(40) A Comparative Pilot Analysis of Cellular Responses to Low-Intensity Resistance Exercise: With and Without Blood Flow Restriction

Background: High-intensity resistance exercise (RE) has been shown to initiate a cascade of immune responses that are essential for the restoration of both normal physiological function and muscle growth. Blood flow restriction (BFR) training, which utilizes low-intensity exercise combined with venous occlusion has been shown to elicit similar improvements in muscle mass and strength; however, the mechanisms underpinning the efficacy of BFR remain elusive. Considering the involvement of the immune system in muscle recovery and hypertrophy, an examination of immune responses to low-intensity exercise, with and without BFR is necessary.

Purpose: To examine the effects of low intensity RE with and without BFR on cellular immune responses.

Methods: Fourteen untrained women (21.5±2.5yrs., 164.4 ± 6.8cm, 75.7 ± 21.6kg) completed two experimental trials (ET) over the course of an 8-week training program. Participants were randomly assigned to train with BFR (n=8) or without (n=6) (NoBFR). Training was completed two days per week and consisted of leg press, leg extensions, and leg curls (1 x 30 repetitions & 3 x 15 repetitions with 30 seconds rest between sets). Participants assigned to the BFR condition exercised with cuffs inflated at 60% of their total occlusion pressure, while those in the NoBFR condition exercised without cuffs. ET1 was performed during the first training session of week 2 and consisted of a pre-exercise (PRE) blood sample, a training session, and two post-exercise blood samples: immediately post- (IP) and 60-minutes post-exercise (60P). ET2 was conducted in an identical fashion to ET1 during the first training session of week 8. Blood samples were analyzed for complete blood counts and used to calculate cellular inflammation markers of neutrophil to lymphocyte ratio (NLR), platelet to lymphocyte ratio (PLR), and systemic immune-inflammation index (SII). An expectation maximization algorithm was used to impute any missing values for dependent variables. All missing data were deemed to be missing completely at random (MCAR), as determined by Little's MCAR test. Data imputation was performed for each subscale (same variable along ET time points) for each treatment group independently. Separate three-way (Group x Time x ET) repeated measures ANOVA were used to examine changes in NLR, PLR, and SII.

Results: No significant interactions, main effects of group, or ET were reported for any outcome variables (p>.05). Significant main effects for time were observed for NLR (p=.022), PLR (p=.011), and SII (p=.050). NLR and PLR were significantly lower at IP compared to PRE (p=.006 and p=.000) and 60P (p=.011 and p=.005), respectively. SII, was significantly higher at 60P compared to IP (p=.024) but was not significantly different from PRE (p=.073).

Conclusions: There were no significant differences in cellular immune responses to low-load RE between the BFR and NoBFR groups, however the low-load RE regimen induced notable acute changes in clinical cellular inflammation markers. Moreover, there were no significant cellular adaptations to the exercise bout following 8 weeks of training. PRACTICAL APPLICATIONS: Low intensity RE with and without BFR induced similar leukocyte modulation post-exercise in untrained women. This investigation provides further insight into the mechanisms associated with BFR training and indicates that BFR does not induce a significantly greater immune response post-exercise than low-intensity exercise alone.

Acknowledgements: Portions of this project were made possible through a doctoral grant award generously provided by the National Strength and Conditioning Association (NSCA).