Association Between Time to Peak Sweat Lactate and Oxygen Uptake Kinetics During Constant-Load Exercise

Breath-by-breath gas exchange is required to characterise the oxygen uptake (VO2) response at exercise onset, limiting repeated assessment outside the laboratory. In this single-centre study, 36 collegiate athletes completed an incremental cycling test and two 30 min constant-load tests at 60–70% of peak work rate, at least 7 days apart, while sweat lactate was recorded continuously from the upper arm with a wearable biosensor. We examined whether the time to peak sweat lactate (sLApeak time) was associated with two indices of that response—the phase 2 time constant (τ) and the time to the operationally defined end of phase 2 (fin2)—and whether any association was reproduced on a separate day. sLApeak time correlated moderately with fin2 (r = 0.65 and 0.70) but weakly with τ (r = 0.47 and 0.26) and the oxygen deficit (r = 0.37 and 0.35). fin2 remained associated after multivariable adjustment for τ and peak VO2 (β = 1.7 and 1.6; p = 0.002 and 0.019). However, test–retest reproducibility of sLApeak time and fin2 was poor (intraclass correlation coefficients 0.53 and 0.26), and analyses included 16–32 participants. These preliminary findings support only a group-level association with the VO2 transition duration, not individual-level monitoring.