title: Tendon elongation influences the amplitude of interpolated doublets in the assessment of activation in elderly men.
abstract: 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 degrees (dorsiflexion), 0 degrees , and 20 degrees (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 20 degrees . In the EM, PCD torque relative to MVC torque was significantly lower at 20 degrees compared with 0 degrees (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.
authors.affiliation: Institute for Biophysical and Clinical Research into Human Movement, Manchester Metropolitan University, Alsager Campus, Hassall Road, Alsager, Cheshire ST7 2HL, UK. c.morse@mmu.ac.uk
authors.forename: Christopher I
authors.initials: CI
authors.lastname: Morse
authors.forename: Jeanette M
authors.initials: JM
authors.lastname: Thom
authors.forename: Karen M
authors.initials: KM
authors.lastname: Birch
authors.forename: Marco V
authors.initials: MV
authors.lastname: Narici
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D000843:Ankle Joint / Q000502:physiology*; D003936:Diagnosis, Computer-Assisted / Q000379:methods*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D010808:Physical Examination / Q000379:methods*; D013314:Stress, Mechanical; D013710:Tendons / Q000000981:diagnostic imaging* / Q000502:physiology*; D019415:Torque; D014463:Ultrasonography