Cardiac Output Dependency On Exercising Muscle Mass During Small and Large Muscle Exercise

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There may be limitations to blood flow to larger muscle masses during exercise. PURPOSE: To determine the relation between cardiac output (CO) and stroke volume (SV) and the muscle mass engaged during submaximal exercise. We hypothesized: 1) For absolute CO (mL/min) and SV (ml/beat), legs would be greater than arms; 2) Arms would be greater than legs, for CO (ml/kg muscle mass/min) and SV (ml/kg muscle mass/min). 3) For CO and SV, large arms would be greater than small arms and large legs would be approximately the same as small legs. METHODS: Fifteen male volunteers (ages: 18 to 26) participated. Testing order was randomly assigned. CO and SV were measured throughout incremental workloads. RESULTS: Both the slope (SL) and y-intercept (INT) of the CO (mL/min)/watt relationship were greater (P < 0.05) during arm exercise (SL = 135.3, INT = 11579.7 mL/min) when compared to leg (SL = 92.7, INT = 7906.3 mL/min). For the SV (mL/beat)/watt relationship, INT was greater (P < 0.001) during arm exercise (arm = 157.6 mL/beat, leg = 117.0 mL/beat). For CO (mL/kg of muscle mass/min)/watt, SL was greater during arm exercise (Arm: M = 15.5, SD = 6.8; Leg: M = 4.0, SD = 1.2). The INT were greater during arm exercise (Arm: M = 1296.2 mL/kg/min, SD = 300.8; Leg: M= 334.8 mL/kg/min, SD = 82.5). For SV (mL/kg muscle mass/beat) both the SL and INT were significantly greater (P < 0.05) during arm exercise (Arm: SL M = 0.042, INT M = 17.828 mL/kg/beat; Leg: SL M = 0.00834, INT M = 4.969 mL/kg/beat). During leg exercise, both large and small muscle groups had a large increase in SV at the onset of exercise with the large muscle group continuing to show a subtle increase in SV while the small muscle group showed a subtle decrease. During arm exercise, both groups increased CO throughout the test, but the large muscle mass group showed a greater and more rapid increase. Both groups increased SV dramatically upon initiation of exercise but SV displayed a plateau for the large muscle group while the small muscle mass group decreased slightly. CONCLUSION: CO and SV response to submaximal were greater during arm versus leg ergometry. Correcting for muscle mass magnified these differences.