Maximal Lactate Steady State is Altered in the Heat

Effect of acute heat exposure on the determination of critical power and W' in women and men

The goal of this study was to investigate to what extent acute heat exposure would affect the parameters of the power-duration relationship, i.e. CP and W', using multiple constant workload tests to task failure, in women and men. Twenty four young physically active participants (12 men, 12 women) performed 3-5 constant load tests to determine CP and W', both in temperate (TEMP; 18°C) and hot (HOT; 36°C) environmental conditions. A repeated-measures ANOVA was executed to find differences between TEMP and HOT, and between women and men. In HOT, CP was reduced by 6.5% (227 ± 50 vs. 212 ± 47 W), while W' increased 12.4% (16.4 ± 4.4 vs. 18.5 ± 5.6 kJ). No significant two-way sex × temperature interactions were observed, indicating that the environmental conditions did not have a different effect in men compared with women. The intersection of the average curvatures in TEMP and HOT occurred at 137 s and 280 W in women, and 153 s and 397 W in men. Acute heat exposure had an impact on the parameters CP and W', i.e. CP decreased whereas W' increased. The increase in W' might be a consequence of the mathematical modelling for the used test methodology, rather than a physiological accurate value of W' in HOT. No differences induced by heat exposure were observed between women and men.

The effect of acute heat exposure on the determination of exercise thresholds from ramp and step incremental exercise

PURPOSE

The aim of this study was to examine how respiratory (RT) and lactate thresholds (LT) are affected by acute heat exposure in the two most commonly used incremental exercise test protocols (RAMP and STEP) for functional evaluation of aerobic fitness, exercise prescription and monitoring training intensities.

METHODS

Eleven physically active male participants performed four incremental exercise tests, two RAMP (30 W·min^-1) and two STEP (40 W·3 min^-1), both in 18 °C (TEMP) and 36 °C (HOT) with 40% relative humidity to determine 2 RT and 16 LT, respectively. Distinction was made within LT, taking into account the individual lactate kinetics (LT_IND) and fixed value lactate concentrations (LT_FIX).

RESULTS

A decrease in mean power output (PO) was observed in HOT at LT (-6.2 ± 1.9%), more specific LT_IND (-5.4 ± 1.4%) and LT_FIX (-7.5 ± 2.4%), compared to TEMP, however not at RT (-1.0 ± 2.7%). The individual PO difference in HOT compared to TEMP over all threshold methods ranged from -53 W to +26 W. Mean heart rate (HR) did not differ in LT, while it was increased at RT in HOT (+10 ± 8 bpm).

CONCLUSION

This study showed that exercise thresholds were affected when ambient air temperature was increased. However, a considerable degree of variability in the sensitivity of the different threshold concepts to acute heat exposure was found and a large individual variation was noticed. Test design and procedures should be taken into account when interpreting exercise test outcomes.

Determining Validity of Critical Power Estimated Using a Three-Minute All-Out Test in Hot Environments

The aim of this study was to investigate the effects of heat on the validity of end-test power (EP) derived from a 3-min all-out test (3MT), which is considered as an alternative method for determining the conventional critical power. Twelve male cyclists were required to perform incremental exercise tests (IET) and 3MTs in both high temperature (HT; 35 °C) and thermoneutral temperature (NT; 22 °C) environments. Maximal oxygen uptake (VO_2max), and first and second ventilatory thresholds (VT₁ and VT₂, respectively) against the power output (wVO_2max, wVT₁, and wVT₂) were measured during IETs. EP was recorded during the 3MTs. A significant correlation was observed between wVT₂ and EP under NT (r = 0.674, p < 0.05) and under HT (r = 0.672, p < 0.05). However, wVO_2max, wVT₁, wVT₂, and EP were significantly higher in NT than in HT (p < 0.05). In conclusion, although the physiological stress induced by HT might impair exercise performance, the EP derived from 3MT can validly estimate wVT₂ under HT conditions.

Psychophysiological Responses in Emergency Medical Technician Students during Simulated Work Activities in a Hot Environment

This study compared physiological responses and cognitive performance during simulated work activities in heat to a thermoneutral condition. First responders perform physically demanding activities in a hot environment which may impose additional burdens on tactical personnel during daily tasks. Ten healthy (8 men and 2 women) participants performed two consecutive simulated work activities with two repetitions of each activity (10 min walking on treadmill and 15 sandbag lifts) under heat and thermoneutral conditions. A Stroop color word test (SCWT) and total mood disturbance (TMD) were obtained at first and second baseline (B1, B2), after a 30-min resting period (B3), and recovery (R1). At the end of the trial, core temperature (Tc), skin temperature (tsk), and mean body temperature (Tb) were higher in the heat condition compared to neutral condition (all p ≤ 0.05), whereas oxygen uptake, heart rate, and mean arterial pressure were not significantly different between conditions. There were no differences in scores of SCWT and TMD between conditions. However, TMD was significantly improved after two successive bouts of exercise compared to B3 (all p ≤ 0.05). This investigation shows that two successive simulated work activities did not induce the detrimental influence on thermoregulatory and cognitive responses. Extended work activities in a hot and humid environment may impose a psychophysiological burden and need to be investigated.

Time to exhaustion during cycling is not well predicted by critical power calculations

Three to 5 cycling tests to exhaustion allow prediction of time to exhaustion (TTE) at power output based on calculation of critical power (CP). We aimed to determine the accuracy of CP predictions of TTE at power outputs habitually endured by cyclists. Fourteen endurance-trained male cyclists underwent 4 randomized cycle-ergometer TTE tests at power outputs eliciting (i) mean Wingate anaerobic test (WAnT_mean), (ii) maximal oxygen consumption, (iii) respiratory compensation threshold (VT₂), and (iv) maximal lactate steady state (MLSS). Tests were conducted in duplicate with coefficient of variation of 5%-9%. Power outputs were 710 ± 63 W for WAnT_mean, 366 ± 26 W for maximal oxygen consumption, 302 ± 31 W for VT₂ and 247 ± 20 W for MLSS. Corresponding TTE were 00:29 ± 00:06, 03:23 ± 00:45, 11:29 ± 05:07, and 76:05 ± 13:53 min:s, respectively. Power output associated with CP was only 2% lower than MLSS (242 ± 19 vs. 247 ± 20 W; P < 0.001). The CP predictions overestimated TTE at WAnT_mean (00:24 ± 00:10 mm:ss) and MLSS (04:41 ± 11:47 min:s), underestimated TTE at VT₂ (-04:18 ± 03:20 mm:ss; P < 0.05), and correctly predicted TTE at maximal oxygen consumption. In summary, CP accurately predicts MLSS power output and TTE at maximal oxygen consumption. However, it should not be used to estimate time to exhaustion in trained cyclists at higher or lower power outputs (e.g., sprints and 40-km time trials). Novelty CP calculation enables to predict TTE at any cycling power output. We tested those predictions against measured TTE in a wide range of cycling power outputs. CP appropriately predicted TTE at maximal oxygen consumption intensity but err at higher and lower cycling power outputs.

Validity and reliability of the 3-min all-out running test to measure critical velocity in hot environments

This study's aim was to investigate the test-retest reliability of the 3-min all-out running test (3MRT) in hot environments. Twelve male sprinters (age 21.2 ± 1.8 years; height 1.78 ± 0.01 m; weight 71.0 ± 1.6 kg; [Formula: see text] 55.0 ± 1.0 mL kg^-1 min^-1) performed an incremental exercise test in a laboratory, during which the first and second ventilatory thresholds (VT₁ and VT₂) and [Formula: see text] were determined. In addition, they performed two 3MRTs on an outdoor track in a hot environment, during which the critical velocity (CV) and anaerobic capacity (D') were estimated. Significant reproducibility was found in CV and D' (ICC = 0.74 and 0.61, P < 0.05). The average CV in 3MRTs (3.09 ± 0.13 m s^-1) correlated significantly with VT₁ (3.13 ± 0.07 m s^-1, P < 0.05). The 3MRT is a reliable tool for measuring CV and D', while CV from 3MRT in a hot environment was identical to VT₁.

Short-term heat acclimation improves the determinants of endurance performance and 5-km 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.

Maximal power output estimates the MLSS before and after aerobic training

The purpose of this study is to present an equation to predict the maximal lactate steady state (MLSS) through a VO2peak incremental protocol. Twenty-six physically active men were divided in two groups (G1 and G2). They performed one maximal incremental test to determine their VO2peak and maximal power output (Wpeak), and also several constant intensity tests to determine MLSS intensity (MLSSw) on a cycle ergometer. Group G2 underwent six weeks of aerobic training at MLSSw. A regression equation was created using G1 subjects Wpeak and MLSSw to estimate the MLSS intensity (MLSSweq) before and after training for G2 (MLSSweq = 0.866 x Wpeak-41.734). The mean values were not different (150±27W vs 148±27W, before training / 171±26W vs 177±24W, after training) and significant correlations were found between the measured and the estimated MLSSw before (r²=0.49) and after training (r²=0.62) in G2. The proposed equation was effective to estimate the MLSS intensity before and after aerobic training.

Efeitos do calor no OBLA: comparação entre ambiente quente e temperado

O OBLA (onset of blood lactate accumulation) é um método utilizado para estimar o limiar de lactato (LL). Entretanto, ainda não está claro o efeito da temperatura ambiente sobre o OBLA. O objetivo do presente estudo foi comparar o OBLA em ambiente quente (40ºC) e temperado (22ºC). Nove homens (idade: 23,9±2,4 anos; massa corporal: 75,9±7,3 kg e VO2máx: 47,8±4,9 mL•kg-1•min-1) realizaram teste progressivo em cicloergômetro para determinação da potência máxima (Wmáx) e do OBLA nos dois ambientes. A Wmáx (195±25W vs 225±28W) e a potência no OBLA (153±30W vs 165±32W) foram menores no ambiente quente do que no temperado. A frequência cardíaca no OBLA-40 foi maior do que no OBLA-22 (171±8 vs 153±10 bpm, respectivamente). Não foi observada diferença no consumo de oxigênio no OBLA-22 e OBLA-40 (31,65±5,21 vs 31,12±6,82 mL•kg-1•min-1). Estes resultados indicam que as condições ambientais influenciam a determinação do OBLA.

Efeito das cargas de treinamento sobre parâmetros fisiológicos de futebolistas

O objetivo desse estudo foi verificar os efeitos de três semanas de treinamentos com intensidades monitoradas sobre a capacidade aeróbia de futebolistas profissionais. Quatorze futebolistas integrantes de equipe da primeira divisão do Campeonato Brasileiro de 2010, foram avaliados pré e pós três semanas de treinamento. O limiar anaeróbio (LAn) foi determinado pelo método bi-segmentado, para isso quatro esforços submáximos de 800 metros com intensidades de 10, 12, 14 e 16 km/h foram aplicados. Trinta três sessões de treinamentos foram quantificadas em zonas de acordo com frequência cardíaca referente ao LAn (FC LAn): Z1 - 10% abaixo, Z2 - 90-100% e Z3 - acima da FC LAn. Durante os treinamentos os jogadores permaneceram 31,17±14,86%, 42,96±14,90% e 25,87±16,67% em Z1, Z2 e Z3, respectivamente. Não foram encontradas diferenças significativas no LAn (pré = 13,29 ± 0,71 km∙h-1; pós=12,85 ± 0,90 km∙h-1), percepção subjetiva de esforço correspondente ao LAn (pré = 11,53 ± 1,45 u.a; pós=11,23 ± 1,53 u.a) e FC LAn (pré = 166,64 ± 10,69 bpm; pós = 174,50 ± 10,89 bpm), indicando que três semanas de treinamento são insuficiente para gerar adaptações positivas no LAn de futebolistas.