The effects of rhythmic handgrip exercise on muscle sympathetic nerve activity: A systematic review and meta-analysis

This systematic review and meta-analysis was conducted to quantify the sympathetic response to rhythmic handgrip exercise in healthy and diseased populations. Structured searches of databases were performed until June 12, 2024. We included all primary studies (other than systematic reviews and meta-analyses), and inclusion criteria were: population (all populations); intervention (rhythmic handgrip); comparator (baseline); and outcome (MSNA, BP, HR). Forty-nine studies (n = 930) were included. Burst frequency was elevated by 6.1 bursts/min during rhythmic handgrip (95 % CI, 4.52, 7.63; I² = 53 %; p < 0.00001) across all populations. Similarly, burst incidence and total activity showed significant increases during handgrip (BI: MD, 3.0 bursts/100 hbs; 95 % CI, 0.11, 5.85; I² = 0 %; p = 0.04; TA: MD, 49.4 a.u.; 95 % CI, 36.56, 62.20; I² = 86 %; p < 0.00001). Subgroup analyses found greater responses in MSNA during rhythmic handgrip in healthy individuals compared to cardiovascular diseases and other conditions. Specifically, the change in burst frequency during handgrip (p = 0.0009) and total activity during handgrip (p < 0.00001) suggest a blunted sympathetic response to rhythmic handgrip in diseased populations. Meta-regression analyses in healthy populations found no relationship between the volume of handgrip applied with the associated change in sympathetic activity; however, there was a significant positive relationship between both the change in heart rate (slope = 0.131; adjusted R² = 0.2773; p = 0.002) and the change in mean blood pressure (slope = 0.163; adjusted R² = 0.3594; p < 0.001) with handgrip volume. An increase in MSNA is observed during rhythmic handgrip despite ranging protocols, populations, and co-interventions. These results suggest exercise is a unique stressor and challenges the understanding of general sympathetic hyperactivity in diseased populations.