Monday, February 16, 2009

Performance Research for February: Central fatigue exercise 3

I am pounded ya with more studies, but I know you can handle it. See my notes below as always and be sure to check out round 1 and round 2.

The effects of head cooling on endurance and neuroendocrine responses to exercise in warm conditions.

Ansley L, Marvin G, Sharma A, Kendall MJ, Jones DA, Bridge MW. School of Psychology and Sport Sciences, Northumbria University, Newcastle upon Tyne, United Kingdom.

The present study investigated the effects of head cooling during endurance cycling on performance and the serotonergic neuroendocrine response to exercise in the heat. Subjects exercised at 75 % VO(2max) to volitional fatigue on a cycle ergometer at an ambient temperature of 29+/-1.0 C, with a relative humidity of approximately 50 %.

Head cooling resulted in a 51 % (p<0.01)>

There were no indications of peripheral mechanisms of fatigue either with, or without, head cooling, indicating the importance of central mechanisms. Exercise in the heat caused the release of prolactin in response to the rise in rectal temperature. Head cooling largely abolished the prolactin response while having no effect on rectal temperature.

Tympanic temperature and sinus skin temperature were reduced by head cooling and remained low throughout the exercise. It is suggested that there is a co-ordinated response to exercise involving thermoregulation, neuroendocrine secretion and behavioural adaptations that may originate in the hypothalamus or associated areas of the brain.

CONCLUSON: Our results are consistent with the effects of head cooling being mediated by both direct cooling of the brain and modified cerebral artery blood flow, but an action of peripheral thermoreceptors cannot be excluded.

My Notes: Remember in round 1 where we saw that brain heating may affect performance. If that is true, then brain COOLING should INCREASE performance and according to this study, it is true. Here is my multi million dollar idea---make a head garment for cardio bunnies to wear that cools their noggin. When you make billions, keep me in mind and let me visit your island in Fiji.
Be thankful you were not in this study, as they measured rectal temps during exercise. Yikes!

Dehydration: cause of fatigue or sign of pacing in elite soccer?

Edwards AM, Noakes TD. UCOL Institute of Technology, Faculty of Health Sciences, Palmerston North, New Zealand.

Numerous studies have suggested that dehydration is a causal factor to fatigue across a range of sports such as soccer; however, empirical evidence is equivocal on this point. It is also possible that exercise-induced moderate dehydration is purely an outcome of significant metabolic activity during a game. The diverse yet sustained physical activities in soccer undoubtedly threaten homeostasis, but research suggests that under most environmental conditions, match-play fluid loss is minimal ( approximately 1-2% loss of body mass), metabolite accumulation remains fairly constant, and core temperatures do not reach levels considered sufficiently critical to require the immediate cessation of exercise. A complex (central) metabolic control system which ensures that no one (peripheral) physiological system is maximally utilized may explain the diversity of research findings concerning the impact of individual factors such as dehydration on elite soccer performance.

In consideration of the existing literature, we propose a new interpretative pacing model to explain the self-regulation of elite soccer performance and, in which, players behaviourally modulate efforts according to a subconscious strategy. This strategy is based on both pre-match (intrinsic and extrinsic factors) and dynamic considerations during the game (such as skin temperature, thirst, accumulation of metabolites in the muscles, plasma osmolality and substrate availability), which enables players to avoid total failure of any single peripheral physiological system either prematurely or at the conclusion of a match.

CONCLUSION: In summary, we suggest that dehydration is only an outcome of complex physiological control (operating a pacing plan) and no single metabolic factor is causal of fatigue in elite soccer.

My Notes: Timmy Noakes is at it again with a cool (get it, I make bad pun,hahaha) study on dehydration. It makes sense that there is not one SINGLE factor. Physiology is messy, non linear and complicated.