788-5 Does Abnormal Recovery of Skeletal Muscle Contribute to Fatigue During Repetitive Activities in CHF?

Abstract

We have previously shown that skeletal muscle endurance and early (5 minutes) recovery of muscle function are impaired in CHF. Since abnormal muscle recovery could explain the fatigue commonly experienced by CHF patients during repetitive activities, the present study examined whether subsequent recovery of muscle function is prolonged and whether this is associated with impaired recovery of submaximal exercise capacity. 18 class I–IV CHF patients (peak VO 2 16 ± 1 ml/kg/min) and 10 age-matched sedentary controls (CON, peak VO 2 26 ± 1) underwent serial 9-min self-powered treadmill tests and evaluations of quadriceps function over a 24 hr period. Muscle function was assessed by measurements of maximum voluntary contraction force (MVC in ft-Ibs). work during 25 knee extensions (WORK in ft-Ibs), and endurance ratio (ER, the ratio of average peak torque during final 3 to initial 3 repetitions) using an isokinetic dynamometer at baseline and after 10 min, 30 min, 1 hr, 3 hr and 24 hr. Distance walked in 9 min (DIS in m) was measured at baseline and after 30 min, 1 hr, 3 hr and 24 hr. At baseline, CHF patients walked less far (367 ± 32 vs 667 ± 27 m, p < 0.001) and performed less knee extensor work (1075 ± 116 vs 1390 ± 110 ft-Ibs, P < 0.05) than controls. MVC and ER also trended lower in CHF patients (80 ± 4 vs 90 ± 6 ft-Ibs, p = 0.15, and 0.51 ± 0,03 vs 0.58 ± 0.02, P = 0.11, respectively. Although DIS and WORK remained significantly lower in CHF patients at each subsequent time point, there was complete recovery to baseline values in both groups by the first repeat measurement. As compared to baseline, the DIS walked on subsequent tests ranged from 99–108% and 100–102% of baseline in CHF patients and controls, respectively. Similarly, WORK ranged from 93–103%, and 99–105% of baseline, MVCfrom 97–106% and 95–104%, and ER from 98–119% and 108–117%, in patients and controls, respectively. Therefore, we conclude that the fatigue experienced during daily activities by CHF patients is not due to impaired recovery of muscle function and is not manifested as a delay in the recovery of submaximal exercise capacity.