Sports experts and coaches have been continuously looking for new approaches and methods to improve athletic performance across different sports. Out of the methods proposed are the hypoxic and the hyperoxic training methods, which have recently gained popularity. Hyperoxia was previously used in special clinics; however, it has become easily accessible to athletes with the development of ‘on-the-spot’ equipment. The proposed study aims at determining the potential impact of added hyperoxic conditions during recovery and post-high-intensity interval training (HIIT) in hypoxic conditions. The study posed two hypotheses: a combination of intermittent high intensity hypoxic training and recovery in hyperoxia significantly improves the aerobic capacity than when recovering in normoxia and a combination of intermittent high intensity hypoxic training and recovery in hyperoxia significantly improves the oxygen transport parameters than when recovering in normoxia. The study’s sample included 49 athletes, aged 18 to 20. Athletes were divided into three groups adhering to the intervention protocol as follows: (1) Hypo+Hyper group (N=16) which performed HIIT in hypoxia with a recovery protocol 15 minutes at FiO2=0.40, (2) Hypo group (N=16) which performed HIIT in hypoxia followed by recovery in normoxia, and (3) a control group (N=17) which performed their everyday activities. Each of the four weeks, the intensity of the HIIT and continuous training is increased by 5%. HIIT hypoxia exercise protocol consists of six bouts of one minute at 80 to 95% of HRmax, each week at higher rate, respectively, followed by 2 minutes at 60% of HRmax. The study adopted a quantitative approach through recording athletes’ blood samples pre- and post- intervention to measure red blood cell parameters related to oxygen transport as well as the aerobic capacity measured by the all-out treadmill test. The intervention lasted for four weeks with three sessions of training per week. The most evident changes recoded among the groups within the aerobic endurance parameters pertain to the hyper-hypo group. At maximal exertion the significant changes were observed in maximal oxygen uptake (VO2max) and the maximal speed reached as Hypo-Hyper group had a larger increase as opposed to control group as expected (p < 0.05 and p <0.01, respectively) as well as opposed to Hypo group (p<0.01). Significant changes at anaerobic threshold involved significant increase in oxygen uptake when Hypo-Hyper group was compared to controls (P<0.05) while in only Hypo group that effect was not confirmed. As for hematological parameters, the most important change pertain to significant hemoglobin increase within the Hypo+Hyper group as opposed to the control group (p<0.01). The significant difference in hemoglobin between the Hypo group and controls was not noted. The study contributes to the body of knowledge regarding the effects of such a design on aerobic endurance parameters and the effects of HIIT training in hypoxia and hyperoxia recovery and concludes that the optimal training method for short periods like 4 weeks is that of the high intensity interval training group with hyperoxia recovery (HIIT+O2), accepting both hypotheses proposed by this doctoral dissertation. Indeed, a combination of intermittent high intensity hypoxic training and recovery in hyperoxia significantly improves the aerobic capacity and the oxygen transport parameters than when recovering in normoxia.