Patients with symptomatic peripheral arterial occlusive disease have a claudication-limited peak exercise performance that is improved with exercise training. The effects of training on skeletal muscle metabolism were evaluated in 26 patients with claudication, randomized into a 12-wk program of treadmill training (enhances muscle metabolic activity in normal subjects), strength training (stimulates muscle hypertrophy in normal subjects), or a nonexercising control group. Gastrocnemius muscle biopsies were performed at rest and before and after training. After 12 wk, only treadmill training improved peak exercise performance and peak oxygen consumption. Treadmill training did not alter type I or type II fiber area and did not increase citrate synthase activity but was associated with an increase in the percentage of denervated fibers (from 7.6 +/- 5.4 to 15.6 +/- 7.5%, p < 0.05). Improvement in exercise performance with treadmill training was associated with a correlative decrease in the plasma (r = -0.67) and muscle (r = -0.59) short-chain acylcarnitine concentrations (intermediates of oxidative metabolism). Patients in the strength and control groups had no changes in muscle histology or carnitine metabolism, but strength-trained subjects had a decrease in citrate synthase activity. Thus treadmill training increased peak exercise performance, but this benefit was associated with skeletal muscle denervation and the absence of a "classic" mitochondrial training response (increase in citrate synthase activity). The present study confirms the relationship between skeletal muscle acylcarnitine content and function in peripheral arterial occlusive disease, demonstrating that the response to treadmill training was associated with parallel improvements in intermediary metabolism.

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