Abstract
Introduction: Methods of preventing and treating knee injuries have changed with the rapid development and refinement of knee braces. These knee braces are intended to stabilize knee during rotational and anteroposterior forces development. They offer a useful adjunct to the treatment and rehabilitation of ligamentous knee injuries. The knee brace, however, compresses the soft tissue of the thigh and leg. External compression may abnormally elevate intramuscular pressure, decrease local muscle blood flow or muscle oxygenation. The purpose of this study was to compare the muscle oxygen status during planter flexion with and without knee brace. Methods: Eight healthy men participated as subjects. They performed two trials with (Brace) and without knee brace (Control). Each trial consisted of 5 intermittent submaximal ankle planter flexion exercises for 1 min with 3-min recovery. Relative levels of HbO2/MbO2 (NIR-oxygenation) and Hb/Mb (NIR-deoxygenation) were measured in the medial head of gastrocnemius muscle using near infrared spectroscopy (NIR). NIR is noninvasive and obtains signal at .5second intervals from about 1.5 cm deep in the muscle. Blood lactate concentration was also measured at rest and after each trial. Results: NIR-oxygenation and NIR-deoxygenation averages are shown in Figure 1. NIR-oxygenation decreased and NIR-deoxygenation increased during contraction, and returned to resting level during recovery. In Brace trials, it was significantly different from control trials during contraction and recovery. The rate of recovery of NIR-oxygenation was slower in Brace than control trial. The blood lactate concentration immediately after each trial was significantly higher in Brace compared with control.Figure 1: Changes of NIR-oxygenation and NIR-deoxygenation during the intermittent planter flexion with (Brace;○) and without knee brace (Control;○), c; contraction for 1 min, rec; recovery for 3 min Knee brace was worn from 2min-rest in Brace trial. Values are means ± SD. *significantly difference between Brace and control trialsDiscussion: One of the most interesting findings was that muscle oxygen status determined by NIR was different between Brace and control trial. Knee brace produced higher deoxygenation level and slower recovery of O2 resaturation. Light surface compression (30 to 50mmHg) influences on the blood vessels, especially vein. O2 resaturation determined by NIR is a function of O2 delivery and utilization. This study suggests that the knee brace compressed the soft tissue of the thigh, such that exercise hyperemia was reduced and venous blood pooling was increased in the gastrocnemius muscle. Furthermore, it is suggested that reduced oxygen delivery was responsible for the higher blood lactated concentrations. From these findings, athletes and coaches should be aware of potential adverse effects of knee brace on oxygen delivery and muscle metabolism. External compression from knee brace might be responsible for premature muscle fatigue.
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