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

Abstract

This study examined the oxygen uptake (V˙O2) 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˙O2. The time constants for phase II V˙O2 (τ) and HR (τ) kinetics were determined by fitting a monoexponential curve from the end of phase I until 3 min of exercise. V˙O2 τ and HR τ values were significantly (P<0.001) slower in arm cranking [V˙O2 τ = 66.4 (3.0) s; HR τ = 74.7 (4.4) s] than in leg cycling [V˙O2 τ = 42.0 (1.9) s; HR τ = 55.6 (3.5) s]. The V˙O2 slow component (V˙O2SC) 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˙O2SC and the slower V˙O2 τ with arm exercise are consistent with a greater recruitment of metabolically inefficient type II muscle fibres during arm cranking than during leg cycling.