Author(s): DudleyJavoroski S, Littmann AE, Chang SH, McHenry CL, Shields RK
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Abstract OBJECTIVE: To compare paralyzed quadriceps force properties and femur compressive loads in an upright functional task during conventional constant-frequency stimulation and force feedback-modulated stimulation. DESIGN: Crossover trial. SETTING: Research laboratory. PARTICIPANTS: Subjects (N=13; 12 men, 1 woman) with motor-complete spinal cord injury. INTERVENTIONS: Subjects performed 2 bouts of 60 isometric quadriceps contractions while supported in a standing frame. On separate days, subjects received constant-frequency stimulation at 20Hz (CONST) or frequency-modulated stimulation triggered by a change in force (FDBCK). During FDBCK, a computer algorithm responded to each 10\% reduction in force with a 20\% increase in stimulation frequency. MAIN OUTCOME MEASURES: A biomechanical model was used to derive compressive loads on the femur, with a target starting dose of load equal to 1.5 times body weight. RESULTS: Peak quadriceps force and fatigue index were higher for FDBCK than CONST (P<.05). Within-train force decline was greater during FDBCK bouts, but mean force remained above CONST values (P<.05). As fatigue developed during repetitive stimulation, FDBCK was superior to CONST for maintenance of femur compressive loads (P<.05). CONCLUSIONS: Feedback-modulated stimulation in electrically activated stance is a viable method to maximize the physiologic performance of paralyzed quadriceps muscle. Compared with CONST, FDBCK yielded compressive loads that were closer to a targeted dose of stress with known osteogenic potential. Optimization of muscle force with FDBCK may be a useful tactic for future training-based antiosteoporosis protocols. Copyright © 2011 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All rights reserved.
This article was published in Arch Phys Med Rehabil
and referenced in International Journal of Physical Medicine & Rehabilitation