Wednesday, 24 August 2011

My VO2 max

Today I took part in an interesting research project at The Physiological Laboratory of the University of Cambridge. Dr Christof Schwiening is investigating the relationship between VO2max, body temperature and sweat production. For those not versed in human physiology, VO2 max it is the maximum amount of oxygen that an individual can take up per minute. It is one measure of the aerobic capacity of the cardiorespiratory system (the heart, lungs and blood vessels), and thus a pretty good indicator of an individual fitness level.

Hence VO2max is often of interest to endurance athletes, as it constitutes a physiological benchmark for one's fitness. Many things can affect VO2max: age, gender, fitness and training, changes in altitude, and action of the ventilatory muscles. Like all things in human physiology, there is probably a strong genetic component, with some lucky individuals being blessed with exceptional physiques (and very high VO2max) while most of us fit in the middle of a normal distribution.

But in most individuals aerobic exercise and training will improve one's VO2max, by triggering changes in the body's muscular, cardiovascular, and neurohumoral systems that lead to improvement in functional capacity and strength: the body becomes more efficient at carrying oxygen. In essence exercise and training will fine tune the amazing machinery that is the human body.

Dr Schwiening's project is concerned with testing the hypothesis that the amount of sweat produced for a given body temperature is a simple function of VO2max.While you exercise the extra energy released by the body slowly increases the internal body temperature. Sweating is the body's own natural cooling system. It is known that men sweat more than women [1], Dr Schwiening thinks that the difference in the two genders can be explained by VO2max alone (typically men enjoy a higher VO2max than us ladies). The idea is that fitter individuals sweat more efficiently: they sweat more at lower body temperature, thus preventing overheating. 

I was asked to perform two sets of exercise tests on a fixed exercise bike. The first was a conventional extrapolated VO2max test in which my oxygen uptake was measured with a spirometer while measuring the corresponding heart rate at fixed incremental stages (from 100bpm to 140bpm). The second test involved having my sweat collected and weighted during a set period of exercise (around 20 minutes at 140bpm) while measuring body temperature with a standard infra-red ear thermometer.

The  VO2max obtained by either method was then compared. And sure enough, the sweat/temperature method was pretty accurate at predicting my (very average) VO2max, only slightly overestimating the value of around 36 ml/kg/min. It was very interesting to see how well sweat production and body temperature correlated: in the first 10 minutes of exercise my body temperature steadily increased by about half a degree, in response my sweat production peaked and eventually the body temperature was restored to normal.
The other half of the experiment, strikingly illustrated the linear relationship between oxygen consumption and effort (as measured by heart rate), the graph was kindly provided by Dr Schwiening.

Hopefully as I get fitter doing my Gold challenge, my VO2max ought to improve, and the line should get steeper. However, slightly off-puttingly, it should also mean that I will sweat more and at lower exercise intensities!

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