Neuromuscular fatigue in prostate cancer patients undergoing radiation therapy

Objective: To determine the etiology of fatigue in prostate cancer patients undergoing radiation therapy (RT). Methods: Thirteen prescreened men (60 to 76 years in age, 58 to 130kg in body weight) were evaluated for neuromuscular fatigue (NMF) of the tibialis anterior (TA) muscle, cardiopulmonary fatigue (CPF), and psychological-subjective fatigue (PSF) at 1 to 2 weeks before RT (Pre), at the end of 8 weeks of RT (RT), and at 5 to 6 weeks after completion of RT (Post). Outcome Measures: For NMF, the TA muscle was fatigued by sustained isometric contraction at 80% of maximum voluntary contraction for 60 seconds on a force dynamometer. Neuromuscular efficiency (NME) expressed as a ratio of isometric force (in Newtons) and respective integrated electromyograms were measured. For CPF, stress testing was performed on a treadmill using the modified Bruce protocol. Piper Fatigue Scale, Beck Depression Inventory, and Epworth Sleepiness Scale were administered to evaluate PSF. Data Analysis: Paired t tests, single factor analysis of variance, and nonparametric analysis. Results: At RT, there was a significant decline in NME of TA at the beginning (18.4%, p < .01) and the end (29.2%, p < .001) of sustained muscle contraction for 60 seconds. Post values were lower but nonsignificant in comparison with Pre values. NME recovered within 5 to 6 weeks after RT. No abnormalities were detected in CPF or PSF. No correlation was found between the decline in NME and psychological status of the patients. Conclusion: Results provide definitive evidence of transient decline in NME in prostate cancer patients at the completion of RT. The effect seems to be specific for neuromuscular performance alone and is independent of the cardiovascular or psychological status of the patients. (C) 1997 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation.