Intrinsic Properties of the Knee Extensor Muscles After Subacute Stroke

Abstract

Horstman AM, Gerrits KH, Beltman MJ, Koppe PA, Janssen, TW, de Haan A. Intrinsic properties of the knee extensor muscles after subacute stroke. Objective To characterize muscle properties of paretic lower-limb (PL) and nonparetic lower-limb (NL) knee extensors in patients with subacute stroke. Design Case-control study. Setting Rehabilitation center research laboratory. Participants Patients with subacute stroke (n=14) and able-bodied age-matched control subjects (n=12). Interventions Not applicable. Main Outcome Measures Half relaxation times (HRTs) and maximal rates of torque development (MRTDs) were assessed as indicators of contractile speed using both voluntary and electrically evoked contractions. Moreover, changes in torque were measured during a fatigue protocol (35 electrically evoked intermittent contractions; 1.5s on, 2s off) and recovery. Results No differences among groups were found for normalized MRTDs during electrically evoked contractions ( P=.117). However, during voluntary contractions both PLs (53% of control, P=.022) and NL (71% of control, P<.001) had significantly lower MRTD compared with control. Both PL (134% of control, P=.001) and NL (123% of control, P=.032) had significantly higher HRTs than control, indicating muscle slowing in patients with subacute stroke. PLs fatigued more and faster than control ( P=.011) and both PL and NL recovered slower ( P<.001). Conclusions The changes in HRTs and fatigue suggest adaptations in muscle properties toward slower, more fatigable muscle shortly after stroke. The inability to make use of contractile speed because of impaired neural activation seems the most limiting factor during the initial phase of torque development in PL. Thus, besides strengthening, muscle endurance and speed should also be addressed during rehabilitation.