EXERCISE PERFORMANCE AND GASTROCNEMIUS MUSCLE CHARACTERISTICS IN PERIPHERAL ARTERIAL DISEASE

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PURPOSE We aimed to measure whole body exercise capacity (walking and cycling), local calf muscular strength and endurance, and various morphological characteristics of the medial gastrocnemius muscle in 16 PAD patients (age: 63 y, BMI: 25.9) and 13 healthy control (CON) subjects (age: 62, BMI 25.9). METHODS Whole body exercise capacities were measured with incremental treadmill and cycle tests. Calf strength was measured as peak force on an isokinetic dynamometer, and calf endurance was measured using an incremental isokinetic plantar flexion protocol. A resting muscle sample was taken from the medial gastrocnemius of the most diseased limb (that with the lowest ankle: brachial systolic pressure index) in the PAD patients and a randomly chosen limb in the CON subjects, and it was analysed histochemically for fibre type, fibre area, capillary to fibre ratio, capillary contacts per fibre and the relative optical density of glycogen per fibre. RESULTS Whole body and local calf muscle exercise performance was 25–59% lower in the PAD patients compared with CON. PAD patients had a relatively greater proportion of type IIA (PAD:27%; CON:16%) and lower proportion of type I (PAD: 49%; CON:62%) muscle fibres, fewer capillaries per fibre (PAD:1.63; CON:2.12), and tended to have smaller fibre areas (^10%). In PAD patients only, muscle strength, area of all three fibre types, capillary contacts with type I and IIA fibres, and the relative optical density of glycogen in type I fibres were positively correlated (P less than 0.05) with treadmill and cycling performance. CONCLUSION These data suggest that a low muscle capillary supply, fibre area and glycogen content in type I fibres are related to exercise intolerance in PAD, and confirms that low calf muscle strength is also an aspect of exercise intolerance in this clinical population.