The bilateral movement condition facilitates maximal but not submaximal paretic-limb grip force in people with post-stroke hemiparesis

Abstract

Objectives: Although healthy individuals have less force production capacity during bilateral muscle contractions compared to unilateral efforts, emerging evidence suggests that certain aspects of paretic upper limb task performance after stroke may be enhanced by moving bilaterally instead of unilaterally. We investigated whether the bilateral movement condition affects grip force differently on the paretic side of people with post-stroke hemiparesis, compared to their non-paretic side and both sides of healthy young adults.

Methods: Within a single session, we compared: (1) maximal grip force during unilateral vs. bilateral contractions on each side, and (2) force contributed by each side during a 30% submaximal bilateral contraction.

Results: Healthy controls produced less grip force in the bilateral condition, regardless of side (-2.4% difference), and similar findings were observed on the non-paretic side of people with hemiparesis (-4.5% difference). On the paretic side, however, maximal grip force was increased by the bilateral condition in most participants (+11.3% difference, on average). During submaximal bilateral contractions in each group, the two sides each contributed the same percentage of unilateral maximal force.

Conclusions: The bilateral condition facilitates paretic limb grip force at maximal, but not submaximal levels.

Significance: In some people with post-stroke hemiparesis, the paretic limb may benefit from bilateral training with high force requirements.

Figure 1

Maximal grip force (kg) in the unilateral and bilateral conditions in one control participant (A) and one person with hemiparesis (B). Each graph represents a 5-second trial. Arrows and numerical values indicate peak force (kg). On the non-paretic side of the person with hemiparesis, and on each side of the healthy young adult, grip force was diminished in the bilateral condition compared to the unilateral condition. The paretic side, however, produced greater peak grip force in the bilateral condition than it did in the unilateral condition.

Figure 2

Maximal grip force (kg) in unilateral and bilateral conditions (mean ± 1 SE, data was normally distributed as shown by Kolmogorov-Smirnov tests, p > 0.20). In the control group (●; data pooled for dominant and non-dominant hands), peak grip force was 2.4% less in the bilateral condition than it was in the unilateral condition. For the group of participants with hemiparesis, the effect of condition differed between the two sides. The non-paretic side (■) showed 4.5% less peak grip force in the bilateral condition compared to the unilateral condition. On the paretic side (□), grip force was 11.3% greater in the bilateral condition.

Figure 3

Differences between unilateral and bilateral maximal force on the non-paretic (■) and paretic (□) sides in participants with hemiparesis. Negative values indicate a bilateral deficit (less force produced in the bilateral condition vs. unilateral), while positive values indicate bilateral facilitation (greater force produced in the bilateral condition vs. unilateral). Nine of the 16 participants with hemiparesis showed bilateral facilitation on the paretic side. The percent difference in force across conditions was not related to the severity of paretic limb grip force impairment. For each side, Spearman rho < 0.50 and p > 0.05.

Figure 4

Submaximal grip force in the bilateral condition in one control (A) and one person with hemiparesis (B). The last 3 seconds of data, marked with a gray block, represent the interval during which grip force of the two hands combined was maintained within the target range. Numbers indicate the amount of force each side contributed during that interval, expressed as a percentage of that side's maximal unilateral grip force. Group data (C), show no significant difference between sides in either group (p > 0.05). The lack of a significant difference between sides in the participants with hemiparesis suggests that the bilateral condition did not enhance submaximal grip force production on the paretic side.