A systematic review of muscle morphology and function in intermittent claudication

Intermittent claudication (IC) is frequently associated with deterioration in walking capacity and physical function, and it can often result in an impairment in balance. Whereas supervised exercise is recommended by the National Institute for Health and Care Excellence as the first-line treatment, the mechanism behind walking improvement is poorly understood. The existing literature suggests that there may be some physiologic change to the skeletal muscle contributing to the functional impairment, but these data are conflicting. We therefore sought to undertake a systematic review to clarify the muscle properties of patients with IC.

A systematic review of randomized and nonrandomized trials that investigated the role of muscle function in patients diagnosed with IC was undertaken using MEDLINE, Cochrane Central Register of Controlled Trials, and Embase databases. The searches were limited from 1947 to June 2016 in the English language.

The search yielded a total of 506 articles, of which 206 were duplicate articles. Of the remaining 300, a total of 201 were excluded from full-text analysis; 99 full-text articles were assessed for eligibility, with 30 articles deemed appropriate for inclusion in the review. There were four main categories of functional outcome measures: muscle strength, muscle size, muscle fiber type, and muscle metabolism. A total of 2837 patients were included in the study. Nine studies reported on muscle strength, incorporating isometric, concentric, eccentric, and endurance measures. Eight studies reported on muscle size, incorporating circumference, computed tomography scans, and ultrasound imaging techniques. Eleven studies reported on muscle fibers, incorporating fiber type proportions, fiber size, and capillarity measures. Seven papers reported on muscle metabolism, incorporating adenosine diphosphate recovery and phosphocreatine recovery measures.

Previous literature has found clear evidence that strength (of the calf and thigh musculature) and calf characteristics are related to mortality and functional declines. However, this review has demonstrated the vast array of muscle groups assessed and multiple methods employed to determine strength; therefore, it is unclear exactly what measure of "strength" is impaired. Furthermore, the underlying morphologic causes of potential changes in strength are unclear. This information is essential for designing optimal exercise interventions. The data acquired during this systematic review are heterogeneous, with a substantial lack of high-quality intervention-based studies. Future research should endeavor to establish standardized testing procedures and to implement randomized controlled trials for targeted therapeutic interventions.