Author(s): HAPP, K., BARAWI, S., NIEDERER, D., BEHRINGER, M., Institution: GOETHE UNIVERSITY FRANKFURT, Country: GERMANY, Abstract-ID: 1381

INTRODUCTION:
Blood flow restriction (BFR) training enables strength adaptations at low loads, yet its impact on exercise-induced muscle damage (EIMD) remains controversial. Differences in load, occlusion pressure and proximity to failure may explain inconsistent findings. This study examined the independent and combined effects of load-pressure configurations and effort on EIMD.
METHODS:
Fourty participants (25.1 +/- 2.97 y; 174.1 +/- 10.62 cm; 70.1 +/- 13.84 kg) performed unilateral leg extension under four BFR conditions: low load (30% 1RM) with 50% arterial occlusion pressure (LL-LP) or moderate load (60% 1RM) with 75% occlusion (ML-MP), each performed with three repetitions in reserve (3RIR) or to failure (FAIL), resulting in LL-LP-3RIR, LL-LP-FAIL, ML-MP-3RIR and ML-MP-FAIL. Outcomes included isometric peak torque (primary), pain (VAS), blood lactate, and relative total tonnage. A 2 x 2 factorial linear mixed model was applied with Exercise Condition and Effort as fixed factors, whereby the Exercise Condition x Effort x Time interaction represented the combined group x time effect.
RESULTS:
Relative total tonnage showed a main effect of Exercise Condition (F(1,104.893)=44.06, p<0.001), a main effect of Time (F(3,105.00)=123.21, p<0.001), and a significant Time x Effort x Exercise Condition interaction (F(10,99.61)=9.08, p<0.001), whereas Effort was not significant. LL-LP-FAIL produced the highest relative load, ML-MP-FAIL the lowest.
For lactate, a significant Exercise Condition x Effort x Time interaction was observed (F(10,98.72)=4.96, p<0.001), with main effects of Effort (F(1,102.15)=19.84, p<0.001) and Time (F(4,99.21)=54.32, p<0.001), but not Exercise Condition. FAIL conditions elicited higher lactate, particularly LL-LP-FAIL vs ML-MP-3RIR at 1, 7 and 10 min post (p<0.003).
Pain ratings showed a significant three-way interaction (F(13,131.89)=3.15, p<0.001) and a main effect of Exercise Condition (F(1,144.29)=6.97, p<0.009). LL-LP-FAIL induced higher pain at 24 h vs ML-MP-FAIL and ML-MP-3RIR (p<0.001) and at 48 h vs all other conditions (p<0.003).
Isometric peak torque revealed a significant Exercise Condition x Effort x Time interaction (F(13,133.32)=6.01, p<0.001), with main effects of Effort (F(1,126.06)=5.15, p=0.025) and Time (F(4,148.00)=12.59, p<0.001), but not Exercise Condition. At 24 h, LL-LP-FAIL and ML-MP-FAIL showed greater force reductions vs their 3RIR counterparts (p<0.003). Impairments persisted at 48 h, particularly vs ML-MP-3RIR (p<0.002). LL-LP-FAIL showed the largest decrements, whereas ML-MP-3RIR showed minimal impairment.
CONCLUSION:
In conclusion, the combination of exercise condition and proximity to failure determines acute and muscle damage responses during BFR. But, mechanical output and pain are primarily driven by load-pressure configuration, whereas metabolic stress and functional impairment are predominantly explained by proximity to failure. Failure amplifies EIMD particularly when combined with prolonged metabolic exposure under low-load BFR.