Author(s): HELBIN, J., LATOCHA, A., KASZUBA, M., Institution: AWF KATOWICE, PL634-019-53-42, Country: POLAND, Abstract-ID: 900

INTRODUCTION:
Hypoxia is a state in which oxygen is not available in sufficient amounts to tissues. Hypoxia can be divided into global (low oxygen environment) and local (methods of limiting blood flow in the limb). Blood flow restriction (BFR) is a training method used to induce local hypoxia by applying inflatable cuffs to the proximal part of a limb, temporarily restricting blood flow. In practice, the BFR method appears to be more accessible than global hypoxia. It has been demonstrated that a single bout of resistance exercises increases adrenaline levels and might temporarily impair performance; however, it is unclear how hypoxic conditions and their types moderate such responses. The aim of this study was to compare the effects of low-intensity resistance training in normoxia, global hypoxia, and local hypoxia conditions on lower-limb force output and adrenaline levels, and to determine whether the type of hypoxia moderates such responses.

METHODS:
Twenty-one healthy and physically active participants (age: 22 ± 2 years, body mass: 77.3 ± 12.6 kg, body height: 178 ± 8 cm) were randomly assigned to one of the following conditions: i) low intensity under normoxia [N] (n=7); ii) low intensity with BFR [BFR] (n=7); iii) low intensity under normobaric hypoxia [H] (simulated altitude of 3500 m; n=7). The experimental session consisted of 4 sets of 30/15/15/15 repetitions on a leg press machine with a load of previously determined as 30% of one repetition maximum. Before and immediately after finishing the experimental session, a venous blood sample was taken to assess the level of adrenaline. To assess lower-limb force output, participants performed maximal isometric half-squat on a force platform before and approximately 5 minutes after training session.

RESULTS:
Two-way ANOVA did not show any statistically significant interaction (p=0.688), nor main effects of condition (p=0.605) and time (p=0.407) on force output during the maximal isometric half-squat. Friedman’s test showed significant differences in adrenaline levels (p<0.001; test=13.762). Post-hoc comparisons showed a significant increase in adrenaline levels after training compared to baseline values (mean difference=11.76±19.27 pg/ml; p=0.001), with no differences observed between groups.
CONCLUSION:
Several studies have shown that adrenaline plays a crucial role in cardiovascular and respiratory adjustments, as well as in substrate mobilization and utilization, potentially leading to positive adaptations to exercise. Previous research has found that acute bouts of heavy resistance exercise increase adrenaline levels. Our results indicated a marked increase in the concentration of this catecholamine after low-intensity resistance training across all studied conditions. Additionally, the absence of significant differences in force output between conditions suggests that neither H nor BFR induced greater muscle fatigue compared to low-intensity resistance training in normoxia.