Fatigue During High-Intensity Endurance Exercise

Abstract

The purpose of this study was to examine the effects of hot (37° C) and cool (10° C) environments on cycling time to exhaustion (TTE), pH, lactate, and core temperature (Tc). Eleven endurance-trained subjects completed 4 TTE trials: Hot 80% VO2max (H80), Cool 80% (C80), Hot 100% (H100), and Cool 100% VO2max (C100). Esophageal temperature and blood was sampled before, every 5 minutes, at exhaustion, and 3 minutes after exercise and analyzed for lactate, pH, and HCO3-. Multifactorial analysis of variance with repeated measures was used to determine differences between mean values (± SD). Time to exhaustion was shorter in H100 and C100 vs. H80 and C80 (5.64 ± 1.49 minutes, 5.83 ± 1.03 minutes, 12.82 ± 2.0 minutes, and 24.85 ± 6.0 minutes, respectively) and shorter in H80 vs. C80 (p < 0.01). The pH at exhaustion was different among all conditions (7.17 ± 0.06, 7.15 ± 0.07, 7.21 ± 0.04, and 7.24 ± 0.06 units for H100, C100, H80, and C80, respectively, p = 0.02). The Tc at exhaustion was lower in H100 and C100 (37.93 ± 0.67 and 37.62 ± 0.58° C) vs. H80 and C80 (38.54 ± 0.51° C and 38.53 ± 0.38° C) (p < 0.01). In H80 and C80, the higher Tc likely played a greater role in the termination of exercise, whereas, in H100 and C100, pH and metabolic changes may have been more important. Despite these differences, neither an upper limit for Tc nor a lower limit for pH was identified; thus, fatigue based entirely on peripheral factors was not supported, and a combination of peripheral and central processes must be considered. The practical implications of these findings are that aerobic exercise at or near VO2max may be impacted more by metabolic factors, whereas lower intensities (∼80% VO2max) may be affected more by heat stress; these differences should be considered when training for events of this type.

Ingestion of High Molecular Weight Carbohydrate Enhances Subsequent Repeated Maximal Power: A Randomized Controlled Trial

“…Maximal aerobic capacity was determined using a graded protocol conducted on a cycle ergometer (Ergometer 894E, Monark, Vansbro, Sweden). The test consisted of 3-min stages for the first 12 min, followed by 2-min stages thereafter until V̇O 2max was reached [ 18 ]. Throughout the test, respiratory gas exchange was measured using an open-circuit gas analysis system (True One, Parvo Medics, Sandy, Utah), and heart rate was monitored using a telemetry system (Polar Electro E600, Polar Electro Inc, Lake Success, New York).…”

The effects of sodium bicarbonate supplementation at individual time‐to‐peak blood bicarbonate on 4‐km cycling time trial performance in the heat

“…Combine this with greater level of extracellular lactate during exercise in the heat versus thermoneutral conditions for the same given exercise, this suggests a greater level of acidosis is present (Robergs, Ghiasvand, & Parker, 2004). Unsurprisingly, Mitchell, Rogers, Basset, and Hubing (2014) reported a significant reduction in exercise capacity (time to exhaustion) in hot environments (37°C) compared to cool environments (10°C) at both 80% and 100% VO 2max . It is intuitive to suggest therefore that nutritional interventions that could support ATP production via anaerobic energy pathways and reduce acidic stress may mitigate the deleterious physiological changes caused by exercising in the heat.…”

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

“…Another explanation for the declines in performance during 3MTs in HT might be the respiratory muscle fatigue. Mitchell et al [27] reported that heat stress could reduce the time to exhaustion during high-intensity exercise and is accompanied by greater ventilatory responses than for a cool environment. The results of this study found that the VE in HT was higher than that in NT during 3MT.…”