Review by Dr. Laurie Malone
Sandroff, B. M., Sosnoff, J. J., & Motl, R. W. (2013). Physical fitness, walking performance, and gait in multiple sclerosis. Journal of the Neurological Sciences, in press. http:// dx.doi.org/10.1016/j.jns.2013.02.021
Multiple sclerosis (MS) is a chronic disease that attacks the central nervous system, which is made up of the brain, spinal cord, and optic nerves (www.nationalmssociety.org). Symptoms vary from mild (numbness in the limbs) to severe (paralysis, loss of vision). Each person is affected differently so the progress, severity, and specific symptoms of MS are difficult to predict.
Walking impairment is commonly seen in persons with MS at both the early and advanced stages of the disease. Based on several studies that have examined a variety of walking outcomes, it has been shown that speed of walking, walking endurance, and overall gait kinematics are impaired in persons with MS.
Speculation that a relationship exists between physiological deconditioning and walking impairment, and the notion that modifying exercise behavior might positively affect this relationship, led to the recent study by Sandroff, Sosnoff and Motl (2013). Their study examined the associations among aerobic capacity, balance, lower limb strength asymmetries, walking performance, and gait kinematics in 31 persons with MS and 31 healthy matched controls (18-54 years of age; 27 females and 4 males each group). The authors hypothesized that 1) all three aspects of physical fitness would explain differences in walking and gait variables between persons with MS and controls and 2) that each aspect of physical fitness would independently explain variance in walking performance and gait variables in persons with MS.
To assess aerobic capacity, peak oxygen consumption was measured during an incremental exercise test. Balance measures were based on center of pressure motion during quiet standing on a force platform. Peak isometric muscle torques of the knee extensors and flexors on each side were measured using an isokinetic dynamometer. To determine side-to-side disparity in muscle strength, a muscle strength asymmetry score for both knee extensors and flexors was calculated.
Walking performance was evaluated by a series of tests: 1) time to walk 25 ft as quickly and safely as possible, 2) distance walked in 6 minutes when instructed to walk as fast and as far as possible, 3) a 12-item self-report measure of the impact of MS on walking. To measure gait kinematics, participants completed 4 trials of normal, comfortable paced walking on an electronic walkway, which recorded velocity (cm/s), cadence (steps/min), step length (cm), base of support (cm), and time spent in double support (percentage of gait cycle).
There were four key findings from the study. They indicated that:
1. When comparing individuals with MS to the matched control group, significant differences in both fitness and walking and gait variables existed.
2. Walking performance and gait parameters in individuals with MS were associated with aerobic capacity, balance, and lower limb strength asymmetries, while in the matched controls the parameters were affected by aerobic capacity and knee extensor asymmetry.
3. Aerobic capacity explained group difference in gait velocity and time spent in double support, while both aerobic capacity and knee extensor asymmetry explained difference in the 25-foot timed trial, six minute walking distance, and step length.
4. The main explanations for significant variation in walking performance and gait parameters in people with MS are aerobic capacity and lower limb strength asymmetries.
Overall, the results support the hypothesis that physiological deconditioning explains variability in walking impairment in persons with MS. As a whole, the results highlight the importance of including both aerobic and strength exercises in an exercise training intervention for persons with MS. Specifically, a targeted exercise program to improve aerobic fitness and reduce lower limb strength asymmetry might produce improvements in walking performance and gait problems in persons with MS.