Millions of people each year spend some portion of their time using mobility aids to facilitate periods of non-weight bearing ambulation. The use of these devices changes the loading conditions of the lower extremities, which may result in skeletal muscle adaptations. The purpose of this work was to evaluate the effects of 3 types of mobility aids on lower-extremity muscle activity. Evaluation was based on 1) measured muscle activation signals using electromyography (EMG), and 2) measured joint kinematics and ground reaction forces, which were used to predict muscle forces. 16 healthy subjects (7 female, 9 male), ages 18-27 participated in the study. Subjects were instructed to ambulate using each of three mobility aids (crutches, a knee scooter and a temporary-injury prosthesis) as well as normal walking. EMG and motion capture were used to obtain bilateral data from the lower half of the body during ambulation on each of these mobility aids and walking (10 trials on each per subject). Muscles studied were right and left vastus lateralis (VLR, VLL), rectus femoris (RFR, RFL), Biceps femoris long head (BFR, BFL), and gastrocnemius medialis (GMR, GML). Joint kinematics and ground reaction force data (joint kinetics) were acquired using a standard camera-based motion capture system. The measured joint kinetics were used as inputs to the open source musculoskeletal biomechanics software OpenSim (SimTK, Stanford, CA), which allowed prediction of muscle force data for a representative subject during each mode of ambulation. As compared to walking, the following differences in EMG activation were significant. For the knee scooter, increases in VLR, RFR, BFL and decreases in GMR. For the TI prosthesis, increases in VLR, RFR, BFR, VLL, RFL, GML and decreases in GMR. For crutches, increases in BFR, VLL, RFL, BFL, GML and decreases in VLR, GMR. Muscle force results were similar, but demonstrated inadequacy of current musculoskeletal simulation software to resolve muscle forces during non-weight bearing portions of gait based solely on kinetic data. Results for walking data were similar to what is reported in the literature for normal gait. This study provides useful bilateral data that describe measured lower-extremity EMG activation amplitudes and muscle force predictions based on kinetic data during ambulation using three different ambulatory aids, compared to normal walking. Based on a criteria of maintaining muscle activation, the TI prosthesis proved most effective among the devices tested. The data presented will be valuable to clinicians in providing insight into which mobility aid may be best suited for a particular patient. It is anticipated that these data will provide designers of mobility aids with a protocol for evaluation of designs based on their potential to cause or prevent muscle adaptations.



College and Department

Ira A. Fulton College of Engineering and Technology; Mechanical Engineering



Date Submitted


Document Type





leg, crutches, knee scooter, mobility aid, electromyography