In repeated sprints in hypoxia (RSH), athletes run short sprints under 30 seconds as fast as they can. They experience incomplete recoveries in hypoxic conditions. The exercise to rest time ratio is less than 1:4, which means for every 30 second all out sprint, there is less than 120 seconds of rest.When comparing RSH and repeated sprints in normoxia (RSN), studies show that RSH improved time to fatigue and power output. RSH and RSN groups were tested before and after a 4-week training period. Both groups initially completed 9–10 all-out sprints before total exhaustion. After the 4 week training period, the RSH group was able to complete 13 all out sprints before exhaustion and the RSN group only completed 9.Possible physiological advantages from RSH include compensatory vasodilation and regeneration of phosphocreatine (PCr). The body's tissues have the ability to sense hypoxia and induce vasodilation. The higher blood flow helps the skeletal muscles maximize oxygen delivery. A greater level of PCr resynthesis augments the muscles power production during the initial stages of high-intensity exercise.RSH is still a relatively new training method and is not fully understood.