Fatigue characteristics following ankle fractures.

The purpose of the study was to examine the effects of surgical and nonsurgical treatment of previously immobilized ankle fractures on voluntary and evoked contractile properties before and following fatigue. Twelve control and 12 previously immobilized (4-14 wk postfracture) internally fixated and nonfixated ankles were investigated before and following an isometric, intermittent, submaximal, fatigue protocol of the plantar flexors. Before fatigue, fracture groups had significantly lower force output (42.7 vs 78.8 Nm) and muscle activation (78.3 vs 98.7%) than controls. Decreased activation may be attributed to the inhibitory effects of injured muscle and swelling. All groups had similar force and muscle activation decreases (7-10%) following fatigue; however, the internally fixated group performed significantly fewer contractions during the fatigue test (19) than the nonfixated (71) and controls (61). In contrast to the other groups, internally fixated subjects experienced increased (13%) rather than decreased EMG activity (controls: 10.9%, nonfixated: 21.1%). M-waves and twitch torques potentiated to a similar extent in the fracture groups (4.5 and 5.7%) but decreased significantly in the control group (24.2 and 9.8%). The similar fatigue durations of non-fixated subjects compared with controls may be attributed to a lack of impairment in nonfixated neuromuscular propagation and contractile kinetics, while the increased fatigability of fixated subjects with a similar lack of evoked contractile property impairments suggested a greater intrinsic fatigability.