Q: What is exercise? Why do it?
A: Exercise is muscle exertion (use), requiring the expenditure of energy. It can be very roughly divided into two major categories: aerobic and resistance (sometimes called “strengthening”). Aerobic exercise helps maintain overall fitness, especially cardiac and respiratory health. If muscles are intact and functioning, then resistance, or strengthening, exercise helps increase muscle mass and the force muscles can generate. However, some muscle diseases severely limit the ability of muscles to increase mass or force because they limit the regenerative capacity of muscle tissue. Additional benefits of exercise are maintenance of flexibility, preservation of bone density and mood elevation. Because exercise requires energy (calorie burning), it offsets the intake of dietary calories and may help keep weight in check.
Q: What does or doesn’t the medical literature tell us about exercise and neuromuscular disease?
A: Unfortunately, there isn’t a lot known about exercise in neuromuscular disease, but some studies have been conducted that shed some light on the subject.
“We know so little,” says Ted Abresch, director of research at the Research & Training Center for Neuromuscular Disease at the University of California at Davis. (The MDA Neuromuscular Disease Clinic at UC Davis is part of the MDA Clinical Research Network that supports studies in Duchenne muscular dystrophy.)
|Ted Abresch, who directs the Research & Training Center for Neuromuscular Disease at UC Davis, says studies of exercise in this area have been hard to interpret. Photo: Emi Manning, UC Davis|
Abresch says some forms of exercise are beneficial in neuromuscular disease, but unfortunately, it’s usually not prescribed unless patients specifically ask.
Studies of exercise, he says, have largely been “messy” and hard to interpret, because often there aren’t adequate control groups (groups assigned not to exercise), and because people with different diseases are often studied together. At his center, he says, “We’re looking at what people are actually doing, and we’re looking at wearable technologies to see how much they’re walking or sitting, so we can get a baseline and then see if an exercise prescription makes a difference.” (A pedometer, which measures how many steps a person takes, is an example of a wearable technology. For more on this subject, see Quest Tech.)
Abresch says the only thing he can say with certainty is that adults with slowly progressive muscular dystrophies (such as limb-girdle, facioscapulohumeral and myotonic dystrophies) showed improvements with moderate exercise. “The one program we did that seemed to work well was a walking program, where we put pedometers on people and asked them to walk 25 percent more over time than they did initially. They reduced weight, said they felt better and did better on quality-of-life testing.”
Q: Can exercise hurt me?
A: If you have a neuromuscular disease (and even if you don’t), some types of exercise can hurt you. It’s always a good idea to consult with your physician before starting an exercise program and, ideally, to work with a physical therapist who understands your disorder. There are, however, some general precautions to take.
Many neuromuscular diseases affect the heart muscle, and that adds an extra requirement for caution. Cardiac abnormalities figure prominently in many muscular dystrophies, particularly Duchenne, Becker, myotonic and Emery-Dreifuss MDs, as well as in Friedreich’s ataxia. If someone has a cardiomyopathy (heart-muscle degeneration), the pumping action of the heart is impaired, and the muscle won’t respond to exercise the way a healthy heart would. It may thicken (hypertrophy) in an attempt to meet the increased workload of exercise, resulting in diminished blood-holding capacity. Or it may dilate, causing the heart to become floppy and relatively ineffective as a pump.
When cardiomyopathy or other types of heart disease render the heart’s pumping action insufficient in supplying the body’s cells with the blood supply they need, the person is said to be in “heart failure.”
The traditional view of exercise for people with heart failure has been that it should be undertaken with great caution, if at all. But at a meeting of the American Heart Association in November, 2008 investigators from Duke University and Thomas Jefferson University reported results of a long-term, large-scale study of heart failure patients assigned to an exercise or a usual-care group. The study found that exercise was safe for study participants with heart failure and lowered their risk of hospitalization or death.
The study included 2,331 patients from 82 study sites who were followed for an average of two-and-a- half years. Those in the exercise group started with three 30-minute sessions per week on a stationary bicycle or treadmill. After 18 sessions, they transitioned to 40 minutes five days a week. Those in the usual-care group continued their usual medical therapy and were encouraged to be active, but they were not given a specific exercise program.
It’s imperative for anyone with a disease that affects the heart to consult a cardiologist before beginning an exercise program. Chances are, if your skeletal muscles are up to the task, some degree of exercise can be undertaken.
Then there’s the critical issue of whether or not exercise can weaken and damage muscles already made fragile by a dystrophy. This is a particular concern in the dystrophies in which the muscle-fiber membrane is compromised. These are Duchenne, Becker and the sarcoglycan-deficient forms of limb-girdle MDs. In these diseases, a type of muscle contraction called eccentric can seriously damage already weakened muscle-fiber membranes and ultimately destroy muscle tissue.
An eccentric contraction is what happens when a muscle is used in a braking action. When extending your arm slowly while holding a weight, your muscles act as a brake to prevent your arm from flopping down suddenly. Or when walking down a steep hill, your leg muscles use eccentric contractions to keep you from falling forward. This type of muscle activity is best avoided.
In inflammatory muscle diseases like polymyositis and dermatomyositis, active exercise during an acute flareup of the disease can exacerbate the inflammation and make things worse. Range-of-motion (ROM) exercise with someone assisting or doing all the work (passive ROM) is fine and may help keep joints flexible. Exercise should progress in duration and intensity as the disease comes under control with medication. When the disease is no longer active, recreational aerobic exercise, such as biking and swimming, and progressive resistance exercise, can be helpful in maintaining strength and cardiovascular health.
Recently, studies have shown that, in some muscle diseases where the fiber membrane is disrupted (such as Duchenne and type 2D limb-girdle muscular dystrophies), signals that normally tell blood vessels to open (dilate) during exercise don’t occur. The signals aren’t sent because a molecule called nitric oxide synthase, which starts the process, can’t anchor itself to the membrane. The implications of this problem aren’t yet clear. However, researchers believe this mechanism may explain some of the significant fatigue some patients feel with even mild exercise.
In diseases of the motor neurons, such as spinal muscular atrophy (SMA) and amyotrophic lateral sclerosis (ALS), there’s a theoretical concern that too much exercise can hasten the loss of these musclecontrolling nerve cells. These cells, the theory goes, not only are compromised by the disease, but they may be overburdened by trying to compensate for neighboring cells that have been lost.
Studies in mice with an ALS-like disease have shown that mice that ran regularly on a treadmill at a low speed survived longer than average, but mice that ran regularly on a treadmill at a high speed survived a shorter time than average. The researchers found the mice did best when exercise periods were interspersed with rest. However, they acknowledge that they don’t know whether these findings apply to humans with ALS or other motor neuron diseases.
To add to the uncertainty, studies in mice with an SMA-like disease found regular running resulted in better motor function, a longer life span, and more surviving motor neurons compared to mice that didn’t participate in the training. But again, extrapolation to humans is risky.
Perhaps the most dramatic instances of damage resulting from certain types of exercise are those that can occur in the metabolic muscle diseases, such as Pompe disease (acid maltase deficiency), McArdle disease (myophosphorylase deficiency), carnitine palmityl transferase (CPT) deficiency, and others in this category, including diseases involving the mitochondria, where much of a cell’s energy is produced.
In these disorders, a biochemical defect is almost invariably associated with exercise intolerance, and normal exercise is impossible because of extreme fatigue, muscle pain and/or cramps.
If a patient pushes beyond the limits of fatigue or pain, acute muscle breakdown can occur, spilling muscle proteins like myoglobin into the bloodstream and potentially damaging the kidneys.
“Trainers like to say ‘no gain without pain,’ says Alfred Slonim, a pediatric endocrinologist at Columbia University, “but in metabolic muscle disease it’s ‘no gain with pain.’”
On the other hand, Slonim says, “When you turn a person into a couch potato or a wheelchairdependent patient, their muscle status deteriorates from disuse.”
He recommends light aerobic conditioning exercise, such as walking on a treadmill, or using a stationary bicycle, under the watchful eye of a physician or knowledgeable physical therapist. Light resistance training, using weights of no more than 5 or 10 pounds, is OK for some, he says, after they’ve done some aerobic exercise.
Q: Does proper exercise reduce pain?
A: “Proper” exercise sometimes can reduce certain kinds of pain. For instance, if pain is due to stiffness in the joints or prolonged sitting or lying in one position, gentle stretching or range-of-motion exercises can relieve it. However, severe muscle cramps or pain, either immediately or a day or two later, are an indication that the exercise may be doing some damage, and it should be either stopped or reduced in duration or intensity.
Q: Is there one kind of exercise that’s good for anyone with a neuromuscular disease?
A: If there’s any kind of exercise that comes close to being universally good for people with neuromuscular disease, it’s probably moving in the water. The buoyancy of water makes exercise easier and reduces stress on the joints. However, actual swimming, especially for those with cardiac abnormalities, can be risky, and should be approved by a physician.
Also, cold water can make myotonia (inability to relax muscles) much worse, especially in the condition known as paramyotonia congenital (PMC). “If swimming, particularly in cold water, PMC patients are at increased risk of an attack [of myotonia], and in the water, this can be life-threatening,” says MDA grantee Louis Ptacek, a neurologist and muscle physiologist at the University of California San Francisco. “No one should swim alone, but particularly not PMC patients.”
Q: Will exercise cause me to lose weight?
A: Sometimes — or it may at least offset some of the weight gain that usually accompanies a sedentary lifestyle. Aerobic exercise is what’s usually recommended for weight loss or maintenance, since it directly burns calories. However, recent research has suggested that resistance exercise, which builds muscle (at least in some people), also can be beneficial. Muscle is where most fuel is metabolized for energy, so if there is more muscle, theoretically, there is more fuel burned instead of stored as fat.
A program at UC Davis in which people with slowly progressive muscular dystrophies were given pedometers and asked to increase their walking time by 25 percent resulted in weight loss, “feeling better,” and scoring better on quality-of-life measures.
Q: How hard should a person with neuromuscular disease expect to work at aerobic exercise?
A: This, of course, depends on the disease in question and its severity, the age and condition of the person, and their cardiac and respiratory status.
But as a general rule, physicians recommend that patients with neuromuscular diseases do submaximal aerobic exercise, which means activity that maintains the heart rate at about 65 percent of its maximum.
The maximum heart rate can be calculated by subtracting one’s age from 220. Multiply that number by 0.65 to get 65 percent. So, for example, the submaximal heart rate for a person who is 30 years old is: 220 - 30 = 190; 190 x 0.65 = approximately 123 beats per minute.
Another way of assessing aerobic exercise is to see whether you can talk while doing it. If you can’t talk, says Ted Abresch of the UC Davis Center, you’re doing something too fast or for too long.
Submaximal aerobic exercises include pool therapy, walking or bicycling on a flat surface.
Q: How hard should a person with neuromuscular disease expect to work at resistance exercise?
A: As above, it depends on disease type and severity and the individual patient’s condition. In general, one should consider only light resistance exercise. Lifting more than 5 or 10 pounds or resisting more than 5 to 10 pounds (for instance, using a stretchable band or a moveable device you push against) is likely to cause muscle-fiber destruction. In most neuromuscular diseases, muscle fibers are difficult or impossible to regenerate.
Abresch says studies at UC Davis found high-resistance exercise wasn’t any more beneficial than moderate-resistance exercise in patients with slowly progressive muscular dystrophies.
Q: How do rest and recovery fit into an exercise strategy?
A: At UC Davis, they use a “one-rep max” strategy, says director Ted Abresch. “That means they lift a weight, then we give them 15 minutes of rest, and then they get a weight that’s a little heavier.” Patients only go on to the next weight if the previous weight was easy to lift. They’re told to stop when the weight is no longer easily lifted.
Resting at intervals so that heart rate doesn’t go above 65 percent of maximum is a general recommendation for aerobic exercise.
There’s an exception to most rules, however. In periodic paralysis, it’s during a rest following exercise that patients are most likely to experience an attack of paralysis.
In hyperkalemic periodic paralysis, attacks can come on within seconds or minutes or even up to an hour after ceasing vigorous exercise, says neurologist Louis Ptacek. For instance, sitting in a chair after doing housework can make someone too weak to get up from the chair 30 minutes later.
In hypokalemic periodic paralysis, the attacks are more likely to come on the morning following the exercise.
People can sometimes ward off an attack of paralysis by continuing their activity and slowing down very gradually or by “walking off” the weakness early in an attack.
Q: What about people who can’t exercise in the usual sense? Can a daily power chair roll through the mall or the adrenaline rush of video games contribute to fitness?
A: It’s not clear that this type of exercise can improve fitness. However, it may help restore energy and reduce fatigue, as well as reduce depression and, if done in a group, offset social isolation.
Q: In the absence of clear answers, what should a person who wants to exercise do?
A: In most cases, people can do moderate-intensity aerobic training. Some can do moderate-intensity resistance training in muscles that can still work against gravity (for instance, muscles that can extend the leg from a seated position with the knee bent).
People always should check with their neuromuscular disease specialist and, if they have a disease that involves the heart, with a cardiologist, before beginning an exercise program.
People also need to know how to recognize the warning signs that tell them they’ve gone too far. See “Warning: Read Me First!”