Volume 44 Number 3 2007
Pages 429 — 436

Abstract - Leg stiffness and electromyography of knee extensors/flexors: Comparison between older and younger adults during stair descent

Miao-Ju Hsu, PhD;1 Shun-Hwa Wei, PhD;2 Young-Hue Yu, MD;3 Ya-Ju Chang, PhD4*

1Faculty of Physical Therapy, College of Health Science, Kaohsiung Medical University and Department of Rehabilitation, Kaohsiung Medical University Hospital, Kaohsiung City, Taiwan; 2Graduate Institute of Rehabilitation Science and Technology, National Yang Ming University, Taipei City, Taiwan; 3Department of Physical Medicine and Rehabilitation, Taipei City Hospital, Yang Ming Branch, Taipei City, Taiwan; 4Physical Therapy Department and Graduate Institute of Rehabilitation Science, Chang Gung University, Taiwan

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.

Key words: coactivation, elderly, EMG, knee extensor/flexor, leg loading rate, leg stiffness, preactivation, rehabilitation, stair descent, stair walking.

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