Carl A. James

Reliability and validity of skin temperature measurement by telemetry thermistors and a thermal camera during exercise in the heat.

New technologies afford convenient modalities for skin temperature (TSKIN) measurement, notably involving wireless telemetry and non-contact infrared thermometry. The purpose of this study was to investigate the validity and reliability of skin temperature measurements using a telemetry thermistor system (TT) and thermal camera (TC) during exercise in a hot environment. Each system was compared against a certified thermocouple, measuring the surface temperature of a metal block in a thermostatically controlled waterbath. Fourteen recreational athletes completed two incremental running tests, separated by one week. Skin temperatures were measured simultaneously with TT and TC compared against a hard-wired thermistor system (HW) throughout rest and exercise. Post hoc calibration based on waterbath results displayed good validity for TT (mean bias [MB]=-0.18 °C, typical error [TE]=0.18 °C) and reliability (MB=-0.05 °C, TE=0.31 °C) throughout rest and exercise. Poor validity (MB=-1.4 °C, TE=0.35 °C) and reliability (MB=-0.65 °C, TE=0.52 °C) was observed for TC, suggesting it may be best suited to controlled, static situations. These findings indicate TT systems provide a convenient, valid and reliable alternative to HW, useful for measurements in the field where traditional methods may be impractical.

Physiological responses to incremental exercise in the heat following internal and external precooling

Twelve males completed three incremental, discontinuous treadmill tests in the heat [31.9(1.0) °C, 61.9(8.9)%] to determine speed at two fixed blood lactate concentrations (2 and 3.5 mmol/L), running economy (RE), and maximum oxygen uptake ( V ˙ O 2 m a x ). Trials involved 20 min of either internal cooling (ICE, 7.5 g/kg ice slurry ingestion) or mixed‐methods external cooling (EXT, cold towels, forearm immersion, ice vest, and cooling shorts), alongside no intervention (CON). Following precooling, participants ran 0.3 km/h faster at 2 mmol/L and 0.2 km/h faster at 3.5 mmol/L (P = 0.04, partial η2 = 0.27). Statistical differences were observed vs CON for ICE (P = 0.03, d = 0.15), but not EXT (P = 0.12, d = 0.15). There was no effect of cooling on RE (P = 0.81, partial η2 = 0.02), nor on V ˙ O 2 m a x (P = 0.69, partial η2 = 0.04). An effect for cooling on physiological strain index was observed (P < 0.01, partial η2 = 0.41), with differences vs CON for EXT (P = 0.02, d = 0.36), but not ICE (P = 0.06, d = 0.36). Precooling reduced thermal sensation (P < 0.01, partial η2 = 0.66) in both cooling groups (P < 0.01). Results indicate ICE and EXT provide similar physiological responses for exercise up to 30 min duration in the heat. Differing thermoregulatory responses are suggestive of specific event characteristics determining the choice of cooling. Precooling appears to reduce blood lactate accumulation and reduce thermoregulatory and perceptual strain during incremental exercise.

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.

Short term heat acclimation improves the determinants of endurance performance and 5,000 m running performance in the heat.

This study investigated the effect of 5 days of controlled short-term heat acclimation (STHA) on the determinants of endurance performance and 5-km performance in runners, relative to the impairment afforded by moderate heat stress. A control group (CON), matched for total work and power output (2.7 W·kg-1), differentiated thermal and exercise contributions of STHA on exercise performance. Seventeen participants (10 STHA, 7 CON) completed graded exercise tests (GXTs) in cool (13 °C, 50% relative humidity (RH), pre-training) and hot conditions (32 °C, 60% RH, pre- and post-training), as well as 5-km time trials (TTs) in the heat, pre- and post-training. STHA reduced resting (p = 0.01) and exercising (p = 0.04) core temperature alongside a smaller change in thermal sensation (p = 0.04). Both groups improved the lactate threshold (LT, p = 0.021), lactate turnpoint (LTP, p = 0.005) and velocity at maximal oxygen consumption (vV̇O2max; p = 0.031) similarly. Statistical differences between training methods were observed in TT performance (STHA, -6.2(5.5)%; CON, -0.6(1.7)%, p = 0.029) and total running time during the GXT (STHA, +20.8(12.7)%; CON, +9.8(1.2)%, p = 0.006). There were large mean differences in change in maximal oxygen consumption between STHA +4.0(2.2) mL·kg-1·min-1 (7.3(4.0)%) and CON +1.9(3.7) mL·kg-1·min-1 (3.8(7.2)%). Running economy (RE) deteriorated following both training programmes (p = 0.008). Similarly, RE was impaired in the cool GXT, relative to the hot GXT (p = 0.004). STHA improved endurance running performance in comparison with work-matched normothermic training, despite equality of adaptation for typical determinants of performance (LT, LTP, vV̇O2max). Accordingly, these data highlight the ergogenic effect of STHA, potentially via greater improvements in maximal oxygen consumption and specific thermoregulatory and associated thermal perception adaptations absent in normothermic training.

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.

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.

Defining the determinants of endurance running performance in the heat

ABSTRACT In cool conditions, physiologic markers accurately predict endurance performance, but it is unclear whether thermal strain and perceived thermal strain modify the strength of these relationships. This study examined the relationships between traditional determinants of endurance performance and time to complete a 5-km time trial in the heat. Seventeen club runners completed graded exercise tests (GXT) in hot (GXTHOT; 32°C, 60% RH, 27.2°C WBGT) and cool conditions (GXTCOOL; 13°C, 50% RH, 9.3°C WBGT) to determine maximal oxygen uptake (V̇O2max), running economy (RE), velocity at V̇O2max (vV̇O2max), and running speeds corresponding to the lactate threshold (LT, 2 mmol.l−1) and lactate turnpoint (LTP, 4 mmol.l−1). Simultaneous multiple linear regression was used to predict 5 km time, using these determinants, indicating neither GXTHOT (R2 = 0.72) nor GXTCOOL (R2 = 0.86) predicted performance in the heat as strongly has previously been reported in cool conditions. vV̇O2max was the strongest individual predictor of performance, both when assessed in GXTHOT (r = −0.83) and GXTCOOL (r = −0.90). The GXTs revealed the following correlations for individual predictors in GXTHOT; V̇O2max r = −0.7, RE r = 0.36, LT r = −0.77, LTP r = −0.78 and in GXTCOOL; V̇O2max r = −0.67, RE r = 0.62, LT r = −0.79, LTP r = −0.8. These data indicate (i) GXTHOT does not predict 5 km running performance in the heat as strongly as a GXTCOOL, (ii) as in cool conditions, vV̇O2max may best predict running performance in the heat.

Short-term heat acclimation and precooling, independently and combined, improve 5 km running performance in the heat

Abstract James, CA, Richardson, AJ, Watt, PW, Willmott, AGB, Gibson, OR, and Maxwell, NS. Short-term heat acclimation and precooling, independently and combined, improve 5-km time trial performance in the heat. J Strength Cond Res 32(5): 1366–1375, 2018—Following heat acclimation (HA), endurance running performance remains impaired in hot vs. temperate conditions. Combining HA with precooling (PC) demonstrates no additive benefit in intermittent sprint, or continuous cycling exercise protocols, during which heat strain may be less severe compared to endurance running. This study investigated the effect of short-term HA (STHA) combined with mixed methods PC, on endurance running performance and directly compared PC and HA. Nine amateur trained runners completed 5-km treadmill time trials (TTs) in the heat (32° C, 60% relative humidity) under 4 conditions; no intervention (CON), PC, short-term HA (5 days—HA) and STHA with PC (HA + PC). Mean (±SD) performance times were; CON 1,476 (173) seconds, PC 1,421 (146) seconds, HA 1,378 (116) seconds and HA + PC 1,373 (121) seconds. This equated to the following improvements versus CON; PC −3.7%, HA −6.6% and HA + PC −7.0%. Statistical differences were only observed between HA and CON (p = 0.004, d = 0.68, 95% CI [−0.27 to 1.63]) however, similar effect sizes were observed for HA + PC vs. CON (d = 0.70, 95% CI [−0.25 to 1.65]), with smaller effects between PC vs. CON (d = 0.34, 95% CI [−0.59 to 1.27]), HA vs. PC (d = 0.33, 95% CI [−0.60 to 1.26]) and HA + PC vs. PC (d = 0.36, 95% CI [−0.57 to 1.29]). Pilot testing revealed a TT typical error of 16 seconds (1.2%). Precooling offered no further benefit to performance in the acclimated individual, despite modest alleviation of physiological strain. Maintenance of running speed in HA + PC, despite reduced physiological strain, may indicate an inappropriate pacing strategy therefore, further familiarization is recommended to optimize a combined strategy. Finally, these data indicate HA, achieved through cycle training, yields a larger ergogenic effect than PC on 5-km running performance in the heat, although PC remains beneficial when HA is not possible.