title: Effects of isometric handgrip protocol on blood pressure and neurocardiac modulation.
abstract: 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.
authors.affiliation: Department of Kinesiology, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada. millarpj@mcmaster.ca
authors.forename: P J
authors.initials: PJ
authors.lastname: Millar
authors.forename: M J
authors.initials: MJ
authors.lastname: MacDonald
authors.forename: N
authors.initials: N
authors.lastname: McCartney
mesh_terms: D000367:Age Factors; D000368:Aged; D000375:Aging; D000704:Analysis of Variance; D001341:Autonomic Nervous System / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology*; D002319:Cardiovascular System / Q000294:innervation*; D005080:Exercise Test; D005260:Female; D018737:Hand Strength / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D008465:Mechanoreceptors; D010101:Oxygen Consumption