This section reviews a variety of research studies which have been conducted regarding physical activity and multiple sclerosis, and is divided into four categories: effects of physical activity on persons with multiple sclerosis, best exercises and measurement of exercise and strength capacities, fatigue response, and motivation to exercise.
Effects of Physical Activity on Persons with Multiple Sclerosis
Despite the improvements in physical fitness and quality of life that persons with multiple sclerosis attain from engaging in exercise programs, limitations such as cardiovascular dysautonomia and neurological problems can affect the degree of improvement. The following studies address to what extent the limitations and/or deconditioning affect progress in exercise training.
Some studies have uncovered the effects of cardiovascular dysautonomia. Pepin et al. (1996) studied 104 subjects with multiple sclerosis and 25 control subjects to investigate whether they would show an abnormal heart rate and/or blood pressure response to exercise through isometric handgrip exercises. During the exercise, heart rate, blood pressure, and RPE (rate of perceived exertion) were measured continuously. Results showed that in some cases, subjects with multiple sclerosis could not elicit an increase in arterial pressure response, most likely because of autonomic dysfunction. Control subjects' mean arterial pressure (diastolic pressure + 1/3 [systolic pressure - diastolic pressure]) was 47 mm Hg, and subjects with MS' mean arterial pressure was 28.2 mm Hg, though the increase in heart rate at the point of fatigue was normal in both groups.
Other studies have highlighted the benefits of physical activity despite limitations. Petajan et al. (1996) randomized 54 subjects with multiple sclerosis (EDSS scores of 6 or less) into exercise and nonexercise groups for 15 weeks of aerobic exercise, 3 sessions per weeks for a 40 minute duration. While disability status did not change for subjects with mild to moderate disability, fitness improvements included a Vo2max increase of 22%, a PWC (physical work capacity) increase of 48%, and significant decreases in skinfolds, triglyceride, and very low density lipoprotein. They concluded that these improvements were not directly correlated to degree of neurological deficiencies.
Similarly, Ng & Kent-Braun (1996) highlighted the physical activity potential of subjects with multiple sclerosis. They measured levels of physical activity in 17 subjects with multiple sclerosis (10 had the relapsing remitting and 8 had the chronic progressive clinical presentations) and 15 control subjects with an accelerometer (TriTrac-R3D) and a questionnaire (7-d RQ self reported recall questionnaire). Though the study did confirm that subjects with multiple sclerosis demonstrated lower degrees of physical activity compared to controls, subjects with multiple sclerosis also demonstrated the following peripheral changes in muscle: decreased oxidative capacity, increased fatigue, and impaired metabolic response to exercise. Such qualities are equivalent to those of healthy subjects after deconditioning and indicate that problems in muscle functioning caused by disuse may be reversed with muscle training.
When cardiovascular training has been used to improve function of specific muscle groups, the results have not been as positive. Rodgers et al. (1999) involved 18 subjects with multiple sclerosis (EDSS scores of 1-6.5) in a 6 month exercise program to examine improvement in gait abnormalities. Subjects utilized cycle ergometry (combined arm/leg cycling and upright or recumbent ergometers) 3 sessions per week for a 30 minute duration. Gait analysis and tests of maximal Vo2max were administered pre and post the exercise program. Though aerobic fitness improved, no clinically significant improvements in gait were achieved: mean velocity cadence significantly decreased (approximately .79 m/s to .72 m/s) and maximum hip extension and total hip flexion extension range decreased (176.0°(6.8) to 172.0°(6.5) goniometer measured). The investigators concluded by questioning what exercises/stretching could prevent such reductions and how gait and balance affect energy utilization.
Best Exercises and Measurement of Aerobic and/or Strength Capacities
Regarding best exercises, in 1992 Ponichtera et al. measured muscle torque at several speeds for both concentric and eccentric contraction on 9 subjects with multiple sclerosis and 9 healthy controls who generated isokinetic contractions of the quadriceps and hamstrings on an isokinetic dynamometer. They concluded that strengthening programs focusing on concentric exercises at 90 degrees per second may be the preferred strengthening exercise for subjects' quadriceps and hamstring muscles.
In 1993, the same team examined maximum aerobic capacity in 9 subjects with multiple sclerosis (EDSS 1-4) and 9 control subjects on recumbent leg ergometers on land and in water. They determined that some persons with multiple sclerosis (depending on level of impairment) could attain maximum aerobic capacity without side effects, whereas those with more physical impairments would need more adjustments, such as for leg cycling (Ponichtera et al., 1993).
In 1995, Ponichtera et al. studied the best means of exercise testing and practice for persons with multiple sclerosis. Vo2max was measured in a discontinuous, progressive intensity exercise test on 10 subjects with multiple sclerosis and 10 control subjects generating each of 3 modes of ergometry (leg, arm, and leg/arm) on 3 separate days. The investigators concluded that the combined leg/arm ergometry is preferred because (1) upper extremities need more training and training legs alone is insufficient, and (2) using leg and arm power disburses the exercise load over a larger muscle mass and there is less possibility for "localized" fatigue.
Regarding measurement of strength capacities, Pepin et al. (1998), conducted a study of 14 subjects with multiple sclerosis who performed isometric handgrip contractions at 30% maximal voluntary contractions (MVC) to the point of fatigue. The results showed that it is possible to get consistent reliable responses to this exercise, despite motor dysfunction. (The MVC reliability estimates were 0.98.) The authors, however, did question the replicability of their findings for subjects with higher EDSS levels.
Researchers studying fatigue during exercise have attempted to isolate and measure fatigue and weakness/strength components, and have questioned to what extent the fatigue is due to intrinsic physiological deficits or deconditioning.
Recently, Schwid et al. (1999) studied the quantitative assessment of motor fatigue and strength in 20 subjects with multiple sclerosis and 20 control subjects. Maximal voluntary isometric strength, motor fatigue, and static fatigue were tested and retested by different exercise and strength tests in 2 distinct sessions, in order to measure test-retest reliability. Results showed that though subjects with multiple sclerosis had more fatigue for sustained contractions, repetitive contractions, and ambulation, motor fatigue was different from weakness since the fatigue was not correlated with weakness from individual muscles. This suggests that strength and motor fatigue can be quantified reliably.
In 1994, Kent-Braun et al. studied a sample of 6 subjects with multiple sclerosis and 8 control subjects to investigate the role of metabolism in muscle fatigue during exercise. They measured the peak force generated from a maximal voluntary isometric contraction during 3 sessions and determined that for mildly impaired persons with multiple sclerosis, muscle fatigue during exercise is not related to metabolic, but to activation failures. It was observed that decreases in force during exercise were because of peripheral, not central mechanisms. In 1995 and 1996, the same team studied electrically-stimulated exercise training for subjects with multiple sclerosis and discovered that the fatigue during exercise is because of muscle intrinsic, not metabolic, properties (Kent-Braun et al., 1996)(Sharma et al., 1995).
Motivation to Exercise
Because of the chronic and relapsing characteristics of multiple sclerosis, adherence to an exercise program for participants with multiple sclerosis can be difficult. Stuifbergen & Roberts studied 629 subjects with multiple sclerosis on health promotion behaviors and quality of life according to disability status. Subjects responded to a range of instruments measuring these qualities. They found that subjects with benign sensory and relapsing remitting multiple sclerosis, more than those with progressive multiple sclerosis, were more likely to commit to physical activity and spiritual growth practices (1997). These findings underscore the importance of encouragement and support for participants with multiple sclerosis in a physical activity program, particularly those participants with a higher disability status.