The \u201csecond wind\u201d in McArdle\u2019s 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 \ub1 4 yr) and a control group of six mitochondrial myopathy patients (51 \ub1 6 yr) performed two repetitions (CWR1 and CWR2) of 6-min constant work rate exercise ( 3c50% of peak work rate) separated by 6-min (SHORT) or 18-min (LONG) recovery. Pulmonary O 2 uptake (VO2), HR, cardiac output, rates of perceived exertion, vastus lateralis oxygenation {changes in deoxygenated Hb and myoglobin Mb concentrations, A[deoxy(Hb+Mb)], by near-infrared spectroscopy} were determined. In McA, VO2 (0.86 \ub1 0.2 vs. 0.95 \ub1 0.1 l/min), HR (113 \ub1 10 vs. 150 \ub1 13 beats/min), cardiac output (11.6 \ub1 0.6 vs. 15.0 \ub1 0.8l/min), and rates of perceived exertion (11 \ub1 2 vs. 14 \ub1 3) were lower, whereas A[deoxy(Hb+Mb)] was higher (14.7 \ub1 2.3 vs. -0.1 \ub1 4.6%) in CWR2-SHORT vs. CWR1; the "overshoot" of A[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 mitochondrial myopathy patients 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. Copyright \ua9 2014 the American Physiological Society