Most studies have shown that persons with MS will not respond to an acute bout of exercise in the same way as the average, age- and gender-matched, non-disabled, adult without MS. Furthermore, variability in the type and magnitude of symptoms seen with this disease often results in a wide range of responses to acute exercise. In spite of the variability, one common effect of acute exercise in individuals with MS is an overwhelming sense of fatigue during the recovery period following exercise.
To understand basic physiologic responses to an acute bout of exercise, it is helpful to use the two directions commonly taken in the literature as it relates to: 1) muscle performance (i.e., strength and endurance) and 2) cardiovascular responses (i.e., heart rate, blood pressure, oxygen utilization).
Muscle Performance: There is evidence to show that in the absence of documented spasticity or use of anti-spasmodic drugs, muscle endurance for persons with MS during a sustained isometric contraction at 30% of maximal voluntary contraction (MVC) is similar to that of a non disabled, healthy adult. While these findings appear to be in direct conflict with many earlier studies of acute muscle response, it is important to consider that in none of the earlier studies was the presence of spasticity and/or the use of anti-spasmodic drugs controlled in the design. Some research has shown that in the presence of an upper motor neuron lesion, antagonist muscles are also activated during concentric contraction of an agonist. This supports the hypothesis that spasticity is one of the factors that can reduce agonist force production in persons with MS . In contrast, antagonists are not stretched during the eccentric contraction, while the agonist receives additional stretch to facilitate its contraction. Research has shown that spasticity can contribute to a significantly lower force production during concentric knee extension; but force production during eccentric knee extension for these same individuals can be normal. Therefore, it is believed that the common MS symptom of spasticity may be one factor that can contribute to reduced concentric muscle performance in this population. There is ample evidence from other patient populations with spasticity that these individuals would have difficulty producing force, as well as experience trouble in controlling forces that modulate movement speed and direction.
However, to believe that spasticity is the sole contributor to differences in isometric muscle endurance observed between MS and non-MS persons would be naïve. Other contributors to observed differences have been attributed to: conduction block of demyelinated fibers, reduced muscle metabolic responses to voluntary exercise in persons with MS, muscle weakness related to fiber atrophy of exercising muscles, and sensory deficits.
Maximal muscle force during sustained dynamic exercise has also been shown to be consistently lower for persons with MS. Commonly, this has been observed during tests of maximal aerobic power using leg cycling or combination leg/arm cycling protocols. During maximal upright and recumbent leg cycling, patients with MS were able to exercise at loads that were 20-68% less than matched controls. Performance during arm cranking and combined arm/leg cycling shows similar findings: 31% lower during arm cranking and 24% lower during combined arm/leg cycling. Once again, the source of this reduced muscle strength during dynamic exercise is thought to be related to reduced muscle metabolic responses, muscle weakness secondary to muscle fiber atrophy, and muscle weakness secondary to spasticity, sensory loss, and behavioral disuse.
Acute Cardiorespiratory Responses: Physiological responses to an acute bout of submaximal aerobic exercise appear to be normal for many persons with MS. Heart rate (HR), blood pressure (BP), and oxygen uptake (VO2) have been shown to increase in a linear fashion to increases in workload. This is also true of ventilatory responses such as respiratory rate and minute ventilation. Furthermore, these responses are consistent over a wide range of impairment levels. However, there is some evidence that HR response, while linear, may be blunted (i.e., less increase per absolute workload increment) in some persons with MS . This may not be true of all persons with MS. Use of the standard practice of calculating 220 - age (HRmax) and subsequently establishing a target HR range between 60 - 70% of HRmax is a safe method for this population.
Maximal aerobic power (VO2max) has been shown to vary greatly based on the degree of physical impairment and neurological symptoms present. When compared to that of healthy adults, even minimally-impaired MS clients will perform more poorly (i.e., lower VO2max), regardless of whether the test is performed using leg, arm, or combined arm/leg exercise. Comparison of VO2max (ml/kg/min) of 20 minimally- to moderately-impaired sedentary persons with MS against normative fitness standards showed that 75% fell into the "low fitness" range, while 15% and 10% were "fair" and "average", respectively. In these same studies, HRmax at test termination has often not been at a level that would be termed "maximum" (i.e., 220 - age). The inability to reach a predicted HRmax before test termination is believed to be related to a need to terminate the exercise test due to local muscle fatigue rather than cardiovascular limitations. When queried using the Category Ratio Rating of Perceived Exertion Scale (1-10 scale), subjects consistently rated "peripheral" stress higher than "central" (i.e., cardiovascular). Both higher during submaximal and maximal levels of exercise.
Aerobic exercise endurance (i.e., time to fatigue) will also vary greatly among clients with MS. Furthermore, endurance time does not appear to be directly related to the level of physical impairment. At a moderate level of exercise (i.e., 50% VO2max) patients have been able to exercise for as little as 15 minutes to as long as 60 minutes. Again, the correlational analysis found no relationship between endurance time and the level of physical impairment.
Chronic Exercise Response: There is very little research regarding the effects of training on muscle performance in persons with MS. However, from the available research, we can conclude that MS patients have the capacity to improve muscle strength following a supervised program of aerobic exercise training. Several researchers have reported an average improvement of 17% in upper extremity isometric strength (sum of 4 different muscle groups), and an 11% improvement in lower extremity isometric strength (sum of 5 different muscle groups) in persons with MS. Improvement in muscle performance during leg cycling following 24 weeks of supervised aerobic exercise training has been reported to be as high as 29%. Certainly, these findings are very encouraging, but more research is needed to completely understand the benefits of training on muscle performance in this population.
A supervised program of aerobic exercise for as little as 15 weeks can improve aerobic fitness level (i.e., VO2max) in some persons with MS. Improvement in aerobic fitness has been reported to be as little as 22% and as great as 48%. Less dramatic changes are often seen in more severely impaired persons (+7%). This raises an important issue regarding the development of realistic expectations based upon the baseline impairment level of the individual. Subtle neurological changes may not be observable to the clinician. However, small unnoticeable changes may affect exercise training outcomes. It is important to carefully monitor neurological changes by periodically interviewing the client regarding subjective impressions of their disease status. Consideration must also be given to the fact that training outcomes observed under strict supervision may not be similar outside of the supervised, controlled program environment, as would be the case of a home exercise program.
Exercise/Fitness/Functional Testing: General principles of fitness testing as outlined by the American College of Sports Medicine can be appropriately applied to many persons in this population. However, when evaluating fitness in the person with MS, it is important to consider special needs related to the specific symptoms experienced by the client.
Flexibility: Because many MS patients experience lower extremity spasticity, flexibility may be restricted in the hip, knee and ankle joints. Hip flexor, hamstring, and gastroc-soleus tightness is particularly problematic and should be evaluated in the sitting position (e.g., Sit-and-Reach Test). Use of this particular test will serve to eliminate any problem with balance during testing. Lateral trunk flexibility should also be evaluated from a sitting position or, if standing, the clinician may place his/her hands on the client's waist to prevent loss of balance.
Balance: To truly appreciate how balance deficits might affect the MS client's ability to perform exercise safely, balance should be evaluated under both static and dynamic conditions. A fairly short and easy battery of tests can be found using the Berg Balance Scale. This test is valid for neurological conditions such as MS and takes approximately 15 minutes to administer. The results of this test will provide a better understanding of the client's ability to exercise safely using standard equipment.
Aerobic Fitness: As previously noted, many persons with MS experience problems with balance. In addition, foot drop associated with dorsiflexor weakness can be present prior to exercise or it may be easily initiated shortly after the onset of weight-bearing exercise. Therefore, for safety purposes, aerobic fitness is best evaluated using a bicycle ergometer. Even so, this mode of exercise testing can also present challenges. Ankle clonus (i.e., spasmodic alternation of contraction and relaxation of muscles), and sensory abnormalities (e.g., numbness, tingling, and deficits in joint proprioception) can make it difficult for the client to keep their feet on the pedals. The use of standard toe clips and Velcro-secured heel straps can reduce or eliminate this problem.
The general procedures for submaximal testing of cardiorespiratory endurance using a cycle ergometer published by the American College of Sports Medicine can be applied to this population. However, workloads suggested in standard test such as the YMCA Cycle Ergometry Protocol or the Astrand-Rhyming test may need to be reduced. Modification of these protocols can be accomplished simply by beginning with a warm-up phase of no-load pedaling, followed by a fixed rate pedaling at 50 W for 6 minutes (84) or proceed with increments of 0.25 kp at 50 rpm until the appropriate HR response is achieved. Of these two protocols, the latter may be more appropriate with extremely sedentary MS clients (male and female), who may have maximal workload capacities less than 50 W.
Muscular Strength and Endurance: The general procedures for measuring muscle strength and endurance suggested by the American College of Sports Medicine can be applied to this population. Again, to proceed safely, any reduction in joint range of motion, sensory loss (upper and lower extremity), coordination deficits, ataxia and spasticity need to be considered prior to testing. Suggestions for activities and special considerations during testing, training and counseling are summarized in Table 2 and 3, respectively.