Electronic Thesis and Dissertation Repository

Degree

Master of Science

Program

Kinesiology

Supervisor

Dr. Anthony Vandervoort

Abstract

The force-velocity relationship of skeletal muscle dictates that with increasing velocity of muscle shortening there is an exponential decrease in force production. However, during lengthening muscle actions, with increasing velocity there is a rapid increase then plateau in force. It is unknown whether ECC strength continues to increase at very-fast velocities (>200o/s). PURPOSE: To investigate ECC strength of the dorsiflexors over a large range of velocities in younger and older men. METHODS: Isometric neuromuscular properties (voluntary & electrically evoked) were assessed at 40o of plantar flexion on a CYBEX dynamometer. Nine younger (~24y) and 9 older (~76y) healthy men performed, in random order, one isokinetic lengthening contraction over a 50o range of motion (5o DF- 45oPF) at ten angular velocities; 15, 30, 45, 60, 120, 210, 270, 300, 330, 360o/s. RESULTS: Participant voluntary activation was >99% in both older and younger. Older were 31% weaker than the young for ISO strength. At all velocities, old had a greater ECC:ISO ratio compared to young. Additionally, there was a velocity-dependence of strength in both groups, in which absolute ECC strength increased as velocity increased. Old and young ECC strength at 15o/s was 17% and 37% greater than ISO strength; while at 360o/s ECC strength was 49% and 88% greater, respectively. CONCLUSION: Both old and young had continuing increases in ECC ankle dorsiflexion strength as the velocity of the lengthening contraction increased. Furthermore, relative to isometric levels, the older group showed particularly enhanced torque production at the higher velocities of muscle lengthening.

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