Plantar flexor muscle weakness and fatigue in spastic cerebral palsy patients

Background: Patients with cerebral palsy develop an important muscle weakness which might affect the aetiology and extent of exercise-induced neuromuscular fatigue. Aim: This study evaluated the aetiology and extent of plantar flexor neuromuscular fatigue in patients with cerebral palsy. Methods: Ten patients with cerebral palsy and 10 age- and sex-matched healthy individuals (similar to 20 years old, 6 females) performed four 30-s maximal isometric plantar flexions interspaced by a resting period of 2-3 s to elicit a resting twitch. Maximal voluntary contraction force, voluntary activation level and peak twitch were quantified before and immediately after the fatiguing task. Results: Before fatigue, patients with cerebral palsy were weaker than healthy individuals (341 +/- 134 N vs. 858 +/- 151 N, p < 0.05) and presented lower voluntary activation (73 +/- 19% vs. 90 +/- 9%, p < 0.05) and peak twitch (100 +/- 28 N vs. 199 +/- 33 N, p < 0.05). Maximal voluntary contraction force was not significantly reduced in patients with cerebral palsy following the fatiguing task (-10 +/- 23%, p > 0.05), whereas it decreased by 30 +/- 12% (p < 0.05) in healthy individuals. Conclusions: Plantar flexor muscles of patients with cerebral palsy were weaker than their healthy peers but showed greater fatigue resistance. What this paper adds: Cerebral palsy is a widely defined pathology that is known to result in muscle weakness. The extent and origin of muscle weakness were the topic of several previous investigations; however some discrepant results were reported in the literature regarding how it might affect the development of exercise-induced neuromuscular fatigue. Importantly, most of the studies interested in the assessment of fatigue in patients with cerebral palsy did so with general questionnaires and reported increased levels of fatigue. Yet, exercise-induced neuromuscular fatigue was quantified in just a few studies and it was found that young patients with cerebral palsy might be more fatigue resistant that their peers. Thus, it appears that (i) conflicting results exist regarding objectively-evaluated fatigue in patients with cerebral palsy and (ii) the mechanisms underlying this muscle fatigue in comparison to those of healthy peers remain poorly understood. The present study adds important knowledge to the field as it shows that when young adults with cerebral palsy perform sustained maximal isometric plantar flexions, they appear less fatigable than healthy peers. This difference can be ascribed to a better preservation of the neural drive to the muscle. We suggest that the inability to drive their muscles maximally accounts for the lower extent of exercise-induced neuromuscular fatigue in patients with cerebral palsy. (c) 2016 Elsevier Ltd. All rights reserved.