Skeletal muscle dysfunction is now recognized as an indicator of advanced COPD, and exercise, including lower and upper extremity training and respiratory muscle training, combined with adjunctive therapies such as noninvasive ventilation, supplemental oxygen, and various drug therapies, all contribute to improved quality of life for COPD patients.

For many patients with chronic obstructive pulmonary disease (COPD), the thought of exercise provokes great anxiety. In some instances, this anxiety discourages the patient from engaging in exercise. Over the past several decades, much research has shown the benefits of exercise for patients with chronic lung disease. All patients with chronic lung disease should be made familiar with the potential benefits of exercise and should be encouraged to pursue regular exercise.

Many factors contribute to exercise intolerance in COPD. The respiratory mechanisms limiting exercise include development of hypoxemia secondary to ventilation-perfusion mismatching and/or the development of dynamic hyperinflation. Many nonrespiratory factors limiting exercise must also be considered, including the normal aging process, systemic inflammation, nutritional impairment, and low levels of circulating anabolic hormones. All of these factors play a role in the development of skeletal-muscle dysfunction, which ultimately results in exercise intolerance.

Skeletal-muscle dysfunction is now recognized as an indicator of advanced COPD.1 Several studies2 have shown that exercise causes a reversal of skeletal-muscle dysfunction and other morphological and metabolic changes seen in the skeletal muscles of patients with COPD. In addition, physical exercise can reduce the fear of dyspnea and improve overall quality of life.

There is substantial variation in exercise-training programs, which may employ training of the lower-extremity muscles, upper-extremity muscles, respiratory muscles, or some combination of these three. There is also considerable debate3,4 about the optimal exercise protocol and the intensity, duration, and frequency of training for various muscle groups that should be applied in COPD. Many investigators seem to agree that endurance exercise for the lower extremities should be the primary exercise modality. The roles of upper-body, respiratory-muscle, and strength training remain undefined.5

Lower-Extremity Training
A comprehensive pulmonary rehabilitation program includes education, psychosocial intervention and support, physical and occupational therapy, training in self-management, and the acquisition of dyspnea-reduction skills. Lower-extremity training is usually part of the program. Several evidence-based reviews5,6 have noted the benefits of lower-extremity training and have recommended its inclusion in all rehabilitation programs.

The frequency, intensity, and duration of exercise should be individualized. In general, however, exercise should be performed at submaximal work capacity (with intensity increasing every fifth session), and it should last a minimum of 30 minutes per session. By the end of the program, exercise duration should approach an hour per session. The optimal level of exercise training in COPD is yet to be determined.

Earlier research4 focused on high-intensity exercise carried out at 60% to 80% of the patient’s maximum workload. Significant physiological training effects were noted, in comparison with exercise at 30% to 50% of maximum workload; these effects included an increase in maximum oxygen consumption, a delay in reaching the anaerobic threshold, a decrease in heart rate (at isowork levels), and an increase in the skeletal muscles’ oxidative capacity. The patients in this study had moderate COPD, so these results may not be applicable to patients with severe COPD.

A recent review6 systematically evaluated and summarized the results of 15 randomized, controlled trials that compared exercise protocols for patients with COPD. A combination of strength and endurance exercises led to larger improvements than endurance training alone in health-related quality of life. Interval exercise training (brief exercise at very high levels of intensity repeated after a rest period) and continuous exercise (lasting 20 to 30 minutes at a submaximal workload) seemed to be of similar effectiveness.7

More research is needed to assess the relative benefits and disadvantages of various types of lower-extremity training exercises and to define the optimal level of exercise intensity more fully.

Upper-Extremity Training
Upper-extremity training can be used for patients with COPD8-10 and can be conducted using either a supported modality (such as an arm ergometer) or an unsupported modality (such as dowels and weights). The benefits of upper-extremity training include improvements in arm endurance and strength, an increased sense of well-being, and a reduction in the metabolic demands of arm movement.

Only limited research regarding the optimal mode or intensity of training is available. When an arm ergometer is used, exercise is conducted at a submaximal level, with gradual increases in intensity and duration taking place every fourth to fifth session. When dowels and weights are used, they are lifted for eight to 10 repetitions. After a rest period, the exercises are then repeated over a 30-minute period. More weight can be added to the dowel every fourth to fifth session. Many patients may experience more dyspnea during arm exercise than during leg exercise at a comparable level, but unsupported arm exercise involving eight to 10 repetitions for a total of 30 minutes per session results in dyspnea reductions and improvements in health-related quality of life comparable to those produced by high-intensity lower-extremity training.11

Respiratory-Muscle Training
Some controversy exists regarding the effects of respiratory-muscle training for patients with COPD. Various devices for respiratory-muscle training are available; these are flow-resistive or threshold-loading products. Generally, respiratory-muscle training begins at 35% of the patient’s maximal inspiratory pressure and takes place for 30 minutes per day over at least 5 days per week. As with other types of exercise training, many different protocols have been studied, but the optimal level of respiratory-muscle training is not yet known.

Recent guidelines4 state that respiratory-muscle training should be used for certain patients with COPD, particularly those who exhibit respiratory-muscle weakness. Several studies12,13 have further defined the importance of respiratory-muscle training in COPD. Sturdy et al12 evaluated a protocol of 2 minutes of training at 70% of maximal inspiratory pressure (measured using a handheld breathing valve) followed by 1 minute of rest, repeated six times, and showed that respiratory-muscle training can be used successfully as part of a comprehensive pulmonary rehabilitation program. This therapy was well tolerated and resulted in substantial improvements in respiratory-muscle strength and endurance, whole-body exercise capacity, and quality of life.

Maintenance
The beneficial effects of exercise training are known, for the short term, for patients who complete comprehensive pulmonary rehabilitation programs. Recent studies14,15 have shown that the beneficial effects of lower-extremity training continue for up to 2 years if the patient is involved in an ongoing maintenance program. Such a program should consist of weekly patient contact with the training staff and monthly supervised exercise. A study16 involving inspiratory respiratory-muscle training showed that continued training over a 1-year period resulted in a sustained increase in inspiratory-muscle strength, inspiratory-muscle endurance, and distance walked.

Adjunctive Therapies
Simple exercise training using a cycle ergometer or treadmill is currently the standard of care for patients with COPD. Various supplemental therapies have been shown to be of benefit; these include supplemental oxygen, noninvasive ventilation, mechanical aids for walking, and various drug therapies. The use of supplemental oxygen in patients who did not develop hypoxemia during exercise resulted in an improvement in overall work rate and endurance over a 7-week period.17 The use of noninvasive ventilation during exercise training resulted in an improvement in peak oxygen consumption and a reduced ventilatory equivalent at maximum exercise.18 The use of a rolling stroller as a walking aid improved overall distance walked and decreased dyspnea.19 Recently, the use of tiotropium (an inhaled anticholinergic medication) caused an improvement in endurance during comprehensive pulmonary rehabilitation.20 These supplemental modalities may be of benefit to many patients with COPD who are undergoing exercise training.

Summary
Exercise impairment is nearly universal in patients with severe COPD due to debilitation and muscle dysfunction. Exercise training is an important part of the rehabilitation process. Various types of exercise training involving the lower extremities, the upper extremities, and the respiratory muscles have been shown to improve skeletal muscle function, improve exercise endurance, improve quality of life, and decrease the level of dyspnea for patients with COPD. While the optimal training regimen is yet to be fully defined, a regular, sustained exercise program should be part of the comprehensive therapy afforded all patients with COPD.

Brian W. Carlin, MD, is assistant professor of medicine, Drexel University School of Medicine, Allegheny General Hospital, Pittsburgh.

References
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