Weppler and Magnusson (“Increasing Muscle Extensibility: A Matter of Increasing Length or Modifying Sensation?” March 2010) offer clarification on points made on page 443 of their article. Specifically, they clarify that they were referring to research with subjects who were neurologically intact and asymptomatic and that the biomechanical effects of contract/relax stretching involve both a sensory modification and a viscoelastic effect. Revised parts are bolded below:
Experimental evidence does not support any of these assertions in studies involving subjects who were neurologically intact and asymptomatic.13,14,54,55 Stretch reflexes have been shown to activate during very rapid and short stretches of muscles that are in a mid-range position, producing a muscle contraction of short duration.54 However, most studies of subjects who were neurologically intact and asymptomatic and whose muscles were subjected to a long, slow, passive stretch into end-range positions, did not demonstrate significant activation of stretched muscles.14,54,56,57 Even studies that simulated ballistic (cyclic and high-velocity) stretching demonstrated no evidence of significant stretch reflex activation of muscles both in human26 and animal23 models. In a study that evaluated the effects of a single “contract-relax” stretch,25 no significant electromyographic activity was observed during stretch application and no shift of passive torque/angle curves was observed aside from what could be attributed to viscoelastic stretch relaxation. Several short-term (3 and 6 weeks’ duration) stretching studies45,58 demonstrated similar findings: no significant electromyographic activity during initial and final testing and no shift of passive torque/angle curves. The increase in end-range joint angles, therefore, could not be attributed to neuromuscular relaxation.14,25,45,58
- © 2010 American Physical Therapy Association
Issue highlights
