Predictive and Reactive Grip Force Responses to Rapid Load Increases in People With Multiple Sclerosis

Abstract

ObjectivesTo determine the effects of multiple sclerosis (MS) on predictive and reactive grip force control in a catching task and on clinical tests of hand function. DesignCase-control study with matched-pairs control group. SettingUniversity prevention and rehabilitation center. ParticipantsParticipants (N=30) consisted of people with multiple sclerosis (PwMS) (n=15) and healthy controls (n=15), matched for sex, age, and hand dominance. InterventionsNot applicable. Main Outcome MeasuresPerformance on the Expanded Disability Status Scale (EDSS), Nine-Hole Peg Test (9-HPT), Jebsen-Taylor Hand Function Test (JTHFT), and 2-point discrimination (2PD) was evaluated. To analyze grip force control, blindfolded subjects held a receptacle equipped with grip force and acceleration sensors in their hand. In a catching task, a weight was dropped from (1) the experimenter's hand unexpectedly into the receptacle (reactive force control); and (2) from the subject's opposite hand (predictive force control). Grip forces and time lags were analyzed. ResultsPwMS (mean EDSS ± SD, 4.2±1.86) had impairments in the 9-HPT and JTHFT (P<.001). The 2PD did not differ significantly between PwMS and controls. During reactive force control (catching task 1), PwMS showed significantly higher grip forces immediately after impact (P<.05), and a significant prolongation of the time from grip force increase until reaching the peak of grip force (P<.001). PwMS and controls did not differ during predictive force control (catching task 2; P>.1). ConclusionsExaggerated grip force responses and alterations of timing after an unpredictable perturbation, combined with preserved grip force control during predictable conditions, is a characteristic pattern of fine motor control deficits in MS. Measures of reactive grip force responses may be used to complement neurologic assessments. Further studies exploring the usefulness of these measures should be performed in a broader community of PwMS.