title: Leg stiffness and electromyography of knee extensors/flexors: comparison between older and younger adults during stair descent.
abstract: This study investigated differences in knee extensor/flexor electromyography (EMG), leg loading rate, and leg stiffness in older and younger men during stair descent. Sixteen older men (mean +/- standard deviation [SD] = 72 +/- 4.5 years) and sixteen younger men (mean +/- SD = 21.2 +/- 0.5 years) were recruited. The EMG signals were recorded from the rectus femoris and the biceps femoris, while an electrogoniometer measured knee joint angle changes, and a force platform recorded the ground reaction forces (GRFs). We calculated leg stiffness by dividing the first peak GRF by the corresponding leg displacement. We used the Student's t-test to examine group differences. Results showed that the older subjects had 78.6% higher preactivated EMG values in the knee extensor and 128% greater coactivity in the knee extensors/ flexors in the prelanding phase. At the impact phase, we observed leg stiffness to be 26.6% greater in the older than the younger subjects. The older subjects needed 94.6% more support time in performing push-off and also developed a compensatory strategy in stair descent, which altered the scaling of muscle preactivity and increased leg stiffness.
authors.affiliation: Faculty of Physical Therapy, College of Health Science, Kaohsiung Medical University, Kaohsiung City, Taiwan.
authors.forename: Miao-Ju
authors.initials: MJ
authors.lastname: Hsu
authors.forename: Shun-Hwa
authors.initials: SH
authors.lastname: Wei
authors.forename: Young-Hue
authors.initials: YH
authors.lastname: Yu
authors.forename: Ya-Ju
authors.initials: YJ
authors.lastname: Chang
mesh_terms: D000367:Age Factors; D004576:Electromyography; D005081:Exercise Therapy / Q000379:methods*; D005500:Follow-Up Studies; D006801:Humans; D007717:Knee / Q000503:physiopathology*; D007866:Leg / Q000503:physiopathology*; D008297:Male; D009128:Muscle Spasticity / Q000175:diagnosis / Q000503:physiopathology* / Q000534:rehabilitation; D009129:Muscle Tonus / Q000502:physiology*; D018482:Muscle, Skeletal / Q000503:physiopathology*; D016138:Walking / Q000502:physiology*; D055815:Young Adult