Isokinetic strength and fatigability in patients with multiple sclerosis. The relationship between gait speed and isokinetic parameters

Introduction

Multiple sclerosis (MS) is a chronic disease characterized by inflammation and demyelisation of the central nervous system. Decline of muscular performances, fatigue, weakness and spasticity are the most common and disabling symptoms characterizing this neurological disease.

Undoubtedly, objective assessments of muscle function would be relevant to deliver the most appropriate treatment and to appraise possible training effects resulting from rehabilitation.

The purposes of this study were to assess muscle strength and fatigue of knee flexors and extensors in patients with multiple sclerosis by means of an isokinetic dynamometer. Relations between isokinetic results and gait speed were also investigated.

Methods

Eight patients (49 +/- 7 years old) suffering from multiple sclerosis (with unaided gait) were included in this study. Bilateral knee flexor and extensor performances were assessed using a Cybex Norm dynamometer. Maximal isokinetic strength was measured at 60°/s (3 repetitions) and 180°/s (5 repetitions). Thereafter, patients performed a fatigue protocol consisting in 30 successive maximal-intensity knee flexions and extensions at 180°/s angular velocity. Fatigue was analysed using the cumulative work parameter (corresponding to the sum of work developed through the 30 movements) and a fatigue index (ratio between work developed during 3 last contractions and 3 first contractions). Gait speeds corresponded to the time necessary to subject for walking at maximal speed on a 7.62 m and 100 m long walkway.

Results

Isokinetic parameters (strength and fatigue) appeared to be decreased in MS patients comparatively to normative data [1]. Knee flexors/extensors ratio was reduced for some patients, yet MS subjects displayed no significant bilateral asymmetry, suggesting a bilateral weakness process.

Significant negative correlations (- 0.76 < r < - 0.95, p < 0.05) between gait speeds (measured through a 7.62 m and 100 m long walkway) and hamstring isokinetic parameters (peak torque and cumulative work) were observed. In contrast, we did not find any correlation between gait speed and quadriceps isokinetic performances, except for the correlation between gait speed on 100 m long walkway and fatigue index (0.78 < r < 0.89, p < 0.05).

Discussion and conclusion

Objective evaluation of muscle performance deficiencies in patients with MS appears essential for designing a successful rehabilitation program. However, no consensus has been established with regard to the most relevant isokinetic protocol modalities for assessing patients suffering form central nervous system lesions. Our preliminary results underlined that gait speed was negatively correlated to hamstring isokinetic parameters (strength and cumulative work). Interestingly, no patient included in our study reported increased symptoms such as spasticity during or after the test, indicating that MS patients are able to perform strength and fatigue isokinetic assessments.

References

[1] Maquet D, Croisier JL, Renard C, Crielaard JM. Muscle performance in patients with fibromyalgia, Joint Bone Spine 69 :293-9, 2002.