Changes in Exercise Capacity Following Prolonged Endurance Training and Detraining in Mitochondrial Myopathy

Abstract

Patients with mitochondrial myopathies (MM) due to mtDNA mutations in skeletal muscle often suffer disabling exercise intolerance. Our previous studies suggest that short duration (14 weeks) endurance training improves exercise capacity and increases the activity of rate-limiting enzymes. The effect of a longer duration exercise training program followed by a period of detraining of equal duration has not been studied. PURPOSE: To assess the effect of 26 weeks of regular endurance training followed by 26 weeks of detraining on exercise capacity in patients with severe muscle oxidative impairment due to mitochondrial myopathy. METHODS: Ten MM patients were randomized into two groups (MMA, n=5 & MMB, n=5) and underwent 26 weeks of cycle exercise training. Patients in MMA followed cycle training with a 26 week detraining period whereas patients in MMB did not complete a detraining period. Peak work, oxygen uptake (VO2) and submaximal heart rate and blood lactate were determined at baseline, after 26 weeks of cycle training and following 26 weeks of detraining. RESULTS: Compared to baseline, training increased peak work from 83+25 to 96+38 W and significantly increased VO2 from 1.233+0.334 to 1.432+0.478 L/min (p=0.047) in MMA. Similar changes were seen in MMB following training: 80+24 to 89+28W and 1.173+0.274 to 1.301+0.309 L/min. During submaximal exercise, peak heart rate significantly decreased 134+14 to 116+21 (p=0.028) in MMA and 137+10 to 124+15 bpm (p=0.036) in MMB as did venous lactate (5.1+3.9 to 3.1+2.4 in MMA & 3.9+1.0 to 2.7+0.9 mM (p=0.007) in MMB). After 26 weeks of detraining following 26 weeks of training, peak work and VO2 fell to 88+29 W and 1.306+0.385 L/min respectively. During submaximal exercise, after the 26 week detraining period compared to post training, heart rate (116+21 vs 123+16 bpm) and lactate levels (3.1+2.4 vs 4.1+3.2 mM) were higher. CONCLUSION: Twenty-six weeks of endurance training in MM improved tolerance of submaximal exercise and peak work and oxidative capacities. Detraining of an equal magnitude in duration resulted in a return of physiological adaptations toward baseline.