They are made up of the same stuff as everyone else, namely fat, muscle, and bone. However, their body composition differs, only by the total volume and relative proportion of these tissues. The ability to change strength, speed, and endurance is the reason athletes train, and in response to training remarkable changes in body composition occur, reflected by the physical demands of training.
This is nicely outlined by a paper published in this month’s issue of the Journal of Sports Sciences , looking at the changes in body composition of Inter-County level hurlers over time, using dual energy x-ray absorptiometry (DXA) to measure fat and muscle tissue. Over the course of the ‘pre-season’ ramping up to the All-Ireland Championships, where training volume and intensity will increase; during this 2 to 3 month period these athletes will gain 1 to 2 kg muscle whilst losing 2 to 3 kg of fat. This change is remarkable considering these athletes are not professionals, holding down other jobs outside of training, yet able to maintain the highest levels of performance. Once the season is over and the training demands are reduced, all the fat lost in the pre-season is regained, but some of the muscle is maintained.
Over the course of four-seasons this cycling of fat in and out of season is repeated season-to-season, and whilst the muscle fluctuates in response to changes in training also, what we see is a gradual net gain over time. Over the period which this data was obtained the team in question were in the Championship final 3 out of the 4 seasons (answers on a postcard), so this is reflective phenotypical change at the highest level of performance.
The differences in body composition between athletes and everyone else is acquired as well as inherited, and the acquired phenotype can change rapidly over of a training cycle, so, to get a true reflection of what an athlete is made up of, it would be necessary to also consider the time of year or current training status.
Davies, R.W., Toomey, C., McCormack, W., O’Neill, C., Hughes, K. and Jakeman, P., 2017. Seasonal changes in body composition of inter-county Gaelic Athletic Association hurlers. Journal of sports sciences, 35(24), pp.2427-2432.
Robert Davies is a Research Assistant in Exercise Physiology at the Physical Education & Sport Sciences Department at the University of Limerick.
View his profile here.
Rob can be contacted at : firstname.lastname@example.org