Table 5.
Effects of constant-workload exercise on quadriceps muscle functions
| COPD |
||||||
|---|---|---|---|---|---|---|
| Ctrl | PAV | He:21% O2 | 60% O2 | He:40% O2 | Healthy Ctrl | |
| Power output, W | 62 ± 7 | 62 ± 7 | 62 ± 7 | 62 ± 7 | 62 ± 7 | 124 ± 6 |
| Exercise time, min | 9.8 ± 1.2 | 9.8 ± 1.2 | 9.8 ± 1.2 | 9.8 ± 1.2 | 9.8 ± 1.2 | 14.7 ± 0.0 |
| Percent change from preexercise to 10 min postexercise | ||||||
| Potentiated single twitch, N | −25.0 ± 1.6 | −17.9 ± 2.0*† | −18.0 ± 1.5*† | −17.3 ± 1.6*† | −18.0 ± 1.6*† | −1.9 ± 0.8*‡ |
| MRFD, N/s | −20.9 ± 2.1 | −14.1 ± 2.0*† | −12.3 ± 2.3*† | −14.8 ± 2.1*† | −14.8 ± 1.5*† | −1.7 ± 1.6*‡ |
| MRR, N/s | −22.9 ± 2.6 | −14.9 ± 0.7*† | −14.0 ± 2.9*† | −16.0 ± 1.7*† | −14.2 ± 1.6*† | −2.4 ± 1.5*‡ |
| CT, s | −5.4 ± 0.3 | −4.6 ± 0.7 | −5.1 ± 0.5 | −4.6 ± 0.7 | −3.8 ± 0.2 | −4.8 ± 0.6 |
| RT0.5, s | 5.0 ± 2.1 | 1.8 ± 0.9*†‡ | 1.8 ± 0.6*†‡ | 2.1 ± 0.9*†‡ | 2.4 ± 0.6*† | 0.6 ± 1.6*‡ |
| MVC peak force, N | −9.0 ± 1.3 | −4.2 ± 1.0*† | −3.7 ± 0.6*† | −3.8 ± 1.2*† | −3.8 ± 0.6*† | 1.0 ± 0.7*‡ |
| Percent voluntary muscle activation | −1.3 ± 0.5 | −0.9 ± 1.2‡ | 0.2 ± 0.8‡ | −0.5 ± 0.9‡ | −0.2 ± 1.3‡ | 0.2 ± 0.5*‡ |
Values are expressed as means ± SE. Peripheral fatigue was assessed via supramaximal magnetic stimulation of the femoral nerve before and 10 min after exercise. Changes in fatigue variables are expressed as percent change from preexercise baseline to 10 min after the termination of exercise. MRFD, maximal rate of force development; MRR, maximal rate of relaxation; CT, contraction time; RT0.5, one-half relaxation time; MVC, maximal voluntary contraction. Percent muscle activation is based on superimposed twitch technique. Majority of variables changed significantly compared with baseline 10 min after exercise (P < 0.01). Preexercise, resting mean values for potentiated single twitch force, MRFD, MRR, CT, RT0.5, MVC, and percent voluntary muscle activation were similar in the 2 groups (COPD and Healthy-Control): 167 ± 7 and 149 ± 16 N (P = 0.30), 1,403 ± 65 and 1,295 ± 160 N/s (P = 0.35), 922 ± 53 and 775 ± 85 N/s (P = 0.11), 0.27 ± 0.00 and 0.27 ± 0.00 s (P = 0.09), 0.15 ± 0.01 and 0.15 ± 0.01 s (P = 0.70), 467 ± 31 and 330 ± 48 N (P < 0.05), and 96.0 ± 1.3% and 93.7 ± 2.0% (P = 0.33), respectively.
P < 0.05 vs. COPD-Ctrl;
P < 0.05 vs. Healthy;
not significantly different from preexercise baseline.