Responses to an isometric leg-exercise test predicts sex-specific training-induced reductions in resting blood pressure after isometric leg training

Isometric training, using either isometric handgrip (IHG) or isometric bilateral-leg (IBL) protocols, is an effective method of lowering resting systolic blood pressure (SBPrest). However, the reductions in SBPrest seen after training vary widely between individuals. Predicting likely training-induced reductions in SBPrest could make it possible to optimise the effects of the training in all participants. It is known that post-IHG training reductions in SBPrest can be predicted by SBP responses to a 2 minute IHG task in both hypertensive and older normotensives (Millar et al., 2009; Badrov et al., 2013). However, the predictability of such a test in younger individuals and when using a comparable IBL task, has not been established. Furthermore, it is not known whether these simple isometric tests can predict reductions in ambulatory SBP (mean 24-hour, SBPamb) as well as SBPrest. Therefore, the purpose of this study was to determine whether an IBL test can be used to predict training-induced reductions in SBPrest and SBPamb following 10 weeks of IBL training in young men and women.Resting and ambulatory BP (SBPrest and SBPamb) were measured prior to and following 10 weeks of IBL training using an isokinetic dynamometer (4, 2-minute contractions at 20% MVC with 2 minute rest periods, 3/week) in 20 normotensive individuals (10 men, age=21 ± 4 years; 10 women, age=23 ± 5 years). SBP responses to the IBL test (single 2-minute period of IBL exercise) was derived by calculating the difference between peak SBP and mean baseline SBPrest. Pearson’s product moment correlation coefficient was used to assess the relationship between the blood pressure responses to a short 2-minute IBL test and the magnitude of the reductions in SBPrest and SBPamb after IBL training.ResultsThere were significant reductions in men and women’s SBPrest (7.4±5.1mmHg, p=0.0001 & 5.7±4.1mmHg, p=0.001) and SBPamb (4.0±1.9mmHg, p=0.011 & 6.1±5.8mmHg, p=0.0001) following training. These changes in SBPrest were strongly correlated with pre-training SBP response to the IBL test in both men (r=-0.83, p=0.003, SEE=3.03) and women (r = -0.81, p=0.004, SEE=2.56). However, the magnitude of the reductions in SBPamb were not correlated with SBP response to the IBL test (men, r=-0.44, p=0.199, SEE=1.76; women, r=-0.23, p=0.517, SEE=6.01).These results support previous research which has identified that IBL training is an effective tool for lowering both resting and ambulatory BP. Furthermore, a simple isometric exercise test can be used as a tool to predict reductions in resting SBP, but not ambulatory SBP, after IBL training in both men and women. This test could be used to optimise the effects of this type of training in a wider range of participants, perhaps through modification of the training, to suit the anticipated effects in different individuals

Establishing Equivalent Training Intensities for Isometric Bilateral-Leg and Handgrip Exercise Using the Category Ratio Scale

Isometric handgrip (IHG) training is commonly undertaken at an exercise intensity of 30% of a subject’s maximum voluntary contraction (MVC) (McGowan et al., 2007). Matching this intensity with isometric bilateral-leg (IBL) exercise is difficult due to the different muscle mass involved. Comparative studies (Howden et al., 2002) have tended to use different exercise intensities without providing a strong rationale. Therefore, the purpose of this study was to use the Category Ratio Scale (CR-10) to establish equivalent exercise intensities for IHG and IBL, based on participant effort perception and to test the extent to which intensity can be matched, when using this method during training sessions. A total of 26 healthy participants (male, n = 18; female, n = 8) undertook two minutes of unilateral IHG to establish the mean CR-10 values. Then, performed IBL exercise at 15, 20 and 25%MVC. The IBL intensity at which CR-10 most-closely matched the values for IHG, was identified as 20%MVC. Subsequently, an IHG and IBL training session was used, to test the extent to which the intensities were matched, according to effort perception. Ten participants (male, n = 6; female, n = 4) undertook 4 x 2 minutes unilateral IHG (30%MVC) and IBL (20%MVC) training, with 2 minutes recovery between contractions with CR-10 measured at the end of each exercise bout. A one-way independent ANOVA was used to identify the IHG and IBL intensities that were most-closely matched. To determine whether CR-10 values were significantly different during the IHG and IBL training sessions, a two-way mixed-model ANOVA was used.The intensity at which CR-10 was most-closely matched between IHG and IBL was 20%MVC. There were significant differences in the CR-10 values between IHG contractions at 30%MVC and IBL at 25%MVC and 15%MVC (P > 0.05) but not at 20%MVC (P 0.05).These results suggest when performing IBL exercise, the intensity most closely matching the IHG intensity (30%MVC) is 20%MVC. Furthermore, it can be seen from the simulated training sessions that CR-10 does not significantly differ between the two intensities until the final 2-minute bout. Therefore, it may be advantageous when undertaking one-off IBL exercise or IBL training protocols with the purpose of comparing data to that from IHG, to use 20%MVC. However, when a 4 x 2 minute training protocol is used, it may be necessary to attenuate the intensity of the 4th bout of IBL

Establishing endangered species recovery criteria using predictive simulation modeling

Listing a species under the Endangered Species Act (ESA) and developing a recovery plan requires U.S. Fish and Wildlife Service to establish specific and measurable criteria for delisting. Generally, species are listed because they face (or are perceived to face) elevated risk of extinction due to issues such as habitat loss, invasive species, or other factors. Recovery plans identify recovery criteria that reduce extinction risk to an acceptable level. It logically follows that the recovery criteria, the defined conditions for removing a species from ESA protections, need to be closely related to extinction risk. Extinction probability is a population parameter estimated with a model that uses current demographic information to project the population into the future over a number of replicates, calculating the proportion of replicated populations that go extinct. We simulated extinction probabilities of piping plovers in the Great Plains and estimated the relationship between extinction probability and various demographic parameters. We tested the fit of regression models linking initial abundance, productivity, or population growth rate to extinction risk, and then, using the regression parameter estimates, determined the conditions required to reduce extinction probability to some pre-defined acceptable threshold. Binomial regression models with mean population growth rate and the natural log of initial abundance were the best predictors of extinction probability 50 years into the future. For example, based on our regression models, an initial abundance of approximately 2400 females with an expected mean population growth rate of 1.0 will limit extinction risk for piping plovers in the Great Plains to less than 0.048. Our method provides a straightforward way of developing specific and measurable recovery criteria linked directly to the core issue of extinction risk

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

The Impact Of Blood Pressure Dipping Status On Cognition, Mobility and Cardiovascular Health In Older Adults Following An Exercise Program

Objectives: To determine whether a dual-task gait and aerobic exercise intervention differentially impacted older adults with normal blood pressure (BP) dipping status (dippers) compared to those with nondipping status (nondippers). Methods: This study was a secondary analysis involving participants (mean age = 70.3 years, 61% women) who attended a laboratory-based exercise intervention over a 6-month period (40 min/day and 3 days/week). Participants were assessed in measures of cognition, mobility, and cardiovascular health at baseline, 3, 6, and 12 months (after a 6-month no-contact follow-up). Results: We observed improvements in cognition in both groups at 6 and 12 months, although no between-group differences were seen. Nondippers demonstrated superior improvements in usual gait velocity and step length after the exercise intervention compared to dippers. Dippers reduced daytime systolic BP at 6 and 12 months to a greater extent than nondippers. Discussion: BP dipping status at baseline did not influence exercise benefits to cognition but did mediate changes in mobility and cardiovascular health

Effects of Isometric Resistance Training and a Maintenance Dose on Ambulatory Blood Pressure and Morning Blood Pressure Surge in Young Normotensives

Introduction Hypertension, a modifiable risk factor for cardiovascular disease (CVD) is associated with approximately one third of deaths globally each year. Diurnal blood pressure (BP) variability and more specifically morning blood pressure surge (MBPS) are associated with increased risk of stroke, end-organ damage and are considered to be destabilising factors for atherosclerotic plaques. Isometric resistance training (IRT) has been shown to reduce ambulatory BP and MBPS following 8-10 weeks of training. However, there is no data at present which has established the dose of training needed to maintain these reported reductions following the initial IRT period. Therefore, the purpose of this study was to determine the effects of IRT on ambulatory BP and the MBPS in young normotensives following (i) 8 weeks of IRT and (ii) 8 weeks of a once a week maintenance dose. Methods Twenty-five normotensive individuals (15 men, age=21±4 years; 10 women, age=22±3 years) were randomly assigned to a training-maintenance (TRA-MT, n=13) or control (CON, n=12) group. Ambulatory BP and MBPS were measured prior to, after an 8-week (3 days/week) training period and following an 8-week maintenance period (1 day/week) of bilateral leg IRT using an isokinetic dynamometer (4 x 2-minute contractions at 20% MVC with 2-minute rest periods). A two-way repeated measures MANOVA was used to assess the within and between groups changes in ambulatory BP and MBPS. MBPS was calculated as: mean systolic BP 2 hours after waking, minus the lowest sleeping 1-hour mean systolic BP. Results There were significant reductions in 24-h ambulatory systolic BP following IRT (pre-to-post training, -7±5 mmHg, p=0.001) and these reductions remained after the maintenance period (pre-to-post maintenance, -6±4 mmHg, p=0.000). There were significant reductions in daytime BP (pre-to-post training, -5±5 mmHg, p=0.034) which remained following maintenance (pre-to-post maintenance, -5±5 mmHg, p=0.02), but there was no change in night-time systolic BP (pre-to-post training, -2±5 mmHg, p=0.685) or post maintenance period (pre-to-post maintenance, 1±6 mmHg, p=0.94). Additionally, there were significant reductions in the MBPS (pre-to-post training, -9±10 mmHg, p=0.005) which were maintained post maintenance period (pre-to-post maintenance, -8±11 mmHg, p=0.014). Additionally, significant correlation was identified between the magnitude of the change in MBPS and the magnitude of changes in mean SBP 2-h after waking (r = 0.78, P=0.002). Discussion These results provide further evidence that IRT causes significant reductions in MBPS in addition to the previously reported reductions in ambulatory BP. Additionally, these reductions seem to be maintained with a reduced exercise dose. These findings may also have important clinical implications, the significant reductions in the MBPS offer the potential for meaningful CVD and stroke risk reduction, provided these effects can be demonstrated in those who are at risk

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

Effects of isometric resistance training and detraining on ambulatory blood pressure and morning blood pressure surge in young normotensives : Isometric resistance training and detraining

Isometric resistance training (IRT) has been shown to reduce resting and ambulatory blood pressure (BP), as well as BP variability and morning BP surge (MBPS). However, there are no data available regarding how long after cessation of IRT these effects are maintained. Therefore, the purpose of this study was to determine the effects of 8 weeks of detraining on resting BP, ambulatory BP and MBPS following 8 weeks of IRT in a population of young normotensive individuals and to further substantiate previously reported reductions in MBPS following IRT. Twenty-five apparently healthy participants with resting BP within the normal range (16 men, age = 23 ± 6 years; 9 women, age = 22 ± 4 years, resting BP: 123 ± 5/69 ± 7 mmHg) were randomly assigned to a training-detraining (TRA-DT, n = 13) or control (CON, n = 12) group. Resting BP, ambulatory BP and MBPS were measured prior to, after 8 weeks of bilateral leg IRT using an isokinetic dynamometer (4 × 2-min contractions at 20% MVC with 2-min rest periods, 3 days/week) and following an 8-week detraining period. There were significant reductions in 24-h ambulatory systolic BP (SBP) and calculated SBP average real variability (ARV) following IRT that were maintained after detraining (pre-to-post detraining, −6 ± 4 mmHg, p = 0.008, −2 ± 1.5 mmHg, p = 0.001). Similarly, the training-induced decreases in daytime SBP and daytime SBP ARV (pre-to-post detraining, −5 ± 6 mmHg, p = 0.001; −2 ± 1.2 mmHg, p = 0.001, respectively), MBPS (pre-to-post detraining, −6 ± 9 mmHg, p = 0.046) and resting SBP (pre-to-post detraining, −4 ± 6 mmHg, p = 0.044) were preserved. There were no changes in night-time or night-time SBP ARV across all time points (pre-to-post detraining, −1 ± 8 mmHg, p = 1.00, −0.7 ± 2.9 mmHg, p = 1.00). These results confirm that IRT causes significant reductions in resting BP, ambulatory BP, ambulatory ARV and MBPS. Importantly, the changes remained significantly lower than baseline for 8 weeks after cessation of training, suggesting a sustained effect of IRT

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