Mark Hayes

The influence of hot humid and hot dry environments on intermittent-sprint exercise performance

PURPOSE To examine the effect of a hot humid (HH) compared with a hot dry (HD) environment, matched for heat stress, on intermittent-sprint performance. In comparison with HD, HH environments compromise evaporative heat loss and decrease exercise tolerance. It was hypothesized that HH would produce greater physiological strain and reduce intermittent-sprint exercise performance compared with HD. METHOD Eleven male team-sport players completed the cycling intermittent-sprint protocol (CISP) in 3 conditions, temperate (TEMP; 21.2°C ± 1.3°C, 48.6% ± 8.4% relative humidity [rh]), HH (33.7°C ± 0.5°C, 78.2% ± 2.3% rh), and HD (40.2°C ± 0.2°C, 33.1% ± 4.9% rh), with both heat conditions matched for heat stress. RESULTS All participants completed the CISP in TEMP, but 3 failed to completed the full protocol of 20 sprints in HH and HD. Peak power output declined in all conditions (P < .05) but was not different between any condition (sprints 1-14 [N = 11]: HH 1073 ± 150 W, HD 1104 ± 127 W, TEMP, 1074± 134; sprints 15-20 [N = 8]: HH 954 ± 114 W, HD 997 ± 115 W, TEMP 993 ± 94; P > .05). Physiological strain was not significantly different in HH compared with HD, but HH was higher than TEMP (P < .05). CONCLUSION Intermittent-sprint exercise performance of 40 min duration is impaired, but it is not different in HH and HD environments matched for heat stress despite evidence of a trend toward greater physiological strain in an HH environment.

The effects of single versus twice daily short term heat acclimation on heat strain and 3000 m running performance in hot, humid conditions

Endurance performances are impaired under conditions of elevated heat stress. Short term heat acclimation (STHA) over 4-6 days can evoke rapid adaptation, which mitigate decrements in performance and alleviate heat strain. This study investigated the efficacy of twice daily heat acclimation (TDHA) compared to single session per day heat acclimation (SDHA) and normothermic training, at inducing heat acclimation phenotype and its impact upon running performance in hot, humid conditions. Twenty one, moderately trained males were matched and assigned to three groups; SDHA (mean±SD) (peak oxygen consumption [V̇O2peak] 45.8±6.1mLkg(-1)min(-1), body mass 81.3±16.0kg, stature 182±3cm), TDHA (46.1±7.0mLkg(-1)min(-1), 80.1±11.9kg, 178±4cm) or control (CON) (47.1±3.5mLkg(-1)min(-1), 78.6±16.7kg, 178±4cm). Interventions consisted of 45min cycling at 50% V̇O2peak, once daily for 4d (SDHA) and twice daily for 2d (TDHA), in 35°C, 60% relative humidity (RH), and once daily for 4 days (CON) in 21°C, 40% RH. Participants completed a pre- and post-intervention 5km treadmill run trial in 30°C, 60% RH, where the first 2km were fixed at 40% V̇O2peak and the final 3km was self-paced. No statistically significant interaction effects occurred within- or between-groups over the 2-4 days intervention. While within-group differences were found in physiological and perceptual measures during the fixed intensity trial post-intervention, they did not statistically differ between-groups. Similarly, TDHA (-36±34s [+3.5%]) and SDHA (-26±28s [+2.8%]) groups improved 3km performances (p=0.35), but did not differ from CON (-6±44s [+0.6%]). This is the first study to investigate the effects of HA twice daily and compare it with traditional single session per day STHA. These STHA protocols may have the ability to induce partial adaptive responses to heat stress and possibly enhance performance in environmentally challenging conditions, however, future development is warranted to optimise the administration to provide a potent stimuli for heat adaptation in athletic and military personnel within a rapid regime.

Peak power output provides the most reliable measure of performance in prolonged intermittent-sprint cycling

Abstract The aims of this study were to determine the reliability of an intermittent-sprint cycling protocol and to determine the efficacy of one practice session on main trials. Eleven men, moderately trained team-sport athletes, completed three visits to the laboratory involving a graded-exercise test and practice session and two trials of a Cycling Intermittent-Sprint Protocol separated by three days. Data for practice and main trials were analysed using typical error of measurement, intra-class correlation and least-products regression to determine reliability. Typical error of measurement (expressed as a coefficient of variation) and intra-class correlation for peak power output from all 20 sprints for trial 1 and trial 2 were 2.9 ± 12.8% (95% confidence interval: 2.0–5.0%) and 0.96 (95% confidence interval: 0.85–0.99), respectively. Typical errors of measurement and intra-class correlation for mean power output for all 20 sprints for trials 1 and 2 were 4.2 ± 11.9% (95% confidence interval: 2.9–7.4%) and 0.90 (95% confidence interval: 0.66–0.97), respectively. The results suggest that peak power output provides a more reliable measure than mean power output. The Cycling Intermittent-Sprint Protocol provides reliable measures of intermittent-sprint performance.

Short-term heat acclimation prior to a multi-day desert ultra-marathon improves physiological and psychological responses without compromising immune status

ABSTRACT Multistage, ultra-endurance events in hot, humid conditions necessitate thermal adaptation, often achieved through short term heat acclimation (STHA), to improve performance by reducing thermoregulatory strain and perceptions of heat stress. This study investigated the physiological, perceptual and immunological responses to STHA prior to the Marathon des Sables. Eight athletes (age 42 ± 4 years and body mass 81.9 ± 15.0 kg) completed 4 days of controlled hyperthermia STHA (60 min·day‒1, 45°C and 30% relative humidity). Pre, during and post sessions, physiological and perceptual measures were recorded. Immunological measures were recorded pre-post sessions 1 and 4. STHA improved thermal comfort (P = 0.02), sensation (P = 0.03) and perceived exertion (P = 0.04). A dissociated relationship between perceptual fatigue and Tre was evident after STHA, with reductions in perceived Physical (P = 0.04) and General (P = 0.04) fatigue. Exercising Tre and HR did not change (P > 0.05) however, sweat rate increased 14% (P = 0.02). No changes were found in white blood cell counts or content (P > 0.05). Four days of STHA facilitates effective perceptual adaptations, without compromising immune status prior to an ultra-endurance race in heat stress. A greater physiological strain is required to confer optimal physiological adaptations.

Power relative to body mass best predicts change in core temperature during exercise-heat stress

Abstract Gibson, OR, Willmott, AGB, James, CA, Hayes, M, and Maxwell, NS. Power relative to body mass best predicts change in core temperature during exercise-heat stress. J Strength Cond Res 31(2): 403–414, 2017—Controlling internal temperature is crucial when prescribing exercise-heat stress, particularly during interventions designed to induce thermoregulatory adaptations. This study aimed to determine the relationship between the rate of rectal temperature (Trec) increase, and various methods for prescribing exercise-heat stress, to identify the most efficient method of prescribing isothermic heat acclimation (HA) training. Thirty-five men cycled in hot conditions (40° C, 39% R.H.) for 29 ± 2 minutes. Subjects exercised at 60 ± 9% V[Combining Dot Above]O2peak, with methods for prescribing exercise retrospectively observed for each participant. Pearson product moment correlations were calculated for each prescriptive variable against the rate of change in Trec (° C·h−1), with stepwise multiple regressions performed on statistically significant variables (p ⩽ 0.05). Linear regression identified the predicted intensity required to increase Trec by 1.0–2.0° C between 20- and 45-minute periods and the duration taken to increase Trec by 1.5° C in response to incremental intensities to guide prescription. Significant (p ⩽ 0.05) relationships with the rate of change in Trec were observed for prescriptions based on relative power (W·kg−1; r = 0.764), power (%Powermax; r = 0.679), rating of perceived exertion (RPE) (r = 0.577), V[Combining Dot Above]O2 (%V[Combining Dot Above]O2peak; r = 0.562), heart rate (HR) (%HRmax; r = 0.534), and thermal sensation (r = 0.311). Stepwise multiple regressions observed relative power and RPE as variables to improve the model (r = 0.791), with no improvement after inclusion of any anthropometric variable. Prescription of exercise under heat stress using power (W·kg−1 or %Powermax) has the strongest relationship with the rate of change in Trec with no additional requirement to correct for body composition within a normal range. Practitioners should therefore prescribe exercise intensity using relative power during isothermic HA training to increase Trec efficiently and maximize adaptation.

The reliability of a heat acclimation state test prescribed from metabolic heat production intensities

Acclimation state indicates an individuals phenotypic response to a thermally stressful environment, where changes in heat dissipation capacity are determined during a heat acclimation state test (HAST). Variations in thermoregulatory and sudomotor function are reported while exercising at intensities relative to maximal oxygen uptake. This inter-individual variation is not true when intensity is prescribed to elicit a fixed rate of metabolic heat production (Ḣprod). This study investigated the reliability of peak Tre and two composite measures (sweat gain and sweat setpoint) derived from indices of thermosensitivity during a HAST prescribed from Ḣprod intensities. Fourteen participants (mean±SD; age 23±3 years, stature 174±7cm, body mass 75.0±9.4kg, body surface area 1.9±0.1m(2), peak oxygen consumption [V̇O2peak] 3.49±0.53Lmin(-1)) completed a lactate threshold-V̇O2peak test and two duplicate Ḣprod HASTs on a cycle ergometer. The HAST consisted of three, 30-min periods of exercise at fixed Ḣprod intensities relative to body mass (3, 4.5 and 6Wkg(-1)), within hot dry conditions (44.7±1.8°C and 18.1±4.7% relative humidity). Peak Tre (38.20±0.36 vs. 38.16±0.42°C, p=0.54), sweat setpoint (36.76±0.34 and 36.79±0.38°C, p=0.68) and sweat gain (0.37±0.14 and 0.40±0.18gs(-1)°C(-1), p=0.40) did not differ between HASTs. Typical error of measurement (TEM), coefficient variation (CV) and intra-class coefficient of correlation (ICC) were 0.19°C, 0.5% and 0.80 for peak Tre, 0.21°C, 0.6% and 0.65 for sweat setpoint and 0.09gs(-1)°C(-1), 28% and 0.68 for sweat gain, respectively. The use of fixed Ḣprod intensities relative to body mass is a reliable method for measuring Tre and ascertaining sweat setpoint during a HAST, whereas, sweat gain displays greater variability. A Ḣprod HAST appears sufficiently reliable for quantifying heat acclimation state, where TEM in peak Tre and sweat setpoint are small enough to identify physiologically meaningful improvements post-intervention.

Physiological and perceptual responses to exercising in restrictive heat loss attire with use of an upper-body sauna suit in temperate and hot conditions

ABSTRACT The aim of this experiment was to quantify physiological and perceptual responses to exercise with and without restrictive heat loss attire in hot and temperate conditions. Ten moderately-trained individuals (mass; 69.44±7.50 kg, body fat; 19.7±7.6%) cycled for 30-mins (15-mins at 2 W.kg−1 then 15-mins at 1 W.kg−1) under four experimental conditions; temperate (TEMP, 22°C/45%), hot (HOT, 45°C/20%) and, temperate (TEMPSUIT, 22°C/45%) and hot (HOTSUIT, 45°C/20%) whilst wearing an upper-body “sauna suit”. Core temperature changes were higher (P<0.05) in TEMPSUIT (+1.7±0.4°C.hr−1), HOT (+1.9±0.5°C.hr−1) and HOTSUIT (+2.3±0.5°C.hr−1) than TEMP (+1.3±0.3°C.hr−1). Skin temperature was higher (P<0.05) in HOT (36.53±0.93°C) and HOTSUIT (37.68±0.68°C) than TEMP (33.50±1.77°C) and TEMPSUIT (33.41±0.70°C). Sweat rate was greater (P<0.05) in TEMPSUIT (0.89±0.24 L.hr−1), HOT (1.14±0.48 L.hr−1) and HOTSUIT (1.51±0.52 L.hr−1) than TEMP (0.56±0.27 L.hr−1). Peak heart rate was higher (P<0.05) in TEMPSUIT (155±23 b.min−1), HOT (163±18 b.min−1) and HOTSUIT (171±18 b.min−1) than TEMP (151±20 b.min−1). Thermal sensation and perceived exertion were greater (P<0.05) in TEMPSUIT (5.8±0.5 and 14±1), HOT (6.4±0.5 and 15±1) and HOTSUIT (7.1±0.5 and 16±1) than TEMP (5.3±0.5 and 14±1). Exercising in an upper-body sauna suit within temperate conditions induces a greater physiological strain and evokes larger sweat losses compared to exercising in the same conditions, without restricting heat loss. In hot conditions, wearing a sauna suit increases physiological and perceptual strain further, which may accelerate the stimuli for heat adaptation and improve HA efficiency.

Females exposed to 24 h of sleep deprivation do not experience greater physiological strain, but do perceive heat illness symptoms more severely, during exercise-heat stress

ABSTRACT There is limited and inconclusive evidence surrounding the physiological and perceptual responses to heat stress while sleep deprived, especially for females. This study aimed to quantify the effect of 24 h sleep deprivation on physiological strain and perceptual markers of heat-related illness in females. Nine females completed two 30-min heat stress tests (HST) separated by 48 h in 39°C, 41% relative humidity at a metabolic heat production of 10 W · kg−1. The non-sleep deprived HST was followed by the sleep deprivation (SDHST) trial for all participants during the follicular phase of the menstrual cycle. Physiological and perceptual measures were recorded at 5 min intervals during the HSTs. On the cessation of the HSTs, heat illness symptom index (HISI) was completed. HISI scores increased after sleep deprivation by 28 ± 16 versus 20 ± 16 (P = 0.01). Peak (39.40 ± 0.35°C vs. 39.35 ± 0.33°C) and change in rectal temperature (1.91 ± 0.21 vs. 1.93 ± 0.34°C), and whole body sweat rate (1.08 ± 0.31 vs. 1.15 ± 0.36 L · h−1) did not differ (P > 0.05) between tests. No difference was observed in peak, nor rise in: heart rate, mean skin temperature, perceived exertion or thermal sensation during the HSTs. Twenty-four hours sleep deprivation increased perceptual symptoms associated with heat-related illness; however, no thermoregulatory alterations were observed.

The Acute Effect of Training Fire Exercises on Fire Service Instructors

Abstract Fire service instructors (FSI) regularly experience different types of fire exercises, however the strain experienced from these scenarios is not well understood. This study aims to identify the physiological and perceptual strain of Fire Service Instructors (FSI) to three training exercises: DEMO, ATTACK, COMPARTMENT, and the different roles performed: SETTER, INSTRUCTOR. The study also aims to assess the effect that different exercise patterns over a day (BOX, MULTI, COMBINATION) have on immunological responses. Sixteen FSI (age: 41 ± 8 years, body mass: 83.7 ± 6.7 kg, height: 177.0 ± 6.7 cm) were recruited, with 10 FSI completing the three exercises. Physiological and perceptual measures were collected prior to and immediately post each exercise. Venous blood samples were collected at the beginning and end of each day. One-way analysis of variance (ANOVA) were conducted to assess differences in physiological variables between exercise types, independent samples t-tests were conducted between roles. Day changes in hematological variables were assessed by paired sample t-tests and analyzed by one-way ANOVAs to identify differences between exercise patterns. The COMPARTMENT exercise resulted in a greater change in rectal temperature (ΔTre) (0.49 ± 0.28 °C) than both the DEMO (0.23 ± 0.19 °C, p = 0.045) and ATTACK (0.27 ± 0.22 °C, p = 0.016). Within the COMPARTMENT exercise, the SETTER resulted in a greater ΔTre and rating of perceived exertion than the INSTRUCTOR (0.67 ± 0.29 °C vs. 0.43 ± 0.18 °C, p = 0.027 and 14 ± 2 vs. 11 ± 2, p = 0.001, respectively). Following a day of fire exercises white blood cells (WBC), neutrophils, lymphocytes (LYMPH), monocytes (MONO), platelets (PLT), mean platelet volume (MPV), Interleukin (IL)-6, and cardiac troponin T (cTnT) all increased (p < 0.05). Exercise patterns containing a COMPARTMENT exercise resulted in greater PLT, MPV, and IL-6. Total daily variation in ΔTre was correlated with post-exercise WBC, MONO, and LYMPH. COMPARTMENT exercises produce the greatest physiological strain, with the SETTER role within this exercise causing the greatest ΔTre. Although predominately physiological responses remain within safe limits. Exercise patterns that include a COMPARTMENT exercise also generate a greater inflammatory response.

Fire Service Instructors' Working Practices: A UK Survey

ABSTRACT Analysis of Fire Service Instructors (FSI) working practices and health is needed to minimise health risks related to heat illness, cardiovascular events and immunological stress. Online surveys were distributed to UK FSI and Firefighters (FF). One hundred and thirty FSI (age: 43 ± 7yrs) and 232 FF (age: 41 ± 8yrs) responded. FSI experienced 2–10 live fires per week, with 45% of FSI reporting management does not set a limit on the number of exposures. Few FSI followed hydration guidelines, or cooling methods. New symptoms of ill health were reported by 41% of FSI and 21% of FF. FSI with ≥11 Breathing Apparatus exposures per month were 4.5 times (95% CI 1.33–15.09) more likely to experience new symptoms. A large proportion of FSI are experiencing new symptoms of illness after starting their career, and guidelines on exposure and hydration are not universally in place to reduce the risk of future health problems.