Brace modification improves aerobic performance in Charcot-Marie-Tooth disease: a single-subject design

Ankle-foot orthoses (AFOs) can lower energy expenditure in patients with hemiplegia by 10%-13%. Review of the lower motor injury literature reveals insufficient physiologic evidence supporting the use or modification of AFOs in patients with lower motor neuron injury and, specifically, progressive conditions such as Charcot-Marie-Tooth disease. We sought to test the hypothesis that optimal AFOs would improve submaximal aerobic performance and submaximal perceived exertion, while producing no change in maximal aerobic capacity.

In an individual with Charcot-Marie-Tooth disease, a single-subject design study was used. An A-B-A design was used, with "A" corresponding to use of the patient's old AFOs and "B" corresponding to the newly prescribed AFOs. The subject underwent treadmill exercise tolerance testing using a modified Balke protocol. Indirect calorimetry was used to measure oxygen consumption per unit time (VO2), and the Borg scale was used to measure perceived exertion.

At the same submaximal exercise intensities, VO2, rate-pressure product, and perceived exertion were all reduced when using the modified AFOs. Additionally, these conditions allowed the subject to conduct the treadmill exercise test 20% longer. Maximal VO2 remained constant under all conditions.

Optimizing the AFO prescription in a patient with Charcot-Marie-Tooth disease can enhance physiologic performance and perceived exertion at submaximal activity levels. Larger controlled trials are necessary to further demonstrate such benefits in patients with progressive neuropathy and other causes of lower motor neuron injury.