Kinetics of oxygen uptake during arm cranking with the legs inactive or exercising at moderate intensities

The purpose of this study was to compare the kinetics of oxygen uptake (V̇O₂) during arm cranking with the legs inactive or exercising. Each subject (n=8) performed three exercise protocols: 6-min arm cranking at an intensity of 60% of peak oxygen uptake (V̇O_2peak, AC₆₀) and 6-min combined arm cranking and leg cycling in which AC₆₀ was added to on-going leg cycling at an intensity of 20% or 40% of V̇O_2peak (LC₂₀ and LC₄₀: AC₆₀LC₂₀ and AC₆₀LC₄₀, respectively). After the onset of arm cranking, V̇O₂ tended to increase until the end of arm cranking in all of the three exercise modes. The amplitudes of this increase in V̇O₂ were 0.98 (0.18), 0.93 (0.16) and 0.84 (0.12) l.min⁻¹ during AC₆₀, AC₆₀LC₂₀ and AC₆₀LC₄₀, respectively, and there were significant differences between values for each exercise. The data are presented as means and standard deviations. There were no significant differences in the effective V̇O₂ time constant, partial O₂ deficit, and the difference between the values of V̇O₂ measured at 3 and 6 min in the three exercise modes. The present results indicate that the amplitude of the increase in V̇O₂ is reduced during arm cranking with the legs exercising, that this reduction becomes greater with increases in the intensity of leg cycling, and that the rate of increase in V̇O₂ is not affected by the additional muscle mass of the legs exercising below moderate intensities. The decrease in the amplitude of increase in V̇O₂ might be caused by reduction in oxygen supply to the exercising arms due to large muscle mass and/or overlaps of activity of stabilizing muscles during combined arm and leg exercise.