Effect of Heat and Heat Acclimatization on Cycling Time Trial Performance and Pacing

Abstract

PurposeThis study aimed to determine the effects of heat acclimatization on performance and pacing during outdoor cycling time trials (TT, 43.4 km) in the heat.MethodsNine cyclists performed three TT in hot ambient conditions (TTH, approximately 37°C) on the first (TTH-1), sixth (TTH-2), and 14th (TTH-3) days of training in the heat. Data were compared with the average of two TT in cool condition (approximately 8°C) performed before and after heat acclimatization (TTC).ResultsTTH-1 (77 ± 6 min) was slower (P = 0.001) than TTH-2 (69 ± 5 min), and both were slower (P < 0.01) than TTC and TTH-3 (66 ± 3 and 66 ± 4 min, respectively), without differences between TTC and TTH-3 (P > 0.05). The cyclists initiated the first 20% of all TT at a similar power output, irrespective of climate and acclimatization status; however, during TTH-1, they subsequently had a marked decrease in power output, which was partly attenuated after 6 d of acclimatization and was further reduced after 14 d. HR was higher during the first 20% of TTH-1 than that in the other TT (P < 0.05), but there were no differences between conditions from 30% onward. Final rectal temperature was similar in all TTH (40.2°C ± 0.4°C, P = 1.000) and higher than that in TTC (38.5°C ± 0.6°C, P < 0.001).ConclusionsAfter 2 wk of acclimatization, trained cyclists are capable of completing a prolonged TT in a similar time in the heat compared with cool conditions, whereas in the unacclimatized state, they experienced a marked decrease in power output during the TTH.

Will the Conscious–Subconscious Pacing Quagmire Help Elucidate the Mechanisms of Self-Paced Exercise? New Opportunities in Dual Process Theory and Process Tracing Methods

“…Furthermore, decisions are often subject to a variety of influences including emotional state, previous experience, perception and social context. This perspective is consistent with findings from two recent reviews of pacing [20,21] in which the complexities of making pacing decisions were highlighted, particularly in regard to processing a wide array of situational cues and sensoryperceptual information. The present manuscript adopts a contemporary psychological perspective of decision-making in pacing, which is very accommodating of athleteenvironment interactions.…”

“…An overly strong focus on only this leaves other exciting and useful areas of exploring human behaviour in sports context relatively unattended. For example, athlete-environment interactions as described in a recent review [20], are a crucial factor in understanding the regulation of exercise intensity. In this review, a framework is proposed based on ecological psychology and the interdependence of perception and action.…”

Self-paced exercise in hot and cool conditions is associated with the maintenance of %V̇o2peak within a narrow range

“…Moreover, the percentage of peak heart rate maintained in all time trials, as well as the RPE responses (Fig. 5), were similar to those of experienced cyclists undertaking self-paced efforts of similar length/duration in field and laboratory settings (26,30,42).…”

“…The lower power output noted at the start of the time trial in the HOT condition was somewhat atypical and may stem from subjects consciously adopting a conservative approach, knowing that four separate time trials had to be performed. Indeed, power output in the heat usually matches that of cooler conditions for the first 10 -15 min of time trials (10,27,28,30,42,46), unless participants are inexperienced at performing such tasks (40), or the self-paced effort is preloaded with exercise in the heat (9). Hettinga et al (18) also showed that cycling in the heat decreases gross efficiency by 0.9% relative to cooler conditions.…”

“…When undertaken in the heat, prolonged self-paced exercise performance is significantly impaired relative to cool conditions (10,27,28,42,46). The impairment in performance is mediated by the complex interplay of multiple physiological systems (e.g., nervous, metabolic) (8,34,45), with the development of thermal strain potentially modulating a performance-limiting increase in cardiovascular strain (5,27,28,30). Indeed, a narrowing core-to-skin temperature gradient during exercise-heat stress increases the skin blood flow requirement for heat dissipation (5,35,36).…”