untrained individuals (21 ± 3 y; 5 female) completed 30 sessions of progressive resistance training (12 weeks), performing 4 × 8 unilateral knee extensions at 70% of 1RM. One randomly-allocated thigh was heated during, and for 20 min after, each session using an electric pad eliciting muscle temperatures of >38 °C (HOT); the contralateral limb remained unheated (CON). Training intensity was progressed using 4-weekly strength assessments. Quadricep lean mass (measured using DXA) increased by 15 ± 7% in HOT (p = 0.00) and 15 ± 6% in CON (p = 0.00); the difference being trivial (p = 0.94). Peak isokinetic torque at 90°.s^-1 increased by 30 ± 25% (HOT; p = 0.00) and 34 ± 33% (CON; p = 0.01), with no difference (p = 0.84) between limbs. Rate of torque development increased ∼40%, with no difference between limbs (p = 0.73). The increase in 3-RM strength was also similar in HOT (75 ± 16%) and CON (71 ± 14%; p = 0.80 for difference). No differences in mass or strength changes were evident between sexes. In conclusion, supplemental heating of active muscle during and after each bout of resistance training showed no clear positive (or negative) effect on training-induced hypertrophy or function.

Depression of leukocyte protein synthesis, immune function and growth performance induced by high environmental temperature in broiler chickens

In tropical and semitropical regions, raising broiler chickens out of their thermal comfort zone can cause an added economic loss in the poultry industry. The cause for the deleterious effects on immunity and growth performance of broilers under high environmental temperatures is still poorly understood. Therefore, the aim of the current investigation was to evaluate the effect of heat stress on leukocytes protein synthesis and immune function as a possible direct cause of low performance in broiler chickens under such condition. In this study, 300 one-day-old male broiler chicks (Cobb500™) were randomly assigned into 2 groups with 5 replicates of 30 chicks each. From 21 to 42 days of age, one group was exposed to non-stressed condition at 24 °C and 50% relative humidity (control group), while the other group was exposed to heat stress at 35 °C and 50% relative humidity (HS group). At 42 days of age, blood samples were collected from each group to evaluate stress indicators, immune function, and leukocytes protein synthesis. Production performance was also recorded. Noteworthy, protein synthesis in leukocytes was significantly (P < 0.05) inhibited in HS group by 38% compared to control group. In contrast, the phosphorylation level on threonine 56 site (Thr⁵⁶) of eukaryotic elongation factor (eEF2), which indicates the suppression of protein translation process through altering the protein elongation phase, was significantly threefold higher in HS group than in control (P < 0.05). In addition, an increase in stress indicators was markedly (P < 0.05) presented in the HS birds by twofold increase in heterophil/lymphocyte (H/L) ratio and threefold increase in plasma corticosterone level compared to control. Furthermore, the immune function was significantly (P < 0.05) suppressed in HS birds than control (0.99 vs. 1.88 mg/mL plasma IgG, 89.2 vs. 148.0 μg/mL plasma IgM, 4.80 vs. 7.20 antibody titer against SRBC, and 1.38 vs. 3.39 stimulation index of lymphocyte proliferation in HS vs. control group, respectively). Moreover, results on the broiler performance indicate that HS birds had a significant (P < 0.05) lower body weight gain by 58%, lower feed consumption by 39%, higher conversion ratio by 27%, and higher mortality by more than three times, compared to control birds. In conclusion, our results demonstrate that the inhibition of leukocyte protein synthesis through increasing the level of eEF2 Thr⁵⁶ phosphorylation may play a key role in the observed decrease in immune function and growth performance with the high mortality rate encountered in broiler chickens under heat stress environment.

Acute effects of heated resistance exercise in female and male power athletes

PURPOSE

To determine the effects of heated resistance exercise on thermal strain, neuromuscular function and hormonal responses in power athletes.

METHODS

Sixteen (n = 8 female; 8 male) highly trained power athletes completed a combined strength and power resistance exercise session in hot (HOT ~30 °C) and temperate (CON ~20 °C) conditions. Human growth hormone (hGH), cortisol and testosterone concentrations in plasma, peak power (counter-movement jump, CMJ) and peak force (isometric mid-thigh pull) were measured before and after each training session; thermoregulatory responses were monitored during training.

RESULTS

Skin temperature, thermal sensation and thermal discomfort were higher in HOT compared with CON. Sweat rate was higher in HOT for males only. Compared with CON, HOT had trivial effects on core temperature and heart rate. During HOT, there was a possible increase in upper-body power (medicine ball throw) in females [3.4% (90% CL -1.5, 8.6)] and males [(3.3% (-0.1, 6.9)], while lower-body power (vertical jump) was enhanced in males only [3.2% (-0.4, 6.9)]. Following HOT, CMJ peak power [4.4% (2.5; 6.3)] and strength [8.2% (3.1, 13.6)] were enhanced in female athletes, compared with CON, while effects in males were unclear. Plasma hGH concentration increased in females [83% (18; 183)] and males [107% (-21; 444)] in HOT compared with CON, whereas differential changes occurred for cortisol and testosterone.

CONCLUSION

Heated resistance exercise enhanced power and increased plasma hGH concentration in female and males power athletes. Further research is required to assess the ergogenic potential of resistance exercise in the heat.

Considerations on mTOR regulation at serine 2448: implications for muscle metabolism studies

The mammalian target of rapamycin (mTOR) complex exerts a pivotal role in protein anabolism and cell growth. Despite its importance, few studies adequately address the complexity of phosphorylation of the mTOR protein itself to enable conclusions to be drawn on the extent of kinase activation following this event. In particular, a large number of studies in the skeletal muscle biology field have measured Serine 2448 (Ser2448) phosphorylation as a proxy of mTOR kinase activity. However, the evidence to be described is that Ser2448 is not a measure of mTOR kinase activity nor is a target of AKT activity and instead has inhibitory effects on the kinase that is targeted by the downstream effector p70S6K in a negative feedback loop mechanism, which is evident when revisiting muscle research studies. It is proposed that this residue modification acts as a fine-tuning mechanism that has been gained during vertebrate evolution. In conclusion, it is recommended that Ser2448 is an inadequate measure and that preferential analysis of mTORC1 activation should focus on the downstream and effector proteins, including p70S6K and 4E-BP1, along mTOR protein partners that bind to mTOR protein to form the active complexes 1 and 2.

Passive heat acclimation improves skeletal muscle contractility in humans

The aim of this study was to investigate the effect of repeated passive heat exposure (i.e., acclimation) on muscle contractility in humans. Fourteen nonheat-acclimated males completed two trials including electrically evoked twitches and voluntary contractions in thermoneutral conditions [Cool: 24°C, 40% relative humidity (RH)] and hot ambient conditions in the hyperthermic state (Hot: 44–50°C, 50% RH) on consecutive days in a counterbalanced order. Rectal temperature was ~36.5°C in Cool and was maintained at ~39°C throughout Hot. Both trials were repeated after 11 days of passive heat acclimation (1 h per day, 48–50°C, 50% RH). Heat acclimation decreased core temperature in Cool (−0.2°C, P < 0.05), increased the time required to reach 39°C in Hot (+9 min, P < 0.05) and increased sweat rate in Hot (+0.7 liter/h, P < 0.05). Moreover, passive heat acclimation improved skeletal muscle contractility as evidenced by an increase in evoked peak twitch amplitude both in Cool (20.5 ± 3.6 vs. 22.0 ± 4.0 N·m) and Hot (20.5 ± 4.7 vs. 22.0 ± 4.0 N·m) (+9%, P < 0.05). Maximal voluntary torque production was also increased both in Cool (145 ± 42 vs. 161 ± 36 N·m) and Hot (125 ± 36 vs. 145 ± 30 N·m) (+17%, P < 0.05), despite voluntary activation remaining unchanged. Furthermore, the slope of the relative torque/electromyographic linear relationship was improved postacclimation ( P < 0.05). These adjustments demonstrate that passive heat acclimation improves skeletal muscle contractile function during electrically evoked and voluntary muscle contractions of different intensities both in Cool and Hot. These results suggest that repeated heat exposure may have important implications to passively maintain or even improve muscle function in a variety of performance and clinical settings.

Heat stress and dehydration in adapting for performance: Good, bad, both, or neither?

Physiological systems respond acutely to stress to minimize homeostatic disturbance, and typically adapt to chronic stress to enhance tolerance to that or a related stressor. It is legitimate to ask whether dehydration is a valuable stressor in stimulating adaptation per se. While hypoxia has had long-standing interest by athletes and researchers as an ergogenic aid, heat and nutritional stressors have had little interest until the past decade. Heat and dehydration are highly interlinked in their causation and the physiological strain they induce, so their individual roles in adaptation are difficult to delineate. The effectiveness of heat acclimation as an ergogenic aid remains unclear for team sport and endurance athletes despite several recent studies on this topic. Very few studies have examined the potential ergogenic (or ergolytic) adaptations to ecologically-valid dehydration as a stressor in its own right, despite longstanding evidence of relevant fluid-regulatory adaptations from short-term hypohydration. Transient and self-limiting dehydration (e.g., as constrained by thirst), as with most forms of stress, might have a time and a place in physiological or behavioral adaptations independently or by exacerbating other stressors (esp. heat); it cannot be dismissed without the appropriate evidence. The present review did not identify such evidence. Future research should identify how the magnitude and timing of dehydration might augment or interfere with the adaptive processes in behaviorally constrained versus unconstrained humans.

Modulating exercise-induced hormesis: Does less equal more?

Hormesis encompasses the notion that low levels of stress stimulate or upregulate existing cellular and molecular pathways that improve the capacity of cells and organisms to withstand greater stress. This notion underlies much of what we know about how exercise conditions the body and induces long-term adaptations. During exercise, the body is exposed to various forms of stress, including thermal, metabolic, hypoxic, oxidative, and mechanical stress. These stressors activate biochemical messengers, which in turn activate various signaling pathways that regulate gene expression and adaptive responses. Historically, antioxidant supplements, nonsteroidal anti-inflammatory drugs, and cryotherapy have been favored to attenuate or counteract exercise-induced oxidative stress and inflammation. However, reactive oxygen species and inflammatory mediators are key signaling molecules in muscle, and such strategies may mitigate adaptations to exercise. Conversely, withholding dietary carbohydrate and restricting muscle blood flow during exercise may augment adaptations to exercise. In this review article, we combine, integrate, and apply knowledge about the fundamental mechanisms of exercise adaptation. We also critically evaluate the rationale for using interventions that target these mechanisms under the overarching concept of hormesis. There is currently insufficient evidence to establish whether these treatments exert dose-dependent effects on muscle adaptation. However, there appears to be some dissociation between the biochemical/molecular effects and functional/performance outcomes of some of these treatments. Although several of these treatments influence common kinases, transcription factors, and proteins, it remains to be determined if these interventions complement or negate each other, and whether such effects are strong enough to influence adaptations to exercise.