Oxygen uptake and heart rate kinetics during heavy exercise: a comparison between arm cranking and leg cycling

This study examined the oxygen uptake ((V) over circleO(2)) and heart rate (HR) kinetics during arm cranking and leg cycling at work rates above the anaerobic threshold (AT). Ten untrained male subjects [21.6 (1.3) years] completed two 7 min 15 s constant-load arm cranking and two leg cycling tests at a power output halfway between the mode-specific AT and peak (V) over circleO(2). The time constants for phase II (V) over circleO(2) (tau) and HR (tau) kinetics were determined by fitting a monoexponential curve from the end of phase I until 3 min of exercise. 02 T and HR T values were significantly (P<0.001) slower in arm cranking [(V) over circleO(2) tau = 66.4 (3.0) s; HR tau = 74.7 (4.4) s] than in leg cycling [(V) over circleO(2) tau = 42.0 (1.9) s; HR tau = 55.6 (3.5) s]. The (V) over circleO(2) slow component ((V) over circleO(2SC)) accounted for a significantly (P<0.001) greater percentage of the total exercise response during arm cranking [23.8 (1.6)%] than during leg cycling [14.2 (1.5)%]. The greater relative (V) over circleO(2SC) and the slower (V) over circleO(2) tau with arm exercise are consistent with a greater recruitment of metabolically inefficient type II muscle fibres during arm cranking than during leg cycling.