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Related Experiment Videos

Increased spinal excitability does not offset central activation failure.

J M Kalmar1, C Del Balso, E Cafarelli

  • 1Department of Biology, Rm 346 Bethune College, York University, Toronto, ON, Canada.

Experimental Brain Research
|March 1, 2006
PubMed
Summary
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Caffeine did not prevent fatigue-induced declines in maximal voluntary contraction or activation, despite increasing spinal excitability. Reduced spinal excitability did not limit maximal activation after fatigue.

Area of Science:

  • Exercise Physiology
  • Neuroscience
  • Human Performance

Background:

  • Central activation failure is a key factor in muscle fatigue.
  • Reduced spinal excitability is hypothesized to contribute to this failure.
  • Caffeine is known to increase central nervous system excitability.

Purpose of the Study:

  • To investigate if caffeine-induced increases in spinal excitability could enhance post-fatigue maximal voluntary activation and contraction.
  • To determine if reduced spinal excitability limits maximal voluntary activation following fatigue.

Main Methods:

  • Ten male subjects underwent two sessions: one with caffeine (6 mg/kg) and one with placebo.
  • Spinal excitability was assessed via H reflex recruitment curves (H(slp)/M(slp)).

Related Experiment Videos

  • Maximal voluntary contraction (MVC) and maximal voluntary activation (using twitch interpolation) were measured before and after a fatigue protocol.

    • Main Results:

    • MVC torque and % activation declined significantly post-fatigue in both placebo and caffeine trials.
    • Caffeine attenuated the decline in spinal excitability (H(slp)/M(slp)) compared to placebo.
    • Caffeine did not prevent the reduction in maximal voluntary activation or MVC torque.
    • Decline in spinal excitability correlated with EMG(max) but not with % activation or MVC torque.

    Conclusions:

    • Caffeine increases spinal excitability but does not prevent central activation failure or performance decline after fatigue.
    • Fatigue-induced reduction in spinal excitability does not appear to be the primary limiting factor for maximal voluntary activation.