Background: Resistance training is proven to have health benefits and increase muscle strength and muscle hypertrophy when performed at higher loads (>60% 1 repetition max). Blood flow restriction (BFR) training in combination with low-load resistance training results in significantly greater muscle strength and hypertrophy than regular low-load resistance training. BFR decreases blood flow to the working musculature, increasing lactateaccumulation because of low oxygen levels. After exercise individuals may experience delayed onset muscle soreness (DOMS). Sex differences in physical activities such as muscular strength and endurance are widely observed in current literature, however, studies investigating sex differences in lactate levels and DOMS after BFR training on the upper extremities are scarce.

Aim: The aim of this study was to investigate the differences in lactate levels and delayed onset muscle soreness between healthy strength-trained young men and women after a bout of blood flow-restricted exercise.

Methods: The study conducted was of a quasi-experimental design. Sixteen participants (7 men and 9 women) were included in the study. The study was divided into two occasions. The first occasion included blood pressure and arterial occlusion pressure measurements as well as one repetition max assessment. On the second occasion, participants performed a BFR training protocol and lactate levels were measured before and immediately after the protocolin mmol/L. The participants received a form to fill in their perceived DOMS (best-worst, 0-10) 24, 48, and 72 hours after protocol termination on a visual analog scale (VAS) ranging from 0-10. All data were non-normally distributed and therefore results were presented as median and min-max. Mann-Whitney U tests were conducted to measure sex differences.

Results: No significant difference in lactate levels before (p=0.395) and after (p=0.522) were observed between the sexes. Women displayed significantly higher experienced DOMS at the 48-hour (men; 1 (0-2), women; 3 (1-7), p=0.015) and 72-hour (men; 0 (0-1), women; 1 (0-5), p=0.012) marks but failed to reach significance (men; 2 (1-3), women; 4 (1-8), p=0.053) at the 24-hour mark.

Conclusions: There was no difference in blood lactate between the sexes after a bout of BFR exercise on the upper extremities in healthy strength-trained young men and women. Women experience a higher DOMS after BFR training. Since the research into sex differences in blood lactate and DOMS is lacking, further studies with larger sample sizes are needed to evaluate if these findings are reflected on a larger scale.