While the industrialized world adopts a sedentary lifestyle, ultramarathon running races have become increasingly popular in the last few years, notably in the US, Europe, Japan, Korea, and South Africa. The ability to run long distances is also considered to have played a role in human evolution [
1]. This makes the issue of ultra-long distance physiology relevant. Ultramarathons are basically either performed on mostly flat roads or tracks, or run on varied terrain trails. They comprise races that are completed over the space of multiple days (for example, 6 days), with the winner being the one that covers the most distance within this set period of time or races that cover a specified distance during a single stage, which normally range from 50 km to 160.9 km or over several stages. The paper by Schütz
et al. [
2] explores the physiological changes that occur in runners during this latter type of events, probably one of the most demanding physical exercise in humans, maybe only overpassed by polar expeditions (for example, Scott's party man-hauling their sleds across the Antarctic for 159 days in 1911/1912, [
3]) or other individual challenges such as the run around Europe in 2009/2010, that is, 27,012 km in 1 year (74 km/day), by the Frenchman Serge Girard. We recently reviewed the origin of muscle fatigue after prolonged exercises lasting from 30 minutes to several hours [
4] and found that the knee extensors isometric strength loss increased in a non-linear way with exercise duration, that is, there was a plateau after approximately 20 h of running. Recent findings from our group confirm this result for an even longer mountain ultramarathon (Tor des Geants, 330 km; unpublished results). These fatigue studies and other experiments conducted on inflammation [
5], cardiovascular or renal consequences [
6,
7], endocrine/energetic aspects (see for example [
8]) help to understand acute consequences of an ultra-endurance exercise (generally shorter than 24 h, more rarely 2 or 6 days) but do allow examining recovery process, that is, tissue degeneration/regeneration over several days of extreme physical load.