One size does not fit all: Methodological considerations and recommended solutions for intramuscular temperature assessment.

Intramuscular temperature kinetics can provide insightful information for exercise and environmental physiology research. However, currently, there are no consistent method descriptions or guidelines for muscle temperature assessment in the literature. Studies have reported a great variation in muscle temperature assessment, from 1.5 cm under the skin to 4 cm under the muscle fascia. Moreover, a large variation in body composition components among participants exacerbates this issue, changing the depth and the muscle to be tested. For instance, in young adults (25 ± 5 yrs), the thigh subcutaneous fat thickness can vary from 0.11 to 1.69 cm, and vastus lateralis thickness from 1.62 to 3.38 cm; in older adults (68.5 ± 3 yrs), subcutaneous fat thickness plus gastrocnemius medialis thickness can vary from 1.03 to 3.22 cm. This variation results in inconsistent resting muscle temperature profiles and muscle temperature kinetics during and after an exercise or environmental thermal stress interventions (hot or cold). Hence, one fixed size does not fit all. Standardization and consistency in muscle temperature assessment procedures across studies are required to allow a better understanding and translation of the influence of a given stressor (exercise or thermal) on muscle temperature kinetics. This methodological manuscript i) summarizes the differences in muscle temperature assessment procedures and techniques used across different studies, ii) discusses current concerns related to variations in intramuscular needle depth, and subcutaneous fat and muscle thickness when assessing muscle temperature, and iii) suggests a systematic and more robust approach, based on individual body composition characteristics, to be considered when assessing intramuscular temperature.

Increases in muscle temperature by hot water improve muscle contractile function and reduce motor unit discharge rates.

PURPOSE: Examine the effects of 42°C hot-water immersion on muscle contraction function and motor unit discharge rates. Voluntary and evoked contraction assessments were examined first with a concomitant increase in the core and muscle temperature, and thereafter with increased muscle temperature but cooled core temperature. METHODS: Fifteen participants (24.9 ± 5.6 years) performed neuromuscular assessments before, after, and ~15-min after either 90-min of 42°C (hot) or 36°C (control) water immersion. Maximal voluntary contraction (MVC) assessment of knee extension was performed along with surface electromyography (sEMG) (vastus lateralis and medialis [VL, VM]) and voluntary activation level (VAL). Resting evoked twitch was elicited for peak torque and time to peak torque analysis. In addition, the VL and VM motor unit discharge rates (MUDR) were measured. RESULTS: After hot-water immersion (core temperature ↑1°C; muscle temperature ↑2.4°C), MVC torque and VAL decreased (p < 0.05). The sEMG (VL and VM) and peak twitch torque did not change (p > 0.05), while time to peak torque decreased (p = 0.007). The VL and VM MUDR decreased, showing a time effect, after both water immersion conditions (36 and 42°C) (p > 0.001). Fifteen minutes after the hot-water immersion (core temperature at baseline; muscle temperature ↑1.4°C), MVC torque returned to baseline, but VAL remained lower. The sEMG (VL and VM) remained unchanged. Peak twitch torque increased (p < 0.002) and time to peak torque remained lower (p = 0.028). The MUDR remained lower after both water immersion conditions (p < 0.05). CONCLUSION: Increased core temperature evoked by 42°C hot-water immersion decreases MVC torque and VAL. However, a passive increase in muscle temperature improved evoked muscle contractile function (i.e., time to peak torque [after] and peak twitch torque [~15 min after]). Moreover, a passive increase in muscle temperature reduced the required MUDR to attain the same torque.

Potential role of passively increased muscle temperature on contractile function.

Declines in muscle force, power, and contractile function can be observed in older adults, clinical populations, inactive individuals, and injured athletes. Passive heating exposure (e.g., hot baths, sauna, or heated garments) has been used for health purposes, including skeletal muscle treatment. An acute increase in muscle temperature by passive heating can increase the voluntary rate of force development and electrically evoked contraction properties (i.e., time to peak twitch torque, half-relation time, and electromechanical delay). The improvements in the rate of force development and evoked contraction assessments with increased muscle temperature after passive heating reveal peripheral mechanisms' potential role in enhancing muscle contraction. This review aimed to summarise, discuss, and highlight the potential role of an acute passive heating stimulus on skeletal muscle cells to improve contractile function. These mechanisms include increased calcium kinetics (release/reuptake), calcium sensitivity, and increased intramuscular fluid.

Effect of Divergent Solar Radiation Exposure With Outdoor Versus Indoor Training in the Heat: Implications for Performance.

ABSTRACT: O'Connor, FK, Doering, TM, Minett, GM, Reaburn, PR, Bartlett, JD and Coffey, VG. Effect of divergent solar radiation exposure with outdoor versus indoor training in the heat: implications for performance. J Strength Cond Res 36(6): 1622-1628, 2022-The aim of this study was to determine physiological and perceptual responses and performance outcomes when completing high-intensity exercise in outdoor and indoor hot environments with contrasting solar radiation exposure. Seven cyclists and 9 Australian Football League (AFL) players undertook cycling trials in hot conditions (≥30 °C) outdoors and indoors. Cyclists completed 5 × 4 minutes intervals (∼80% peak power output [PPO]) with 2 minutes recovery (∼40% PPO) before a 20-km self-paced ride. Australian Football League players completed a standardized 20 minutes warm-up (∼65% mean 4-minute power output) then 5 × 2 minutes maximal effort intervals. Heart rate (HR), PO, ratings of perceived exertion (RPE), thermal comfort (TC), and thermal sensation (TS) were recorded. Core (Tc) and skin temperature (Tsk) were monitored in cyclists alone. In both studies, ambient temperature, relative humidity, and solar radiation were monitored outdoors and matched for ambient temperature and relative humidity indoors, generating different wet bulb globe temperature (WBGT) for cyclists, but the similar WBGT for AFL players through higher relative humidity indoors. The statistical significance was set at p ≤ 0.05. Cyclists' HR (p = 0.05), Tc (p = 0.03), and Tsk (p = 0.03) were higher outdoors with variable effects for increased RPE, TS, and TC (d = 0.2-1.3). Power output during intervals was not different between trials, but there were small-moderate improvements in cyclists' PO and 20-km time indoors (d = 0.3-0.6). There was a small effect (d = 0.2) for AFL players' mean PO to increase outdoors for interval 4 alone (p = 0.04); however, overall there were small-moderate effects for lower RPE and TS indoors (d = 0.2-0.5). Indoor training in hot conditions without solar radiation may promote modest reductions in physiological strain and improve performance capacity in well-trained athletes.

Short-term heat acclimation preserves knee extensor torque but does not improve 20 km self-paced cycling performance in the heat.

PURPOSE: This study investigated the effect of 5 days of heat acclimation training on neuromuscular function, intestinal damage, and 20 km cycling (20TT) performance in the heat. METHODS: Eight recreationally trained males completed two 5-day training blocks (cycling 60 min day-1 at 50% peak power output) in a counter-balanced, cross-over design, with a 20TT completed before and after each block. Training was conducted in hot (HA: 34.9 ± 0.7 °C, 53 ± 4% relative humidity) or temperate (CON: 22.2 ± 2.6 °C, 65 ± 8% relative humidity) environment. All 20TTs were completed in the heat (35.1 ± 0.5 °C, 51 ± 4% relative humidity). Neuromuscular assessment of knee extensors (5 × 5 s maximum voluntary contraction; MVC) was completed before and after each 20TT and on the first and last days of each training block. RESULTS: MVC torque was statistically higher after 5 days of HA training compared to CON (mean difference = 14 N m [95% confidence interval; 6, 23]; p < 0.001; d = 0.77). However, 20TT performance after 5 days of HA training was not statistically different to CON, with a between-conditions mean difference in the completion time of 68 s [95% confidence interval; - 9, 145] (p = 0.076; d = 0.35). CONCLUSION: Short-term heat acclimation training may increase knee extensor strength without changes in central fatigue or intestinal damage. Nevertheless, it is insufficient to improve 20 km self-paced cycling performance in the heat compared to workload-matched training in a temperate environment. These data suggest that recreationally trained athletes gain no worthwhile performance advantage from short-term heat-training before competing in the heat.

Analysing the predictive capacity and dose-response of wellness in load monitoring.

This study aimed to identify the predictive capacity of wellness questionnaires on measures of training load using machine learning methods. The distributions of, and dose-response between, wellness and other load measures were also examined, offering insights into response patterns. Data (n= 14,109) were collated from an athlete management systems platform (Catapult Sports, Melbourne, Australia) and were split across three sports (cricket, rugby league and football) with data analysis conducted in R (Version 3.4.3). Wellness (sleep quality, readiness to train, general muscular soreness, fatigue, stress, mood, recovery rating and motivation) as the dependent variable, and sRPE, sRPE-TL and markers of external load (total distance and m.min-1) as independent variables were included for analysis. Classification and regression tree models showed high cross-validated error rates across all sports (i.e., > 0.89) and low model accuracy (i.e., < 5% of variance explained by each model) with similar results demonstrated using random forest models. These results suggest wellness items have limited predictive capacity in relation to internal and external load measures. This result was consistent despite varying statistical approaches (regression, classification and random forest models) and transformation of wellness scores. These findings indicate practitioners should exercise caution when interpreting and applying wellness responses.

Mobilizing serum factors and immune cells through exercise to counteract age-related changes in cancer risk.

An increasing body of evidence suggests that age-related immune changes and chronic inflammation contribute to cancer development. Recognizing that exercise has protective effects against cancer, promotes immune function, and beneficially modulates inflammation with ageing, this review outlines the current evidence indicating an emerging role for exercise immunology in preventing and treating cancer in older adults. A specific focus is on data suggesting that muscle- derived cytokines (myokines) mediate anti-cancer effects through promoting immunosurveillance against tumourigenesis or inhibiting cancer cell viability. Previous studies suggested that the exercise-induced release of myokines and other endocrine factors into the blood increases the capacity of blood serum to inhibit cancer cell growth in vitro. However, little is known about whether this effect is influenced by ageing. Prostate cancer is the second most common cancer in men. We therefore examined the effects of serum collected before and after exercise from healthy young and older men on the metabolic activity of androgen-responsive LNCaP and androgen-unresponsive PC3 prostate cancer cells. Exercise-conditioned serum collected from the young group did not alter cell metabolic activity, whereas post-exercise serum (compared with pre-exercise serum) from the older men inhibited the metabolic activity of LNCaP cancer cells. Serum levels of candidate cancer-inhibitory myokines oncostatin M and osteonectin increased in both age groups following exercise. Serum testosterone increased only in the younger men postexercise, potentially attenuating inhibitory effects of myokines on the LNCaP cell viability. The data from our study and the evidence in this review suggest that mobilizing serum factors and immune cells may be a key mechanism of how exercise counteracts cancer in the older population.

Muscle temperature kinetics and thermoregulatory responses to 42 °C hot-water immersion in healthy males and females.

PURPOSE: To determine the vastus lateralis muscle temperature kinetics during and after passive heating, to exam the effect of sex on thermoregulatory responses, and the thermal safety and tolerance of the 42 °C hot-water immersion protocol. METHODS: Thirty participants (15 males, 15 females) underwent a 2 h 42 ºC hot-water immersion to the waist level. Vastus lateralis, rectal and skin temperature, thermal sensation, heart rate and blood pressure (BP) were measured during the passive heating and recovery period. Participant recovery was monitored until muscle temperature returned to baseline. RESULTS: Vastus lateralis temperature increased to a maximal value of 39.0 ± 0.11 °C (P < 0.001), reaching a plateau after ~ 83.5 min of hot-water immersion and returning to baseline after ~ 115.8 min of recovery. Despite the anthropometric differences between males and females (e.g., height, body mass, body fat %, and fat thickness; P < 0.05), thermoregulatory responses showed no differences between sexes (P > 0.05). No change was found in systolic BP (~ 117 mmHg; P = 0.061). Peak rectal temperature (38.8 ± 0.14 °C; P < 0.001), heart rate (~ 100 bpm; P < 0.001), and diastolic BP (↓ ~ 13 mmHg; P < 0.001) during the hot-water immersion indicated the safety of the protocol. While skin temperature (~ 35.4 °C; P < 0.001) and thermal sensation (~ 5.95 AU; P < 0.001) confirmed protocol tolerance. CONCLUSION: These data demonstrate lower-body 42 °C hot-water immersion to increase vastus lateralis temperature and plateau ~ 2.8 °C above baseline. This amplitude of muscle temperature change aligns with reported cellular adaptation and muscle growth. Thermal strain incurred from this protocol appears safe and tolerable, positioning it well for health-related prescription.

Effects of passive heating intervention on muscle hypertrophy and neuromuscular function: A preliminary systematic review with meta-analysis.

Passive heating has been therapeutically used to treat a range of health conditions. Further, this intervention presents as a potential exercise mimetic strategy showing acute and chronic effects on skeletal muscle adaptation and neuromuscular systems. This systematic review and meta-analysis aimed to synthesise the existing evidence on the effects of passive heating on muscle hypertrophy and neuromuscular function. Seven databases were searched (i.e., PubMed, Web of Science, Scopus, CINAHL, EMBASE, Cochrane, and SPORTDiscus) from 1937 to October 2019. Eligible studies included original papers using healthy animals or human samples (≥18 years; both sexes) that have used a control group or condition. Ten original articles were included in this review and four in the meta-analysis. The meta-analysis detected an increase in muscle mass in animal samples seven days after passive heating (I2 = 65%, P < 0.01). The systematic review showed preliminary evidence that repeated passive heating exposures may promote muscle hypertrophy in animals and humans. Moreover, augmented muscle strength (involuntary and voluntary) may be observed after long-term passive heating (animals and humans) and increases in corticospinal excitability in humans after a single passive heating session. Passive heating has shown some potential benefits for skeletal muscle mass gain and muscle force improvement. Therefore, it is plausible to suggest that passive heating might be a worthwhile alternative to be recommended as an exercise mimetic for those people who lack or are unable to complete sufficient exercise.

The Effect of Overreaching on Neuromuscular Performance and Wellness Responses in Australian Rules Football Athletes.

Campbell, PG, Stewart, IB, Sirotic, AC, and Minett, GM. Title: The effect of overreaching on neuromuscular performance and wellness responses in Australian rules football athletes. J Strength Cond Res 34(6): 1530-1538, 2020-This study seeks to evaluate the effect of periodized fluctuations in training load on wellness and psychological questionnaires, perceived exertion, performance, and neuromuscular measures in team-sport athletes. Thirteen amateur Australian rules football athletes completed 6 weeks of periodized training, consisting of 2-week normal training (NT), intensified training (IT), and taper training (TT). Training sessions were quantified using global positioning system devices, heart-rate, and session rating of perceived exertion (sRPE), with wellness (general soreness, sleep quality/quantity, readiness to train, fatigue, stress, mood, and motivation) questionnaires collected daily. Psychological (Recovery-Stress Questionnaire for Athletes) and physical performance (countermovement jump, cycle ergometer peak power, 30-m sprint, and 2-km time trial) markers were measured after each training period. Perceived (sRPE) and mechanical loading were higher for IT than NT, and IT than TT (p < 0.03; d = 0.65-25.34). Cycle ergometer peak power, 30-m sprint, 2-km time trial, and countermovement jump height showed reductions in performance after IT compared to initial testing (p < 0.02; d = 0.51-1.46), with subsequent increases in performance after TT (p < 0.04; d = 0.66-2.27). Average wellness was higher during NT compared to IT (p = 0.005; d = 1.11). Readiness to train did not significantly differ from NT to IT or TT (p < 0.55; d = <0.59); however, readiness to train did improve during TT after the IT (p = 0.01; d = 1.05). The disturbances in performance, perceptual, and mood states may indicate a state of functional overreaching. The findings suggest that an averaged wellness score may be useful in potentially identifying overreaching. However, despite the popularity of wellness in monitoring systems, these measures overall demonstrated a limited capacity to differentiate between periodized fluctuations in load.

Thermal Infrared Imaging Can Differentiate Skin Temperature Changes Associated With Intense Single Leg Exercise, But Not With Delayed Onset of Muscle Soreness.

Muscle damage and soreness associated with increased exercise training loads or unaccustomed activity can be debilitating and impact the quality of subsequent activity/performance. Current techniques to assess muscle soreness are either time consuming, invasive or subjective. Infrared thermography has been identified as a quick, non-invasive, portable and athlete friendly method of assessing skin temperature. This study assessed the capability of thermal infrared imaging to detect skin temperature changes that may accompany the inflammatory response associated with delayed onset muscular soreness (DOMS). Eight recreationally trained participants (age 25 ± 3 years, mass 74.9 ± 13.6 kg, training minutes 296 ± 175 min·wk-1) completed 6 sets of 25 maximal concentric/eccentric contractions of the right knee flexors/extensors on a dynamometer to induce muscle damage and DOMS. The left knee extensors acted as a non-exercise control. Neuromuscular performance, subjective pain assessment and infrared thermography were undertaken at baseline, 24 and 48 hr post the DOMS-inducing exercise protocol. Data were analysed using Bayesian hierarchical regression and Cohen's d was also calculated. Maximal voluntary contraction torque was statistically lower at 24 hr (d = -0.70) and 48 hr (d = -0.52) compared to baseline, after the DOMS-inducing exercise protocol. These neuromuscular impairments coincided with statistically higher ratings of muscle soreness at 24 hr (d = 0.96) and 48 hr (d = 0.48). After adjusting for ambient temperature, anterior thigh skin temperature was statistically elevated at 24 hr, but not 48 hr, compared with baseline, in both the exercised and non-exercised leg. Thigh temperature was not different statistically between legs at these time points. Infrared imaging was able to detect elevations in skin temperature, at 24 hrs after the DOMS inducing exercise protocol, in both the exercised and non-exercised thigh. Elevations in the skin temperature of both thighs, potentially identifies a systemic inflammatory response occurring at 24 hr after the DOMS-inducing exercise protocol.

The effect of cycling in the heat on gastrointestinal-induced damage and neuromuscular fatigue.

PURPOSE: This study investigated the effect of exercise in the heat on neuromuscular function, gastrointestinal damage, endotoxemia and inflammatory cytokines. METHODS: Eight male cyclists completed two 60 min cycling trials in both hot (HOT 34.5 ± 0.1 °C and 53 ± 1% relative humidity) and temperate environments (CON 20.2 ± 0.3 °C and 55 ± 3% relative humidity). The cycling task comprised of alternating 3 min intervals at a moderate-vigorous intensity (50% and 70% of maximum power output; Pmax) for 30 min, followed by 30 min at moderate intensity (40-50% Pmax). Neuromuscular function was assessed at pre-, post-exercise and 60 min post-exercise. Circulating levels of endotoxins, inflammatory cytokines and markers of gut permeability and damage were also collected at these time points. Heart rate, core temperature, skin temperature, perceived exertion, thermal sensation and comfort were also measured. RESULTS: Post-exercise voluntary activation of HOT (87.9% [85.2, 90.8]) was statistically lower (mean difference - 2.5% [- 4.5, - 0.5], d = 2.50) than that of CON (90.5% [87.8, 93.2]). The HOT trial resulted in statistically elevated (+ 69%) markers of gastrointestinal damage compared to CON (mean difference 0.424 ng mL-1 [0.163, 0.684, d = - 3.26]), although this was not observed for endotoxin, other inflammatory markers, or gastrointestinal permeability. CONCLUSIONS: This research provides evidence that short-duration cycling in the heat results in sub-optimal neuromuscular activation and increased expression of gastrointestinal damage markers, without a simultaneous elevation in circulating endotoxins or pro-inflammatory cytokines.

Acute glutamine supplementation does not improve 20-km self-paced cycling performance in the heat.

INTRODUCTION: The premise of this study was to investigate the effect of acute glutamine supplementation on 20 km time trial cycling performance in the heat, neuromuscular function, inflammation and endotoxemia. METHODS: Twelve cyclists completed two, 20-km time trials (20TT) in 35 °C (50% relative humidity). Participants ingested either glutamine (GLUT; 0.9 g kg-1 fat-free mass) or a placebo (CON) 60 min before each 20TT. Physiological and perceptual measures were recorded during each 20TT, and neuromuscular function assessed pre- and post-exercise. Venous blood was analysed for endotoxins, markers of gut damage (inflammatory fatty acid binding protein; I-FABP) and inflammatory cytokines (interleukin-6, IL-6; tumour necrosis factor-alpha, TNF-α). Data were analysed using linear mixed models in a Bayesian framework. RESULTS: 20TT in the heat increased I-FABP and elevated inflammatory cytokines (IL-6 and TNF-α) compared to pre-exercise values but did not result in endotoxemia. Completion time was not statistically different between conditions (mean difference [95% credible interval] = 11 s [- 23, 44]). Relative to CON, GLUT did not alter any physiological or perceptual measures during the 20TT. CONCLUSION: Glutamine supplementation does not improve 20TT performance in the heat or preserve neuromuscular function when compared to a placebo. These findings suggest that glutamine is not an ergogenic aid or prophylactic intervention for heat-induced gut damage during short-duration self-paced exercise in hot environments.

Sleep quantity and quality during consecutive day heat training with the inclusion of cold-water immersion recovery.

Exercise in the heat is a common occurrence among athletes and often is intentional in order to gain heat acclimation benefits, however, little is known about how such training may affect sleep. Therefore, this study investigated five days of training in the heat of varying intensity and duration and inclusion of cold-water immersion (CWI) recovery on sleep quantity and quality. Thirty recreationally-trained male participants completed five days of heat training (HT) and were randomised into three interventions including (i) 90 min cycling at 40% power at maximal aerobic capacity (Pmax) with 15 min passive recovery (90HT); (ii) 90 min cycling at 40% Pmax with 15 min CWI recovery (90CWI); or (iii) 30 min cycling alternating between 40% and 70% Pmax, with 15 min passive recovery (30HT). Sleep quality and quantity were assessed using Actigraphy and sleep diaries during five baseline nights (BASE) and five nights of HT which included subjective sleep quality and objective assessments of sleep quantity and quality. Total time asleep and perceived sleep quality were reduced, while awake duration and wake after sleep onset (WASO) were increased (p = 0.001-0.01) during HT compared to BASE. Latency was shorter for 30HT compared to 90HT during HT (p = 0.02), however, no differences between interventions for all other sleep variables (p > 0.05). The reduction in total sleep time due to increases in average wake duration during HT may be due to the unaccustomed increased in training frequency. Of note, reducing training in the heat duration per day improved sleep latency and sleep quality with no effect on total sleep time, while the addition of CWI has minimal effect on sleep quality or quantity.

The effect of high versus low intensity heat acclimation on performance and neuromuscular responses.

This study examined the effect of exercise intensity and duration during 5-day heat acclimation (HA) on cycling performance and neuromuscular responses. 20 recreationally trained males completed a 'baseline' trial followed by 5 consecutive days HA, and a 'post-acclimation' trial. Baseline and post-acclimation trials consisted of maximal voluntary contractions (MVC), a single and repeated countermovement jump protocol, 20km cycling time trial (TT) and 5×6s maximal sprints (SPR). Cycling trials were undertaken in 33.0 ± 0.8°C and 60 ± 3% relative humidity. Core (Tcore), and skin temperatures (Tskin), heart rate (HR), rating of perceived exertion (RPE) and thermal sensation were recorded throughout cycling trials. Participants were assigned to either 30min high-intensity (30HI) or 90min low-intensity (90LI) cohorts for HA, conducted in environmental conditions of 32.0 ± 1.6°C. Percentage change time to complete the 20km TT for the 90LI cohort was significantly improved post-acclimation (-5.9 ± 7.0%; P=0.04) compared to the 30HI cohort (-0.18 ± 3.9%; P<0.05). The 30HI cohort showed greatest improvements in power output (PO) during post-acclimation SPR 1 and 2 compared to 90LI (546 ± 128W and 517 ± 87W, respectively; P<0.02). No differences were evident for MVC within 30HI cohort, however, a reduced performance indicated by % change within the 90LI (P=0.04). Compared to baseline, mean Tcore was reduced post-acclimation within the 30HI cohort (P=0.05) while mean Tcore and HR were significantly reduced within the 90LI cohort (P=0.01 and 0.04, respectively). Greater physiological adaptations and performance improvements were noted within the 90LI cohort compared to the 30HI. However, 30HI did provide some benefit to anaerobic performance including sprint PO and MVC. These findings suggest specifying training duration and intensity during heat acclimation may be useful for specific post-acclimation performance.

Whole-body cryotherapy (extreme cold air exposure) for preventing and treating muscle soreness after exercise in adults.

BACKGROUND: Recovery strategies are often used with the intention of preventing or minimising muscle soreness after exercise. Whole-body cryotherapy, which involves a single or repeated exposure(s) to extremely cold dry air (below -100 °C) in a specialised chamber or cabin for two to four minutes per exposure, is currently being advocated as an effective intervention to reduce muscle soreness after exercise. OBJECTIVES: To assess the effects (benefits and harms) of whole-body cryotherapy (extreme cold air exposure) for preventing and treating muscle soreness after exercise in adults. SEARCH METHODS: We searched the Cochrane Bone, Joint and Muscle Trauma Group Specialised Register, the Cochrane Central Register of Controlled Trials, MEDLINE, EMBASE, CINAHL, the British Nursing Index and the Physiotherapy Evidence Database. We also searched the reference lists of articles, trial registers and conference proceedings, handsearched journals and contacted experts.The searches were run in August 2015. SELECTION CRITERIA: We aimed to include randomised and quasi-randomised trials that compared the use of whole-body cryotherapy (WBC) versus a passive or control intervention (rest, no treatment or placebo treatment) or active interventions including cold or contrast water immersion, active recovery and infrared therapy for preventing or treating muscle soreness after exercise in adults. We also aimed to include randomised trials that compared different durations or dosages of WBC. Our prespecified primary outcomes were muscle soreness, subjective recovery (e.g. tiredness, well-being) and adverse effects. DATA COLLECTION AND ANALYSIS: Two review authors independently screened search results, selected studies, assessed risk of bias and extracted and cross-checked data. Where appropriate, we pooled results of comparable trials. The random-effects model was used for pooling where there was substantial heterogeneity. We assessed the quality of the evidence using GRADE. MAIN RESULTS: Four laboratory-based randomised controlled trials were included. These reported results for 64 physically active predominantly young adults (mean age 23 years). All but four participants were male. Two trials were parallel group trials (44 participants) and two were cross-over trials (20 participants). The trials were heterogeneous, including the type, temperature, duration and frequency of WBC, and the type of preceding exercise. None of the trials reported active surveillance of predefined adverse events. All four trials had design features that carried a high risk of bias, potentially limiting the reliability of their findings. The evidence for all outcomes was classified as 'very low' quality based on the GRADE criteria.Two comparisons were tested: WBC versus control (rest or no WBC), tested in four studies; and WBC versus far-infrared therapy, also tested in one study. No studies compared WBC with other active interventions, such as cold water immersion, or different types and applications of WBC.All four trials compared WBC with rest or no WBC. There was very low quality evidence for lower self-reported muscle soreness (pain at rest) scores after WBC at 1 hour (standardised mean difference (SMD) -0.77, 95% confidence interval (CI) -1.42 to -0.12; 20 participants, 2 cross-over trials); 24 hours (SMD -0.57, 95% CI -1.48 to 0.33) and 48 hours (SMD -0.58, 95% CI -1.37 to 0.21), both with 38 participants, 2 cross-over studies, 1 parallel group study; and 72 hours (SMD -0.65, 95% CI -2.54 to 1.24; 29 participants, 1 cross-over study, 1 parallel group study). Of note is that the 95% CIs also included either no between-group differences or a benefit in favour of the control group. One small cross-over trial (9 participants) found no difference in tiredness but better well-being after WBC at 24 hours post exercise. There was no report of adverse events.One small cross-over trial involving nine well-trained runners provided very low quality evidence of lower levels of muscle soreness after WBC, when compared with infrared therapy, at 1 hour follow-up, but not at 24 or 48 hours. The same trial found no difference in well-being but less tiredness after WBC at 24 hours post exercise. There was no report of adverse events. AUTHORS' CONCLUSIONS: There is insufficient evidence to determine whether whole-body cryotherapy (WBC) reduces self-reported muscle soreness, or improves subjective recovery, after exercise compared with passive rest or no WBC in physically active young adult males. There is no evidence on the use of this intervention in females or elite athletes. The lack of evidence on adverse events is important given that the exposure to extreme temperature presents a potential hazard. Further high-quality, well-reported research in this area is required and must provide detailed reporting of adverse events.

Ice vests extend physiological work time while wearing explosive ordnance disposal protective clothing in hot and humid conditions.

BACKGROUND: Explosive ordnance disposal (EOD) technicians may be required to work in hot, humid environments while wearing heavy protective clothing. We investigated the ability of an ice vest to attenuate physiological strain and subsequently extend work tolerance. METHODS: Eight male participants (24.3 ± 4.1 yr, 51.9 ± 4.6 mL kg-1 min-1) walked (4.5 km h-1) in simulated hot and humid conditions (35 °C; 50% relative humidity). Participants wore either an EOD suit (CON) or EOD and ice vest (IV). Heart rate, core and skin temperature were recorded continuously. RESULTS: Participants walked longer in IV compared to CON (8.1 ± 7.4 min, p < .05). Over 90% of trials were terminated based on participants reaching 90% of their maximum heart rate. IV resulted in cooled skin (p < .001) and a physiologically negligible change in core temperature (p < .001). A condition by time interaction was identified for heart rate (p < .001), with a lower rate of rise in the IV condition. CONCLUSIONS: The cardiovascular inefficiency that limited performance was attenuated in the IV condition. The ice vest facilitated heat loss from the periphery; thus, the observed reduction in heart rate may reflect the preservation of central blood volume. The results identify the efficiency of a simple, inexpensive ice vest to assist EOD technicians working in the heat.

Core Temperature Response to Cold Water Immersion in Heat Stroke Patients Is Non-Linear and Unrelated to Sex or Body Size.

PURPOSE: Cold water immersion (CWI) is the most effective treatment for exertional heat stroke (EHS). However, knowledge on core temperature response during CWI treatment and the relation with patient characteristics (i.e., sex, anthropometrics) is limited. Therefore, the current study aimed to examine the core temperature response (in °C) during CWI treatment of recreational athletes participating in large running events and investigate the impact of sex and anthropometric characteristics on the cooling rate (in °C/min). METHODS: This observational study includes 57 athletes (n = 22 females; 39%) who suffered from EHS during an exercise event in the Netherlands. After admission to the medical facilities, a rectal temperature (Trec) probe was inserted and all clothing was removed before immersion in an ice bath (6.4 ± 1.6 °C). Rectal temperature was continuously measured throughout treatment, and treatment was continued until Trec ≤ 38.9 °C, or based on the decision of the emergency physician. RESULTS: Initial Trec did not differ between males (41.3 ± 0.9 °C) and females (41.2 ± 0.8 °C, p = 0.83). A non-linear response to CWI was observed, with the decrease in Trec beginning after 6 minutes of CWI. The decrease in Trec did not differ between both sexes (ptime*sex = 0.96). The cooling rate did not differ between males (0.21 ± 0.15 °C/min) and females (0.19 ± 0.08 °C/min, p = 0.55), and was not related to body mass, body surface area and body surface area to mass ratio (all p-values >0.05). CONCLUSIONS: We demonstrated that the cooling rate during CWI did not differ between men and women suffering from EHS, and that the Trec response to CWI is non-linear and not dependent on anthropometric characteristics. This suggests that no sex differentiation is needed in the EHS treatment guidelines and confirms the necessity to continuously monitor Trec during treatment.

Passive heat therapy: a promising preventive measure for people at risk of adverse health outcomes during heat extremes.

The world is experiencing increased frequency, duration, and severity of life-threatening heat extremes. Most hospitalizations and excess deaths during extreme heat events are associated with preexisting diseases in older adults. As climate change persists, the global population ages and the number of individuals with chronic diseases expands, more people are at risk of adverse health outcomes during extreme heat events. Therefore, proactive preventive measures are urgently needed to mitigate heat-related health risks within these populations. In this context, passive heat therapy (e.g., hot baths, saunas, and water-perfused suits) emerges as a promising countermeasure to improve physiological resilience to a warming planet. Passive heating improves cardiovascular function and overall health in older adults and individuals living with chronic diseases, offering the prospect of reducing cardiovascular strain during hotter days. Moreover, some studies suggest that passive heat therapy can be an effective strategy for heat acclimation (i.e., improved thermoregulation). This review describes the existing literature on the effects of passive heat therapy on cardiovascular and thermoregulatory responses in individuals with higher heat-related health risks and explores the use of passive heating as a strategy for heat acclimation to mitigate health risks during extreme heat events.NEW & NOTEWORTHY Passive heat therapy improves cardiovascular function and health in middle-aged and older adults living with or without chronic diseases. In addition, preliminary studies indicate that passive heat interventions can induce heat acclimation, improving thermoregulatory responses. Thus, passive heat therapy could serve as a preventive measure for people at risk of adverse health outcomes during extreme heat events, improving resilience to ongoing climate change.