(6) INTRA-SET NEUROMUSCULAR RESPONSES DURING LOW AND MODERATE PRESSURE BLOOD FLOW RESTRICTION EXERCISE

PURPOSE: A range (40-80%) of arterial occlusion pressures (AOP) are used during low-load resistance exercise with blood flow restriction (LLBFR). Higher AOPs (80%) tend to increase discomfort during exercise, while low (40%) and moderate (60%) AOPs tend to be better tolerated. However, less is known regarding the acute motor unit recruitment and fatigue responses during low and moderate AOP LLBFR. Therefore, the purpose of this investigation was to assess intra-set neuromuscular responses during LLBFR with 40% and 60% AOP.

Methods: Thirty-one recreationally active men (n= 15) and women (n=16) completed this study (22±3 years, 170.5±9.5 cm, 67.8±13.8 kg). Participants completed 1 familiarization and 2 exercise visits. During exercise visits, participants completed 75-repetitions (1×30, 3×15, 30 seconds of intra-set rest) of dynamic bilateral leg extension muscle actions (1-second concentric, 1-second eccentric) at 30% of 1 repetition maximum (1RM) with either 40% or 60% AOP (randomly assigned). Surface electromyography (EMG) of the vastus lateralis was recorded during each exercise bout. The concentric phase of each repetition was recorded, normalized to 1RM, then the average of 5 repetition intervals (i.e., repetition 1-5, 6-10, etc.) was analyzed to determine EMG root mean square (amplitude) and mean power frequency. Set 1 was analyzed using a 2 (Condition [40% AOP, 60% AOP]) × 6 (Time [repetitions 1-5, 6-10, 11-15, 16-20, 21-25, 26-30]) repeated measures ANOVA. Sets 2-4 were analyzed using separate 2 (Condition [40% AOP, 60% AOP]) × 3 (Time [repetitions 1-5, 6-10, 11-15]) repeated measures ANOVAs.

Results: For EMG amplitude, there were no significant (p=0.094-0.626) Condition×Time interactions or significant (p=0.077-0.746) main effects for Condition, but there were significant (p< 0.001) main effects for Time for sets 1-4. Specifically, during set, 1 repetitions 1-5 (49.7±20.6%), 6-10 (50.2±21.0%), 11-15(52.7±23.4%)< 16-20 (55.6±24.2%)< 21-25 (59.3±24.0%)< 26-30 (63.5±25.6%), during sets 2-4 repetitions 1-5 (56.8±27.2% - 67.4±27.5%)< 6-10 (66.6±29.8% - 78.2±36.8%)< 11-15 (75.8±29.3 – 90.9±39.4%). For EMG frequency, there were no significant (p=0.286-0.658) Condition×Time interactions. There was a significant main effect for Condition during set 2 (p=0.012) and a significant (p< 0.001) main effects for Time during sets 1, 3, and 4. During set 2, EMG frequency was lower during 60% AOP (101.3±29.5%) compared to 40% AOP (109.2±47.3%). Collapsed across Condition, during set 1 repetitions 1-5 (116.4±49.1%), 6-10 (114.1±44.4) > 11-15 (111.2±44.7%) > 16-20 (108.5±40.8%) > 21-25 (105.0±36.2%) > 26-30 (102.4±35.4%) and during sets 3 and 4 repetitions 1-5 (106.1±42.9%; 104.5±43.8) > 6-10 (105.6±43.6%; 102.8±43.0%) > 11-15 (100.7±41.7%; 98.7±38.5%).

Conclusion: In general, 40% and 60% AOP elicited similar intra-set changes in EMG amplitude and frequency during LLBFR exercise. Furthermore, the decrease in EMG frequency between sets 2 and 3 may have been due to an accumulation of metabolic byproducts. These results suggested low and moderate AOP elicit similar neuromuscular recruitment and fatigue responses. PRACTICAL APPLICATIONS: Similar intra-set responses between 40% and 60% cuff pressure suggested that practitioners can effectively use either cuff pressure during LLBFR. Furthermore, if discomfort from higher cuff pressures is a concern, 40% cuff pressure is a viable option to generate similar physiological responses.

Acknowledgements: None