Effects of isometric handgrip protocol on blood pressure and neurocardiac modulation

Isometric handgrip (IHG) remains a well-studied cardiovascular and autonomic stimulus, however the effects of rhythmic IHG protocols remain largely unknown. The purpose of this study was to investigate the acute effects of 4 IHG protocols on blood pressure (BP) and neurocardiac reactivity and recovery responses. 12 healthy older participants (70±5 yrs, ♀=4) each completed 4 bilateral 12-min protocols (sham, IHG1, IHG2, IHG3) on separate visits. IHG1, IHG2, and IHG3 consisted of 4×2-min, 8×1-min, and 16×30-s isometric contractions, respectively, each completed at 30% MVC, while sham consisted of 4×2-min contractions completed at 3% MVC. BP and neurocardiac modulation were assessed during and following each protocol. Systolic BP (SBP) reactivity was increased during IHG1 compared to IHG2 (p<0.05), IHG3 (p<0.05), and sham (p<0.01), although during recovery delta SBP was lower following IHG1 (p<0.01), IHG2 (p<0.01), and IHG3 (p<0.05), compared to sham. Sample entropy, a measure of nonlinear heart rate variability was reduced during IHG1 (p<0.01) and IHG2 (p<0.05), while increased following IHG1 (p<0.05) and IHG3 (p<0.05), compared to sham. In conclusion, recovery responses from rhythmic IHG appear independent of contraction and/or rest period frequency-duration relationships. Investigation of rhythmic IHG protocols warrants further examination.