Relations between strength and endurance of leg skeletal muscle and cardiopulmonary exercise testing parameters in...

The relations between muscle strength, muscle endurance, and cardiopulmonary parameters were investigated in patients with chronic heart failure.

The subjects comprised 33 outpatients with stable chronic heart failure (27 men, 6 women, mean age 60.3 +/- 12.7 years). A pedal-type isokinetic device was used throughout the study. The safety of the study protocol was examined first. Maximum muscle power (peak power), an index of muscle strength, was measured for 6 consecutive revolutions(3 revolutions of each leg). The strength decrement index (SDI) was measured for 20 consecutive maximal revolutions (10 revolutions in each leg). The SDI is an index of muscle endurance and compares the mean power for revolutions 9 and 10 with that for revolutions 2 and 3. Each subjects underwent symptom-limited cardiopulmonary exercise testing with a cycle ergometer on another day.

No subject experienced continuous abnormal heart rate or blood pressure response, chest pain, ischemic ST-T change, or severe arrhythmia. The peak power and the SDI were correlated with the anaerobic threshold (r = 0.42, 0.52, respectively), with peak oxygen uptake (r = 0.66, 0.61), and with the increase in oxygen uptake per unit increase in work rate (r = 0.43, 0.63). However, the slope of the ventilation equivalent to carbon dioxide output was correlated only with the SDI (r = -0.54) and the time constant for the oxygen uptake decrease was correlated only with the peak power (r = -0.46).

Peak functional capacity depends on both muscle strength and endurance, and subjective symptoms in daily activity, especially dyspnea on exertion, depend mainly on muscle endurance in patients with chronic heart failure.