Stroke-related effects on maximal dynamic hip flexor fatigability and functional implications

Abstract

Introduction: Stroke-related changes in maximal dynamic hip flexor muscle fatigability may be more relevant functionally than isometric hip flexor fatigability.

Methods: Ten chronic stroke survivors performed 5 sets of 30 hip flexion maximal dynamic voluntary contractions (MDVC). A maximal isometric voluntary contraction (MIVC) was performed before and after completion of the dynamic contractions. Both the paretic and nonparetic legs were tested.

Results: Reduction in hip flexion MDVC torque in the paretic leg (44.7%) was larger than the nonparetic leg (31.7%). The paretic leg had a larger reduction in rectus femoris EMG (28.9%) between the first and last set of MDVCs than the nonparetic leg (7.4%). Reduction in paretic leg MDVC torque was correlated with self-selected walking speed (r2=0.43), while reduction in MIVC torque was not (r2=0.11).

Conclusions: Reductions in maximal dynamic torque of paretic hip flexors may be a better predictor of walking function than reductions in maximal isometric contractions.

Keywords: dynamic contractions; hip flexors; neuromuscular fatigue; stroke; walking.

Figure 1

A) Mean (± SE) percent reduction in MDVC torque. The paretic leg had a significantly larger reduction (P = 0.002) in torque when compared to the non-paretic leg. B) Mean (± SE) percent reduction in MIVC torque. There was no significant difference in percent torque reduction between the paretic and non-paretic leg (P = 0.08). One subject maximally extended instead of flexing the non-paretic leg following the fatigue protocol, and this measurement was excluded. C) Mean (± SE) percent reduction in RF EMG area. The paretic leg has a significantly greater (P = 0.01) change in RF EMG area between the first and last set MDVCs compared to the non-paretic leg. Data were rejected in 2 of the non-paretic leg EMG measurements and 1 of the paretic leg EMG measurements due to poor signal-to-noise ratio. D) Correlation between percent reduction in MDVC torque and self-selected walking speed. There was a significant negative correlation (r²=0.43, P = 0.01) between percent reduction in MDVC torque and self-selected walking speed but not between MIVC torque and self-selected walking speed in the paretic legs (P = 0.33).