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1 Institute for Biophysical and Clinical Research into Human Movement, Manchester Metropolitan University, Alsager, Cheshire, United Kingdom
* To whom correspondence should be addressed. E-mail: c.morse{at}mmu.ac.uk.
This study investigated the influence of tendon elongation (TE), on post contraction doublet (PCD) torque in the assessment of activation, in the plantarflexors of nine elderly males (EM, age: 73.7 ± 3.6 years) and nine young males (YM, age: 24.7 ± 4.7 years). Plantarflexion maximal voluntary contractions (MVC) and activation were assessed at ankle joint angles of -20 deg (dorsiflexion), 0 deg and 20 deg (plantarflexion). Across the ankle joint angles tested, compared to YM, the EM had a 36 - 49% lower plantarflexion 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 to YM at -20 deg (P < 0.05), but no different at 0 deg and 20 deg. In the EM, PCD torque relative to MVC torque was significantly lower at 20 deg compared to 0 deg (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.
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