Journal
JOURNAL OF APPLIED PHYSIOLOGY
Volume 98, Issue 1, Pages 221-226Publisher
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/japplphysiol.00774.2004
Keywords
torque; plantar flexion; dorsiflexion
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This study investigated the influence of tendon elongation (TE) on postcontraction doublet (PCD) torque in the assessment of activation in the plantar flexors of nine elderly men (EM, age 73.7 +/- 3.6 yr) and nine young men (YM, age 24.7 +/- 4.7 yr). Plantar flexion maximal voluntary contractions (MVC) and activation were assessed at ankle joint angles of -20degrees ( dorsiflexion), 0degrees, and 20degrees ( plantar flexion). Across the ankle joint angles tested, compared with YM, the EM had a 36 - 49% lower plantar flexion MVC ( P < 0.01), TE was greater by 25 - 31% ( P < 0.01), and electromechanical delay was 65 - 108% greater ( P < 0.01). Activation ( PCD torque to interpolated doublet torque) was 15% lower in EM compared with YM at - 20 degrees ( P < 0.05), but no different at 0 and 20degrees. In the EM, PCD torque relative to MVC torque was significantly lower at 20degrees compared with 0degrees ( P < 0.05). Electromechanical delay was positively correlated with TE (R-2 = 0.489, P < 0.01). In conclusion, this investigation demonstrates that, although a negative association exists between TE and PCD torque, the consequence of a greater TE on the estimation of activation in EM is negligible. This is due to a greater influence of ankle joint angle on the occlusion of a superimposed doublet, which counteracts the lesser influence of joint angle on TE and PCD torque. However, a greater TE in EM was found to significantly increase electromechanical delay, which is expected to influence the time needed for postural readjustments.
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