Monday, April 20, 2009

Performance Research for April : Central Fatigue during Exercise part 2

More info for yas on why do you actually stop a heavy training set, high intensity exercise etc.

I have some comments to get to yet on the treadmill post, so hang in there with me. Excellent comments by all and much appreciated!

I am excited that I have 7 exercise tests for the Energy Drink study in the lab this week, which brings me closer to wrapping up the data collection portion, although it equals more cat naps in my car and more coffee.

Congrats to all the new RKCs that passed this past weekend! Sorry I was not able to stop down there, but excellent work! If anyone is around here for the next one and is interested in a Z Health session to optimize your performance, drop me a line---first come first serve.

On to the studies....

Voluntary activation and cortical activity during a sustained maximal contraction: an fMRI study.

Post M, Steens A, Renken R, Maurits NM, Zijdewind I. Department of Medical Physiology, University Medical Center Groningen, University of Groningen, The Netherlands.

Motor fatigue is an exercise-induced reduction in the force-generating capacity. The underlying mechanisms can be separated into factors residing in the periphery or in the central nervous system. We designed an experiment in which we investigated central processes underlying motor fatigue by means of magnetic resonance imaging in combination with the twitch interpolation technique. Subjects performed a sustained maximal abduction (2 min) with the right index finger. Brain activation was recorded with an MR scanner, together with index finger abduction force, EMG of several hand muscles and interpolated twitches.

Mean activity per volume was calculated for the primary motor cortex and the secondary motor areas (supplementary motor, premotor, and cingulate areas) as well as mean force and mean rectified EMG amplitude. Results showed a progressive decline in maximal index finger abduction force and EMG of the target muscles combined with an increase in brain activity in the contralateral primary motor cortex and secondary motor areas. Analysis of the twitches superimposed on the sustained contraction revealed that during the contraction the voluntary drive decreased significantly.

CONCLUSION: In conclusion, our data showed that despite an increase in brain activity the voluntary activation decreased. This suggests that, although the central nervous system increased its input to the relevant motor areas, this increase was insufficient to overcome fatigue-related changes in the voluntary drive.

My Notes: Hmmm, perhaps we are seeing a blend of peripheral and central fatigue out in the really real world?

Estimation of critical torque using intermittent isometric maximal voluntary contractions of the quadriceps in humans.

Burnley M. Department of Sport and Exercise Science, Aberystwyth University, Ceredigion, United Kingdom.

To determine whether the asymptote of the torque-duration relationship (critical torque) could be estimated from the torque measured at the end of a series of maximal voluntary contractions (MVCs) of the quadriceps, eight healthy men performed eight laboratory tests. Following familiarization, subjects performed two tests in which they were required to perform 60 isometric MVCs over a period of 5 min (3 s contraction, 2 s rest), and five tests involving intermittent isometric contractions at approximately 35-60% MVC, each performed to task failure. Critical torque was determined using linear regression of the torque impulse and contraction time during the submaximal tests, and the end-test torque during the MVCs was calculated from the mean of the last six contractions of the test.

During the MVCs voluntary torque declined from 263.9 +/- 44.6 to 77.8 +/- 17.8 N x m. The end-test torque was not different from the critical torque (77.9 +/- 15.9 N x m; 95% paired-sample confidence interval, -6.5 to 6.2 N x m). The root mean squared error of the estimation of critical torque from the end-test torque was 7.1 N x m. Twitch interpolation showed that voluntary activation declined from 90.9 +/- 6.5% to 66.9 +/- 13.1% (P < style="font-weight: bold;">indicating the development of both central and peripheral fatigue.

CONCLUSION: These data indicate that fatigue during 5 min of intermittent isometric maximal voluntary contractions of the quadriceps leads to an end-test torque that closely approximates the critical torque.

My notes: see my comment above!