Changes in body composition in triathletes during an Ironman race We studied 8 men on Ironman Switzerland in 8 men, which has the burden on an effect on the composition of the body. The weight took 1.9 kg, with this decrease due to 0.4 kg of fat and 1.4 kg of fat-free mass.The density of the calf muscles decreased, the sodium in the blood as well as the density and the osmolality of the urine took.
We conclude that the decrease in the density of the calf muscles is due to a decrease in muscle glycogen in the calf. All details below https://pubmed.ncbi.nlm.nih.gov/23748466/