The effects of short recovery duration on VO₂ and muscle deoxygenation during intermittent exercise

This study compared the oxygen uptake (VO₂) and muscle deoxygenation (DHHb) of two intermittent protocols to responses during continuous constant load cycle exercise in males (24 year ± 2, n = 7). Subjects performed three protocols: (1) 10 s work/5 s active recovery (R), R at 20 W (INT1): (2) 10 s work/5 s R, R at moderate intensity (INT2); and (3) continuous exercise (CONT), all for 10 min, on separate days. The work rate of CONT and the 10 s work of INT1 and INT2 were set within the heavy intensity domain. VO₂ and DHHb data were filtered and averaged to 5 s bins. Average VO2 (80-420 s) was highest during CONT (3.77 L/min), lower in INT2 (3.04 L/min), and lowest during INT1 (2.81 L/min), all (p<0.05). Average DHHb (80-420 s) was higher during CONT (p<0.05) than both INT exercise protocols (CONT; 25.7 ± 0.9 a.u. INT1; 16.4 ± 0.8 a.u., and INT2; 15.8 ± 0.8 a.u.). The repeated changes in metabolic rate elicited oscillations in DHHb in both intermittet protocols, whereas oscillations in VO₂ were only observed during INT1. The greater DHHb during CONT suggests a reduction in oxygen delivery compared to oxygen consumption relative to INT. The higher VO₂ for INT 2 versus INT 1 and similar DHHb during INT suggests an increase in oxygen delivery during INT 2. Thus the different demands of INT1, INT2, and CONT protocols elicited differing physiological responses to a similar heavy intensity power output. These intermittent exercise models seem to elicit an elevated O₂ delivery condition compared to CONT.