The influence of mechanically and physiologically imposed stiff-knee gait patterns on the energy cost of walking.
OBJECTIVE
To investigate the relative roles of mechanically imposed and physiologically imposed stiff-knee gait (SKG) patterns on energy cost.


METHODS
Repeated-measures, within-subjects design.


METHODS
Research laboratory.


METHODS
Individuals (N=20) without musculoskeletal, neuromuscular, or cardiorespiratory limitations.


METHODS
Participants walked on an instrumented treadmill at their self-selected overground gait speed for 3 randomly ordered conditions: (1) control, (2) mechanically imposed stiff-knee gait (SKG-M) using a lockable knee brace, and (3) physiologically imposed stiff-knee gait (SKG-P) using electrical stimulation to the quadriceps. Each condition was performed with 0% and 20% body weight support. Indirect calorimetry determined net metabolic power, and motion capture measured lower extremity joint kinematics and kinetics.


METHODS
Net metabolic power, knee flexion angle, circumduction, hip hiking, and hip flexion and ankle plantarflexion moments.


RESULTS
Participants walked at 1.25±.09m/s. Net metabolic power was significantly increased by 17% in SKG-M and 37% in SKG-P compared with control (mean increase: .66±.60W/kg for SKG-M; 1.39±.79W/kg for SKG-P; both P<.001). Furthermore, SKG-P required greater net metabolic power than SKG-M (P<.001). Simulated SKG was associated with increased circumduction and hip hiking. Despite no change in ankle plantarflexion moments (P=.280), the hip flexion moment was increased during SKG-P (.43±.15Nm/kg·m) compared with control (.31±.08Nm/kg·m; P<.001).


CONCLUSIONS
The increase in energy cost associated with simulated SKG was due in part to abnormal mechanical compensations, and in part to an increase in quadriceps activity. Understanding the mechanisms underlying the increase in quadriceps activity will enable a reduction in the energy cost of walking with SKG.
Department of Allied Health Sciences, Division of Physical Therapy, University of North Carolina, Chapel Hill, NC 27599-7135, USA. mlewek@med.unc.edu
Michael D
MD
Lewek
Abigail J
AJ
Osborn
Clinton J
CJ
Wutzke
D000704:Analysis of Variance; D001696:Biomechanical Phenomena; D004558:Electric Stimulation / Q000379:methods; D004734:Energy Metabolism / Q000502:physiology*; D005260:Female; D005684:Gait / Q000502:physiology*; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology*; D008297:Male; D052097:Quadriceps Muscle / Q000502:physiology; D016059:Range of Motion, Articular / Q000502:physiology*; D012016:Reference Values; D012494:Sampling Studies; D013314:Stress, Mechanical; D016138:Walking / Q000502:physiology; D055815:Young Adult