Correlation between the proportion of fast fibers in the biceps brachii muscle and the relative torque during elbow flexion in subjects with clinical hypothesis of myopathy

Muscular strength production may be impaired in myopathic patients. Myopathies represent a heterogeneous group of diseases with distinct clinical and morphological characteristics. It has been hypothesized that functional performance findings may be related to the predominant fiber type expressed in the muscle analyzed. Objective: To correlate the proportion of type 2 fibers in the biceps brachii muscles of subjects with a clinical hypothesis of myopathy with their peak isometric and isokinetic torque during elbow flexion. Method: Seven subjects with a clinical hypothesis of myopathy participated in this study: four females of mean age 37 years (sd = 9), weight 73kg (sd = 26) and height 155cm (sd = 6); and three males of mean age 39 years (sd= 1), weight 88kg (sd = 5) and height 172cm (sd = 4). The muscle fiber proportion was analyzed using the mATPase technique. One month after taking biopsies, the subjects performed concentric isometric and isokinetic strength tests for elbow flexion and extension using an isokinetic dynamometer. The isometric and isokinetic peak torques at 90 degree s- super(1) and 180 degree - super(1) were evaluated and the relative 90 degree (RT90) and 180 degree (RT180) torques were calculated. Spearman's correlation (r) was used for statistical analyses. Results: The proportion of type 2 fibers correlated positively with RT180 (r = 0.89, p = 0.01), and there was a moderate correlation with RT90 (r = 0.75, p = 0.05). Conclusions: The results suggest that the contractile behavior of type 2 fibers was not modified in these subjects. The isokinetic dynamometer was shown to be an instrument capable of noninvasively evaluating muscle fiber type predominance.