The effects of isometric handgrip and post-exercise circulatory occlusion on muscle sympathetic nerve activity: A systematic review and meta-analysis

This systematic review and meta-analysis was conducted to identify a ‘normative' sympathetic response to isometric handgrip and post-exercise circulatory occlusion. Structured searches of databases were performed until June 2024. We included all primary studies (other than systematic reviews and meta-analyses), and inclusion criteria were: population (all populations); intervention (isometric handgrip and post-exercise circulatory occlusion); comparator (baseline); and outcome (MSNA). One-hundred fifty-eight studies (n = 3551) were included. Burst frequency was elevated during handgrip (n = 1853; MD, 12.19bursts/min; 95 % CI, 11.09, 13.28; I 2 = 94 %; p < 0.00001) and during PECO (n = 948; MD, 11.42bursts/min; 95 % CI, 10.10, 12.75; I 2 = 65 %; p < 0.00001). A similar pattern was observed for burst incidence in handgrip (n = 1074; MD, 8.50bursts/100 hbs; 95 % CI, 7.07, 9.93; I2 = 39 %; p < 0.00001) and PECO (n = 560; MD, 14.87bursts/100 hbs; 95 % CI, 12.65, 17.10; I2 = 43 %; p < 0.00001). Subgroup analyses indicated a larger response in burst frequency and incidence during handgrip exercise in healthy individuals compared to individuals with cardiovascular diseases or other conditions (p < 0.05). A similar response in burst frequency to PECO was observed with subgroup differences between healthy individuals and individuals with cardiovascular diseases and other conditions (p < 0.00001). MSNA is elevated during handgrip exercise across a range of handgrip protocols, populations, and co-interventions. Increases in MSNA during PECO supports the role of the metaboreflex separate to the exercise pressor reflex. A blunted sympathetic response to handgrip and PECO in individuals with cardiovascular diseases contradicts the current understanding of general sympathetic hyperactivity in these populations.