Warming up before high-intensity exercise boosts total oxygen consumption but does not increase time to exhaustion: that's the conclusion of a small-scale Scottish study comparing the effects of active, passive or no warm-up on metabolism and performance.

Eight healthy men volunteered for three identical experimental trials performed one week apart under identical conditions. An exercise test involving cycling on an ergometer at 120% of maximal power output for 30 seconds was followed by one minute's rest, then a performance test involving cycling to exhaustion, again at 120% of maximal output. Each trial was preceded by one of three experimental conditions:

Active warm-up - cycling at 40% of maximal power output for 5 minutes, followed by 1 minute's rest, then 4 15s sprints at 120% of maximal power output, with 15s rest between sprints;

Passive warm-up - sitting quietly in an environmental chamber maintained at constant temperature (45πC) and relative humidity (70%) until muscle temperature reached the same value achieved during active warm-up;

Control - sitting on the examination couch in the laboratory for the 'warm-up' period.

A range of measurements was carried out before, during and after the trials and key results were as follows:

Muscle temperature was significantly higher after active and passive warm-up than in the control trial, with no significant difference between the two warm-up trials;

After warm-up, heart rates were elevated for all three groups, although they were higher after passive warm-up than for the control condition and higher still after active warm-up;

After active warm-up, blood lactate was higher than in the passive and control trials, with no significant difference between the latter two, although lactate concentrations were higher than resting values for both these groups from after the 30s exercise test. In fact, the change in blood lactate concentration from before to after this test was greater in the passive and control trials than in the active trial, as was the rise to peak lactate concentrations after the performance test, although the overall level was lower than in the active trial;

Total oxygen uptake during the exercise test was higher in the active and passive trials than in the control trial, with no difference between the first two trials;

There was no significant difference between trials during the performance test, as measured by exercise time to exhaustion.

'The results...', explain the authors, 'demonstrate that after an active warm-up there is an increase in total VO2 and a blunted blood lactate response during exercise compared to no warm-up...This would suggest that after an active warm-up the observed differences in metabolic responses during high-intensity exercise may not be due entirely to elevations in muscle temperature.'

They speculate that the blunted blood lactate response observed during the active trial may be associated with an increased rate of lactate clearance from the blood by skeletal muscle after active warm-up.

'The main finding of this study,' they conclude, 'is that, although the mechanism by which muscle temperature is elevated influences certain metabolic responses during high-intensity exercise of short duration, muscle temperature does not appear to be the sole determinant of energy metabolism during exercise.

'Despite the differing metabolic and physiological responses observed during exercise, however, there was no significant difference in short-duration, high-intensity performance irrespective of whether exercise was preceded by active, passive or no warm-up.'

J Sports Sci 2001 Sep 19(6), pp693-700

Isabel Walker