Abstract
Purpose: The purpose of this study was to determine the effect of 3 consecutive days of endurance training under hypoxia on muscle damage, inflammation, and performance responses.Methods: Nine active healthy males completed two trials in different periods, consisting of either 3 consecutive days of endurance training under hypoxia [fraction of inspired oxygen (Fio2): 14.5%, HYP] or normoxia (Fio2: 20.9%, NOR). They performed daily 90-min sessions of endurance training consisting of high-intensity endurance interval pedaling [10 × 4-min pedaling at 80% of maximal oxygen uptake () with 2 min of active rest at 30% of ] followed by 30-min continuous pedaling at 60% of during 3 consecutive days (days 1–3). Venous blood sample, muscular performance of lower limb, and score of subjective feelings were determined every morning (days 1–4) to evaluate muscle damage and inflammation. On day 4, subjects performed an incremental exercise test (IET) to evaluate the performance response.Results: Pedaling workload during daily endurance training was significantly lower in the HYP trial (interval exercise: 166 ± 4 W) than in the NOR trial (194 ± 8 W; P < 0.0001). Serum creatine kinase (CK) and high-sensitivity C-reactive protein (hsCRP) concentrations did not significantly change during days 1–4 in either trial. Maximal voluntary contraction (MVC) of knee extension (P < 0.0001) and drop jump (DJ) index (P = 0.004) were significantly decreased with training in both trials, with no significant difference between trials. The muscle soreness and fatigue scores significantly increased in both trials (P < 0.0001). However, the HYP trial showed a significantly lower score of fatigue on day 4 compared with the NOR trial (P = 0.004). Maximal aerobic power output during IET on day 4 did not significantly differ between trials.Conclusion: Three consecutive days of endurance training under hypoxia induced comparable levels of muscle damage, inflammation, and performance responses compared with the same training under normoxia.
Highlights
The use of training under hypoxia is widely accepted among endurance athletes to improve endurance capacity, and considerable evidence supports the efficacy of this training procedure (Dufour et al, 2006; Czuba et al, 2011, 2017)
Three consecutive days of endurance training under hypoxia induced comparable levels of muscle damage, inflammation, and performance responses compared with the same training under normoxia
Exercise-induced interleukin 6 (IL-6) elevation did not differ between hypoxia and normoxia (Sumi et al, 2018). These results suggest that endurance exercise under hypoxia causes less exercise-induced muscle damage and reduction of endurance capacity compared with the same exercise under normoxia using equivalent relative exercise intensity
Summary
The use of training under hypoxia (hypoxic training) is widely accepted among endurance athletes to improve endurance capacity, and considerable evidence supports the efficacy of this training procedure (Dufour et al, 2006; Czuba et al, 2011, 2017). Many previous studies have investigated the effects of hypoxic training on exercise capacity or health status, whereas the effects on muscle damage and inflammatory responses have not been well-established. Exercise-induced muscle damage and inflammatory responses may play a role in promoting muscle mass and muscle regeneration (Allen et al, 1999; Britto et al, 2020), whereas excessive responses during training period would suppress training adaptations (Smith, 2003). Information regarding muscle damage and inflammatory responses during the training period would help prevent overtraining syndrome or decrease the risk of injury (e.g., muscle strain) in working muscle (Smith, 2003; Meeusen et al, 2013)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
