Karin H. Gerrits

Intrinsic muscle strength and voluntary activation of both lower limbs and functional performance after stroke.

The objective of this study was to assess the nature of muscle weakness in both legs after stroke compared with able‐bodied control individuals and to examine whether there is a relationship between the degree of muscle weakness and coactivation of knee extensors and flexors as well as voluntary activation capacity of knee extensors of both paretic and non‐paretic legs and indices of functional performance. Maximal voluntary isometric torques of knee extensors (MVCe) and flexors (MVCf) were determined in 14 patients (bilaterally) and 12 able‐bodied controls. Simultaneous measurements were made of torque and surface EMG from agonist and antagonist muscles. Coactivation was calculated. Supramaximal triplets were evoked with electrical stimulation to estimate maximal torque capacity and degree of voluntary activation of knee extensors. MVCs, activation and coactivation parameters were correlated to scores of seven functional performance tests. MVCe, MVCf and voluntary activation were lower in paretic lower limb (PL) compared with both non‐paretic lower limb (NL) and control. Besides, all these parameters of NL were also lower than control. Electrically evoked torque capacity of knee extensors of PL was about 60% of both NL and control, which were not significantly different from each other. Strong significant correlations between strength, as well as voluntary activation, and functional performance were found. Coactivation did not correlate well with functional performance. Thus, whereas for NL activation failure can explain weakness, for PL both activation failure and reduced intrinsic torque capacity are responsible for the severe weakness. Activation capacity and muscle strength correlated strongly to functional performance, while coactivation did not.

Adaptive response of human tendon to paralysis

To gain insight into the adaptive response of human tendon to paralysis, we compared the mechanical properties of the in vivo patellar tendon in six men who were spinal cord–injured (SCI) and eight age‐matched, able‐bodied men. Measurements were taken by combining dynamometry, electrical stimulation, and ultrasonography. Tendon stiffness and Youngs modulus, calculated from force–elongation and stress–strain curves, respectively, were lower by 77% (P < 0.01) and 59% (P < 0.05) in the SCI than able‐bodied subjects. The cross‐sectional area (CSA) of the tendon was 17% smaller (P < 0.05) in the SCI subjects, but there was no difference in tendon length between the two groups. Our results indicate that paralysis causes substantial deterioration of the structural and material properties of tendon. This needs to be taken into consideration in the design of electrical stimulation protocols for rehabilitation and experimental purposes, and when interpreting changes in the contractile speed of paralyzed muscle. Muscle Nerve, 2005

Effects of electric stimulation-assisted cycling training in people with chronic stroke.

OBJECTIVE To evaluate whether leg cycling training in subjects with chronic stroke can improve cycling performance, aerobic capacity, muscle strength, and functional performance and to determine if electric stimulation (ES) to the contralateral (paretic) leg during cycling has additional effects over cycling without ES. DESIGN A randomized controlled trial, with a partial double-blind design. SETTING A rehabilitation center. PARTICIPANTS Twelve stroke patients (range, 18-70 y), more than 5 months poststroke, with lower-extremity hemiparesis. INTERVENTION Subjects were randomly assigned to groups that performed cycling exercise, one with ES evoking muscle contractions and a control group with ES not evoking muscle contractions. Subjects, blinded for group assignment, trained twice a week for 6 weeks. MAIN OUTCOME MEASURES Changes in aerobic capacity and maximal power output, functional performance, and lower-limb muscle strength. RESULTS Aerobic capacity and maximal power output significantly increased by 13.8%+/-19.1% and 38.1%+/-19.8%, but muscle strength was not significantly enhanced after training. Functional performance improved (ie, scores on the Berg Balance Scale increased by 6.9%+/-5.8% (P=.000) and the six-minute walk test improved by 14.5%+/-14.1% (P=.035). There was no significant effect on the Rivermead Mobility Index (P=.165). Training-induced changes were not significantly different between the 2 groups. Changes in cycling performance and aerobic capacity were not significantly related to changes in functional performance. CONCLUSIONS This study showed that a short cycling training program on a semirecumbent cycle ergometer can markedly improve cycling performance, aerobic capacity, and functional performance of people with chronic stroke. The use of ES had no additional effects in this specific group of subjects with chronic stroke.

Isometric muscle function of knee extensors and the relation with functional performance in patients with stroke

OBJECTIVE (1) To examine the isometric strength, speed, and fatigue resistance of the knee extensors of the paretic limb and nonparetic limb in patients with stroke and compare these with able-bodied subjects. (2) To relate the contractile properties with different indices of functional performance. DESIGN Case-control study. SETTING Rehabilitation center research laboratory. PARTICIPANTS Eighteen stroke patients and 10 able-bodied controls. INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES Maximal voluntary torque (MVT), maximal rate of torque development, time to maximal rate of torque development, half relaxation time ((1/2)RT), and fatigue index. Scores on the Functional Ambulation Category scale, Berg Balance Scale, and Rivermead Mobility Index as well as distance walked during the six-minute walk test were obtained. RESULTS MVT of the paretic leg was lower than of the nonparetic leg (P<.05), and both limbs had lower MVT than controls (P<.05). Both the paretic and the nonparetic leg showed longer (1/2)RT compared with controls (P<.05). The fatigue index was reduced in the paretic leg (P<.05) but not in the nonparetic leg compared with controls. MVT and fatigue index of the paretic leg were related to indices of functional performance (r=0.49-0.64; P<.05). CONCLUSIONS Apart from bilateral weakness, knee extensors in patients with stroke showed a lower rate of torque development and relaxation (both paretic and nonparetic leg) and lower fatigue resistance (paretic leg only) than controls, which in part may be a consequence of changes within the muscles. Strength and fatigue resistance relate to functional performance, indicating that these muscle properties should be addressed during rehabilitation. However, future research is needed to elucidate the efficacy of exercise programs.

Knee extensor fatigability after bedrest for 8 weeks with and without countermeasure

We analyzed the effects of gravitational unloading on muscular fatigability and the effectiveness of resistive vibration exercise to counteract these changes. Changes in knee extensor fatigability as a consequence of 8 weeks of horizontal bedrest with or without daily resistive vibration exercise were evaluated in 17 healthy male volunteers. Bedrest increased fatigability (% decrease in maximal voluntary isometric torque per minute exercise) from −7.2 ± 0.5 to −10.2 ± 1.0%/min (P < 0.05), which was accompanied by a decline (of 52.0 ± 3.7%, P < 0.05) in muscle blood flow. Daily resistive vibration exercise training during bedrest prevented increases in fatigability (from −10.8 ± 1.8 to −8.4 ± 1.6%/min, P < 0.05), and mitigated the reduction in blood flow (decline of 26.1 ± 5.1%, P < 0.05). Daily resistive exercise may thus be suggested as an effective countermeasure during spaceflight and illness‐related prolonged bedrest to combat the detrimental changes in muscle endurance that result from gravitational unloading. Muscle Nerve, 2007

Recovery of walking ability using a robotic device in subacute stroke patients: a randomized controlled study.

Abstract Purpose: This study investigates the effectiveness of Lokomat + conventional therapy in recovering walking ability in non-ambulatory subacute stroke subjects involved in inpatient rehabilitation. Method: Thirty first-ever stroke patients completed 8 weeks of intervention. One group (n = 16) received Lokomat therapy twice a week, combined with three times 30 min a week of conventional overground therapy. The second group (n = 14) received conventional assisted overground therapy only, during a similar amount of time (3.5 h a week). The intervention was part of the normal rehabilitation program. Primary outcome measure was walking speed. Secondary outcome measures assessed other walking- and mobility-related tests, lower-limb strength and quality of life measures. All outcome measures were assessed before and after the intervention and at wk 24 and wk 36 after start of the intervention. Results: Patients showed significant (p < 0.05) gains in walking speed, other walking- and mobility related tests, and strength of the paretic knee extensors relative to baseline at all assessments. However, there were no significant differences in improvements in any of the variables between groups at any time during the study. Conclusion: These results indicate that substituting Lokomat therapy for some of conventional therapy is as effective in recovering walking ability in non-ambulatory stroke patients as conventional therapy alone. Implications for Rehabilitation Recovery of walking after stroke is important. Robot-assisted therapy is currently receiving much attention in research and rehabilitation practice as devices such as the Lokomat seem to be promising assistive devices. Technical developments, sub-optimal study designs in literature and new therapy insights warrant new effectiveness studies. Results of a financially and practically feasible study indicate that substituting Lokomat therapy for some of conventional therapy is as effective in recovering walking ability in non-ambulatory stroke patients as compared to conventional overground therapy alone.

Intrinsic properties of the knee extensor muscles after subacute stroke.

UNLABELLED 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.

Influence of knee joint angle on muscle properties of paralyzed and nonparalyzed human knee extensors

Muscles of individuals with a spinal cord injury (SCI) exhibit an unexpected leftward shift in the force (torque)–frequency relationship. We investigated whether differences in torque–angle relationships between SCI and able‐bodied control muscles could explain this shift. Electrically stimulated knee‐extensor contractions were obtained at knee flexion angles of between 30° and 90°. Torque–frequency relationships were obtained at 30°, 90°, and optimum angle. Optimum angle was not different between groups but SCI‐normalized torques were lower at the extreme angles. At all angles, SCI muscles produced higher relative torques at low stimulation frequencies. Thus, there was no evidence of a consistent change in the length of paralyzed SCI muscles, and the anomalous leftward shift in the torque–frequency relationship was not the result of testing the muscle at a relatively long length. The results provide valuable information about muscle changes occurring in various neurological disorders. Muscle Nerve, 2005

Effects of stimulation pattern on electrical stimulation-induced leg cycling performance

Electrical stimulation-induced leg cycling (ES-LC) is beneficial for individuals with spinal cord injury (SCI), but cycling performance is often limited because of rapid fatigue of the stimulated muscles. This study evaluated whether a stimulation pattern with a catchlike-inducing pulse train increased force production and hence cycling performance. Five men with SCI performed ES-LC using different stimulation patterns: (1) the standard pattern with ramp modulation, (2) a pattern with no ramp modulation, (3) a pattern with no ramp modulation but with an initial doublet, and (4) a pattern with a middle doublet. None of the experimental patterns resulted in significantly improved cycling performance compared with the standard pattern. However, during the first 3 min of cycling, the current amplitude was significantly higher with the standard stimulation, suggesting that stimulation with no ramp modulation produces more force at the same submaximal current amplitude. The results do not indicate that stimulation with catchlike-inducing trains with the current parameter settings improves ES-LC performance.

Neuromuscular properties of the thigh muscles in patients with ehlers–danlos syndrome

Introduction: Ehlers–Danlos syndrome (EDS), a connective tissue disorder, may lead to impaired contractile function of lower limb muscles. Methods: To test this hypothesis and to understand the possible mechanisms involved, isometric function of the thigh muscles was investigated at different joint angles (30°, 60°, and 90° of knee flexion) in 7 tenascin‐X (TNX)‐deficient EDS patients. Results: There was reduced maximal voluntary torque of the knee extensors (but not knee flexors) across all joint angles in the patients. Time to reach maximal rate of torque development was delayed, and voluntary activation capacity was reduced in patients compared with controls, particularly at 30°. Conclusions: EDS is associated with muscle weakness, most likely due to increased compliance of the series‐elastic component of muscle tissue and failure of maximal voluntary muscle activation. Further research is required to understand the influence of reduced voluntary activation on the severe fatigue reported by EDS patients. Muscle Nerve, 2013