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The genu effect on plantar flexor power.

Brian H Dalton1, Geoffrey A Power, Matti D Allen

  • 1School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, Canadian Centre for Activity and Aging, London, ON, Canada. bdalton@mail.ubc.ca

European Journal of Applied Physiology
|December 18, 2012
PubMed
Summary

Altering knee joint angle significantly impacts triceps surae muscle function. A flexed knee position reduces plantar flexor power and torque, especially at higher loads, due to gastrocnemii disadvantage.

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Area of Science:

  • Biomechanics
  • Human Physiology
  • Sports Science

Background:

  • The triceps surae muscle group's function is influenced by knee joint angle, affecting the gastrocnemii's contribution.
  • Previous research has not systematically investigated how knee angle affects plantar flexor power across various loads.

Purpose of the Study:

  • To determine the effect of knee joint angle (extended vs. flexed) on plantar flexor torque, velocity, and power.
  • To analyze these effects across a range of external loads (15-75% of maximal voluntary isometric contraction).

Main Methods:

  • Eleven young men performed plantar flexion tasks with the knee in an extended (170°) and flexed (90°) position.
  • Torque, velocity, and power were measured under varying load conditions.
  • Voluntary activation and contractile properties were assessed.

Main Results:

  • Peak torque and maximal voluntary isometric contraction (MVC) torque were significantly lower in the flexed knee position.
  • Plantar flexor power was reduced by 15-24% across all loads in the flexed knee.
  • At lower loads (≤30% MVC), reduced power in the flexed knee was linked to slower shortening velocities; at higher loads, limited torque production was the primary factor.

Conclusions:

  • A flexed knee position disadvantages the gastrocnemii, shifting the torque-power relationship and impairing maximal power production.
  • The gastrocnemii are crucial for plantar flexion torque, modifying loaded shortening velocity, and ultimately, power output.