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Related Experiment Videos

Reflex facilitation during the stretch-shortening cycle.

M H Trimble1, C G Kukulka, R S Thomas

  • 1Department of Physical Therapy, University of Florida, Gainesville,FL 32610-0154, USA. mtrimble@hp.ufl.edu

Journal of Electromyography and Kinesiology : Official Journal of the International Society of Electrophysiological Kinesiology
|May 20, 2000
PubMed
Summary

The stretch-shortening cycle enhances muscle torque through neural mechanisms. Spindle afferent activity during the eccentric phase facilitates neural drive, increasing muscle activation and synchronization.

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Area of Science:

  • Human Physiology
  • Neuroscience
  • Biomechanics

Background:

  • The stretch-shortening cycle (SSC) enhances concentric muscle power.
  • The neural mechanisms underlying SSC potentiation remain unclear.
  • Spindle afferent discharge during eccentric loading may facilitate volitional drive.

Purpose of the Study:

  • To investigate the neural contribution of the SSC to enhanced muscle activation.
  • To determine if spindle afferent activity during the eccentric phase facilitates neural drive.
  • To explore the synchronization of neural drive during SSC.

Main Methods:

  • Compared electromyography (EMG) during reciprocal hopping (RHOP) vs. maximal voluntary isometric contractions (MIVCs).
  • Assessed EMG during concentric-only hops (CHOP) to isolate the effect of the eccentric phase.

Related Experiment Videos

  • Applied high-frequency afferent stimulation (HFS) during MIVCs to mimic spindle afferent activity.

    • Main Results:

    • RHOP and CHOP conditions showed significantly greater peak and mean EMG than MIVCs.
    • RHOP produced higher peak EMG than CHOP, indicating the importance of the eccentric phase.
    • HFS during MIVCs potentiated soleus EMG and provided evidence for EMG synchronization.

    Conclusions:

    • The eccentric phase of the SSC provides neural facilitation.
    • Spindle afferent activity during the eccentric phase enhances volitional neural drive.
    • This neural facilitation may involve synchronization of motor unit activity.