Sunday, January 11, 2009

Performance Research: Heat and Caffeine and Central Fatigue


Just wanted to drop a quick note that I am on my way back from the Z Health Master Trainer Cert and I will have much more information for all of you coming up very soon, so stayed tuned.

On an excellent note I PASSED!!! I needed 90% or higher to pass and I made it! Whoo ha. Wow, it was a crazy intensive 6 day evaluation. I was up early every day and to bed late most nights working of Z Health stuff the whole time. I want to send a HUGE congrats to the the others that passed and to all that were there for their support! I could not have done it by myself alone! More info later in the week.

Here is a cool study below in the meantime on caffeine and heat and one other one on central fatigue.

No effect of nutritional adenosine receptor antagonists on exercise performance in the heat.

Cheuvront SN, Ely BR, Kenefick RW, Michniak-Kohn BB, Rood JC, Sawka MN.

USARIEM. Nutritional adenosine antagonists can enhance endurance exercise performance in temperate environments, but their efficacy during heat stress is not well understood. This double-blinded, placebo controlled study compared the effects of an acute dose of caffeine or quercetin on endurance exercise performance during compensable heat stress (40 masculineC, 20-30%rh). On each of three occasions, ten healthy men performed 30-minutes of cycle ergometry at 50% VO2peak followed by a 15-min performance time trial after receiving either (P) placebo, (C) caffeine (9 mg/kg), or (Q) quercetin (2,000 mg). Serial blood samples, physiological (heart rate, rectal, and mean skin body temperatures), perceptual (ratings of perceived exertion, pain, thermal comfort, motivation), and exercise performance measures (total work and pacing strategy) were made.

Supplementation with C and Q increased pre-exercise blood concentrations of caffeine (55.62 +/- 4.77 microM) and quercetin (4.76 +/- 2.56 microM) above their in vitro inhibition constants for adenosine receptors. No treatment effects were observed for any physiological or perceptual measures, with the exception of elevated rectal body temperatures (0.20 - 0.30 degrees C; P<0.05)>0.05) or the self-selected pacing strategy employed.

Conclusion: These findings indicate that the nutritional adenosine antagonists caffeine and quercetin do not enhance endurance exercise performance during compensable heat stress.

Opioid-mediated muscle afferents inhibit central motor drive and limit peripheral muscle fatigue development in humans.

Amann M, Proctor LT, Sebranek JJ, Pegelow DF, Dempsey JA.

University of Zürich and ETH Zürich; University of Wisconsin-Madison Medical School. We investigated the role of somatosensory feedback from locomotor muscles on central motor drive (CMD) and the development of peripheral fatigue during high-intensity endurance exercise. In a double-blind, placebo-controlled design, eight cyclists randomly performed three 5 km time-trials: control, interspinous ligament injection of saline (5KPlac, L3-L4), or intrathecal fentanyl (5KFent, L3-L4) to impair cortical projection of opioid-mediated muscle afferents. Peripheral quadriceps fatigue was assessed via changes in force output pre- vs post-exercise in response to supra-maximal magnetic femoral nerve stimulation (DeltaQtw). CMD during the time-trials was estimated via quadriceps electromyogram (iEMG).

Fentanyl had no effect on quadriceps strength. Impairing neural feedback from the locomotor muscles increased iEMG during the first 2.5 km of 5KFent vs 5KPlac by 12 +/- 3%

Conclusion: Our results emphasize the critical role of somatosensory feedback from working muscles on the centrally mediated determination of central motor drive and power output.

Attenuated afferent feedback from exercising locomotor muscles results in an overshoot in central motor drive and power output normally chosen by the athlete, thereby causing a greater rate of accumulation of muscle metabolites and excessive development of peripheral muscle fatigue.