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.

Rhythm perturbations in acoustically paced treadmill walking after stroke.

BACKGROUND: In rehabilitation, acoustic rhythms are often used to improve gait after stroke. Acoustic cueing may enhance gait coordination by creating a stable coupling between heel strikes and metronome beats and provide a means to train the adaptability of gait coordination to environmental changes, as required in everyday life ambulation. OBJECTIVE: To examine the stability and adaptability of auditory-motor synchronization in acoustically paced treadmill walking in stroke patients. METHODS: Eleven stroke patients and 10 healthy controls walked on a treadmill at preferred speed and cadence under no metronome, single-metronome (pacing only paretic or nonparetic steps), and double-metronome (pacing both footfalls) conditions. The stability of auditory-motor synchronization was quantified by the variability of the phase relation between footfalls and beats. In a separate session, the acoustic rhythms were perturbed and adaptations to restore auditory-motor synchronization were quantified. RESULTS: For both groups, auditory-motor synchronization was more stable for double-metronome than single-metronome conditions, with stroke patients exhibiting an overall weaker coupling of footfalls to metronome beats than controls. The recovery characteristics following rhythm perturbations corroborated the stability findings and further revealed that stroke patients had difficulty in accelerating their steps and instead preferred a slower-step response to restore synchronization. CONCLUSIONS: In gait rehabilitation practice, the use of acoustic rhythms may be more effective when both footfalls are paced. In addition, rhythm perturbations during acoustically paced treadmill walking may not only be employed to evaluate the stability of auditory-motor synchronization but also have promising implications for evaluation and training of gait adaptations in neurorehabilitation practice.

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.

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.