Isokinetic testing of muscle strength of older individuals with chronic obstructive pulmonary disease: An integrative review

1.Introduction

Chronic obstructive pulmonary disease (COPD), which includes both chronic bronchitis and emphysema, is common among adults of all ages. In the United States, at least, the disease is most prevalent among adults 65 to 84 years of age [1]. As would be expected, patients with COPD have lung-related impairments (e.g., difficulty breathing) as well as activity limitations (e.g., walking long distances) resulting from their obstructive pathology. Though not as widely recognized, patients with COPD have also been shown to demonstrate impairments in skeletal muscle strength. While such impairments have been documented using hand-held and hand-grip dynamometers [2, 3] and field tests such as the sit-to-stand test [4], isokinetic dynamometry is probably the most widely researched strength testing procedure applied to patients with the disease. This review addresses the use of isokinetic dynamometry with patients with COPD. Specifically, the review seeks to describe the isokinetic testing procedures that have been applied to older individuals with COPD and the clinimetric findings obtained using the procedures.

2.Methods

Potentially relevant articles were identified by a search of PubMed on February 18, 2020. The search string used was “isokinet* AND (chronic obstructive pulmonary disease OR COPD).” A hand-search was also conducted. Article titles and abstracts, and where warranted full text, were examined to determine whether articles identified by the searches addressed the isokinetic testing of muscle strength of individuals with COPD. Reviews and articles not written in English were excluded. Articles were also excluded if they failed to provide procedural specifics (e.g., dynamometer used), used a custom isokinetic dynamometer or ergometer, addressed only endurance or accumulated work, or presented no findings relevant to the clinimetric properties of isokinetic testing. Articles retained for this review were examined for information on the sample tested, procedural specifics (e.g., dynamometer used and muscle groups tested), and findings relevant to clinimetric properties (e.g., validity, reliability, and responsiveness).

3.Results and discussion

The PubMed search identified 32 potentially relevant articles. Two additional articles were found by a hand search. One article was eliminated as it was a protocol and presented no findings. Two other articles were excluded because they employed a cycle ergometer rather than a dynamometer. Three articles were rejected because they did not provide important procedural specifics. One article addressed only muscle endurance. Relevant information, therefore, from 27 articles is summarized alphabetically by author in Table 1 [5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31].

Information summarized in the Table shows that isokinetic dynamometers have been used extensively to measure strength of older adults with COPD (mean age of 63.0 to 74.1 years). Isokinetic testing of individuals with COPD has been conducted in at least 9 different countries, but testing has been reported most widely in Brazil and Canada. Utilization of some model of 5 different dynamometers has been described in the literature, but some type of Biodex has been employed most frequently. Most articles providing specifics of isokinetic testing have documented concentric moment at speeds of 30 to 270∘/s with 60∘/s being reported most frequently. Many articles, however, have not specified the mode of the moment tested or reported the measurement of eccentric or isometric moments. Several articles have reported moment normalized against body weight, or measures of work or power. Most research reports have focused on the isokinetic testing of limb muscles (particularly the knee flexors and extensors); no reports of trunk muscle strength were found.

The clinimetric properties of isokinetic testing of individuals with COPD have received considerable attention. Validity has been demonstrated most often by reports of less, though not necessarily significantly less, strength in patients with COPD than in healthy matched individuals [5, 6, 7, 10, 11, 15, 16, 19, 21, 22, 23, 26, 27]. Notably, these strength differences sometimes diminish or disappear when strength measures are normalized against body weight [6]. The validity of isokinetic strength measures has also been supported by significant correlations of isokinetic strength measures with other measures of muscle performance or changes in muscle performance (e.g., leg press and stairclimbing power) [8, 17] and assorted measures of timed mobility (e.g., sit-to-stand, timed-up-and-go, gait time, and six-minute walk test) [8, 14, 17, 30]. Interestingly, the isokinetic strength of some lower limb muscle groups has been correlated significantly, albeit weakly with balance measures [5]. Although isokinetic strength has been found to correlate significantly with VO2 maximum and some other measures of exercise capacity [14, 15, 18] it has not been consistent in this regard [8]. Measures of disease severity, whether represented by pulmonary function tests [11, 15] or GOLD classification [30] are not uniform in their relationship with measures of isokinetic strength.

This review revealed only three studies that addressed the reliability of isokinetic strength measures in COPD. Two reported relative reliability using test-retest intraclass correlation coefficients (0.82–0.97) for measurements obtained a week apart [20, 25]. One of these two studies also reported relative reliability using minimal detectable changes (95%) [25]. The third study simply determined that strength did not differ significantly across sets [28].

This review includes numerous articles showing that isokinetic testing is sensitive to change in strength over time, whether the changes were the result of isokinetic training, another type of training, or some other kind of intervention [9, 10, 12, 13, 15, 22, 23, 24]. This evidence notwithstanding, only one study reported distribution-based measures of responsiveness (minimal detectable changes) [25] and no study reported anchor-based measures of responsiveness (minimum clinically important difference).

The consistency with which muscle weakness has been demonstrated in COPD should alert clinicians to the importance of including the assessment of strength in the overall examination of individuals with the disease. The relationship of muscle strength with physical function and performance adds to the importance of examining muscle strength. Whether muscle weakness in COPD stems for the systemic nature of COPD [32] or physical inactivity [33] on the part of individuals with the disease, appropriate management of the disease requires that strength be addressed. Isokinetic dynamometry may be a superior method for such examination [34].

If isokinetic testing is to be recommended in COPD, further evidence for reliability and responsiveness are required. Although the reliability coefficients reported for isokinetic measurements in COPD are high [20, 25], they were limited to test-retest reliability and derived from studies of less than 15 participants. Only one study provided objective estimates of absolute reliability or distribution-based responsiveness. These limitations, along with the absence of any anchor-based estimates of responsiveness, compromise the ability to establish meaningful goals. They also compromise the capacity to interpret changes in patient performance over time.

This review has several limitations. Most notably, only one bibliographic database (PubMed) was employed. While it is uncertain that the incorporation of additional databases would have markedly altered the results, a broader search may have provided more comprehensive evidence for the conclusions presented herein. A more systematic review may have also allowed for a meta-analysis of some variables and for a quality grading of included articles. Another limitation is the reliance on a single examiner (the author). Consequently, the quality check possible by including a second examiner was not possible.

4.Conclusion

There is considerable research support for measuring the isokinetic strength of older individuals with COPD-mostly in regard to validity. Further information on reliability and responsiveness is needed. In the meantime, it makes sense to include objective strength testing in the assessment of patients with COPD.