Author(s): HAPP, K., SCHWIETE, C., NIEDERER, D., BEHRINGER, M., Institution: GOETHE UNIVERSITY FRANKFURT, Country: GERMANY, Abstract-ID: 1361

INTRODUCTION:
The use of blood flow restriction (BFR) is a well established training method. However, it is still unknown whether increased metabolic stress, possibly caused by higher cuff occlusion pressures, has an additional effect on muscle damage [1]. Therefore we investigated the effects of mechanical and metabolic stress on the extent of BFR exercise-induced muscle damage.
METHODS:
Forty participants (25.4 ± 3.5 years, 68.4 ± 13.1 kg, 173 ± 8.9 cm) were randomly divided into four parallel groups with different BFR occlusion pressures.
Groups were defined as no pressure (NP), low pressure (LP; 50%), medium pressure (MP; 75%) and high pressure (HP; 100%) based on the individually measured limb occlusion pressure (LOP)
Following baseline measurement, participants performed a maximum of four sets with 20 repetitions and 30 seconds rest at 30% of the 1-repetition maximum (1RM) or until reaching muscle failure.
During training, number of completed repetitions (n of reps) and oxygen saturation [%] via near-infrared spectroscopy were recorded.
Muscle damage markers such as isokinetic peak torque [Nm] during knee extension (PT) and subjective pain perception (visual analog scale; VAS) were measured before and 1h, 24h, 48h and 72h after intervention. Potential between-group differences were calculated using repeated measures ANOVAs and post-hoc 95%-confidence interval comparisons.
RESULTS:
We found between-group differences in reps absolved (F(3​,16​) = 50.38, p<.001); with NP and LP completing more reps than MP and HP. Conversely, groups exhibited different oxygen saturation values during exercise (F(3,17.3) = 3.23, p<.05).
Results showed an effect for pain perception (F (12,140) = 2.29, p = .011, n²p = .078), In particular between NP and MP/HP at 24h and 48h post intervention (MD = 2.05, SE = 0.78, t (35) = 2.6, p < .025), (MD = 2.07, SE = 0.76, t (35) = 2.74, p <.025), (MD = 2.05, SE = 0.71, t (35) = 2.87, p < .025), (MD = 1.59, SE = 0.69, t (35) = 2.52, p <.05).
Concentric PT also revealed an interaction effect of group x time with concentric baseline PT as a covariate (F (6,60) = 3.56, p = .004, n²p = .263). Post-hoc confidence interval comparisons show a higher PT reduction for NP compared to MP and HP and for LP compared to HP at 24h post (NP, M = 178, 95%CI [165, 190]), (LP, M = 181, 95%CI [170, 193]), (MP, M = 191, 95%CI [180, 203]), (HP, M = 195, 95%CI [183, 207]).
CONCLUSION:
Training with LP BFR demonstrated muscle damage comparable to non-BFR training, while MP and HP groups showed less muscle damage based on PT reduction, combined with fewer symptoms as evident by lower VAS values. Based on our findings, we assume that higher total load serves as the primary trigger for muscle damage.

[1] Loenneke JP, Thiebaud RS, Abe T. Does blood flow restriction result in skeletal muscle damage? A critical review of available evidence. Scand J Med Sci Sports. 2014 Dec;24(6):e415-422. doi: 10.1111/sms.