The impact of temperature and skeletal muscle oxygen saturation on 40 km cycling time trial performance of male cyclists

Endurance performance declines in non-heat-acclimated athletes in warm conditions. Early studies did not use relevant wind speeds, increasing heat storage, and performance decline. Furthermore, deep hip flexion postures adopted in time-trials (TTs) may limit skeletal muscle oxygenation (SmO₂), compounding problems associated with heat storage in warm-hot environments. The aim of this study was to employ an ecologically valid method of simulating TTs, using wind speeds closely replicating those in the real world (~40 km h^-1). A secondary aim was to investigate how SmO₂ was impacted by environmental conditions. Ten well-trained cyclists volunteered for the study. They completed 3 simulated 40 km TT's in 10, 20, and 30 and 50% relative humidity. TT time was slower in 30°C (3666 ± 172 s) versus 10°C (3531 ± 144 s; p = 0.0029) and 20°C (3528 ± 160 s; p = 0.0033). Mean T_sk was highest in 30°C (34.4 ± 0.1°C) versus 10°C (25.4 ± 1.5°C) and 20°C (30.6 ± 0.3°C; all p < 0.0001). Larger ∆SmO₂ was evident at 10°C (-1.3 ± 0.7%) and 20°C (-1.2 ± 0.7%) versus 30°C (0.4 ± 0.7%; both p < 0.0001). ∆SmO₂ was correlated to ∆heart rate (r = -0.556, p < 0.0001) and power (r = -0.425, p < 0.0001). These data show that simulated TT performance is impaired >20°C.