Stroke-related changes in neuromuscular fatigue of the hip flexors and functional implications

Abstract

Objective: The aim of this study was to compare stroke-related changes in hip flexor neuromuscular fatigue of the paretic leg during a sustained isometric submaximal contraction with those of the nonparetic leg and controls and to correlate fatigue with clinical measures of function.

Design: Hip torques were measured during a fatiguing hip flexion contraction at 20% of the hip flexion maximal voluntary contraction in the paretic and nonparetic legs of 13 people with chronic stroke and 10 age-matched controls. In addition, the participants with stroke performed a fatiguing contraction of the paretic leg at the absolute torque equivalent to 20% maximal voluntary contraction of the nonparetic leg and were tested for self-selected walking speed (10-m Walk Test) and balance (Berg).

Results: When matching the nonparetic target torque, the paretic hip flexors had a shorter time to task failure compared with the nonparetic leg and controls (P < 0.05). The time to failure of the paretic leg was inversely correlated with the reduction of hip flexion maximal voluntary contraction torque. Self-selected walking speed was correlated with declines in torque and steadiness. Berg-Balance scores were inversely correlated with the force fluctuation amplitude.

Conclusions: Fatigue and precision of contraction are correlated with walking function and balance after stroke.

Figure 1

Single subject data for pre and post MVC measurements and fatiguing contractions. (A) Torque generated during a maximal voluntary contraction (MVC) for the non-paretic and paretic leg (S11). (B) Torque generated during the sub-maximal contraction trial for the (ET) protocol (S8).

Figure 2

Mean duration of the sub-maximal hip flexion contraction for (A) the equal effort protocol and (B) the equal torque protocol. Significance between groups is indicated by the asterisk.

Figure 3

Correlations between the time to task failure duration with the Post/Pre MVC torque ratio for the (A) paretic leg and (B) the non-paretic leg and dominant leg of control subjects. The circled square in (A) indicates an outlier not included in the correlation (n = 9).

Figure 4

Correlations between functional measures and neuromuscular fatigue parameters. (A) The change in torque between pre-fatigue and post-fatigue MVC trials was positively correlated with comfortable walking speed in participants with stroke for the equal torque (ET) protocol. The coefficient of variation was negatively correlated with the Ten Meter Walk test (B) and Berg Balance Score (C) for both protocols.