Repeated Remote Preconditioning Improves Muscular Strength By Neuromuscular Adaptations

PURPOSE: Remote ischemic preconditioning (RIPC) is 3 or 4 cycles of brief blood flow blockage followed by blood flow restoration. Our previous study showed that repeated RIPC improves muscular strength in healthy young adults. However, we did not explore the underlying mechanisms in these improvements. Since neuromuscular adaptation plays a key role in early strength gain during resistance training, strength gain from repeated RIPC may be explained by neuromuscular adaptation. Additionally, it is possible that applying more RIPC sites could induce greater strength gain due to larger ischemic areas. The goals of this study were to test whether muscular strength improvements were due to neuromuscular adaptations and whether increasing the number of RIPC sites would result in greater strength gains. METHODS: 30 healthy young adults without cardiovascular disease risk factors were recruited from the local community (n = 30; 18 M, 12 F). Participants were randomly assigned to a control, one-site, and two-site group (10 per group). RIPC training was applied for 1 week (7 consecutive days) using 4 cycles of 5 mins of occlusion with 200 mmHg of pressure followed by 5 mins of reperfusion. Lower limb strength was assessed by isometric knee extension (ISOKE) using the Biodex System 4 before and after 1 week of RIPC. Electromyography (EMG) was measured during ISOKE and used to calculate neuromuscular efficiency (NME). Two ways mixed- model ANOVAs were used to analyze the data. A paired t-test was conducted as a post-hoc test. RESULTS: One week of repeated RIPC improved ISOKE/BW and EMG (ISOKE/BW: 197.1 ± 41.9 vs. 235.6 ± 67.6 Nm 1site, pre vs. post, p < 0.001; EMG: 0.36 ± 0.16 vs. 0.62 ± 0.26, pre vs. post, p = 0.003). However, the two site RIPC did not further improve (ISOKE/BW: 235.6 ± 67.6 vs. 233.3 ± 52.9 Nm, p = 0.802; EMG 0.62 ± 0.26 vs 0.60 ± 0.29, p = 0.319). NME (p = 0.137) did not increase after 1 week of RIPC between groups over time. CONCLUSION: One week of one-site RIPC improved muscular strength, but two-site RIPC did not result in greater strength improvements compared to one-site RIPC. NME did not change in any of the groups. However, EMG increased after one week of repeated RIPC at both one and two- sites. These results suggest that repeated one-site RIPC is sufficient to elicit muscular strength improvement by neuromuscular adaptations. Supported by: This research was supported by the Research, Scholarship, and Creative Activity Support Grant (RSCA), California State University Bakersfield