The present investigation indicates that training for and competing in half and full Ironman triathlons has different effects on erythrocyte antioxidant enzyme activities and oxidative stress.

ObjectivesThis study compared the thermal, physiological and perceptual responses associated with match-play tennis in HOT (∼34°C wet-bulb-globe temperature (WBGT)) and COOL (∼19°C WBGT) conditions, along with the accompanying alterations in match characteristics.Methods12 male tennis players undertook two matches for an effective playing time (ie, ball in play) of 20 min, corresponding to ∼119 and ∼102 min of play in HOT and COOL conditions, respectively. Rectal and skin temperatures, heart rate, subjective ratings of thermal comfort, thermal sensation and perceived exertion were recorded, along with match characteristics.ResultsEnd-match rectal temperature increased to a greater extent in the HOT (∼39.4°C) compared with the COOL (∼38.7°C) condition (p<0.05). Thigh skin temperature was higher throughout the HOT match (p<0.001). Heart rate, thermal comfort, thermal sensation and perceived exertion were also higher during the HOT match (p<0.001). Total playing time was longer in the HOT compared with the COOL match (p<0.05). Point duration (∼7.1 s) was similar between conditions, while the time between points was ∼10 s longer in the HOT relative to the COOL match (p<0.05). This led to a ∼3.4% lower effective playing percentage in the heat (p<0.05). Although several thermal, physiological and perceptual variables were individually correlated to the adjustments in time between points and effective playing percentage, thermal sensation was the only predictor variable associated with both adjustments (p<0.005).ConclusionsThese adjustments in match-play tennis characteristics under severe heat stress appear to represent a behavioural strategy adopted to minimise or offset the sensation of environmental conditions being rated as difficult.

New findings r What is the central question of this study? We examined whether passive hyperthermia exacerbates central fatigue due to an increase in peak muscle relaxation rate, and whether exercise-induced hyperthermia attenuates this response because of a reduction in contractile speed related to peripheral fatigue. r What is the main finding and its importance? Exercise and passive hyperthermia increase muscle relaxation rate. An increase from moderate to severe passive hyperthermia enhances this rate, but without exacerbating force loss or voluntary muscle and cortical activation, relative to exercise. The centrally mediated rate of activation appears sufficient to overcome the increase in peak muscle relaxation. This study examined whether central fatigue was exacerbated by an increase in muscle contractile speed caused by passive hyperthermia (PaH) and whether exercise-induced hyperthermia (ExH) combined with related peripheral fatigue influenced this response. The ExH was induced by cycling at 60% of maximal oxygen uptake in 38 • C conditions and the PaH by sitting in a 48 • C climate chamber. Ten men performed brief (∼5 s) and sustained (30 s) maximal voluntary isometric contractions (MVCs) of the knee extensors at baseline (CON, ∼37.1 • C) and during moderate (MOD, ∼38.5 • C) and severe (SEV, ∼39.5 • C) hyperthermia. Motor nerve and transcranial magnetic stimulation were used to assess voluntary muscle and cortical activation level, along with contractile properties. Brief MVC force decreased to a similar extent during SEV-ExH (−8%) and SEV-PaH (−6%; P < 0.05 versus CON). Sustained MVC force also decreased during MOD-ExH (−10%), SEV-ExH (−13%) and SEV-PaH (−7%; P < 0.01 versus CON). Motor nerve and cortical activation were reduced on reaching MOD (∼3%) and SEV (∼5%) ExH and PaH during the brief and sustained MVCs (P < 0.01 versus CON). Peak twitch force decreased on reaching SEV-ExH and SEV-PaH (P < 0.05 versus CON). Following transcranial magnetic stimulation, during the brief and sustained MVCs the peak muscle relaxation rate increased in ExH and PaH (P < 0.01 versus CON). The increase was greatest during the sustained contraction in SEV-PaH (P < 0.01), but this did not exacerbate central fatigue relative to ExH. These results indicate that during fatiguing cycling exercise in the heat, quadriceps peak relaxation rate increases. However, the centrally mediated rate of activation appears sufficient to overcome even the largest increase in muscle relaxation rate, seen during SEV-PaH.

In this study, we aimed to investigate physiological determinants of endurance performance that best predict 5000-m average run velocity before and after endurance training. Thirty-nine previously untrained participants completed a 5000-m run; a constant velocity test (measuring running economy); and an incremental treadmill test to determine maximal oxygen uptake, final treadmill velocity, and velocity and oxygen uptake at lactate threshold, before and after six weeks of endurance training. Maximal oxygen uptake, final treadmill velocity, and velocity and oxygen uptake at threshold all increased significantly after training (p < 0.05). Average velocity for 5000 m increased significantly (p < 0.05). Running economy was not significantly altered. Correlation analysis revealed final treadmill velocity was most strongly related to 5000-m performance, in both untrained and trained states (r = 0.89, 0.83). Lactate threshold velocity (r = 0.73, 0.76), maximal oxygen uptake (r = 0.55, 0.51) and oxygen uptake at threshold (r = 0.45, 0.45) also showed significant correlations. In contrast, running economy was not significantly related to performance. These results demonstrate that final treadmill velocity in an VO2max test is the single best predictor of 5000-m performance in untrained and trained states. Furthermore, stepwise regression analysis showed that only velocity at lactate threshold significantly improved the accuracy of prediction provided by final treadmill velocity alone.

Environmental heat stress does not aggravate the recovery response from competitive intermittent exercise associated with elevated muscle temperatures and markers of muscle damage, delayed resynthesis of muscle glycogen, and impaired postmatch performance.