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Strategies for Exercise Prescription in Post-Polio Patients

Anne Carrington Gawne, M.D.

Reprinted from POST-POLIO SYNDROME
edited by Halstead & Grimby, © 1995
Hanley & Belfus, Inc., Philadelphia, PA.
Chapter 9, pp 141-164

Lincolnshire Post-Polio Library copy by kind permission of Dr. Gawne.

Appropriate exercises have been shown to improve muscular strength and endurance, improve range of motion, and reduce functional deficits associated with many disabilities. In dealings with the patient with a history of polio, however, several questions arise: How much exercise is enough, and when is it too much? What kinds of exercise are best? What kinds of exercise may he harmful? And are there any guidelines to prescribe a safe and effective exercise program? To answer these questions, it is helpful to first understand the basic principles of exercise physiology, as well as the pathophysiology involved in post-polio syndrome. Following a discussion of these issues is a review of the literature on the effects of exercise in neurologically intact and post-polio individuals. Finally, a new classification system is presented, which will facilitate the prescription of exercise regimens that are both safe and effective in this population.

MUSCLE EXERCISE PHYSIOLOGY

The effects of exercise are seen at two levels. The first is the cellular level, or in the muscle fiber. The second is throughout the cardiovascular and respiratory systems to meet the physiologic demands of the muscle fibers. The two are discussed separately, looking first at muscle strength and then at cardiovascular endurance.

Muscular strength is the maximal force that can be exerted by a muscle.[21] An isometric contraction is one in which tension develops but in which the muscle stays the same length.[48] An isotonic contraction, or, more appropriately, a dynamic contraction, is one in which the muscle shortens (concentric) or lengthens (eccentric) against a constant resistance, with the muscle tension varying somewhat throughout the range of motion.[24,48] An isokinetic contraction is one in which the tension, developed by the muscle as it shortens, is maximal at all joint angles over the full range of motion and in which the velocity remains constant.[56]

When the three types of contractions are compared, the isokinetic one theoretically leads to the greatest improvements in both strength and endurance because it activates a larger number of motor units.[56] However, because it requires special equipment and trained personnel to administer, it is much less readily available. Significant strength gains occur with both eccentric and concentric contractions, and exercise equipment to perform these contractions is easy to find and affordable.[23] The advantages of isometric exercises are limited as the development of strength and endurance is specific to the joint angle at which the muscle is trained. Isometric exercises do have a place with individuals who have joints immobilized secondary to surgery or casting.

The overload principle states that muscles increase in size and strength when forced to contract at tensions close to their maximum.[46] Physiologic changes accompanying increased strength include hypertrophy -- the increase in cross-sectional area of the muscle fibers. Hypertrophy is attributable to one or more of the following changes: increased number of myofibrils per muscle fiber; increased protein, especially in the myosin filament; increased capillary density per fiber; increased amounts and strength of connective tissue; and increased number of fibers from longitudinal fiber splitting.[48] These morphologic changes are seen more frequently with eccentric contractions.

Additional factors responsible for strength gains are central nervous system (CNS) adaptations. These include an increase in the number of motor units activated, an increase in the rate of activation, and increased synchronization of motor unit firing.[56] Such changes occur at the spinal cord level and are responsible for cross-education, a phenomenon seen commonly in a limb contralateral to the trained limb. In general, younger individuals (18 - 26 years old) increase their muscle strength due to hypertrophy, whereas strength gains by older individuals (67 - 72 years old) are predominantly due to CNS adaptations.[49,50]

Atrophy, or the reduction in size of a muscle, occurs with denervation or when an extremity is placed at rest. Morphological changes seen after a muscle has been immobilized include atrophy of type I muscle fibers, whereas atrophy associated with aging is predominantly limited to a decrease in type II fiber area.[56]

PATHOPHYSIOLOGY IN POST-POLIO MUSCLES

In patients with a history of polio, additional changes occur and there is frequently the development of new weakness and atrophy in muscles both affected and apparently unaffected by the virus.[14,18,19,38-40,47] This phenomenon was clinically observed as early as 1917, when Lovett described progressive upper extremity weakness in men with a history of polio who performed farmwork on a daily basis.[47] In the 1950s, Bennett and Knowlton described a similar overuse weakness.[10] More recently, this new weakness has been termed "post-polio muscular atrophy" (PPMA) or "post-polio syndrome" (PPS).[19,40] The etiology of these changes remains uncertain; however, many feel that it is due to overuse.[6,13,15,16,44,53,55,61] At the time of the initial infection there is loss of anterior horn cell nerve terminals with reinnervation by the sprouting of the remaining motor neurons. As a result there is an increase in motor unit territory, and greater requirements are placed on the remaining fibers, stressing the metabolic demands. If the remaining fibers are unable to meet these demands, a slow deterioration may develop, with resulting new weakness and atrophy. In addition to an overuse phenomenon, new weakness may develop due to disuse.[6,35]

Common morphological changes have also been described in muscles with a history of polio. Dalakas et al. evaluated a population of 27 post-polio patients and documented new weakness over an 8-year period.[19] Biopsy findings at follow-up included changes in cell morphology, fiber type grouping, small angulated fibers, and hypertrophy of muscles that were less affected. Grimby et al. demonstrated that morphologic changes seen in patients with post-polio weakness include an increase in fiber area with hypertrophy and an increase in percentage of type I fibers in the weakest or more overused muscles.[27,34,35] Borg et al. also documented an increased percentage in type I fibers. In addition, internal nuclei and fiber splitting were prominent findings.[13]

As a result, a controversy arises about the role of exercise in the individual with a history of polio. Though many of the morphologic findings are actually similar to changes seen in normal muscle, the lack of sufficient reserve places the polio-weakened muscle at risk for further weakness should overuse occur. Following is a review of the literature on exercise in neurologically intact and polio-affected individuals to gain a better understanding of these concepts.

EFFECTS OF STRENGTH-TRAINING PROGRAMS IN NEUROLOGICALLY INTACT INDIVIDUALS

One of the first formal isotonic strengthening programs was described in 1948 by Delorme and Watkins.[23] They introduced the term "progressive resistance exercise" (PRE) and the concept of the ten repetition maximum (10 RM) -- the maximum load a muscle group can lift ten times. For each muscle group to be trained, the exercise program consisted of a total of 30 repetitions, divided into three sets of ten as follows:

set 1 = 10 repetitions at 50% 10 RM
set 2 = 10 repetitions at 75% 10 RM
set 3 = 10 repetitions at 100% 10 RM

Delorme and Watkins recommended the training frequency to be 4 consecutive days per week and were able to show demonstrable gains using this program. Isometric programs have also demonstrated that strength can be gained or maintained with a few maximal contractions held for 5-10 seconds three to five times per week.[41]

EFFECTS OF STRENGTH-TRAINING PROGRAMS IN POST-POLIO INDIVIDUALS

Many studies that have looked at the effect of strengthening exercises from a few weeks to a few years after the acute episode of polio demonstrated that these exercises are responsible for many of the gains in strength seen after the initial episode. In 1948, Delorme and colleagues applied the principle of PREs to 19 post-polio patients.[22] The patients had a history of polio from 1 to 49 years previously. They exercised once daily, 4 days a week, with 10 RM recalculated weekly. Twenty-seven muscle groups were evaluated, and of these, 17 demonstrated gross gains in strength (an increase in the muscle grade) measured with manual muscle testing (MMT). Muscle power in 15 of 27 quadriceps muscles doubled or more than doubled as measured by a spring scale. All except three muscles showed an increase in work capacity. It was noted that the largest improvements were seen in those muscle groups that had begun with greater than antigravity (fair plus) strength. Functional improvements included the ability to perform ordinary activities with less effort and fatigue. Delorme et al. stressed the importance of not putting too much emphasis on MMT alone; therefore, they used the spring scale to quantify strength more accurately. Evidence for functional improvement, however, was largely anecdotal.

Gurewitsch evaluated 13 patients who were in the initial phases of recovery from their polio in 1950.[36] They exercised all but the very weak muscles, with a modification of the protocol of Delorme et al., six to eight times daily, until they reached a state of fatigue. Strength was monitored by MMT. When they reached the point where they could do 20-30 repetitions easily, the exercise load was increased. Both muscle strength and endurance increased 50%. However, care was taken not to increase the workload too rapidly. Gureswitsch recognized that severely affected, atrophic muscles were not appropriate for strengthening. He did not quantify strength or fatigue objectively, which leads to concern, given such a strenuous protocol.

When PPMA was first widely recognized in the early 1980s, additional exercise studies were designed. The investigations included survivors many years after their initial episode of polio and in general demonstrated similar results.

In 1984, Feldman and Soskolne developed an exercise protocol they described as "nonfatiguing strengthening exercises" for a population of six patients with post-polio symptoms.[28,29] They initially evaluated 32 sets of muscles by electromyography (EMG) and assessed strength with a myometer. They described EMG features of absence of insertional activity, normal-appearing motor unit action potentials (MUAPs) with polyphasic potentials, and a decreased interference pattern. The protocol began using 50% of the maximum weight that could be lifted five times (5 RM). The patient began with five repetitions, then gradually increased to 30 repetitions. At this point, the weight was increased to 75% of the original 5 RM. Again the patient started with five repetitions, increasing to 30. The gradual progression was increased until the patient started with five repetitions, increasing to 30. The gradual progression was increased until the patient reached the point where further progression caused fatigue. This was performed three times weekly for a period of 3-6 months. The investigators found that by using this routine for at least 24 weeks, 14 muscles (46%) got stronger, as measured by myometry, 17 (53%) showed no change, and one muscle got weaker. There was no relationship between the degree of initial weakness and improvement in strength. Problems with this study include lack of a clear definition of post-polio syndrome and the description of the EMG changes (normal MUAPs is not a common finding). In addition, the authors did not define the mode in which the repetitions were performed (e.g., continuous versus sets), and there were no controls.

Einarsson and Grimby developed an exercise program in 1987 for 12 post-polio patients, nine of whom had symptoms of PPS.[26] These patients were all walkers with at least 3/5 strength in their quadriceps muscle. Muscle strength was evaluated on a Cybex dynamometer, and muscle biopsies were done before and after training. The training protocol used a warm-up period followed by three sets of eight alternating isokinetic and isometric exercises for a total of 6 weeks. The program was completed without discomfort or evidence of ill effects. Only one leg was trained; the other served as a control. There was a significant strength gain in the trained leg that persisted even past the end of the training period. Follow-up biopsy showed increased fiber area in five of seven patients; however, changes in muscle strength did not correlate significantly with changes in muscle fiber size. This study was notable for performing biopsies to confirm histologically the presence of old polio and for using objective quantitative measurements. The authors did not specify, however, which of the muscles (those with or without new weakness) showed improvement. Use of the contralateral leg as a control is problematic, since many times they are not equally affected. The investigators concluded that increases in strength might be explained through both muscular and neural adaptations.

In 1991, Einarsson described a similar protocol used for muscle conditioning in 30 post-polio patients.[25] These patients had at least 3/5 strength in their quadriceps and a history of polio at least 25 years previously. Muscle strength measurements of knee flexion and extension both isometrically and isokinetically were done initially and at 6 and 12 months. Muscle biopsies confirmed the presence of polio. The program consisted of a warm-up period followed by 12 sets of eight isokinetic knee extension contractions at 180°/s alternating with 12 sets of 4-second isometric contractions. This was performed three times a week for 6 weeks. The knee flexors were not exercised and therefore acted as a control. There was a significant improvement (24%) in knee extension strength, with no change in the strength of the knee flexors. These changes were also associated with subjective positive changes in functional tasks and general well-being. Although functional changes were noted, they were not quantified, and the location of new weakness was not specified.

In that same year, Fillyaw used Delorme's training program on 17 patients who had EMG evidence of polio, muscle strength of fair or above, and evidence of PPS.[30] The quadriceps or biceps was exercised, with the contralateral extremity used as a control. Three sets of ten repetitions with a 5-minute rest between sets were performed every other day. The 10 RM was recalculated every 2 weeks. The patients were instructed to stop if they experienced pain or fatigue. Maximum isotonic torque was measured initially, then every 3 months for 2 years. Sixteen of 17 patients demonstrated significant strength gains, but there was no evidence of increased endurance. The researchers cautioned that the patients undergo periodic quantitative muscle testing under the supervision of a physical therapist to avoid overwork weakness. This study and its method are notable, for they use quantitative measures of both strength and endurance as guidelines, and they test muscles with EMG to verify the presence of old polio.

More recently, Agre and colleagues used a 12-week isotonic strengthening program in subjects with at least fair plus quadriceps strength.[6] The subjects exercised with sandbag weights attached to their ankles, performing six to ten knee extensions holding the weight for 5 seconds, then resting for 25 seconds. This was increased until the patient could perform ten repetitions with a perceived exertion of "very hard" according to Borg's rating of perceived exertion (RPE). In 12 weeks, the average weight that each subject could lift more than doubled. There were neither EMG changes nor an increase in creatine phosphokinase over this time. This study used readily available equipment and quantitative measures of exertion, and it documents that a carefully supervised exercise program can safely increase strength in this population.[1]

Agre and Rodriquez have also described an exercise technique known as "pacing", mixing periods of exercise with periods of rest, in post-polio patients[2-5] (see also Chapter 4). The presence of polio was confirmed by EMG testing, and all measurements were done with objective quantitative measurements. In summary, Agre and Rodriquez evaluated symptomatic polio subjects (those complaining of progressive loss of strength) and tested them on three separate days, at least a week apart.[5] Parameters collected included maximum strength, endurance, work capacity, and time for recovery on an exhausting exercise done with the quadriceps. The authors also measured isometric quadriceps strength during a 3-second maximal volitional contraction (MVC). On the first day, the subject performed a quadriceps contraction at 40% MVC until exhaustion, waited 30 seconds, and then performed a 5-second MVC trial. On the second day, the subject exercised in quartiles with a 2-minute rest between trials. Finally, on the third day, the subject contracted the quadriceps muscle at 40% of MVC for 20 seconds and had a 2-minute rest break, for a total of 18 sessions. The investigators discovered that when the subject paced himself (day 3), there was less evidence of muscle fatigue, increased capacity to perform work, and increased ability to recover strength after activity. The total amount of work done was greatest (237%) on day 3. This study utilized the concept of the RPE as a way to avoid overfatigue. The principle of pacing has been applied only to isometric contraction of one muscle group in individuals known to have at least 3/5 strength and has not been well studied in an exercise program involving the whole body. Nonetheless, the authors successfully specified and compared the results of training programs for muscles that are both getting weaker and remaining stable.

Regarding the long-term safety of an exercise program, most studies are limited at the present time, because they were initiated only within the past few years. Because less objective measures of muscle strength were used in the past, previous studies are less valuable, and manual muscle testing has been shown to be unreliable in comparison to more quantitative measurements, especially in the good to normal range.[3,9,22,43] Dalakas demonstrated a loss of strength in polio patients over a 3-year period using MMT.[18] But Agre and Rodriguez evaluated a group of patients after 1 year and 3 years, using objective quantifiable measurements of muscle strength (peak isometric and isokinetic force) and found no significant strength losses on follow-up[5] (see also chapter 4). Munsat followed 44 patients from 400 to 2,100 days using a quantitative isometric measurement -- the Tufts quantitative neuromuscular exam -- and demonstrated no significant deterioration in muscle force.[52]

More evidence supporting findings of long-term strength gains in affected muscle was demonstrated in a study done by Munin et al.[51] They studied seven patients with quadriceps strength less than 5/5, recent weakness and generalized fatigue on one side, and a contralateral muscle of normal strength without new weakness. They tested patients' strength using an isokinetic/isometric protocol. They consistently saw no decline in strength on either side over a 3-year period. In fact, the strength actually increased. However, all their patients had at least 3/5 strength in the affected quadriceps, and none were older than 60. Unfortunately, neither EMG nor biopsies were performed either to confirm or rule out the presence of anterior horn cell disease in either extremity.

It is the consensus of most authors that quantifiable measures of strength, endurance, and degree of involvement with polio are needed to follow more accurately the long-term effects of an exercise program. A laboratory test (either an EMG or biopsy) also should be performed to either confirm or rule out the presence of polio. In addition, it is imperative to state whether the muscles that are being exercised have symptoms of new weakness.

EFFECTS OF CARDIOVASCULAR TRAINING PROGRAMS IN NEUROLOGICALLY INTACT INDIVIDUALS

Muscular endurance is defined as the ability of a muscle group to perform repeated contractions against a light load for an extended period of time. Cardiovascular endurance describes the ability to perform a sustained activity for an extended period of time and depends on efficient respiratory and cardiovascular systems. Normal changes seen with exercise include an increase in the maximal O2 consumption (VO2 max) accomplished through a combination of factors. There is an increase in stroke volume (SV) with greater cardiac contractibility and efficiency as well as an increase in blood volume and percentage of hemoglobin. Within the lungs there is an increase in vital capacity (VC) and inspiratory capacity. Subsequently, with training, the heart rate per work load decreases so the individual can perform work with less stress. Secondary effects of exercise include increased coronary blood flow due to increased collateral circulation and a decrease in the resting heart rate and blood pressure.[24,56]

A commonly used measure of energy use is the MET, or metabolic equivalent. One MET is equal to the basal energy requirement while sitting and awake (3.5 mL/kg · min). As energy expenditure increases, the MET increases in a linear fashion.[56] Table 1 lists the approximate METs in both activities of daily living (ADLs) and exercise activities.

TABLE 1. Table of Metabolic Equivalents (METS)
1.5-2 METS Doing seated ADLs (eating, facial hygiene, resting)
Doing seated recreation (sewing, playing cards, painting)
Doing seated occupational activities (writing, typing, clerical work)
2-3 METS Standing ADLs (dressing, showering, shaving, light housework)
Standing occupation (mechanic, bartender, auto repair)
Standing recreation (fishing, billiards, shuffleboard)
Walking 2.5 mph
Bike riding 5-6 mph
4-5 METS Doing heavy housework (scrubbing floor, hanging wash)
Canoeing, golfing, playing softball, playing tennis, badminton (doubles)
Social dancing, cross-country hiking
Swimming 20 yd/min
Walking 4 mph (level), (3 mph on 5% grade)
Bike riding 10 mph
6-7 METS Heavy gardening (digging dirt, lawn mowing, hoeing)
Skating, water-skiing Playing tennis, badminton (singles)
Stair-climbing (<27 ft/min)
Swimming 25 yd/min
Walking 5 mph (level) (3.5 mph on 5% grade)
8-9 METS Active occupation (sawing wood, digging ditches, shoveling snow)
Active recreation (downhill skiing, ice hockey, paddleball)
Bike riding 12-14 mph
Stair-climbing (27 ft/min)
Swimming 35 yd/min
Walking 9 mph (level) (3 mph on 15% grade)
Jogging 5-6 mph
Data compiled from numerous sources.[8,56]

Another important tool used in exercise prescription is the RPE developed by Borg.[11,12] This is a scale on which perceived exertion is quantified on a numerical scale, with 6 being very very light and 20 being very, very hard. The American College of Sports Medicine (ACSM) has modified this scale using a 1-10 system (Table 2).[8]

The ACSM has also established minimal guidelines including frequency, intensity, and duration of exercise needed in order to obtain a training effect. Recommended frequency is three or four times per week, duration is 20-30 minutes, and intensity is 70-80% of the person's VO2 max.[9] In addition, the ACSM recommends the following components for any exercise program: warm-up, stretching, exercise, cool down.

TABLE 2. American College of Sports Medicine Rating of Perceived Exertion
Grade Perceived Exertion
0 Nothing
0.5 Very, very weak
1 Very weak
2 Weak
3 Moderate
4 Somewhat strong
5 Strong
6
7 Very strong
8
9
10 Very, very strong
  Maximal
From American College of Sports Medicine: Guidelines for Exercise Testing and Prescription.
Philadelphia, Lea & Febiger, 1986, with permission. (Modified from Borg.[11,12])

EFFECTS OF CARDIOVASCULAR TRAINING PROGRAMS IN POST-POLIO INDIVIDUALS

In 1987, Alba et al. evaluated the work capacity of 35 patients -- 20 females and 15 males -- 33 of whom were complaining of new symptoms, in order to determine their cardiovascular status.[7] The patients performed a graded exercise test using an arm ergometer, a chair ergometer, and a treadmill according to their ambulatory ability. Parameters evaluated included muscle strength using MMT, body weight, maximum METS, maximum heart rate (HRmax), VO2 max, and VC. Alba et al. divided the patients into three subgroups: ambulatory without restriction to moderate restriction, ambulatory with moderately severe to severe restriction, and wheelchair bound. Significant findings included greater weakness in the lower extremities than the upper extremities and a decreased VC, especially in those who smoked or had a history of respiratory involvement. There were also a decreased HRmax, decreased maximal cardiac output, and decreased work capacity (similar to a group of hospitalized patients). Of the three groups, the nonambulatory population was affected most significantly. The researchers recommended that patients partake in any repetitive activity that appealed to them -- if it was considered "safe" -- and recommended stopping the activity if it caused "undue pain, muscle fatigue or a sense of weakness" that required more than the usual time to recover. Though that study is good because it introduces the idea of different ways to assess cardiovascular fitness depending on ambulatory status, the investigators did not specify the degree of involvement of the exercising muscles being exercised. Neither did they compare differences in modalities in a single individual, thus raising the question of the reliability of comparisons of different kinds of exercise.

In 1985, Owens and Jones evaluated the cardiovascular endurance of 21 patients in an electrocardiogram-monitored, symptom-limited, graded exercise test, using either a bicycle or a hand ergometer.[54] They found that the patients had an average maximum fitness level of 5.6 METS, indicative of severe deconditioning. They proposed an exercise program as follows: intensity of 65-80% of reserve heart rate, a duration of 15-30 minutes, and a frequency of three to five times per week on alternate days. The modality used depended on preserved function. Flexibility and warm-up exercises were recommended before each session. However, the authors did not report the results of this proposed exercise regimen in their documentation.

Dean and Ross examined the effects of a modified exercise program in three post-polio patients in 1988.[20] Each subject met the diagnostic criteria for PPS and was ambulatory without assistive devices. One patient was used as an untrained control while the other two walked on a treadmill three times a week at a submaximal rate for a total of 8 weeks, advancing their walking duration from 22 to 31 minutes. RPE was monitored using a 1-10 scale, and pain was monitored using a 1-4 scale. An attempt was made to keep RPE below 2 and pain below 1 (light). After training, on sub-maximal testing, both of the trained subjects demonstrated reductions in VO2, heart rate, blood pressure, RPE, and energy cost at similar work loads when compared to the pretest; the untrained subject showed no change. There was no apparent effect of training on pulmonary function. The mechanism for the change was felt to be both cardiovascular conditioning and muscle adaptation. Although the number of subjects is small, this study has the virtue of clearly quantifying symptoms of pain and perceived exertion.

The following year, Jones and colleagues evaluated cardiorespiratory responses to aerobic training in 16 post-polio patients who participated in a 16-week exercise program.[42] These patients met the following criteria: They had a documented history of polio with subsequent improvement, then a period of stability with new complaints of weakness. They had adequate strength to participate in bicycle ergometry (at least 3/5 in their quadriceps and iliopsoas and 2/5 in their hamstrings and gluteals). Baseline tests, including resting heart rate and blood pressure, HRmax, BPmax, VO2, and VCO2 and expiratory volume (Ve), were performed on a bicycle ergometer. Patients were divided into an exercise group and a control group. The first group exercised three times a week, once under the supervision of the therapist, for a period of 15-30 minutes using a predetermined target heart rate as a guide. Within this population were two subgroups, determined by their maximum METS. Those with a maximum less than 6 METS exercised for 2-3 minutes, with a 1-minute rest; those with a maximum greater than 6 METS exercised for 4-5 minutes, with a 1-minute rest. Significant results on posttest included an improvement in the total exercise time, total work per time, VO2, and Vemax within the exercise group. Though a few subjects dropped out for reasons unrelated to the study, none developed any overuse syndromes or other injury due to their exercise. Problems with this study include that the extent of the initial polio was not documented, and it was not specified whether or not the subjects were using polio-affected muscles to perform their exercise.

In a similar study in 1989, Kriz and colleagues examined the effects of an upper extremity arm ergometry program on 29 subjects with a history of polio who met the following criteria: history of polio with subsequent improvement and stabilization, aged 39-60 years old, and adequate arm strength and torso balance to operate an arm ergometer.[45] The subjects had no cardiovascular medical problems or other, neurological problems and were not already participating in a fitness program. They were divided into an exercise group and a control group. The exercise group participated three times a week in a 16-week training program with 1 day of rest between exercise sessions. The group performed the exercises on an arm ergometer with a heart rate of 70-75% heart rate reserve. The investigators evaluated the following variables: resting heart rate, HRmax, and resting and immediate postexercise blood pressure, as well as exercise time, power, respiratory exchange ratio, respiratory rate, maximum VO2, VCO2, and Ve. After the 16-week program, the group that exercised showed significant improvement in VO2 max, VCO2max, Vemax, power, and exercise time. None of the patients in the exercise group developed problems with pain or overuse. Again, the report did not document the degree of polio involvement in the exercising extremities. In addition, the authors selected subjects younger than 60 years old and without severe weakness.

SUMMARY

Although it has been reported that individuals with a history of polio may develop new weakness many years after the original episode, it has also been shown that these people can gain both muscle strength and cardiovascular endurance from a well-planned training program. For the strengthening of individual muscle groups, the following criteria appear to be necessary: a history of polio with improvement and stabilization and sufficient strength (3/5) to contract that muscle against gravity. There appear to be positive benefits regardless of whether that muscle group is with or without new weakness. The choice of type of exercise program needs to be developed according to both the needs of the individual and the resources available: An isometric program is of benefit for those who have either a joint immobilized in a cast due to surgery or a fracture, whereas an isotonic program is more appropriate for a home exercise program. An isokinetic program appears to be of great benefit whenever the equipment is available, or when a special need arises, such as for strengthening before or after surgery.

The long-term safety of a strenuous strengthening program on muscle that has been severely affected is not known, but the positive effects of exercise on other systems, including cardiovascular and respiratory systems, are clear. It therefore can be concluded that a carefully monitored program is beneficial in selected individuals with a history of polio. It is also possible that many of the secondary symptoms such as generalized fatigue can be reduced as patients become more conditioned and are able to perform similar amounts of work with less expenditure of energy. An ideal cardiovascular program should both exercise the muscles least affected by polio, in order to get maximum cardiovascular benefits, and avoid overuse or secondary degenerative effects on the more affected extremities. For instance, if the legs are the more involved limbs, then the arms can be used in a more strenuous program; or the legs can be exercised if not seriously involved. The exercise program should be initially supervised by a therapist in order to teach proper techniques, including the monitoring of heart rate and RPE. All individuals who are older or with risk factors for cardiovascular disease such as hypertension, smoking, hypercholesterolemia, or a history of coronary artery disease should first undergo a graded exercise test with cardiac monitoring in order to establish the safety of participating in an exercise program. The type of activity should be one that the participant can enjoy so as to reduce lack of interest and subsequent dropout.

A NEW POST-POLIO MUSCLE CLASSIFICATION FOR EXERCISE PRESCRIPTION

In order to prescribe the safest and most appropriate exercise program for the post-polio patients in our clinic, we have developed a limb-specific muscle classification system, the National Rehabilitation Hospital (NRH) Post-Polio Classification.[32] The purpose of the classification is to create a more standardized set of criteria to document the severity of involvement of the polio. This facilitates communication between the therapists and the physician regarding the specificity of the exercise program, sets standards by which to compare the results of clinical trials, and aids in giving recommendations regarding activity, prognosis, and need for assistive equipment. To classify the muscle, a combination of history, physical exam, and EMG is used. When patients are first evaluated, a complete history and physical are performed by the physician, and the patient is referred for a four-extremity EMG.[37] In addition to an evaluation for specific clinical conditions, a screening examination is performed. It includes nerve conduction studies of bilateral median and sensory nerves and at least three muscles in each extremity.[33] Additional benefits of the EMG to the clinician include the ability to rule out other neurological lesions that may require treatment or need to be considered with prescribing an exercise program.[31,33,37]

Following the EMG, each muscle is classified separately and the limb is classified according to the most severely involved muscle. If contralateral extremities exhibited differences and an exercise program uses both, then the exercise program is prescribed on the basis of the most severely affected extremity. Table 3 summarizes this classification system. Table 4 demonstrates the demographic data on 60 consecutive post-polio patients evaluated in our clinic utilizing these methods. Table 5 shows results of the classification of 240 limbs in those 60 patients using the criteria to follow. The distributions of the findings in both the upper and lower extremities are detailed in Figures 1 and 2. Figure 3 is an algorithm that can be used to aid in this classification process.

TABLE 3. The National Rehabilitation Hospital (NRH) Post-Polio Muscle Classification
Class I No clinical polio
Class II Subclinical polio
Class III Clinically stable polio
Class IV Clinically unstable polio
Class V Severely atrophic polio
Data from Gawne and Halstead.[32]

TABLE 4. Demographic Data on 60 Consecutive Post-Polio Outpatients[33]
Sex (M/F) 22/38
Mean age (range), yrs 53 (22-82)
Mean years post-polio 44 (14-80)
Data from Gawne and Halstead.[32]

TABLE 5. NRH Limb Classification of 60 Consecutive Post-Polio Outpatients[32]
NRH
Class
Upper
Extremity
Upper
Extremity
Total
I 63 6 69
II 20 22 42
III 24 40 64
IV 10 27 37
V 3 25 28
TOTAL 120 120 240
Total of 240 limbs measured. Data from Gawne and Halstead.[32]

FIGURE 1. Distribution of upper extremity limbs by NRH class in 60 consecutive post-polio outpatients.[32]
Figure 1 Histogram

FIGURE 2. Distribution of lower extremity limbs by NRH class in 60 consecutive post-polio outpatients.[32]
Figure 2 Histogram

Figure 3 Diagram
FIGURE 3. NRH post-polio muscle classification. (AHCD - anterior horn cell disease; MUAP - motor unit action potentials.)

NRH Class I muscles (no clinical polio) have no history of past or new weakness. Strength ranges from good to normal, and there is no atrophy or sensory or reflex changes. On EMG there is normal insertional activity, with no evidence of muscle membrane instability such as fibrillation potentials or positive sharp waves. Motor unit action potentials (MUAPs) are normal in size and configuration, with normal recruitment.

The objective of the exercise program for Class I muscles or limbs is to increase muscle strength and cardiovascular endurance. Exercise recommendations consist of an initial set of muscle-stretching exercises to increase flexibility, a light warm-up period using the muscles that will be exercised, an exercise program, and, finally, a cool-down period. A strengthening program includes PREs as described by DeLorme,[23] with 1- to 2-minute rest breaks between sets initially. These muscles should be used selectively in order that an aerobic program be able to improve cardiovascular conditioning. When there is no cardiac or respiratory illness, a conditioning program can follow ACSM recommendations for frequency and duration.[8] The ideal frequency of exercise for these extremities should be three or four times a week, for a period of 15-30 minutes at a heart rate of 60-80% of HRmax.[8] Table 1 describes some typical occupational and recreational activities in the 6-9 MET range, which would be appropriate for Class I limbs.

NRH Class II muscles (subclinical polio) have no history of past or new weakness, or, if affected, there was full recovery. Strength is good to normal. Sensation and reflexes are normal. EMG is consistent with anterior horn cell disease. Insertional activity is normal, and there are rarely fibrillations or positive sharp waves. MUAPs are large, with increased polyphasics and decreased recruitment. These muscles probably represent those "unaffected" muscles, previously described by other authors, that eventually get weaker.[14,17,19,57,59,60]

The objectives of the exercise program for Class II extremities are to increase strength in those muscles in the good range and to maintain normal strength in the remainder. If other extremities are more severely affected, Class II extremities can be used to improve cardiovascular endurance. The frequency should be 3 or 4 days a week, for 10-20 minutes. The session should be paced, increasing the frequency of rest breaks until the individual can perform the exercise without significant fatigue either during or after the activity. The frequency of exercise should also be paced, alternating exercise and rest days. As a training effect develops and the individual is able to perform a similar workload with less fatigue, both the amount of resistance used and the frequency and duration of the exercise can be altered to meet the changing increases in strength. But given the threat of PPMA, muscle strength should be monitored to detect overuse weakness early and then decrease the amount of exercise. Maximum activities should be in the 4-7 MET range.

NRH Class III muscles (clinically stable polio) have a remote history of weakness, with some improvement and no complaints of new weakness. On physical examination, the strength ranges from fair to good. Sensation is normal, and reflexes are normal or decreased proportional to the muscle strength and bulk. Atrophy may be present, EMG is consistent with anterior horn cell disease, with normal insertional activity. Sometimes there are fibrillation potentials or positive sharp waves, but generally these are small and sparse. MUAPs are usually larger than those of Class II muscles, with increased polyphasics and decreased recruitment. These muscles represent those previously described as asymptomatic[3]; however, they are now frequently referred to as clinically stable, as suggested by Grimby.

The goals for class III extremities are to at least maintain strength and, if possible, to gain strength in those muscles that are deconditioned. Exercise recommendations include active range of motion (AROM) or passive range of motion (PROM), depending on the strength of the muscle. Strengthening exercises are similar to those in Class II, with further modifications made for pacing and for the exercising of muscles with less than antigravity strength. A typical set of PREs as Feldman has described or an isokinetic program as Einarrson described would also be appropriate. Strength should be carefully monitored and the program modified if weakness develops. Because of weakness and susceptibility to stresses with weight bearing in extremities with degenerative joint disease, non-weight-bearing exercises such as a pool program are preferred. An aerobic program should be paced at a submaximal heart rate. Activities in the 2-5 MET range would be appropriate.

NRH Class IV muscles (clinically unstable polio) are either those that are developing new weakness and atrophy (PPMA) or those previously described as symptomatic.[3] They are weaker, with less dynamic and isometric strength than those in Class III. Sensation is normal, atrophy usually is present, and reflexes are decreased. EMG findings are similar to Class III; however, MUAP amplitude and polyphasics may be increased.[3] Recruitment may be less,[57] and there may be more significant new denervation fibrillations, positive sharp waves.[32,53]

The main goal in this class is to prevent further weakness, so it is recommended first to decrease activity if overuse is suspected. If disuse is suspected or rest does not help, then an exercise program is begun. Exercise recommendations include PROM or AROM. A nonfatiguing exercise program would be appropriate for strengthening. Because many muscles may have less than antigravity strength, exercises should be done in a gravity-eliminated position or in a pool. Muscle strength is carefully monitored. This program should be done no more than three times a week and should be modified if symptoms of pain, new weakness, or fatigue develop. For cardiovascular conditioning, we generally recommend it be used in ADLs only (1-3 METS). As we have found that many of our patients have less affected upper extremities (Figs. 1 and 2), we frequently advise such patients to do a cardiovascular exercise using only their arms, such as swimming or arm ergometry. For those limbs with severe weakness, we recommend avoiding weight bearing by use of assistive devices or a wheelchair or motorized scooter. Bracing is needed for those lower extremities with less than antigravity strength.

NRH Class V muscles (severely atrophic polio) are those that are originally affected, with severe weakness and little improvement. New weakness may be present; however, the muscle is already so weak it is hard to tell if there is new weakness. On physical examination, they are extremely weak (trace to poor), with marked atrophy, no sensory changes, and areflexia. On EMG there are decreased insertional activity; few fibrillation or positive sharp waves; little to no MUAPs, with variable amplitude; increased polyphasics; and markedly decreased recruitment. This class is similar to Dalakas's group 1, with morphological features of fibrosis, necrosis, and other myopathic changes.[17] Such patients may be nonambulatory if they have significant involvement and little functional use of the lower extremities. PROM needs to be done to maintain range of motion. Patients are clearly unable to use these extremities for aerobic exercises or strengthening programs.[36]

The hypotheses on which this classification and its exercise recommendations are based are many. First of all, it is assumed that those with less affected muscles (Classes II and III) will demonstrate many of the physiological changes seen in normal muscle as described earlier. Second, as people get older, some of the motor learning adaptations that De Vries and Grimby discuss can also play a role in exercise training, thus counterbalancing the effects of motor unit dropout. Again, this is seen in the Class II and III muscles. However, when new weakness develops (Class IV) there is usually an indication of overuse, unless that extremity has been immobilized for a period of time, in which case a component of disuse is possible. Last, although difficult to prove, it is possible that many of the symptoms that individuals with post-polios develop -- in particular, fatigue -- are due to deconditioning, as many studies have shown that with conditioning, people are able to perform routine tasks with less fatigue. Though these recommendations have been used successfully in our clinic, and the literature in part supports this, we acknowledge that only through further prospective studies that use these criteria as well as quantitative measurements will the development of more specific guidelines be possible.

CONCLUSION

It has been demonstrated that people with a history of polio can improve muscular strength and endurance as well as cardiovascular conditioning by way of an exercise program. With this in mind and using the limb-specific classification system described earlier, an appropriately trained professional can develop a prescription for a rational exercise program so that post-polio individuals can more safely enjoy many of the additional positive benefits that regular exercise can bring.

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