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First published online April 18, 2006
Journal of Experimental Biology 209, vii (2006)
Copyright © 2006 The Company of Biologists Limited
doi: 10.1242/jeb.02220
Outside JEB |
HEAT UP AND SPEED UP
National Environmental Research Institute, Silkeborg, Denmark
jov{at}dmu.dk
|
Watch an athlete preparing for a race and the one thing they focus on is their warm-up routine. This is because muscle performance is better at warm temperatures. For example increased temperature improves oxygen unloading from hemoglobin and myoglobin and it may also reduce the risk of strains and pulls. Elevated temperature also increases nervous signal transduction and a warmed muscle contracts more vigorously and relaxes more quickly due to increases in the crossbridge cyling and ATP turnover rates. The benefits of increased ATP turnover are most pronounced during intense sprints, when the muscle works close to its maximal limits for a short time. It is, therefore, a paradox that the type I muscle fibres, which are associated with endurance performance, seem to be more responsive to elevated ATP turnover and power output at raised temperatures, than the type IIA fibres associated with sprinting. To investigate this Stuart Gray and his colleagues from University of Strathclyde and Aalborg University investigated the importance of elevated muscle temperature for performance during a 6-second bicycle sprint. In particular they examined the increased scope for ATP turnover and the increased velocity of muscle fibre activation in sprinting warm muscle.
All of the participants in the study performed the same sprint test at both normal and elevated muscle temperatures. But instead of warming the test person's muscles with exercise, they raised their muscle temperature by placing the cyclists in a warm bath. During both `normal' and elevated temperature cycle sprints, the team measured the athletes' power outputs and pedal rates. In addition the scientists took a muscle biopsy from each of the sportsmen immediately before and after the sprint test in order to assess the ATP turnover. Finally, the muscle fibre conduction velocity was measured with a multi channel surface EMG recording from the thigh muscle.
The group found that the 
3°C increase in muscle temperature
significantly increased ATP turnover and that this increase was associated
with an increase in muscle fibre conduction velocity. This indicated that the
increased energy turnover in warmed muscles was linked to the faster
activation of the muscle fibres, and warming was also associated with an in
increase in pedal rate and in total power output so that the maximal power
output was 20% higher when the participants had warm muscles. In contrast
to some previous studies on maximal sprint performance, Gray and colleagues
conducted the sprint test so that the participants were allowed to increase
the sprint speed (pedal rate) instead of increasing the load against which
they were working. Under these conditions, which are probably more realistic
in terms of real sprints, the authors found that the increase in power output
correlated best with the amount of Type IIA `sprint' muscle fibres. Thus, when
the fast muscles fibres are allowed to work fast they also benefit
considerably from the increased temperature and this result resolves the
apparent paradox where it was thought that it was mainly the `endurance'
fibres that benefited from increased ATP-turnover.
Even though an increased ATP turnover and power output at elevated temperatures is not a novel finding in itself, the study by Gray and his team re-emphasises the importance that a few degrees rise in muscle temperature can have for the tissue's function. Considering that sprint competitions are often decided by only a few hundredths of a second it certainly seems to be important to warm up well in order to get ahead.
References
Gray, S. R., De Vito, G., Nimmo, M. A., Farina, D. and Ferguson,
R. A. (2006). Skeletal muscle ATP turnover and muscle fiber
conduction velocity are elevated at higher muscle temperatures during maximal
power output development in humans. Am. J. Physiol. Regul. Integr.
Comp. Physiol. 290,R376
-R382.
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