Exercise Prescription in Multiple Sclerosis

Herbert I. Karpatkin

Introduction

Multiple sclerosis (MS) is a disease of mobility. Although the underlying pathology of demyelination, inflammation, and axonal loss is the target of medical and pharmacologic interventions, the reason that persons with MS (pwMS) often seek medical attention is because they notice a decreased ability to perform mobility tasks such as gait and balance. Although medical management has shown effectiveness in decreasing the underlying pathology of MS, exercise as a means of addressing mobility loss is underutilized. This is somewhat puzzling, as decreased strength and flexibility can be remediated with the proper exercise regime. The limited usage of exercise as a means of treating MS mobility loss suggests that many pwMS are not receiving optimal treatment. Physicians who treat pwMS could potentially achieve better outcomes for their patients if they include as part of their intervention referral to a physical therapist with expertise in MS.

Exercise for Fitness Versus Exercise for Function

To understand the manner in which exercise programs can be effective in pwMS, it is necessary to divide exercise into two basic purposes: exercise for fitness and exercise for function. Although both are types of exercise,
and both can provide benefit, each has a distinct purpose and outcome. Clinicians who utilize exercise programs for pwMS or provide referrals for them must be aware of this difference.

Exercise for Fitness

Exercise for fitness refers to exercise that is intended to result in a generalized response to the body. It has been defined as “any bodily activity that enhances or maintains physical fitness and overall health and wellness.”¹ It is what is commonly thought of as an exercise program. The goals of such a program tend to be more generalized as well, that is, exercise for weight loss, general conditioning, and aerobic fitness. Although exercises such as these are clearly beneficial for all persons, it is important to understand their limitations in MS. Specifically, improving overall fitness may not remediate specific impairments that are re-experienced by pwMS. For example, an impairment such as a foot drop, which can lead to gait and balance difficulties, would be unlikely to be remediated by a biking or swimming program. Although the biking and swimming program may be helpful for achieving general fitness, they would do little, if anything, to remediate the foot drop.

Exercise for Function

In contrast with exercise for fitness, exercise for function is highly specific. It has been defined by O’Sullivan as “interventions designed to incorporate task and context specific practice in areas meaningful to each patient, with an overall goal of functional independence.”² The overarching idea behind this type of exercise is that each exercise is specifically prescribed to achieve a specific functional goal. In this manner, prescribing exercise for function is similar to how a physician prescribes medication; each exercise is intended to address a specific issue affecting the mobility of the patient with MS. Each exercise is prescribed for a specific indication, with a specific dosage. Exercise for function is prescribed following a physical therapy evaluation that has identified specific impairments and functional limitations that restricts the patient’s mobility. The exercises that are prescribed are done so with the specific intention of remediating or ameliorating the diagnosed deficits in movement. The success of the exercises is determined by improvements seen on reevaluation.

The difference between these two types of exercises is important. Like medication, exercise can have both specific and general effects. Like medication, the incorrect exercise for a specific condition can be ineffective and potentially dangerous. Clinicians who provide exercise programs for pwMS or who refer to physical therapists who do should be aware of
the distinction. The following are theoretical examples of (1) an exercise prescription for general fitness and (2) an exercise prescription for specific function.

1. Exercise prescription for general function

1-Stationary bike, 15 minutes a day

2-Sit-ups, 20 repetitions, every day

3-Leg raises, 10 on each leg, every day

Analysis: Even without knowing anything about the patient for whom this exercise program was prescribed, it is obvious that the program is unlikely to address specific deficits. Although stationary bike may have a cardiopulmonary and weight loss effect, it is unlikely to address a walking deficit, which is common in MS. The sit-ups and leg raises would strengthen abdominal and lower extremity muscles, but it is unclear as to how this may relate to specific tasks and activities of daily living that are limited to a patient with MS. Although leg and abdominal weakness may certainly occur in pwMS, these exercises do not appear to be related to a functional activity

1. Exercise prescription for specific function

1-Slow sit to stand exercises, 5 every day

2-Calf stretch on the right calf only, 30 s

3-Toe raises in standing on the right, 5 repetitions, perform right after each calf stretch

Analysis: Again, even without knowing anything about the patient for whom this is prescribed, much can be inferred from the exercises themselves. Sit to stand is an exercise that not only is extremely limited in multiple diagnostic entities³,⁴ but has also been shown to be an excellent means of testing and strengthening lower extremity strength and function.⁵

The Impact of Fatigue on Exercise in Persons With MS

Fatigue is one of the most common findings in MS.⁶ Although it is common in most neurologic conditions,⁷ its prevalence is the highest in MS. Fatigue in MS is multifactorial with both subjective and objective components, central and peripheral components, and primary and secondary components. Each of these components has a unique pathophysiologic substrate and as a result requires different tools for evaluation and intervention.⁸

One of the most important effects of fatigue on pwMS is that it may limit the ability of the patients to exercise at a high-enough volume to achieve optimal benefit. Physical activity is generally lower in pwMS⁹; therefore, asking them to engage in an exercise program when they are already more sedentary than persons without MS is problematic.
For exercise to be of the greatest effect, it needs to be delivered at an appropriate dosage. A certain amount of practice of a task or a certain number of repetitions of an action is needed for exercise training to achieve its goals. However, because of fatigue, many pwMS are unable to achieve this volume. This presents a distinct problem for exercise prescription for patients with MS; exercise is needed to remediate the impairments and functional limitations seen in MS; however, because of one of the primary signs and symptoms of MS, patients are unable to exercise effectively.

Part of the issue with MS fatigue and exercise is due to thermosensitivity. The decreased ability of demyelinated nerves to transmit impulses when temperature is increased is a well-observed phenomenon in MS. During sustained exercise, core temperature increases occur, which decrease conduction through demyelinated nerves, a phenomenon known as activity-dependent conduction block (ADCB).¹⁰ The effect of this is that the very act of exercising in MS decreases the ability to exercise in MS.

Two specific interventions have been utilized to address the limitations in exercise due to fatigue in pwMS. These are intermittent training and cooling.

Intermittent training, also known as interval training and fractionated training, refers to interspersing periods of exercise with periods of rest. Most exercise programs for persons with disabilities are continuous in nature, with patients often urged to push themselves harder when they encounter fatigue. Although this technique may be effective in nondisabled populations, it may be contraindicated in pwMS because of presence of fatigue. Studies showing that pwMS experience less subjective¹¹ and objective¹² fatigue when walking intermittently as opposed to continuously have been conducted. A pilot study by Karpatkin et al suggested that intermittent walking results in greater improvements in gait endurance than continuous walking.¹³ Improved performance with intermittent as opposed to continuous training in pwMS during a straight leg raise training task suggests that intermittent training can be used for resistance training as well as for walking.¹⁴

Multiple modalities for cooling have been suggested, including cooling garments,¹⁵ cold-water immersion,¹⁶ and reflex cooling,¹⁷ with none showing any clear advantage over the other. Multiple studies have supported the effectiveness of cooling in improving physical performance in pwMS. White et al¹³ reported improvements in 25-foot walk test performance following cooling via whole body immersion. Schwid et al¹⁸ found improvements in motor performance and vision following a high-dose cooling regime. Neither of these authors noted sustained improvements in motor function following cooling, and the question of whether a greater volume of exercise resulting in better rehabilitation outcomes would occur with cooling has not been addressed.

Loss of Function due to Inactivity

Although it is presumed that mobility impairments in MS are due predominantly to the primary aspects of the disease (e.g., demyelination of motor tracts, spasticity, sensory loss, diminished motor control), consideration must be paid to the possibility that a great deal of the impairments seen is due to secondary aspects of the disease such as inactivity. Owing to the multiple physical and cognitive impairments that are experienced by pwMS, they are generally less active than those without the disease.⁹,¹⁹ Therefore, much of the mobility loss may not be due to the primary aspects of the disease such as demyelination and inflammation but due to secondary aspects of the disease such as disuse atrophy and learned helplessness. More simply, pwMS may have impaired mobility not just because of the damage to their central nervous system (CNS) but also because they move less. Tasks that are practiced less become more difficult to accomplish. This may in fact underlie a great deal of the weakness and fatigue seen in pwMS.²⁰ This may in fact be positive news for patients with MS, as it suggests that the mobility impairment that they are experiencing is not entirely due to central nervous system damage but at least in part to learned adaptations. Because mobility limitations due to inactivity would be more remediable than those due to CNS damage, improvement in mobility might be more achievable than otherwise thought.

Although there is no known way of determining by evaluation whether mobility loss is due to primary or secondary causes, it is probably the case that mobility loss due to secondary causes would remediate more quickly than those due to primary, as improvements in the former would be due to reconditioning, whereas improvements in function due to remediation of primary impairments would be due to neuroplastic processes.

Dosage/Intensity

The idea that pwMS could benefit from exercise is a relatively recent one. Until recently, it was thought that pwMS should limit exercise, as it could lead to an exacerbation.²¹ A landmark article by Petejean²² et al showed this to not only not be the case but that pwMS responded to exercise in a manner similar to persons without MS, that is, they improved in response to the exercise. However, the question of not only what exercises to perform but also what the dosage and intensity of the exercises should be still remains.

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