Key result
Type II muscle fiber predominance links to exaggerated ammonia and creatine kinase spikes during incremental exercise.
Why the study?
Does incremental exercise testing reveal distinct physiological and metabolic responses in subjects with type II muscle fiber predominance compared to normal individuals?
Cross-Sectional (n=13)
Does incremental exercise testing reveal distinct physiological and metabolic responses in subjects with type II muscle fiber predominance compared to normal individuals?
Subjects with type II muscle fiber predominance exhibit exaggerated increases in ammonia and elevated CK levels during exercise, suggesting a distinct metabolic myopathy termed 'reverse fiber type disproportion.'
May indicate metabolic myopathy in type II predominance; hypothesis-generating for exercise testing before clinical adoption.
INTRODUCTION: In this investigation we characterized the physiological and metabolic responses to incremental exercise in 13 subjects with a predominance of type II fibers on muscle biopsy. METHODS: Subjects underwent incremental exercise testing with measures of maximum oxygen uptake ( V˙O2 max), maximum heart rate (fc max), chronotropic index (fc / V˙O2 slope), maximum ventilation ( V˙emax), blood lactate, ammonia, and creatine kinase (CK) levels. Muscle fiber type was determined by myosin ATPase histochemistry. RESULTS: Muscle biopsies showed more type II fibers (75%) in subjects compared with normal individuals (P < 0.01). Subjects exhibited normal V˙O2 max and end-exercise lactate, whereas ammonia and CK levels at maximum exercise were significantly higher. CONCLUSIONS: Subjects with type II muscle fiber predominance exhibited exaggerated increases in ammonia and elevated CK levels during exercise. Predominance of type II fibers on muscle biopsy is the opposite finding of congenital fiber type disproportion; we suggest these patients be referred to as having "reverse fiber type disproportion." Muscle Nerve 54: 86-93, 2016.
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Cooper et al. (2015) conducted a cross-sectional in Reverse fiber type disproportion (n=13). Predominance of type II muscle fibers vs. Normal individuals was evaluated on Ammonia and creatine kinase levels at maximum exercise. Subjects with type II muscle fiber predominance exhibited exaggerated increases in ammonia and elevated creatine kinase levels during incremental exercise compared with normal individuals.
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