Impaired Neuromuscular Function And Postural Control After A Fatiguing Exercise Performed With The Plantar Flexor Muscles

Mr Francis DEGACHEa, Mr Nicolas MAMIEb, Mr Nicolas PLACEb

a University of Health Sciences, University of Applied Sciences and Arts Western Switzerland, b University of Lausanne

PURPOSE: Postural control of undisturbed standing is known to be centrally regulated. There are also evidences that postural control is impaired with muscle fatigue, i.e. a reduction in stability is usually observed after prolonged or repeated exercise. However, there is little information available about the origin of impaired postural control with muscle fatigue. The aim of the present study was to determine the extent and origin of postural control impairment after a fatiguing exercise performed with the plantar flexors (PF).

METHODS: Ten healthy men (26±3 years) reported to the laboratory for two experimental sessions, performed on separate days in a randomized order. Both sessions consisted in a fatiguing exercise at the PF level (6 series of concentric-eccentric upright PF contractions, 30 s each, 90 s recovery). Neuromuscular fatigue (respectively postural stability) was quantified before and immediately after exercise in one session, whereas postural stability was assessed during quiet standing on a force plate at similar time points in the other experimental session. Neuromuscular alterations were assessed via techniques combining voluntary contractions, transcutaneous tibial nerve electrical stimulations and surface EMG activity recordings from soleus, gastrocnemius lateralis and gastrocnemius medialis muscles.

RESULTS: A progressive reduction in PF maximal voluntary force (MVC: -25±18%, p<0.05) was measured, together with a reduced maximal voluntary activation level (VAL: -14±18%, p<0.05). A reduction in the doublet force at 10 Hz / doublet force at 100 Hz ratio (P10/P100 ratio: -13±6%, p<0.05) was also observed, whereas M-wave properties were well preserved. Various indexes of postural control were altered, such as an increased stabilogram surface (+141±136%, p<0.05). A linear relationship was found between the extent of MVC force loss and the reduction in VAL (r=0.87, p<0.05), but no correlation was found between the loss in VAL and the change in postural control measurements.

CONCLUSION: Although muscle fatigue, as reflected by PF MVC force loss, appears to be of central origin, it seems that other mechanisms, presumably peripheral, explain the alteration of posture in quiet upright stance after exercise.

Keywords : postural control, neuromuscular fatigue, plantar flexor