Pulmonary Rehabilitation* Joint ACCP/AACVPR Evidence-Based Clinical Practice Guidelines

Andrew L. Ries, MD, MPH, FCCP (Chair); Gerene S. Bauldoff, RN, PhD, FCCP; Brian W. Carlin, MD, FCCP; Richard Casaburi, PhD, MD, FCCP; Charles F. Emery, PhD; Donald A. Mahler, MD, FCCP; Barry Make, MD, FCCP; Carolyn L. Rochester, MD; Richard ZuWallack, MD, FCCP; Carla Herrerias, MPH

Disclosures

CHEST. 2007;131(5):4S-42S. 

In This Article

Strength Training in Pulmonary Rehabilitation

Although always recognized as important, improving the function of the muscles of the arms and legs has recently become a central focus of pulmonary rehabilitation. In the course of everyday activities, these muscles are asked to perform two categories of tasks. Endurance tasks require repetitive actions over an extended period of time; walking, cycling, and swimming are examples. Strength tasks require explosive performance over short time periods; sprinting, jumping, and lifting weights are examples. For individuals whose muscles are weak, another category of strength-related tasks may become relevant, such as maintaining balance while standing, rising from a chair, or hoisting objects above head level.

Different characteristics of skeletal muscle enable the performance of endurance and strength tasks. Endurance is facilitated by having machinery capable of the aerobic metabolism of nutrients. Predominance of type I fibers, dense capillarity, high concentrations of enzymes subserving oxidative metabolism, and high mitochondrial density all promote muscle endurance. In contrast, strength is facilitated in muscles, the fibers of which are high in number and large in cross-section, with high fractions of type II fibers.

Some work[79,80,81] has shown that the skeletal muscles of patients with COPD are, in general, dysfunctional. Some structural and biochemical abnormalities would predict poor aerobic function (eg, poor capillarization and type II fiber predominance). However, compared to age-matched healthy subjects, patients with COPD also have low muscle mass,[82,83] especially in the muscles of ambulation; this predicts poor muscle strength.[83,84,85]

In healthy subjects, strength-training programs, in which progressive resistance methods are used to increase the ability to exert or resist force,[86] are capable of profoundly altering muscle structure and biochemistry, even in older subjects.[87,88,89,90] An important principle of training specificity dictates that training programs featuring endurance activities (eg, treadmill walking and bicycle riding) yield muscle changes that improve endurance, while training programs that feature tasks requiring strength (eg, machine weights, free weights, elastic resistance, and lifting the body against gravity) yield muscle changes improving strength. However, more recent work[91,92] has shown that the muscles of elderly subjects may also show improvements in aerobic characteristics after a program of strength training.

In patients with COPD, there is a strong scientific basis for implementing endurance-training programs in regard to both design and benefits. In comparison, programs of strength training have been explored in clinical trials only in more recent years. Since the last review, eight randomized clinical trials relevant to strength training have been published ( Table 6 ), which is a considerable advance on the one study published prior to 1997. This older study (Simpson and colleagues[93]) was not included in the previous review and so has been included in the current analysis. These nine studies[93,94,95,96,97,98,99,100,101] can be separated into those that allow comparison between a control group (ie, either no exercise or endurance exercise)[93,94,95,96,97,98] and a strength-trained group, and those that allow comparison between an endurance-trained group and a group receiving a combined endurance-training and strength-training intervention.[97,98,99,100,101] The latter comparison is especially relevant to rehabilitative practice in which the question is whether the addition of strength training to an endurance-training program produces additional benefits.

The six randomized clinical trials[93,94,95,96,97,98] examining the responses of patients with COPD to a program of strength training have sufficient commonality to be examined as a group. With one exception,[95] the average disease severity was moderately severe (FEV1 range, 38 to 48% predicted). The exception is the study of Clark and colleagues[95] in which patients with very mild COPD were studied (average FEV1, 77% predicted). Collectively, the total number of patients studied was moderate, with the strength-trained group in the various studies comprising 6 to 26 subjects (total, 99 subjects). The training apparatus, exercise repetition, and intensity progression varied among studies (see Storer[102] for a review of suitable strength-training strategies). Program length ranged from 8 to 12 weeks; sessions were held two or three times per week, and session length (when stated) ranged from 40 to 90 min. These program characteristics are similar to those known to be effective in healthy subjects.[103]

The recorded outcomes of these studies include changes in strength, endurance, muscle mass, and disease-specific HRQOL. All six studies[93,94,95,96,97,98] reported improvements in strength. A variety of testing apparatuses were used, and it should be stressed that the measures of strength used in these studies were effort, motivation, and practice dependent. In all studies but one,[96] the change in exercise endurance was also assessed. Results were mixed. The peak exercise level in an incremental cycle ergometer test showed a statistically significant increase in only one of five studies[98]; the duration of a constant-work-rate task increased in three of five studies[93,95,97]; and the 6-min walk distance increased in one of the two studies in which it was assessed.[98] In two studies in which it was measured, muscle mass (assessed by MRI of a quadriceps cross-section[96] or dual-energy x-ray absorptiometry [DEXA] scan of lean leg mass[94]) increased significantly (by 4% and 3%, respectively).

Four studies[97,99,100,101] allowed a comparison of benefits to COPD patients between a combined strength-training and endurance-training program and an endurance-training program alone. These studies examined patients with, on average, moderately severe to severe disease (mean FEV1 range, 33 to 45% predicted). The number of patients included in the strength-training-plus-endurance-training group ranged from 9 to 21 (total, 55 patients). Training programs were 8 to 12 weeks in duration; sessions were held two or three times per week; the duration of strength training per session was generally not stated (it was 45 min in the study by Bernard and colleagues[99]). Strength-training exercises were included for both the arms and the legs.

In all four studies, improvement in measures of muscle strength was superior in the group receiving a strength-training component to that seen among those receiving endurance training alone. In one study,[101] measures of ADLs improved more in the combined-training group. However, measures of the increase in exercise endurance were comparable in the two groups (with the exception of the study by Panton and colleagues,[101] who found a superior increase in the 12-min walk distance in the combined-training group). Two studies[99,101] assessed muscle mass changes; neither detected significant changes in subjects performing endurance training alone, while both showed increases in the groups in whom a strength-training program was added (8% increase in thigh cross-section by CT scan[99] and 5% increase in whole-body lean mass by DEXA scan[101]).

These data can be interpreted to indicate that well-designed strength-training programs increase muscle strength and mass in patients with moderate-to-severe COPD. Strength training, when delivered as an isolated intervention may improve disease-specific quality of life but does not seem to produce additional gains when added to a program of endurance training. Strength training does not produce endurance benefits as consistently as does specific endurance training.

It should be emphasized that, to date, all cited trials featuring combined programs have added a strength-training component to an endurance-training program (ie, essentially doubling the time spent training) rather than substituting part of the endurance-training program with an endurance component. Therefore, whether it is wise for rehabilitation practitioners to include a strength-training component in a session of fixed duration by reducing the time spent in endurance activities cannot be assessed at this time. Importantly, no serious adverse effects of strength training have been reported; these preliminary data suggest that strength training is safe in patients without obvious contraindications (eg, severe osteoporosis). Little information is available on the long-term benefits of strength training in the pulmonary rehabilitation patient. Whether strength gains persist and whether adverse consequences of weakness occur (eg, decreased mobility or injuries due to falls) cannot be determined. Larger, longer term trials are required to resolve these issues. Finally, muscle biopsy studies of the cellular and biochemical adjustments following strength training have yet to be reported; such studies should help to determine the extent to which strength training ameliorates the muscle dysfunction seen in COPD patients.

13. The addition of a strength-training component to a program of pulmonary rehabilitation increases muscle strength and muscle mass. Strength of evidence, 1A

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