Acute physiological responses and muscle recovery in females: a randomised controlled trial of muscle damaging exercise in hypoxia

Abstract

Background: Studies have investigated the effects of training under hypoxia (HYP) after several weeks in a male population. However, there is still a lack of knowledge on the acute hypoxic effects on physiology and muscle recovery in a female population.

Methods: This randomized-controlled trial aimed to investigate the acute effects of muscle damaging exercise, performed in HYP and normoxia (CON), on physiological responses and recovery characteristics in healthy females. Key inclusion criteria were recreationally active female participants between the age of 18 to 35 years without any previous surgeries and injuries, whilst key exclusion criteria were acute pain situations, pregnancy, and medication intake. The females conducted a muscle-damaging protocol, comprising 5 × 20 drop-jumps, in either HYP (FiO₂: 12%) or CON (FiO₂: 21%). Physiological responses, including capillary oxygenation (SpO₂), muscle oxygenation (SmO₂), heart rate (HR), core- (Tcore) and skin- (Tskin) temperature were assessed at the end of each exercise set. Recovery characteristics were quantified by taking venous blood samples (serum creatine-kinase [CK], C-reactive protein [CRP] and blood sedimentation rate [BSR]), assessing muscle swelling of the quadriceps femoris muscle, maximum voluntary isometric contraction (MVIC) of the knee extensor muscles, countermovement jump (CMJ) performance and muscle soreness ratings (DOMS) at 24-, 48- and 72-hrs post-exercise.

Results: SpO₂ (HYP: 76.7 ± 3.8%, CON: 95.5 ± 1.7%, p < 0.001) and SmO₂ (HYP: 60.0 ± 9.3, CON: 73.4 ± 5.8%, p = 0.03) values were lower (p < 0.05) in HYP compared to CON at the end of the exercise-protocol. No physiological differences between HYP and CON were observed for HR, Tcore, and Tskin (all p > 0.05). There were also no differences detected for any recovery variable (CK, CRP, BSR, MVIC, CMJ, and DOMS) during the 72-hrs follow-up period between HYP and CON (all p > 0.05).

Conclusion: In conclusion, our results showed that muscle damaging exercise under HYP leads to reduced capillary and muscle oxygenation levels compared to normoxia with no difference in inflammatory response and muscle recovery during 72 h post-exercise.

Trial registration: NCT04902924, May 26th 2021.

Keywords: Exercise; Hypoxia; Muscle damage; Recovery; Training.

Fig. 1

Schematic illustration of the experimental design

Fig. 2

Physiological responses during the exercise task. Results of (A) capillary oxygen saturation (SpO₂), (B) muscle oxygen saturation of the right vastus lateralis of the quadriceps femoris muscles (SmO₂), (C) heart rate, and (D) core temperature (T_core) in function of time in the HYP and CON groups. BL baseline, ES exercise-set, ^aP < 0.001 HYP vs. CON, ^bP < 0.05 HYP vs. CON, ^cP < 0.001 HYP compared with baseline, ^dP < 0.05 HYP compared with baseline, ^eP < 0.001 CON compared with baseline, ^fP < 0.05 CON compared with baseline

Fig. 3

Subjective and objective recovery characteristics after the exercise task. Results of (A) muscle swelling, (B) delayed onset of muscle soreness (DOMS), (C) countermovement jump (CMJ), and (D) maximum voluntary isometric contraction (MVIC) in function of time in the HYP and CON groups. Values for A, C, and D are normalised to baseline (% mean ± SD) with respect to their initial values. BL baseline, ^aP < 0.001 HYP compared with baseline, ^bP < 0.05 HYP compared with baseline, ^cP < 0.001 CON compared with baseline, ^dP < 0.05 CON compared with baseline