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Sense of Effort Determines Lower Limb Force Production During Dynamic Movement in Individuals With Poststroke Hemiparesis

Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan, asimon{at}umich.edu

Brian M. Kelly, DO

Department of Physical Medicine and Rehabilitation, University of Michigan, Ann Arbor, Michigan

Daniel P. Ferris, PhD

Department of Movement Science, University of Michigan, Ann Arbor, Michigan, Department of Physical Medicine and Rehabilitation, University of Michigan, Ann Arbor, Michigan, Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan

Objective. This study’s purpose was to determine if individuals who have had a stroke primarily use sense of effort to gauge force production during static and dynamic lower limb contractions. If relying on sense of effort while attempting to generate equal limb forces, participants should produce equal percentages of their maximum voluntary strength rather than equal absolute forces in their limbs. Methods. Ten stroke participants performed isometric and isotonic lower limb extensions on an exercise machine. Results. When participants attempted to produce equal bilateral isometric forces, there was a significant difference in absolute force between limbs (ANOVA, P < .0001) but no significant difference when force was normalized to each limb’s maximum voluntary contraction (MVC) force (P = .5129). During bilateral isotonic contractions, participants produced less absolute force in their paretic limb (P = .0005) and less relative force in their paretic limb (normalized to MVC force) when participants were given no instructions on how to perform the extension (P = .0002). When participants were instructed to produce equal forces, there was no significant difference between relative forces in the 2 limbs (P = .2111). Conclusions. For both isometric and isotonic conditions hemiparetic participants relied primarily on sense of effort, rather than proprioceptive feedback, for gauging lower limb force production. This outcome indicates that sense of effort is the major factor determining force production during movements. Lower limb rehabilitation therapies should not only train strength in the paretic limb but should also train patients to recalibrate force-scaling abilities to improve function.

Key Words: Muscle • Sense of effort • Stroke

This version was published on October 1, 2009

Neurorehabilitation and Neural Repair, Vol. 23, No. 8, 811-818 (2009)
DOI: 10.1177/1545968308331163


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