Body weight-supported training in Becker and limb girdle 2I muscular dystrophy.

INTRODUCTION: We studied the functional effects of combined strength and aerobic anti-gravity training in severely affected patients with Becker and Limb-Girdle muscular dystrophies. METHODS: Eight patients performed 10-week progressive combined strength (squats, calf raises, lunges) and aerobic (walk/run, jogging in place or high knee-lift) training 3 times/week in a lower-body positive pressure environment. Closed-kinetic-chain leg muscle strength, isometric knee strength, rate of force development (RFD), and reaction time were evaluated. RESULTS: Baseline data indicated an intact neural activation pattern but showed compromised muscle contractile properties. Training (compliance 91%) improved functional leg muscle strength. Squat series performance increased 30%, calf raises 45%, and lunges 23%. CONCLUSIONS: Anti-gravity training improved closed-kinetic-chain leg muscle strength despite no changes in isometric knee extension strength and absolute RFD. The improved closed-kinetic-chain performance may relate to neural adaptation involving motor learning and/or improved muscle strength of other muscles than the weak knee extensors. Muscle Nerve 54: 239-243, 2016.

Aerobic training in patients with anoctamin 5 myopathy and hyperckemia.

INTRODUCTION: Anoctamin 5 deficiency has recently been defined to cause limb-girdle muscular dystrophy type 2L (LGMD2L) with pronounced hyperCKemia. No treatment interventions have been made so far in this condition. METHODS: In 6 patients with LGMD2L, we studied the effect of home-based, pulse-watch monitored, moderate-intensity exercise on a cycle ergometer for 30 minutes, 3 times weekly, for 10 weeks. Plasma creatine kinase (CK) was assessed before, during, and after the program as a marker of muscle damage. Primary outcome measures were maximum oxygen uptake (VO(2max)) and time in the 5-repetitions-sit-to-stand test (FRSTST). RESULTS: Training resulted in improvements in VO(2max) (27 ± 7%; P = 0.0001) and FRSTST time (35 ± 12%; P = 0.007). Improvements in physiologic and functional muscle testing were accompanied by stable CK levels and no reports of adverse effects. CONCLUSIONS: These findings suggest that supervised aerobic exercise training is safe and effective in improving oxidative capacity and muscle function in patients with anoctamin 5 deficiency.

Late-onset Pompe disease is prevalent in unclassified limb-girdle muscular dystrophies.

OBJECTIVE: Late-onset Pompe disease is a rare, but potentially treatable metabolic myopathy, and therefore should not be overlooked. However, it is not unusual that patients go undiagnosed for many years. We hypothesized that patients with late-onset Pompe disease may have been overlooked in a population of patients with unclassified neuromuscular disease. METHODS: We used DBS (dried blood spots) to screen for Pompe disease in the two largest neuromuscular clinics and one of the main respiratory centers in Denmark. We selected patients with unclassified LGDM (limb-girdle muscular dystrophy), idiopathic elevation of creatine kinase, unexplained myopathy on muscle biopsy, unexplained restrictive respiratory insufficiency or unspecified myopathy for screening. RESULTS: 177 patients were found eligible for inclusion, and 103 (58.2%) patients accepted screening. Three patients with Pompe disease were identified with DBS, and subsequent genetic testing revealed known pathogenic mutations in the GAA gene. All three patients were found among 38 patients with unclassified LGMD (8%). CONCLUSION: Our findings indicate that a DBS should be considered early in the diagnostic work-up of patients with an LGMD phenotype, to rule out Pompe disease. Retrospectively, all 3 patients presented with "red flags" more compatible with Pompe disease than LGMD, including; 1) mild non-dystrophic, myopathic features on muscle biopsy, 2) creatine kinase levels below 1000, and 3) disproportionate axial and respiratory muscle involvement in comparison with limb muscle involvement.

Exercise intolerance in Glycogen Storage Disease Type III: weakness or energy deficiency?

Myopathic symptoms in Glycogen Storage Disease Type IIIa (GSD IIIa) are generally ascribed to the muscle wasting that these patients suffer in adult life, but an inability to debranch glycogen likely also has an impact on muscle energy metabolism. We hypothesized that patients with GSD IIIa can experience exercise intolerance due to insufficient carbohydrate oxidation in skeletal muscle. Six patients aged 17-36-years were studied. We determined VO 2peak (peak oxygen consumption), the response to forearm exercise, and the metabolic and cardiovascular responses to cycle exercise at 70% of VO 2peak with either a saline or a glucose infusion. VO 2peak was below normal. Glucose improved the work capacity by lowering the heart rate, and increasing the peak work rate by 30% (108 W with glucose vs. 83 W with placebo, p=0.018). The block in muscle glycogenolytic capacity, combined with the liver involvement caused exercise intolerance with dynamic skeletal muscle symptoms (excessive fatigue and muscle pain), and hypoglycemia in 4 subjects. In this study we combined anaerobic and aerobic exercise to systematically study skeletal muscle metabolism and exercise tolerance in patients with GSD IIIa. Exercise capacity was significantly reduced, and our results indicate that this was due to a block in muscle glycogenolytic capacity. Our findings suggest that the general classification of GSD III as a glycogenosis characterized by fixed symptoms related to muscle wasting should be modified to include dynamic exercise-related symptoms of muscle fatigue. A proportion of the skeletal muscle symptoms in GSD IIIa, i.e. weakness and fatigue, may be related to insufficient energy production in muscle.

Skeletal muscle metabolism during prolonged exercise in Pompe disease.

OBJECTIVE: Pompe disease (glycogenosis type II) is caused by lysosomal alpha-glucosidase deficiency, which leads to a block in intra-lysosomal glycogen breakdown. In spite of enzyme replacement therapy, Pompe disease continues to be a progressive metabolic myopathy. Considering the health benefits of exercise, it is important in Pompe disease to acquire more information about muscle substrate use during exercise. METHODS: Seven adults with Pompe disease were matched to a healthy control group (1:1). We determined (1) peak oxidative capacity (VO2peak) and (2) carbohydrate and fatty acid metabolism during submaximal exercise (33 W) for 1 h, using cycle-ergometer exercise, indirect calorimetry and stable isotopes. RESULTS: In the patients, VO2peak was less than half of average control values; mean difference -1659 mL/min (CI: -2450 to -867, P = 0.001). However, the respiratory exchange ratio increased to >1.0 and lactate levels rose 5-fold in the patients, indicating significant glycolytic flux. In line with this, during submaximal exercise, the rates of oxidation (ROX) of carbohydrates and palmitate were similar between patients and controls (mean difference 0.226 g/min (CI: 0.611 to -0.078, P = 0.318) and mean difference 0.016 µmol/kg/min (CI: 1.287 to -1.255, P = 0.710), respectively). CONCLUSION: Reflecting muscle weakness and wasting, Pompe disease is associated with markedly reduced maximal exercise capacity. However, glycogenolysis is not impaired in exercise. Unlike in other metabolic myopathies, skeletal muscle substrate use during exercise is normal in Pompe disease rendering exercise less complicated for e.g. medical or recreational purposes.

Anti-gravity training improves walking capacity and postural balance in patients with muscular dystrophy.

Recent studies in patients with muscular dystrophies suggest positive effects of aerobic and strength training. These studies focused training on using bicycle ergometers and conventional strength training, which precludes more severely affected patients from participating, because of their weakness. We investigated the functional effects of combined aerobic and strength training in patients with Becker and limb-girdle muscular dystrophies with knee muscle strength levels as low as 3% of normal strength. Eight patients performed 10 weeks of aerobic and strength training on an anti-gravity treadmill, which offered weight support up to 80% of their body weight. Six minute walking distance, dynamic postural balance, and plasma creatine kinase were assessed 10 weeks prior to training, immediately before training and after 10 weeks of training. Training elicited an improvement of walking distance by 8±2% and dynamic postural balance by 13±4%, indicating an improved physical function. Plasma creatine kinase remained unchanged. These results provide evidence that a combination of aerobic and strength training during anti-gravity has the potential to safely improve functional ability in severely affected patients with Becker and limb-girdle muscular dystrophies.