Hypoxia Therapy for Recovery from Delayed Onset Muscle Soreness (DOMS)

The intervention process will last for five days, with hypoxia administered from Day 1 following the delayed onset muscle soreness (DOMS) induction protocol. All participants will be instructed to maintain their habitual training routines. The intervention will be delivered in groups of three participants. A research assistant (physical therapist) will supervise the exercise and intervention sessions, and will have a session attendace checklist, to assess adherence to the intervention. Day 0: Familiarization During the week prior to DOMS induction and intervention, all participants will attend a familiarization session to become acquainted with the procedures, practice the exercises, undergo an initial graded exercise test to determine VO2max, and complete an initial hypoxia trial session. This trial allows the Mitovit device to assess each participant’s physiological profile. Day 1: DOMS Induction The exercise protocol to induce hamstring DOMS through eccentric contractions will include the following exercises: Nordic Hamstring Exercise (5 sets × 5 reps, rest = 90 s); Bilateral Leg Curl (5 sets × 8 reps, 80% 1RM, rest = 90 s); Romanian Deadlift (5 sets × 8 maximal reps, rest = 90 s), and Bilateral Leg Curl eccentric phase only (5 sets × 8 reps, 130% 1RM, rest = 90 s). The RM of each exercise will be determined using and Enode inertial sensor (Blaumann & Meyer Sports Technology UG. Magdeburg, Germany). Days 1–5: Intervention and Recovery Following DOMS induction, participants will be assigned to one of three interventions: intermittent hypoxia therapy (IHT), hypoxia–hyperoxia therapy (HHT), or control (placebo). Sessions will take place in a controlled environment using a normobaric hypoxia generator. Each session will last 42 minutes, with participants seated in a reclined position, using the MITOVIT Hypoxic Training System (MITOVIT, Germany). The device automatically adjusts hypoxia/hyperoxia exposure according to individual physiological data collected during the trial session. IHT Group: Participants will remain at rest and undergo intermittent hypoxia with a 5:2 ratio. Each cycle will consist of 5 minutes of hypoxia (FiO2 ˜ 12%) followed by 2 minutes of normoxia (FiO2 ˜ 21%), totaling six cycles per session. This protocol yields 30 minutes of hypoxia per session, aiming to achieve an 85% oxygen desaturation threshold. This range safely and effectively activates hypoxia-inducible factor 1-alpha (HIF-1a). Each session will last 42 minutes. HHT Group: Participants will remain at rest and undergo hypoxia–hyperoxia with a 5:2 ratio. Each cycle will include 5 minutes of hypoxia (FiO2 ˜ 12%) followed by 2 minutes of hyperoxia (FiO2 ˜ 30–35%), averaging six cycles per session and totaling 42 minutes. The protocol aims for a mean desaturation of 87%. . The choice of 5-minute hypoxic blocks as the standard duration is based on scientific evidence indicating that this interval is optimal for effectively activating HIF-1a without compromising cellular safety. Safety considerations Peripheral oxygen saturation (SpO2) and heart rate will be continuously monitored. The MITOVIT® Hypoxic Training System is a self-contained normobaric hypoxia generator with an integrated oxygen concentrator and oxygen sensor (no external oxygen tanks required). It includes two synchronized pulse oximeters for continuous SpO2 monitoring and automatically prevents saturation from dropping below the safety threshold of 80%. The device also comprises breathing masks and tubing, and a touchscreen control unit. The chamber or room used for the intervention is not part of the device itself. Participants will also be advised to drink water after each hypoxia session. Equipment will be disinfected after use with an ozone treatment box (Ozone Treatment and Disinfection Box, JBM, Spain) to eliminate bacteria, viruses, and fungi.