Contributed by Kareno Moreno
Muscle Fatigue
Is It All In Our Heads?
I recently read an article in The New York Times Magazine discussing the findings from a study out of England that examined the effects of rinsing your mouth with a carbohydrate sports drink on muscle fatigue. The results suggested the observed improvements in exercise performance when carbohydrate was present in the mouth maybe related to the activation of brain regions associated with reward and motor control. Could improved exercise performance be a matter of stimulating specific regions of our brains? Intrigued by the article, I found the published study in The Journal of Physiology.
Basic Outline of the Study
Researchers Chambers, Bridge and Jones (2009) conducted a two-part study exploring the possibility of central nervous system response to carbohydrates on exercise performance without a peripheral metabolic response. Eight male cyclists regularly involved in endurance training completed one hour time trails where they were given artificially sweetened solutions containing either glucose, maltodextrin or a placebo to rinse around their months at regular intervals. Each athlete completed the trails separately with minimal contact with the investigator to reduce external effects on performance. All the athletes participated in an over night fast and each time trail was separated by 3 rest days to reduce the effects of prior nutrition and fatigue.
The second part of the study was
to determine what, if any, effects of oral rinsing of the carbohydrate
solutions had on the brain. Functional magnetic resonance imaging (fMRI)
was used to identify the regions of the brain activated by each of the
three solutions. This portion of the study was independent of the time
trails and the proportions of glucose and maltodextrin were three times
greater than those used during the exercise performance. This is a limitation
of the study and raises the question of whether the lower doses used
during the time trails would activate the same regions of the brain
as the higher doses. However, the amounts were chosen to replicate as
well as provide comparison with previous glucose studies. The researchers
also pointed out that the fMRI was conducted during rest and the possibility
of exercise induced changes in the body, such as hyperthermia, could
alter the brains response to the carbohydrate solution. It was noted
that replicating the time trails inside the fMRI would be extremely
difficult and the head movement would alter the readings. However, it
would be interesting to see what images resulted during and immediately
following the time trail. Both saccharin and aspartame were used as
artificial sweeteners during the exercise, however only the effects
of saccharin was observed with fMRI. The researchers suggested the only
way this could invalidate their findings was if aspartame activated
similar brain regions as the glucose and maltodextrin, which was considered
unlikely. Over all this was a strong randomized, counterbalanced, double
blind study, which was carefully designed and easily reproducible.
The Results
The results from the time trails
confirmed findings by Carter et al. (2004a), which found a 2.9% performance
improvement using non-sweet maltodextrin solution compared with a plain
water placebo. Chambers, Bridge and Jones (2009) reported a 2% reduction
in completion time with an increase in mean power output with the artificially
sweetened glucose solution compared to the placebo and a 3.1% increase
with the artificially sweetened maltodextrin solution. The fMRI showed
that both the glucose and maltodextrin activated a variety of regions
in the brain, which may be associated with reward and the regulation
of motor activity, that were not activated with the saccharin solution.
Researchers Conclusions
The researchers concluded that
rinsing the month with non-sweetened and sweetened carbohydrate improved
simulated one-hour trail performance. The possible mechanism for this
observed improvement is the various regions of the brain associated
with reward and motor control activated by the carbohydrate. It was
also suggested that the findings support the existence of receptors
in the mouth that are sensitive to carbohydrate regardless of sweetness.
This, of course, requires further investigations.
Implications of the Study
Muscular fatigue has been explained through peripheral metabolic responses to intense exercise, such as the depletion of energy sources, and the accumulation of lactate and hydrogen ions. This study suggests the brain plays a greater role in motor activity and fatigue and may change the way we approach exercise performance.
To read the published research, check out the link below.
Chambers, E.S., Bridge, M.W., and Jones, D.A. (2009) Carbohydrate sensing in the human month:
effects on exercise performance and brain activity. The Journal of Physiology, 587, 8,
1779-1794.
Retrieved August 3, 2009 http://jp.physoc.org/content/
if that so, i will not too much gain exercise.
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