Exercise Intolerance in Facioscapulohumeral Muscular Dystrophy

Purpose Determine 1) if adults with facioscapulohumeral muscular dystrophy (FSHD) exhibit exercise intolerance and 2) potential contributing mechanisms to exercise intolerance, specific to FSHD. Methods Eleven people with FSHD (47 +/- 13 yr, 4 females) and 11 controls (46 +/- 13 yr, 4 females) completed one visit, which included a volitional peak oxygen consumption (V?O-2peak) cycling test. Breath-by-breath gas exchange, ventilation, and cardiovascular responses were measured at rest and during exercise. The test featured 3-min stages (speed, 65-70 rpm) with incremental increases in intensity (FSHD: 20 W per stage; control: 40-60 W per stage). Body lean mass (LM (kg, %)) was collected via dual-energy x-ray absorptiometry. Results V?O-2peak was 32% lower (24.5 +/- 9.7 vs 36.2 +/- 9.3 mL center dot kg(-1)center dot min(-1), P < 0.01), and wattage was 55% lower in FSHD (112.7 +/- 56.1 vs 252.7 +/- 67.7 W, P < 0.01). When working at a relative submaximal intensity (40% of V?O-2peak), wattage was 55% lower in FSHD (41.8 +/- 30.3 vs 92.7 +/- 32.6 W, P = 0.01), although ratings of perceived exertion (FSHD: 11 +/- 2 vs control: 10 +/- 3, P = 0.61) and dyspnea (FSHD: 3 +/- 1 vs control: 3 +/- 2, P = 0.78) were similar between groups. At an absolute intensity (60 W), the rating of perceived exertion was 63% higher (13 +/- 3 vs 8 +/- 2, P < 0.01) and dyspnea was 180% higher in FSHD (4 +/- 2 vs 2 +/- 2, P < 0.01). V?O-2peak was most strongly correlated with resting O-2 pulse in controls (P < 0.01, r = 0.90) and percent leg LM in FSHD (P < 0.01, r = 0.88). Among FSHD participants, V?O-2peak was associated with self-reported functionality (FSHD-HI score; activity limitation: P < 0.01, r = -0.78), indicating a strong association between perceived and objective impairments. Conclusions Disease-driven losses of LM contribute to exercise intolerance in FSHD, as evidenced by a lower V?O-2peak and elevated symptoms of dyspnea and fatigue during submaximal exercise. Regular exercise participation may preserve LM, thus providing some protection against exercise tolerance in FSHD.

Automated summary

This study investigated the exercise intolerance in adults with facioscapulohumeral muscular dystrophy (FSHD) and explored the specific mechanisms contributing to exercise intolerance in FSHD. The results showed that FSHD patients had lower peak oxygen consumption (V?O-2peak) and lower power output at submaximal intensity. They also reported higher ratings of perceived exertion and dyspnea at absolute intensity. These findings suggest that muscle loss in FSHD is a significant factor contributing to exercise intolerance.