Effects of a functional knee brace for ACL insufficiency during treadmill running.

Abstract

To assess the effects of a functional knee brace (FKB) for anterior cruciate ligament insufficiency (ACLI) on physiological and perceptual parameters during treadmill running. Thirteen ACLI subjects (time since injury, 5.8 +/- 5.3 yr), performed an incremental test to exhaustion and two constant load 20-min tests, one at an intensity below lactate threshold (bLT), and the other at an intensity above LT (aLT) each with and without their FKB. Bracing had no effect on peak variables except for higher ratings of perceived exertion at the legs (RPE-L) at the velocities associated with a blood lactate concentration [HLa] of 4.0 mM and at peak. Bracing had no effect when exercising at bLT but did significantly alter the metabolic profile developed during the performance of the aLT tests (83 +/- 0.03% VO2peak). In particular, FKB resulted in elevated blood [HLa] (23%), VO2 (4%), VE (12%), VCO2 [corrected] (7%), and VE/VO2 (7%). HR and slow component VO2 did not differ between the brace and no brace aLT tests. RPE-L and RPE-knee were significantly elevated during aLT when the brace was worn. Suspected mechanisms include alterations in muscle recruitment patterns and/or occlusion. When ACLI individuals wear a FKB during high intensity straight-ahead running exercise of long duration, physiological parameters are affected.