(59) THE EFFECTS OF OFFSET LOADING AND UNILATERAL BLOOD FLOW RESTRICTION ON MUSCLE ACTIVATION AND METABOLIC STRESS DURING BILATERAL BACK SQUAT EXERCISE

Purpose: Offset loading, a resistance training method using asymmetrical loads during bilateral exercises, can be used to address muscle imbalances. Blood flow restriction (BFR), also utilized in resistance exercise, increases strength, endurance, and local muscle mass beyond that of low-intensity resistance training alone. Most research in BFR has focused on bilateral restrictions during exercise; however, to potentially correct limb asymmetries, as is common in sport, unilateral BFR may provide a novel approach to correcting those asymmetries when combined with offset loading. This study aimed to examine the effects of unilateral BFR and offset loading on muscle activation and oxygenation during bilateral back squats. Methods: Seven subjects (Age: 24.8 ± 2.5 yrs.; Height: 173.9 ± 9.6 cm; Weight: 78.2 ± 13.9 kg) completed three different conditions of back squats: traditional (TRAD), offset loading (OS), and offset loading with BFR (OS-BFR) on the non-dominant leg. The offset load for OS and OS-BFR represented a 7.5% difference in load between sides of the barbell. Each condition was completed once in random order. For TRAD and OS, subjects performed 2 sets of 15 repetitions at 55% of 1-RM, with 2 minutes of seated recovery between sets. For OS-BFR, a restriction cuff was placed on the non-dominant limb and inflated to 40% of their limb occlusion pressure. Subjects performed 1 set of 30 repetitions of back squat exercise. Surface electromyography (EMG) was used to assess muscle activation and near-infrared spectroscopy (NIRS) was used to assess muscle deoxygenation for each condition. Heart rate (HR) and Feelings Scale were measured after completion of each set for each condition and averaged. Two-way repeated measures ANOVAs were completed to compare mean muscle activation and oxygenation between loaded and unloaded limbs, with significance established at p < 0.05. Results: There was no significant difference in muscle activation of the quadriceps between conditions (p = 0.786). There was also no significant difference in muscle activation between the loaded and unloaded muscles, respectively (TRAD: 49.8 ± 9.1 vs. 43.4 ± 13.6; OS: 53.5 ± 10.1 vs. 45.5 ± 13.9; OS-BFR: 54.0 ± 16.1 vs. 42.8 ± 13.3 % MVIC, p = 0.124). There was no significant difference in metabolic stress between conditions (p = 0.542). There was also no significant difference in muscle oxygenation between the loaded and unloaded sides (TRAD: 26.9 ± 15.7 vs. 25.0 ± 15.9; OS: 29.2 ± 16.5 vs. 27.1 ± 14.9; OS-BFR: 23.8 ± 11.8 vs. 44.5 ± 37.2 %ΔBSL, p = 0.326). There were no differences in the change in HR from baseline between conditions (TRAD: 85 ± 13; OS: 88 ± 12; OS-BFR: 91 ± 15 bpm, p = 0.658). The pleasantness of exercise, expressed as a change from rest, was significantly different between conditions (TRAD: 0.79 ± 1.5; OS: 0.71 ± 1.73; OS-BFR: -1.00 ± 1.41, p = 0.002). Conclusions: OS-BFR results in similar metabolic stress and muscle activation compared to TRAD back squat exercise; however, feelings of unpleasantness were greater during OS-BFR compared to other conditions. Thus, it may be possible to utilize unilateral BFR to correct muscle imbalances. Practical Applications: Strength and rehabilitation specialists may want to consider utilizing unilateral BFR and offset loading as a potential training tool to correct muscle imbalances, particularly during bilateral lifts such as the back squat. However, caution is advised as the adverse response of the Feelings Scale may indicate poor adherence to this type of training protocol. Acknowledgements: Conway Medical Center College of Health and Human Performance Research Fellowship