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Tendon elongation influences the amplitude of interpolated doublets in the assessment of activation in elderly men

¹Institute for Biophysical and Clinical Research into Human Movement (IRM), Manchester Metropolitan University, Alsager, Cheshire; and ²University of Leeds Institute of Sport and Exercise Science, University of Leeds, Leeds, United Kingdom

Submitted 22 July 2004 ; accepted in final form 26 August 2004

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 –20° (dorsiflexion), 0°, and 20° (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° (P < 0.05), but no different at 0 and 20°. In the EM, PCD torque relative to MVC torque was significantly lower at 20° compared with 0° (P < 0.05). Electromechanical delay was positively correlated with TE (R² = 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.

torque; plantar flexion; dorsiflexion

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