Sex Differences in Durability Following Heavy Intensity Cycling Exercise in Trained Athletes

The ability to withstand impairments in key physiological variables during prolonged exercise, known as "durability," is emerging as an important factor in cycling performance. While females possess physiological characteristics that could confer enhanced durability relative to males, little is known about potential sex differences. Sixteen males (V̇O_2peak 58 ± 6 mL·kg^-1·min^-1) and 16 females (V̇O_2peak 51 ± 3 mL·kg^-1·min^-1) performed an incremental exercise test to exhaustion in visit 1. In visit 2 they performed 90 min of heavy-intensity cycling (HVY) at 110% of gas exchange threshold (GET), followed by another incremental test. During HVY, pulmonary gas exchange (V̇O₂), heart rate (HR), rating of perceived exertion (RPE), near-infrared spectroscopy, and electromyography were recorded, and blood lactate (BLa) was collected. Before and after HVY, maximal voluntary contraction (MVIC), voluntary activation (VA), and potentiated twitches (100 Hz, 10 Hz, Q_tw·pot) of the knee extensors were assessed. Power at GET (-16% ± 15% vs. -2% ± 13%) and respiratory compensation point (-13% ± 10% vs. -6% ± 9%) decreased more in males than females (p ≤ 0.049), whereas V̇O_2peak and its associated power decreased similarly (p ≥ 0.073). All aspects of neuromuscular function decreased (all p < 0.001), without sex differences (p ≥ 0.096). During HVY, HR, V̇O₂ (%peak), relative energy expenditure increased more in males (p ≤ 0.008), whereas respiratory exchange ratio decreased more in females (p = 0.001). BLa was higher in males than females (p ≤ 0.040). Muscle oxygen extraction was lower (p = 0.004) and tissue saturation index higher for females (p < 0.001). The smaller reductions exhibited by females in submaximal thresholds, associated with lesser derangements to oxidative efficiency, suggest considering sex-specific training prescription and pacing strategies.