Thursday, April 16, 2009

Performance Research for April : Central Fatigue and Exercise part 1

Treadmill Update
I updated the post the other day in an attempt to better explain my treadmill thoughts; so go back and check it out if you have not done so

Get Off the Treadmill!

General Update
All is going well, just stupid busy and up at 4:30am tomorrow for more testing again in the lab for my Energy Drink study, which is good. Getting close to the end now.

Some new studies for all of you related to central/peripheral fatigue. Enjoy and see my comments below each one.

Fatigue alters in vivo function within and between limb muscles during locomotion.

Higham TE, Biewener AA. Department of Biological Sciences, Clemson University, 132 Long Hall, Clemson, SC 29634, USA.

Muscle fatigue, a reduction in force as a consequence of exercise, is an important factor for any animal that moves, and can result from both peripheral and/or central mechanisms. Although much is known about whole-limb force generation and activation patterns in fatigued muscles under sustained isometric contractions, little is known about the in vivo dynamics of limb muscle function in relation to whole-body fatigue. Here we show that limb kinematics and contractile function in the lateral (LG) and medial (MG) gastrocnemius of helmeted guineafowl (Numida meleagris) are significantly altered following fatiguing exercise at 2ms-1 on an inclined treadmill.

The two most significant findings were that the variation in muscle force generation, measured directly from the muscles' tendons, increased significantly with fatigue, and fascicle shortening in the proximal MG, but not the distal MG, decreased significantly with fatigue. We suggest that the former is a potential mechanism for decreased stability associated with fatigue. The region-specific alteration of fascicle behaviour within the MG as a result of fatigue suggests a complex response to fatigue that probably depends on muscle-aponeurosis and tendon architecture not previously explored.

CONCLUSION: These findings highlight the importance of studying the integrative in vivo dynamics of muscle function in response to fatigue.

My Notes: This study shows once again that studies done in isolation and in a petri dish may not (heck, are usually) not the same as those done in the whole body. Everything affects everything in the body. Dr. Cobb likes to say "all the body, all the time"

Brain activation in multiple sclerosis: a BOLD fMRI study of the effects of fatiguing hand exercise.

White A, Lee J, Light A, Light K. Department of Exercise & Sport Science and Brain Institute, University of Utah, Salt Lake City, Utah, USA.

BackgroundMultiple sclerosis (MS) patients experience fatigue as a chronic symptom that decreases quality of life. Commonly, fatigue in MS patients is manifested as decreased motor function during or after physical activity and is associated with changes in brain metabolism.ObjectiveTo determine brain activation patterns in MS patients and healthy controls during a simple motor task before and after fatiguing hand-grip exercise.MethodsFunctional magnetic resonance imaging (fMRI) scans were conducted on 10 MS patients and 13 healthy controls during 4-finger flexion and extension in rested and fatigued states.

ResultsBefore the fatigue protocol, MS patients had greater activation in the contralateral primary motor cortex, insula, and cingulate gyrus than controls. Following fatiguing exercise, controls showed increased activation of precentral gyrus and insula while patients did not show any activation increases and actually decreased activity to the insula.

CONCLUSION: Results indicate that before fatiguing exercise, MS patients marshaled more brain activation compared to controls, which may represent functionally adaptive changes in response to demyelination. This increased activation may suggest that patients require more effort to perform even simple motor tasks, possibly because peripheral or central signals for fatigue are chronically enhanced. When fatigued further by muscle contraction, brain activation cannot be further increased.

My Notes: Sounds like the brain is having to work over time to attempt to make up for this difference. I would expect to see changes in the brain and coordination patterns then long term.

Mechanisms of fatigue induced by isometric contractions in exercising humans and in mouse isolated single muscle fibres.

Place N, Bruton JD, Westerblad H. Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.

1. Muscle fatigue (i.e. the decrease in muscle performance during exercise) has been studied extensively using a variety of experimental paradigms, from mouse to human, from single cell to whole-body exercise. Given the disparity of models used to characterize muscle fatigue, it can be difficult to establish whether the results of basic in vitro studies are applicable to exercise in humans. 2. In the present brief review, our attempt is to relate neuromuscular alterations caused by repeated or sustained isometric contraction in humans to changes in excitation-contraction (E-C) coupling observed in intact single muscle fibres, where force and the free myoplasmic [Ca(2+)] can be measured. 3. Accumulated data indicate that impairment of E-C coupling, most likely located within muscle fibres, accounts for the fatigue-induced decrease in maximal force in humans, whereas central (neural) fatigue is of greater importance for the inability to continue a sustained low-intensity contraction.

Based on data from intact single muscle fibres, the fatigue-induced impairment in E-C coupling involves: (i) a reduced number of active cross-bridges owing to a decreased release of Ca(2+); (ii) a decreased sensitivity of the myofilaments to Ca(2+); and/or (iii) a reduced force produced by each active cross-bridge. 4.

CONCLUSION: In conclusion, data from single muscle fibre studies can be used to increase our understanding of fatigue mechanisms in some, but not all, types of human exercise. To further increase the understanding of fatigue mechanisms in humans, we propose future studies using in vitro stimulation patterns that are closer to the in vivo situation.

My Notes: Um, see my comments above about in vitro (petri dish/bench testing) and in vivio (in the body testing). The reality is that research is a back and forth method or in the clinical world they call it "bench top to bed side"