Leg stiffness adjustment for a range of hopping frequencies in humans

• Published in: Journal of biomechanics 2010-02, Vol.43 (3), p.506-511
• Main Authors: Hobara, Hiroaki, Inoue, Koh, Muraoka, Tetsuro, Omuro, Kohei, Sakamoto, Masanori, Kanosue, Kazuyuki
• Format: Article
• Language: English
• Subjects: Adaptation, Physiological - physiology; Adjustment; Ankle; Biological and medical sciences; Biomechanics. Biorheology; Computer Simulation; Elastic Modulus - physiology; Electrodiagnosis. Electric activity recording; Fundamental and applied biological sciences. Psychology; Gait - physiology; Ground reaction force; Human; Humans; Investigative techniques, diagnostic techniques (general aspects); Joint stiffness; Kinematics; Knees; Leg - physiology; Leg spring; Legs; Lower extremity; Male; Mathematical analysis; Medical sciences; Models, Biological; Muscles; Muscular system; Nervous system; Oscillometry - methods; Physical Exertion - physiology; Physical Medicine and Rehabilitation; Stiffness; Tissues, organs and organisms biophysics; Touchdown; Vertebrates: body movement. Posture. Locomotion. Flight. Swimming. Physical exercise. Rest. Sports; Young Adult
• ISSN: 0021-9290; 1873-2380
• DOI: 10.1016/j.jbiomech.2009.09.040

Abstract The purpose of the present study was to determine how humans adjust leg stiffness over a range of hopping frequencies. Ten male subjects performed in place hopping on two legs, at three frequencies (1.5, 2.2, and 3.0 Hz). Leg stiffness, joint stiffness and touchdown joint angles were calculated from kinetic and/or kinematics data. Electromyographic activity (EMG) was recorded from six leg muscles. Leg stiffness increased with an increase in hopping frequency. Hip and knee stiffnesses were significantly greater at 3.0 Hz than at 1.5 Hz. There was no significant difference in ankle stiffness among the three hopping frequencies. Although there were significant differences in EMG activity among the three hopping frequencies, the largest was the 1.5 Hz, followed by the 2.2 Hz and then 3.0 Hz. The subjects landed with a straighter leg (both hip and knee were extended more) with increased hopping frequency. These results suggest that over the range of hopping frequencies we evaluated, humans adjust leg stiffness by altering hip and knee stiffness. This is accomplished by extending the touchdown joint angles rather than by altering neural activity.