The "second wind" in McArdle's disease patients during a second bout of constant work rate submaximal exercise

Patients with McArdle's disease (McA) typically show the "second wind" phenomenon, a sudden decrease in heart rate (HR) and an improved exercise tolerance occurring after a few minutes of exercise. In the present study we investigated whether in McA a first bout of exercise determines a second wind during a second bout, separated by the first by a few minutes of recovery. Eight McA (44±4 years) and a control group of 6 mitochondrial myopathy patients (MM) (51±6 years) performed two repetitions (CWR1 and CWR2) of 6-min constant work rate exercise (~50% of peak work rate) separated by 6-min (SHORT) or 18-min (LONG) recovery. Pulmonary O2 uptake (VO2), HR, cardiac output (Q), rates of perceived exertion (RPE), vastus lateralis oxygenation (?[deoxy(Hb+Mb)], by near-infrared spectroscopy) were determined. In McA VO2 (0.86±0.2 vs. 0.95±0.1 L.min-1), HR (113±10 vs. 150±13 b.min-1), Q (11.6±0.6 vs. 15.0±0.8 L.min-1), RPE (11±2 vs. 14±3) were lower, whereas ?[deoxy(Hb+Mb)] was higher (14.7±2.3 % vs. -0.1±4.6 %) in CWR2-SHORT vs. CWR1; the "overshoot" of ?[deoxy(Hb+Mb)] and the "slow component" of VO2 kinetics disappeared in CWR2-SHORT. No differences (vs. CWR1) were observed in McA during CWR2-LONG, or in MM during both CWR2-SHORT and -LONG. A second wind phenomenon was observed in McA during the second of two consecutive 6-min constant-work rate submaximal exercises. The second wind was associated with changes of physiological variables suggesting an enhanced skeletal muscle oxidative metabolism. The second wind was not described after a longer (18-min) recovery period.