Exercise in Motor Neuron Diseases By Wendy M. King, PT, Clinical Assistant Professor at Ohio State University

Exercise in Motor Neuron Diseases By Wendy M. King, PT The issue of exercise in motor neuron disease has been controversial. Some studies have stated that resistive exercise can damage muscles if a certain percentage of motor units are not functioning. At some point during the denervation process, too forceful an exercise workout may accelerate motor unit damage. And yet there are indications that resistive exercise can be safely performed in persons with SMA if the muscles being exercised are still relatively strong.

Unfortunately, the only way to establish what is happening to motor units directly is through invasive testing. Some small studies involving one or only a few patients have been conducted wherein the patient had constant monitoring of blood levels and motor unit testing (EMG). Because it is expensive and impractical to conduct large double-blind studies looking at these parameters, more knowledge on the subject is needed. Research looking at exercise in humans with neuromuscular disease usually suffered from a small sample size or included subjects with various types of muscular dystrophy and/or motor neuron disease. Studies with animals often involved the mdx mouse, a mouse that is deficient in dystrophin, as are boys with Duchenne muscular dystrophy. Still another reason for our paucity of science on the subject of exercise and motor neuron disease is that it is nearly impossible to accurately verify a person’s home exercise program. Ideally, a clinical trial studying the effects of exercise in SMA would involve participants attending a medical center three or four times a week and participating in a supervised exercise program. I would approach an exercise program cautiously after an extensive baseline strength exam. Keep in mind the challenge of not over-exercising a more proximal stabilizing muscle that may very well be weaker than a targeted distal muscle. I would emphasize energy conservation over core strengthening and endurance training. Our current (although very incomplete) knowledge is that it may be possible to maintain or improve muscle strength in someone with SMA- at least temporarily- by following a carefully supervised exercise program. However, the individual life style of each person must be taken into account before the initiation of an exercise program. Some individuals who have not been at all active before being diagnosed with SMA may be able to increase their exercise program without risking motor unit damage. Others who already have an extremely active life style may not need to do anything differently-or may actually be advised to reduce or eliminate part of their exercise program. Clients with a neuromuscular disease must learn to respect the force of gravity, and never underestimate it. Any person with significant muscle weakness must work much harder than most just to complete his/her activities of daily living. For example, accomplishing such tasks as washing one’s face, dressing or bathing, and performing house or yard work will require more work from weakened muscles because of the weight of the limbs in space. Taken over the course of a day, a week, and then indefinitely, this becomes a strenuous “exercise” program in itself. A physical therapy consultation would allow the patient to devise an appropriate, individualized exercise program. In addition, it is ideal to obtain baseline muscle strength measurements for later comparisons. General guidelines for patients with a neuromuscular disease to consider before initiating an exercise program are: 1. Only perform in a “safe exercise range” 5 that is, avoid overuse muscle damage or disuse muscle atrophy 2. Keep the exercise program short 3. Exercise the same muscles only every other day 4. Gently stretch muscles prior to exercising 5. Keep a daily log that shows the time of each exercise or activity, a description of the exercise/activity, and any symptoms following the exercise/activity 6. Note any signs of overuse such as an increase of muscle cramps, increased or unusual fatigue, or increased muscle twitching following exercise. If these should occur, reduce the exercise program and report the symptoms to the physical therapist. 7. Continue to report back to a physical therapist or another neuromuscular professional for reevaluations. Finally, a discussion about the role of exercise and SMA would not be complete without mentioning the psychological benefits of an exercise program. It is well documented that exercise can increase endorphin levels and promote a feeling of well-being. For an individual who has made exercise a regular part of his or her life style, it may be that the psychological detriments of decreasing or eliminating their physical program seems worse than the possible physical risks of maintaining it. This is a personal decision that each individual must make. It is the responsibility of the physical therapist, however, to make sure that the client understands the possible consequences of his/her decision. The most important rule to remember when discussing the role of exercise with a diagnosis of SMA is: teach your patient to listen to his own body. Depending on whether he/she works fulltime, part time, or not at all; depending on how physically strenuous his occupation may be; depending on what physical responsibilities he may have as a parent, spouse, etc.; all of these are relevant issues that impact on his need and ability to begin and maintain an exercise program. References: 1. Role of Physical Activity and Exercise Training in Neuromuscular Disease. Fowler WM, Frontera WR, ed., American Journal of Physical Medicine and Rehabilitation vol 81, no 11 suppl (2002 Nov): S1-S186. 2. Report on the Muscular Dystrophy Campaign Workshop: Exercise in neuromuscular diseases. Newcastle, January, 2002. Eagle, M, Neuromuscular Disorders 12 (2002) 975-983. 3. Characteristics of isometric and dynamic strength loss following eccentric exercise-induced muscle damage. Byrne C et al, Scandinavian Journal of Medicine and Science in Sports vol 11, no 3 (2001 Jun): 134-40. 4. Eccentric muscle damage: mechanisms of early reduction of force. 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