Androgens, exercise capacity, and muscle function in cystic fibrosis

It is well established that muscle strength and exercise capacity are impaired in adults with cystic fibrosis (CF). Numerous factors have been implicated in this process including nutritional factors, disuse, and corticosteroid use. It is also known that serum testosterone levels are frequently low in adolescent male patients with CF. As testosterone is known to have an effect on peripheral muscle, we aimed to assess the relationship among circulating androgen levels, muscle strength, and exercise capacity in adults with CF.

A prospective observational study was performed. Participants underwent maximal exercise testing and peripheral muscle strength assessment (quadriceps, shoulder flexion, handgrip, maximal inspiratory pressure, and maximal expiratory pressure). Venous blood samples were obtained for the measurement of total testosterone, sex hormone-binding globulin, and albumin. The free testosterone (FT) level was calculated.

A total of 15 subjects completed the study. The patients who were studied had impaired muscle strength and exercise capacity but normal mean androgen levels. Quadriceps strength, SF, and peak oxygen uptake (Vo(2)max) were 40.1 +/- 9.4%, 59.3 +/- 20.3%, and 77.4 +/- 22.2% predicted, respectively. One patient had a low testosterone level, with low FT levels evident in two subjects. There was no correlation between testosterone or FT level with any of the muscle strengths calculated. Neither testosterone or FT level was correlated with exercise capacity or pulmonary function.

Male CF patients with impaired skeletal muscle strength and exercise capacity have normal testosterone levels. Hypogonadism was rare in this group of adult men with CF. These findings would not support the role of testosterone in muscle dysfunction or impaired exercise capacity in CF patients.