Oxygen uptake and muscle desaturation kinetics during intermittent cycling

To investigate the kinetics of O2 uptake (VO2) and m. vastus lateralis [deoxyhemoglobin] ([Hb]) (near-infrared spectroscopy) for supramaximal intermittent cycling.

Six males performed a ramp test for determination of VO2peak and lactate threshold. On different days, they completed four intermittent "work:recovery" tests (10 s:20 s, 30 s:60 s, 60 s:120 s, 90 s:180 s) for 30 min or to the tolerable limit; "work" = 120% peak work rate (WRpeak) attained on the ramp, "recovery" = 20 W.

Arterialized capillary [lactate] ([L]c) profiles were dependent on duty-cycle length and resembled those for constant-load exercise classically used to assign exercise intensity: 10 s:20 s-no increase (i.e., "moderate", with first-order VO2 kinetics); 30 s:60 s-increased but stable (i.e., "heavy," with first-order VO2 kinetics supplemented by a slow component (VO2 sc) that stabilizes); 60s:120s-progressive increase that was more marked for 90 s:180 s (i.e., "very heavy" or "severe," with first-order VO2 kinetics supplemented by a VO2 sc projecting to VO2peak). VO2 and Delta[Hb] oscillated with WR, the ensemble-averaged single-cycle oscillation amplitudes (peak-to-nadir) for each individual subject increasing with WR duty-cycle duration. In the 30-s:60-s test, with [L]c being elevated, there was also a tendency towards a modest VO2 sc, with an increase in individual VO2 peak values early in the test and VO2 not fully recovering back to baseline in recovery. This was more marked for the 60-s:120-s duty cycle: VO2 failed to recover completely back to baseline, and the peaks of the VO2 oscillations increased significantly with time (F = 30.7, P < 0.001); in some cases, VO2peak was attained and exhaustion rapidly ensued.

VO2 kinetics in intermittent exercise over a range of duty-cycle durations tended to associate with blood [lactate] profiles, similarly to previous demonstrations for sustained constant-load exercise.