The threshold ambient temperature for the use of precooling to improve cycling time-trial performance

Purpose: Cycling time trial performance can be compromised by moderate to high ambient temperatures. It has become commonplace to implement pre-cooling prior to competition to alleviate this performance decline. However, little is known about the ambient temperature threshold above which pre-cooling becomes an effective strategy for enhancing endurance performance. It was the aim of this study to investigate the effect of pre-cooling in different environmental temperatures on time trial performance. Methods: Trained cyclists completed two time trials with (COLD) and without (CON) pre-cooling using an ice-vest and sleeves ensemble in ambient temperatures of 24˚C, 27˚C and 35˚C. Results: Time trial performance faster following COLD in both 35˚C (6.2%) and 27˚C (2.6%; both P<0.05) but not 24˚C (1.2%). Magnitude based inferential statistics indicate that COLD was very likely beneficial to performance in 35˚C and likely beneficial in 27˚C and possibly beneficial in 24°C. Mean power was 2.4%, 2.5% and 5.6% higher following COLD and considered to be likely beneficial in 24°C and very likely beneficial in 27˚C and 35˚C. COLD reduced mean skin temperature throughout the warm-up and into the time trial in all ambient temperatures (P<0.05). Sweat loss was lower following COLD in 24˚C and 27˚C but not 35˚C. There was no effect of COLD on gastrointestinal temperature at any point. Conclusions: Pre-cooling with an ice-vest and sleeves is likely to have a positive effect on time trial performance at temperatures above 24˚C, with a clear relationship between ambient temperature and the magnitude of effect of pre-coolin

Ad-libitum drinking and performance during a 40-km cycling time trial in the heat

The aim of this study was to investigate if drinking ad-libitum can counteract potential negative effects of a hypohydrated start caused by fluid restriction during a 40-km time trial (TT) in the heat. Twelve trained males performed one 40-km cycling TT euhydrated (EU: no water during the TT) and two 40-km cycling TTs hypohydrated. During one hypohydrated trial no fluid was ingested (HYPO), during the other trial ad-libitum water ingestion was allowed (FLUID). Ambient temperature was 35.2 ± 0.2°C, relative humidity 51 ± 3% and airflow 7 m·

Hydration in sport and exercise

Hypohydration, defined as a deficit in total body water that exceeds normal daily fluid fluctuations, is typically set as a fluid loss equivalent to >2% of body mass. The evaporation of sweat provides the principle means of heat dissipation during exercise in the heat; typical sweat rates of 300–2000 mL/h during sporting activities are generally not matched by fluid intake, leading to hypohydration. Although there are shortcomings in the literature related to hypohydration and sports performance, it is likely that some scenarios (hot conditions, larger fluid losses and prolonged aerobic exercise) are more at risk of incurring impaired performance. Guidelines for fluid intake during exercise and sporting activity are contentious since they need to span situations in which it is easy to overdrink compared with sweat losses and others in which significant levels of hypohydration occur. Nevertheless, athletes can be guided to develop fluid intake plans that are suited to their specific needs