The Mechanism Underlying the Hypotensive Effect of Isometric Handgrip Training: Is it Cardiac Output Mediated?

Isometric handgrip (IHG) training lowers blood pressure (BP) in normotensive individuals yet the mechanisms remain equivocal, and some evidence suggests that men and women respond differently to training. To date, non-sex specific mechanisms influencing total peripheral resistance, either in response to a single IHG bout or with training, have been a primary research focus, and the effects of acute and chronic IHG on cardiac output (Q) in either sex are under-explored. The purpose of the current study was two-fold: 1) to investigate the effects of IHG training (4, 2-minute sustained bilateral isometric contractions at 30% of maximal contraction, 1-minute rest between, 3X/week for 10 weeks) on resting Q, and 2) to examine the Q response to an IHG bout, and the effects of training on this response. Resting BP (Dinamap Carescape v100, Critikon) was measured after 10 minutes of seated rest in twenty-two normotensive participants (10 women; mean age= 24 ± 5.0 years). To assess Q, aortic root diameter (ARD; 3S-RS probe; Vivid I, GE Healthcare), velocity-timed integral (VTI; P2D probe; Vivid I), and HR (Dinamap) were measured pre- and post- an IHG bout. Both variables were re-assessed post-training. Reductions in resting systolic BP of a similar magnitude (p>0.05) were observed in both men (2.4 ± 6.2 mmHg) and women (2.9 ± 4.6 mmHg) following 10 weeks of training (p=0.04). This was accompanied by reductions in resting Q (p=0.007) in both men (6.6 ± 2.2 to 6.3 ± 1.8 L/min) and women (5.8 ± 0.7 to 5.1 ± 0.8 L/min) and reductions in HR (p=0.036), both of which were similar between sexes (all p>0.05). In both groups, no changes in Q were observed in response to an IHG bout, and this response was similar pre- and post- training (all p>0.05). In conclusion, resting Q is reduced with training, potentially implicating it as a mechanism of post-training BP reductions. The acute response to an IHG bout remains unchanged with training

Using Bilateral and Unilateral Exercise to Better Understand the Blood Pressure Lowering Effects of Isometric Handgrip Training: Preliminary Findings

Isometric handgrip (IHG) training reduces resting blood pressure (BP) in normotensive individuals following 8-10 weeks of unilateral (4 x 2 minute sustained contractions at 30% maximal voluntary contraction (MVC) performed by the non-dominant limb, separated by 4 minutes rest) or bilateral IHG training (contractions alternating between dominant and non-dominant limb, separated by 1 minute rest), performed 3-5 times per week. Investigating the effects of a single bout of unilateral or bilateral IHG on vascular function (brachial artery flow-mediated dilation (FMD) and low-flow mediated constriction (L-FMC)) may provide insight into the underlying hypotensive mechanisms of IHG training. Eight young adult (25.3 ± 3.81 years), normotensive (99.65/61.25 ± 11.72/9.14 mmHg) women performed a single bout of bilateral (n=4) or unilateral (n=4) IHG exercise. FMD and L-FMC were assessed using ultrasound pre- and post-IHG bout. Following a single IHG bout, no significant changes were observed in FMD (unilateral: pre- = 13.56 ± 7.8%, post- =17.26 ± 21%, bilateral: pre- = 17.11 ± 1.1%, post- = 21.18 ± 8.9%) or L-FMC (unilateral: pre- = 3.36 ± 11%, post- =-2.26 ± 16%, bilateral: pre- = -2.86 ± 3.1%, post- = -1.94 ± 9.7%) in either group (all p > 0.05). Taken together these preliminary data suggest that in young healthy women, irrespective of isometric exercise on 1 or 2 limbs, the endothelium is not altered significantly. Further research with a larger sample is warranted to confirm that mechanisms other than improved vascular function play a role in IHG-training induced BP lowering

Isometric handgrip (IHG) training-induced reductions in resting blood pressure: Reactivity to a 2-minute handgrip task identifies responders and non-responders in young normotensive individuals

In people with hypertension, systolic blood pressure (SBP) reactivity to an isometric handgrip task (IHGT), but not a cold pressure task (CPT), is predictive of IHG training-induced reductions in resting SBP. To investigate whether these findings could be extended to include young normotensives, resting BP and BP reactivity to an IHGT (2-minute sustained contraction at 30% maximal voluntary contraction, MVC) and a CPT (2-minute hand immersion in a cold water bath) were measured prior to and following 10 weeks of IHG training (4, 2-minute IHG contractions at 30% MVC, using alternating hands, interspersed with 1-minute rest periods, 3X/week) in 7 normotensive individuals (3 females, 4 males; age=25 ± 5.7 years). BP reactivity was derived by calculating the difference between peak stress BP and mean baseline resting BP. Significant training-induced reductions in resting SBP (p<0.001) were strongly correlated with pre-training SBP reactivity to the IHGT (r=-0.8, p=0.03), but not the CPT (r= 0.2, p=0.6). These preliminary findings suggest that SBP reactivity to a short and simple handgrip task can be used as a predictive tool to identify who will respond best to IHG training. It might be possible to further explore how the IHG training stimulus could be optimized in non-responders, to ensure that they too, experience reductions in resting BP