Acute inspiratory resistance training enhances endothelium-dependent dilation and retrograde shear rate in healthy young adults

Inspiratory resistance training (IRT) yields significant reductions in resting blood pressure and improves vascular endothelial function. Our objective was to quantify the acute effects of IRT on brachial artery flow-mediated dilation (FMD) and shear rates (SRs) in healthy men and women. Twenty young adults (22.9 ± 3.4 years; 10 male, 10 female) completed a single bout of IRT or Rest condition in a randomized crossover design. Brachial artery FMD was performed before, 10 min after, and 40 min after the assigned condition. Brachial artery blood flow velocities were collected during IRT, separated by breathing cycle phase, and converted into SRs. FMD improved 10 min post-IRT (+1.86 ± 0.61%; p = 0.025) but returned to baseline by 40 min post-IRT (p = 0.002). Anterograde SR decreased by 10% and retrograde SR increased 102% during resisted inspiration, relative to baseline SR (p < 0.001). Anterograde SR increased by 7% in men and women (p < 0.001) and retrograde SR decreased by 12% in women but not men (p = 0.022) during unresisted expiration, relative to baseline SR. A single bout of IRT elicits a transient enhancement in FMD in both men and women. Acute IRT-related enhancements in SRs may contribute to sustained improvements in FMD that have been reported previously.

Time-Efficient, High-Resistance Inspiratory Muscle Strength Training Increases Exercise Tolerance in Midlife and Older Adults

PURPOSE

This study aimed to determine if time-efficient, high-resistance inspiratory muscle strength training (IMST), comprising 30 inhalation-resisted breaths per day, improves cardiorespiratory fitness, exercise tolerance, physical function, and/or regional body composition in healthy midlife and older adults.

METHODS

We performed a double-blind, randomized, sham-controlled clinical trial (NCT03266510) testing 6 wk of IMST (30 breaths per day, 6 d·wk -1 , 55%-75% maximal inspiratory pressure) versus low-resistance sham training (15% maximal inspiratory pressure) in healthy men and women 50-79 yr old. Subjects performed a graded treadmill exercise test to exhaustion, physical performance battery (e.g., handgrip strength, leg press), and body composition testing (dual x-ray absorptiometry) at baseline and after 6 wk of training.

RESULTS

Thirty-five participants (17 women, 18 men) completed high-resistance IMST ( n = 17) or sham training ( n = 18). Cardiorespiratory fitness (V̇O 2peak ) was unchanged, but exercise tolerance, measured as treadmill exercise time during a graded exercise treadmill test, increased with IMST (baseline, 539 ± 42 s; end intervention, 606 ± 42 s; P = 0.01) but not sham training (baseline, 562 ± 39 s; end intervention, 553 ± 38 s; P = 0.69). IMST increased peak RER (baseline, 1.09 ± 0.02; end intervention, 1.13 ± 0.02; P = 0.012), peak ventilatory efficiency (baseline, 25.2 ± 0.8; end intervention, 24.6 ± 0.8; P = 0.036), and improved submaximal exercise economy (baseline, 23.5 ± 1.1 mL·kg -1 ⋅min -1 ; end intervention, 22.1 ± 1.1 mL·kg -1 ⋅min -1 ; P < 0.001); none of these factors were altered by sham training (all P > 0.05). Changes in plasma acylcarnitines (targeted metabolomics analysis) were consistently positively correlated with changes in exercise tolerance after IMST but not sham training. IMST was associated with regional increases in thorax lean mass (+4.4%, P = 0.06) and reductions in trunk fat mass (-4.8%, P = 0.04); however, peripheral muscle strength, muscle power, dexterity, and mobility were unchanged.

CONCLUSIONS

These data suggest that high-resistance IMST is an effective, time-efficient lifestyle intervention for improving exercise tolerance in healthy midlife and older adults.

Dietary Supplementation With NAD+-Boosting Compounds in Humans: Current Knowledge and Future Directions

Advancing age and many disease states are associated with declines in nicotinamide adenine dinucleotide (NAD+) levels. Preclinical studies suggest that boosting NAD+ abundance with precursor compounds, such as nicotinamide riboside or nicotinamide mononucleotide, has profound effects on physiological function in models of aging and disease. Translation of these compounds for oral supplementation in humans has been increasingly studied within the last 10 years; however, the clinical evidence that raising NAD+ concentrations can improve physiological function is unclear. The goal of this review was to synthesize the published literature on the effects of chronic oral supplementation with NAD+ precursors on healthy aging and age-related chronic diseases. We identified nicotinamide riboside, nicotinamide riboside co-administered with pterostilbene, and nicotinamide mononucleotide as the most common candidates in investigations of NAD+-boosting compounds for improving physiological function in humans. Studies have been performed in generally healthy midlife and older adults, adults with cardiometabolic disease risk factors such as overweight and obesity, and numerous patient populations. Supplementation with these compounds is safe, tolerable, and can increase the abundance of NAD+ and related metabolites in multiple tissues. Dosing regimens and study durations vary greatly across interventions, and small sample sizes limit data interpretation of physiological outcomes. Limitations are identified and future research directions are suggested to further our understanding of the potential efficacy of NAD+-boosting compounds for improving physiological function and extending human health span.

Time-efficient, high-resistance inspiratory muscle strength training increases cerebrovascular reactivity in midlife and older adults

Aging is associated with increased risk for cognitive decline and dementia due in part to increases in systolic blood pressure (SBP) and cerebrovascular dysfunction. High-resistance inspiratory muscle strength training (IMST) is a time-efficient, intensive respiratory training protocol (30 resisted inspirations/day) that lowers SBP and improves peripheral vascular function in midlife/older adults with above-normal SBP. However, whether, and by what mechanisms, IMST can improve cerebrovascular function is unknown. We hypothesized that IMST would increase cerebrovascular reactivity to hypercapnia (CVR to CO2), which would coincide with changes to the plasma milieu that improve brain endothelial cell function and enhance cognitive performance (NIH Toolbox). We conducted a 6-wk double-blind, randomized, controlled clinical trial investigating high-resistance IMST [75% maximal inspiratory pressure (PImax); 6×/wk; 4 females, 5 males] vs. low-resistance sham training (15% PImax; 6×/wk; 2 females, 5 males) in midlife/older adults (age 50-79 yr) with initial above-normal SBP. Human brain endothelial cells (HBECs) were exposed to participant plasma and assessed for acetylcholine-stimulated nitric oxide (NO) production. CVR to CO2 increased after high-resistance IMST (pre: 1.38 ± 0.66 cm/s/mmHg; post: 2.31 ± 1.02 cm/s/mmHg, P = 0.020). Acetylcholine-stimulated NO production increased in HBECs exposed to plasma from after vs. before the IMST intervention [pre: 1.49 ± 0.33; post: 1.73 ± 0.35 arbitrary units (AU); P < 0.001]. Episodic memory increased modestly after the IMST intervention (pre: 95 ± 13; post: 103 ± 17 AU; P = 0.045). Cerebrovascular and cognitive function were unchanged in the sham control group. High-resistance IMST may be a promising strategy to improve cerebrovascular and cognitive function in midlife/older adults with above-normal SBP, a population at risk for future cognitive decline and dementia.NEW & NOTEWORTHY Midlife/older adults with above-normal blood pressure are at increased risk of developing cognitive decline and dementia. Our findings suggest that high-resistance inspiratory muscle strength training (IMST), a novel, time-efficient (5-10 min/day) form of physical training, may increase cerebrovascular reactivity to CO2 and episodic memory in midlife/older adults with initial above-normal blood pressure.

Neurovascular and hemodynamic responses to mental stress and exercise in severe COVID-19 survivors

Previous studies show that COVID-19 survivors have elevated muscle sympathetic nerve activity (MSNA), endothelial dysfunction, and aortic stiffening. However, the neurovascular responses to mental stress and exercise are still unexplored. We hypothesized that COVID-19 survivors, compared with age- and body mass index (BMI)-matched control subjects, exhibit abnormal neurovascular responses to mental stress and physical exercise. Fifteen severe COVID-19 survivors (aged: 49 ± 2 yr, BMI: 30 ± 1 kg/m2) and 15 well-matched control subjects (aged: 46 ± 3 yr, BMI: 29 ± 1 kg/m2) were studied. MSNA (microneurography), forearm blood flow (FBF), and forearm vascular conductance (FVC, venous occlusion plethysmography), mean arterial pressure (MAP, Finometer), and heart rate (HR, ECG) were measured during a 3-min mental stress (Stroop Color-Word Test) and during a 3-min isometric handgrip exercise (30% of maximal voluntary contraction). During mental stress, MSNA (frequency and incidence) responses were higher in COVID-19 survivors than in controls (P < 0.001), and FBF and FVC responses were attenuated (P < 0.05). MAP was similar between the groups (P > 0.05). In contrast, the MSNA (frequency and incidence) and FBF and FVC responses to handgrip exercise were similar between the groups (P > 0.05). MAP was lower in COVID-19 survivors (P < 0.05). COVID-19 survivors exhibit an exaggerated MSNA and blunted vasodilatory response to mental challenge compared with healthy adults. However, the neurovascular response to handgrip exercise is preserved in COVID-19 survivors. Overall, the abnormal neurovascular control in response to mental stress suggests that COVID-19 survivors may have an increased risk to cardiovascular events during mental challenge.

Novel whole blood transcriptome signatures of changes in maximal aerobic capacity in response to endurance exercise training in healthy women

Maximal aerobic exercise capacity (V̇O₂max) is one of the strongest predictors of morbidity and mortality. Aerobic exercise training can increase V̇O₂max, but inter-individual variability is marked and unexplained physiologically. The mechanisms underlying this variability have major clinical implications for extending human healthspan. Here, we report a novel transcriptome signature related to ΔV̇O₂max with exercise training detected in whole-blood RNA. We used RNA-seq to characterize transcriptomic signatures of ΔV̇O₂max in healthy women who completed a 16-week, randomized controlled trial comparing supervised, higher vs. lower aerobic exercise training volume and intensity (four training groups, fully crossed). We found significant baseline gene expression differences in subjects who responded to aerobic exercise training with robust vs. little/no ΔV̇O₂max, and differentially expressed genes/transcripts were mostly related to inflammatory signaling and mitochondrial function/protein translation. Baseline gene expression signatures associated with robust vs. little/no ΔV̇O₂max were also modulated by exercise training in a dose-dependent manner, and they predicted ΔV̇O₂max in this and a separate dataset. Collectively, our data demonstrate the potential utility of using whole blood transcriptomics to study the biology of inter-individual variability in responsiveness to the same exercise training stimulus.

Sympathetic Neural Overdrive, Aortic Stiffening, Endothelial Dysfunction, and Impaired Exercise Capacity in Severe COVID-19 Survivors: A Mid-Term Study of Cardiovascular Sequelae

BACKGROUND

COVID-19 has become a dramatic health problem during this century. In addition to high mortality rate, COVID-19 survivors are at increased risk for cardiovascular diseases 1-year after infection. Explanations for these manifestations are still unclear but can involve a constellation of biological alterations. We hypothesized that COVID-19 survivors compared with controls exhibit sympathetic overdrive, vascular dysfunction, cardiac morpho-functional changes, impaired exercise capacity, and increased oxidative stress.

METHODS

Nineteen severe COVID-19 survivors and 19 well-matched controls completed the study. Muscle sympathetic nerve activity (microneurography), brachial artery flow-mediated dilation and blood flow (Doppler-Ultrasound), carotid-femoral pulse wave velocity (Complior), cardiac morpho-functional parameters (echocardiography), peak oxygen uptake (cardiopulmonary exercise testing), and oxidative stress were measured ~3 months after hospital discharge. Complementary experiments were conducted on human umbilical vein endothelial cells cultured with plasma samples from subjects.

RESULTS

Muscle sympathetic nerve activity and carotid-femoral pulse wave velocity were greater and brachial artery flow-mediated dilation, brachial artery blood flow, E/e' ratio, and peak oxygen uptake were lower in COVID-19 survivors than in controls. COVID-19 survivors had lower circulating antioxidant markers compared with controls, but there were no differences in plasma-treated human umbilical vein endothelial cells nitric oxide production and reactive oxygen species bioactivity. Diminished peak oxygen uptake was associated with sympathetic overdrive, vascular dysfunction, and reduced diastolic function in COVID-19 survivors.

CONCLUSIONS

Our study revealed that COVID-19 survivors have sympathetic overactivation, vascular dysfunction, cardiac morpho-functional changes, and reduced exercise capacity. These findings indicate the need for further investigation to determine whether these manifestations are persistent longer-term and their impact on the cardiovascular health of COVID-19 survivors.

Deep breathing exercise at work: Potential applications and impact

Hypertension is a major contributor to cardiovascular disease and daily deep breathing exercise (DBE) is a promising intervention to reduce blood pressure and stress in adults. DBE is simple, time-efficient, and does not require specialized equipment, allowing participation in a wide variety of settings. The workplace is an ideal setting to implement DBE at the national level for several reasons, including a large proportion of waking hours spent in the workplace, high levels of sedentary time at work, prevalence of work-related stress, and regular breaks throughout the day potentially reducing worker error. While the degree of adherence to daily workplace DBE will be the responsibility of the individual, employers and managers can (and should) do much to remove barriers to participation. Specifically, this could include: implementing regular short breaks or classes to perform DBE throughout the day, covering subscription costs for smartphone applications that guide DBE, and creating incentive programs for continuing DBE participation. Implementing DBE in the workplace is a pragmatic approach to provide a low-cost blood pressure and stress reduction therapy to a substantial portion of the adult population in the US, at least 50% of whom have high blood pressure.

Cerebrovascular pulsatility index is higher in chronic kidney disease

Patients with chronic kidney disease (CKD) are more likely to die of cardiovascular diseases, including cerebrovascular disease, than to progress to end-stage kidney disease. Cerebrovascular dysfunction, characterized by reduced cerebrovascular reactivity, cerebral hypoperfusion, and increased pulsatile flow within the brain, precedes the onset of dementia and is linked to cognitive dysfunction. However, whether impaired cerebrovascular function is present in non-dialysis dependent CKD is largely unknown. Using transcranial Doppler, we compared middle cerebral artery (MCA) blood velocity response to hypercapnia (normalized for blood pressure and end-tidal CO₂ ; a measure of cerebrovascular reactivity) and MCA pulsatility index (PI; a measure of cerebrovascular stiffness) in patients with stage 3-4 CKD vs. age-matched healthy controls. We also administered the NIH cognitive toolbox (cognitive function), measured carotid-femoral pulse-wave velocity (PWV; aortic stiffness), and assessed ex vivo nitric oxide (NO) and reactive oxygen species (ROS) production from human brain endothelial cells incubated with serum obtained from study participants. MCA PI was higher in patients with CKD vs. controls; however, normalized MCA blood velocity response to hypercapnia did not differ between groups. Similar results were observed in a validation cohort of midlife and older adults divided by the median estimated glomerular filtration rate (eGFR). MCA PI was associated with greater large-elastic artery stiffness (carotid-femoral PWV), worse executive function (trails B time), lower eGFR, and higher ex vivo ROS production. These data suggest that impaired kidney function is associated with greater cerebrovascular stiffness, which may contribute to the known increased risk for cognitive impairment in patients with CKD.

A multi-trial, retrospective analysis of the antihypertensive effects of high-resistance, low-volume inspiratory muscle strength training

Above-normal blood pressure (BP) is a primary risk factor for cardiovascular diseases. In a retrospective analysis of five pilot trials, we assessed the BP-lowering effects of high-resistance inspiratory muscle strength training (IMST) in adults aged 18-82 years and the impact of IMST on maximal inspiratory pressure (PIMAX), a gauge of inspiratory muscle strength and independent disease risk factor. Participants were randomized to high-resistance IMST (75% PIMAX) or low-resistance sham (15% PIMAX) training (30 breaths/day, 5-7 days/wk, 6 wk). IMST (n = 67) reduced systolic BP (SBP) by 9 ± 6 mmHg (P < 0.01) and diastolic BP (DBP) by 4 ± 4 mmHg (P < 0.01). IMST-related reductions in SBP and DBP emerged by week 2 of training (-4 ± 8 mmHg and -3 ± 6 mmHg; P ≤ 0.01, respectively) and continued across the 6-wk intervention. SBP and DBP were unchanged with sham training (n = 61, all P > 0.05). Select subject characteristics slightly modified the impact of IMST on BP. Greater reductions in SBP were associated with older age (β = -0.07 ± 0.03; P = 0.04) and greater reductions in DBP associated with medication-naïve BP (β = -3 ± 1; P = 0.02) and higher initial DBP (β = -0.12 ± 0.05; P = 0.04). PIMAX increased with high-resistance IMST and low-resistance sham training, with a greater increase from high-resistance IMST (+20 ± 17 vs. +6 ± 14 cmH2O; P < 0.01). Gains in PIMAX had a modest inverse relation with age (β = -0.20 ± 0.09; P = 0.03) and baseline PIMAX (β = -0.15 ± 0.07; P = 0.04) but not to reductions in SBP or DBP. These compiled findings from multiple independent trials provide the strongest evidence to date that high-resistance IMST evokes clinically significant reductions in SBP and DBP, and increases in PIMAX, in adult men and women.NEW & NOTEWORTHY In young-to-older adult men and women, 6 wk of high-resistance inspiratory muscle strength training lowers casual systolic and diastolic blood pressure by 9 mmHg and 4 mmHg, respectively, with initial reductions observed by week 2 of training. Given blood pressure outcomes with the intervention were only slightly altered by subject baseline characteristics (i.e., age, blood pressure medication, and health status), inspiratory muscle strength training is effective in lowering blood pressure in a broad range of adults.

Abstract P070: Vascular Conditioning Exercise Acutely Enhances Endothelial Function In Young Adults

Introduction: Vascular conditioning exercise (VCE), otherwise known as high-resistance inspiratory muscle strength training, is a potent non-pharmacological therapy to reduce blood pressure. When performed daily for 6 weeks, systolic blood pressure is reduced by ~6-10 mmHg on average, in part, by increasing nitric oxide-mediated endothelial dependent dilation (EDD). While the adaptations to long-term VCE have been described, the acute effects of VCE that may mediate the long-term vascular adaptations have not been thoroughly investigated.

Hypothesis: We assessed the hypothesis that a single bout of VCE would increase EDD for at least 40 minutes after exercise completion, while arterial stiffness would not be affected.

Methods: Nitric oxide-mediated EDD and ischemia-induced maximal shear rate were assessed with brachial artery flow-mediated dilation, and arterial stiffness was assessed via carotid-femoral pulse wave velocity. Assessments were performed before, 10 minutes after, and 40 minutes after a single bout of VCE (5 sets of 6 breaths at 50% of maximal inspiratory pressure with 1-minute rest intervals) or a time-matched rest interval in nine young adults (22.3 ± 2.6 years; 3 male, 6 female) using a randomized crossover design, with at least 48 hours between visits.

Results: All values are mean difference ± SD. There were no differences between interventions in EDD at baseline (0.73 ± 3.7%; p =0.569). EDD was significantly higher 10 minutes post-VCE, relative to the rest intervention (3.28 ± 3.37%; p = 0.019), but there were no differences at 40 minutes post-intervention (0.01 ± 4.46%; p =0.992). Further, there were no differences in maximal shear rate between measurements (all p -values >0.05), indicating the changes in EDD were not due to a modified hyperaemic response. Lastly, there were no differences in arterial stiffness (Baseline: 0.22 ± 0.75 m/s; Post-10: 0.26 ± 0.51 m/s; Post-40: 0.27 ± 0.33 m/s; all p -values >0.05).

Conclusions: A single bout of VCE transiently enhances EDD in healthy young adults, although this effect disappears within 40 minutes of exercise completion. This acute functional response to VCE can partially explain the large improvements in EDD that are seen in response to daily VCE performance over longer periods.

Inspiratory muscle strength training for lowering blood pressure and improving endothelial function in postmenopausal women: comparison with “standard of care” aerobic exercise

Background: High blood pressure (BP), particularly systolic BP (SBP), is the major modifiable risk factor for cardiovascular diseases and related disorders of aging. SBP increases markedly with aging in women such that the prevalence of above-normal SBP (i.e., ≥120 mmHg) in postmenopausal women exceeds rates in age-matched men. This increase in SBP is associated with vascular endothelial dysfunction, mediated by excessive reactive oxygen species-induced oxidative stress and consequent reductions in nitric oxide bioavailability. Moderate-intensity aerobic exercise is a recommended lifestyle strategy for reducing SBP. However, adherence to aerobic exercise guidelines among postmenopausal women is low (<30%) and aerobic exercise does not consistently enhance endothelial function in estrogen-deficient postmenopausal women. High-resistance inspiratory muscle strength training (IMST) is a time-efficient, adherable lifestyle intervention that involves inhaling against resistance through a handheld device (30 breaths/day). Here, we present the protocol for a randomized controlled trial investigating the efficacy of 3 months of high-resistance IMST compared to guideline-based, “standard-of-care” aerobic exercise training for decreasing SBP and improving endothelial function in estrogen-deficient postmenopausal women with above-normal SBP (120–159 mmHg) at baseline (ClinicalTrials.gov Identifier: NCT05000515).

Methods: A randomized, single-blind, parallel-group design clinical trial will be conducted in 72 (36/group) estrogen-deficient postmenopausal women with above-normal SBP. Participants will complete baseline testing and then be randomized to either 3 months of high-resistance IMST (30 breaths/day, 6 days/week, 75% maximal inspiratory pressure) or moderate-intensity aerobic exercise training (brisk walking 25 min/day, 6 days/week, 40–60% heart rate reserve). Outcome measures will be assessed after 3 months of either intervention. Following end-intervention testing, participants will abstain from their assigned intervention for 6 weeks, after which BP and endothelial function will be assessed to evaluate the potential persistent effects of the intervention on the primary and secondary outcomes.

Discussion: This study is designed to compare the effectiveness of time-efficient, high-resistance IMST to guideline-based aerobic exercise training for lowering SBP and improving endothelial function, and interrogating potential mechanisms of action, in estrogen-deficient postmenopausal women.

Clinical Trial Registration:ClinicalTrials.gov, Identifier: NCT05000515.

Promoting healthy cardiovascular aging: emerging topics

The development of age-related cardiovascular (CV) dysfunction increases the risk of CV disease as well as other chronic age-associated disorders, including chronic kidney disease, and Alzheimer's disease and related dementias. Major manifestations of age-associated CV dysfunction that increase disease risk are vascular dysfunction, primarily vascular endothelial dysfunction and arterial stiffening, and elevated systolic blood pressure. Declines in nitric oxide bioavailability secondary to increased oxidative stress and inflammation are established mechanisms of CV dysfunction with aging. Moreover, fundamental mechanisms of aging, termed the "hallmarks of aging" extend to the CV system and, as such, may be considered "hallmarks of CV aging". These mechanisms represent viable therapeutic targets for treating CV dysfunction with aging. Healthy lifestyle behaviors, such as regular aerobic exercise and certain dietary patterns, are considered "first-line" strategies to prevent and/or treat age-associated CV dysfunction. Despite the well-established benefits of these strategies, many older adults do not meet the recommended guidelines for exercise or consume a healthy diet. Therefore, it is important to establish alternative and/or complementary evidence-based approaches to prevent or reverse age-related CV dysfunction. Targeting fundamental mechanisms of CV aging with interventions such as time-efficient exercise training, food-derived molecules, termed nutraceuticals, or select synthetic pharmacological agents represents a promising approach. In the present review, we will highlight emerging topics in the field of healthy CV aging with a specific focus on how exercise, nutrition/dietary patterns, nutraceuticals and select synthetic pharmacological compounds may promote healthy CV aging, in part, by targeting the hallmarks of CV aging.

Translational Potential of High-Resistance Inspiratory Muscle Strength Training

Age-associated cardiovascular (CV) dysfunction increases the risk for CV diseases. Aerobic exercise training can improve CV function, but only a minority of adults meet aerobic exercise guidelines. High-resistance inspiratory muscle strength training is a time-efficient lifestyle intervention that may promote adherence and improve CV function. However, further investigation is needed to translate inspiratory muscle strength training into the public health domain.

Nitric oxide, aging and aerobic exercise: Sedentary individuals to Master's athletes

Aging is associated with a decline in physiological function and exercise performance. These effects are mediated, at least in part, by an age-related decrease in the bioavailability of nitric oxide (NO), a ubiquitous gasotransmitter and regulator of myriad physiological processes. The decrease in NO bioavailability with aging is especially apparent in sedentary individuals, whereas older, physically active individuals maintain higher levels of NO with advancing age. Strategies which enhance NO bioavailability (including nutritional supplementation) have been proposed as a potential means of reducing the age-related decrease in physiological function and enhancing exercise performance and may be of interest to a range of older individuals including those taking part in competitive sport. In this brief review we discuss the effects of aging on physiological function and endurance exercise performance, and the potential role of changes in NO bioavailability in these processes. We also provide a summary of current evidence for dietary supplementation with substrates for NO production - including inorganic nitrate and nitrite, l-arginine and l-citrulline - for improving exercise capacity/performance in older adults. Additionally, we discuss the (limited) evidence on the effects of (poly)phenols and other dietary antioxidants on NO bioavailability in older individuals. Finally, we provide suggestions for future research.

Nicotinamide Riboside Supplementation for Treating Elevated Systolic Blood Pressure and Arterial Stiffness in Midlife and Older Adults

Background

Aging is the primary risk factor for cardiovascular diseases, the leading cause of death worldwide. Age-related increases in systolic blood pressure (SBP) link advancing age to cardiovascular disease risk. A key mechanism mediating the increase in SBP with aging is stiffening of the large elastic arteries, which occurs due to increases in oxidative stress, inflammation, and vascular smooth muscle tone. Nicotinamide adenine dinucleotide (NAD⁺) is a key molecule in energy metabolism and cellular functioning which declines with advancing age and chronic disease. Dietary supplementation with NAD⁺ precursors, such as nicotinamide riboside, boosts NAD⁺ bioavailability and may improve cardiovascular health. Here, we present the protocol for a randomized, controlled trial investigating the efficacy of 3 months of oral supplementation with nicotinamide riboside for decreasing SBP and arterial stiffness in midlife and older adults with initial above-normal (120–159 mmHg) SBP (ClinicalTrials.gov Identifier: NCT03821623). The primary outcome is casual (resting) SBP and secondary outcomes include 24-h SBP and aortic stiffness. Other outcomes include assessment of safety; tolerability; adherence; diastolic BP; systemic NAD⁺ bioavailability; and circulating biomarkers of oxidative stress, inflammation, and sympathoadrenal activity.

Methods

A randomized, double-blind, placebo-controlled, single-site parallel-group design clinical trial will be conducted in 94 (47/group) midlife and older (age ≥ 50 years) adults with initial above-normal SBP. Participants will complete baseline testing and then will be randomized to either nicotinamide riboside (500 mg, 2×/day, NIAGEN^®; ChromaDex Inc.) or placebo supplementation. Outcome measures will be assessed again after 3 months of treatment.

Discussion

This study is designed to establish the safety and efficacy of the NAD⁺ boosting compound, nicotinamide riboside, for reducing casual and 24-h SBP and aortic stiffness in midlife and older adults with above-normal SBP at baseline, a population at increased risk of cardiovascular diseases.

Clinical Trial Registration

[www.ClinicalTrials.gov], identifier [NCT03821623].

Six Months of Inspiratory Muscle Training to Lower Blood Pressure and Improve Endothelial Function in Middle-Aged and Older Adults With Above-Normal Blood Pressure and Obstructive Sleep Apnea: Protocol for the CHART Clinical Trial

Background: Cardiovascular disease is a major global health concern and prevalence is high in adults with obstructive sleep apnea (OSA). Lowering blood pressure (BP) can greatly reduce cardiovascular disease risk and physical activity is routinely prescribed to achieve this goal. Unfortunately, many adults with OSA suffer from fatigue, daytime sleepiness, and exercise intolerance—due to poor sleep quality and nocturnal hypoxemia—and have difficulty initiating and maintaining an exercise program. High-resistance inspiratory muscle strength training (IMST) is a simple, time-efficient breathing exercise consistently reported to reduce BP in small, selective groups of both healthy and at-risk adults. Herein we present the study protocol for a randomized clinical trial to determine the long-term efficacy of IMST performed regularly for 24 weeks in middle-aged and older adults with OSA. The primary outcome is casual systolic BP. Secondary outcomes are 24-h systolic BP and circulating plasma norepinephrine concentration. Other outcomes include vascular endothelial function (endothelial-dependent and -independent dilation), aortic stiffness, casual and 24-h diastolic BP, and the influence of circulating factors on endothelial cell nitric oxide and reactive oxygen species production. Overall, this trial will establish efficacy of high-resistance IMST for lowering BP and improving cardiovascular health in middle-aged and older adults with OSA.

Methods: This is a single-site, double-blind, randomized clinical trial. A minimum of 92 and maximum of 122 male and female adults aged 50–80 years with OSA and above-normal BP will be enrolled. After completion of baseline assessments, subjects will be randomized in a 1:1 ratio to participate in either high-resistance or sham (low-resistance) control IMST, performed at home, 5 min/day, 5 days/week, for 24 weeks. Repeat assessments will be taken after the 24-week intervention, and after 4 and 12 weeks of free living.

Discussion: This study is designed to assess the effects of 24 weeks of IMST on BP and vascular function. The results will characterize the extent to which IMST can reduce BP when performed over longer periods (i.e., 6 months) than have been assessed previously. Additionally, this study will help to determine underlying mechanisms driving IMST-induced BP reductions that have been reported previously.

Clinical Trial Registration: This trial is registered with ClinicalTrials.gov (Registration Number: NCT04932447; Date of registration June 21, 2021).

Time-Efficient Inspiratory Muscle Strength Training Lowers Blood Pressure and Improves Endothelial Function, NO Bioavailability, and Oxidative Stress in Midlife/Older Adults With Above-Normal Blood Pressure

Background High-resistance inspiratory muscle strength training (IMST) is a novel, time-efficient physical training modality. Methods and Results We performed a double-blind, randomized, sham-controlled trial to investigate whether 6 weeks of IMST (30 breaths/day, 6 days/week) improves blood pressure, endothelial function, and arterial stiffness in midlife/older adults (aged 50-79 years) with systolic blood pressure ≥120 mm Hg, while also investigating potential mechanisms and long-lasting effects. Thirty-six participants completed high-resistance IMST (75% maximal inspiratory pressure, n=18) or low-resistance sham training (15% maximal inspiratory pressure, n=18). IMST was safe, well tolerated, and had excellent adherence (≈95% of training sessions completed). Casual systolic blood pressure decreased from 135±2 mm Hg to 126±3 mm Hg (P<0.01) with IMST, which was ≈75% sustained 6 weeks after IMST (P<0.01), whereas IMST modestly decreased casual diastolic blood pressure (79±2 mm Hg to 77±2 mm Hg, P=0.03); blood pressure was unaffected by sham training (all P>0.05). Twenty-four hour systolic blood pressure was lower after IMST versus sham training (P=0.01). Brachial artery flow-mediated dilation improved ≈45% with IMST (P<0.01) but was unchanged with sham training (P=0.73). Human umbilical vein endothelial cells cultured with subject serum sampled after versus before IMST exhibited increased NO bioavailability, greater endothelial NO synthase activation, and lower reactive oxygen species bioactivity (P<0.05). IMST decreased C-reactive protein (P=0.05) and altered select circulating metabolites (targeted plasma metabolomics) associated with cardiovascular function. Neither IMST nor sham training influenced arterial stiffness (P>0.05). Conclusions High-resistance IMST is a safe, highly adherable lifestyle intervention for improving blood pressure and endothelial function in midlife/older adults with above-normal initial systolic blood pressure. Registration URL: https://www.clinicaltrials.gov; Unique identifier: NCT03266510.

Case studies in physiology: Impact of a long-distance hike on the Pacific Crest Trail on arterial function and body composition in a highly fit young male

The Pacific Crest Trail (PCT) is a 4265‐km hiking trail that extends from the US‐Mexican border to the US‐Canadian border through the mountain ranges of western North America. Individuals who hike the entire length of the trail in one season (4–6 months) perform long daily exercise durations while exposed to extreme environmental temperatures, high altitudes, intense solar radiation, and the consumption of calorie‐rich, nutrient‐poor diets. This case study reports changes in arterial function and body composition in a subject before and after a 112‐day long‐distance hike of the PCT. Brachial artery flow‐mediated dilation, a measure of vascular endothelial function, decreased from: 6.97% to 5.00%. Carotid‐femoral pulse wave velocity, a measure of aortic stiffness, increased from 5.39 to 5.76 m/s. Dual‐energy x‐ray absorptiometry scans detected no major changes in total‐body bone mineral density, fat mass, or lean mass, although there were minor, unfavorable changes in some subregions of the body. It is important for individuals completing a long‐distance hike to be aware of the potential deleterious changes associated with large volumes of exercise and consuming a high‐calorie, low‐quality diet.

Vascular Endothelial Function in Midlife/Older Adults Classified According to 2017 American College of Cardiology/American Heart Association Blood Pressure Guidelines

Background

Impaired endothelial function is thought to contribute to the increased cardiovascular risk associated with above‐normal blood pressure (BP). However, the association between endothelial function and BP classified by 2017 American College of Cardiology/American Heart Association guidelines is unknown. Our objective was to determine if endothelial function decreases in midlife/older adults across the 2017 American College of Cardiology/American Heart Association guidelines BP classifications and identify associated mechanisms of action.

Methods and Results

A retrospective analysis of endothelial function (brachial artery flow‐mediated dilation) from 988 midlife/older adults (aged 50+ years) stratified by BP status (normal BP; elevated BP; stage 1 hypertension; stage 2 hypertension) was performed. Endothelium‐independent dilation (sublingual nitroglycerin), reactive oxygen species–mediated suppression of endothelial function (∆brachial artery flow‐mediated dilation with vitamin C infusion), and endothelial cell and plasma markers of oxidative stress and inflammation were assessed in subgroups. Compared with normal BP (n=411), brachial artery flow‐mediated dilation was 12% (P=0.04), 15% (P<0.01) and 20% (P<0.01) lower with elevated BP (n=173), stage 1 hypertension (n=248) and stage 2 hypertension (n=156), respectively, whereas endothelium‐independent dilation did not differ (P=0.14). Vitamin C infusion increased brachial artery flow‐mediated dilation in those with above‐normal BP (P≤0.02) but not normal BP (P=0.11). Endothelial cell p47^phox (P<0.01), a marker of superoxide/reactive oxygen species–generating nicotinamide adenine dinucleotide phosphate oxidase, and circulating interleukin‐6 concentrations (P=0.01) were higher in individuals with above‐normal BP.

Conclusions

Vascular endothelial function is progressively impaired with increasing BP in otherwise healthy adults classified by 2017 American College of Cardiology/American Heart Association guidelines. Impaired endothelial function with above‐normal BP is mediated by excessive reactive oxygen species signaling associated with increased endothelial expression of nicotinamide adenine dinucleotide phosphate oxidase and circulating interleukin‐6.

Time-efficient physical training for enhancing cardiovascular function in midlife and older adults: promise and current research gaps

Cardiovascular diseases (CVD) remain the leading cause of death in developed societies, and "midlife" (50-64 yr) and older (65+) men and women bear the great majority of the burden of CVD. Much of the increased risk of CVD in this population is attributable to CV dysfunction, including adverse changes in the structure and function of the heart, increased systolic blood pressure, and arterial dysfunction. The latter is characterized by increased arterial stiffness and vascular endothelial dysfunction. Conventional aerobic exercise training, as generally recommended in public health guidelines, is an effective strategy to preserve or improve CV function with aging. However, <40% of midlife and older adults meet aerobic exercise guidelines, due in part to time availability-related barriers. As such, there is a need to develop evidence-based time-efficient exercise interventions that promote adherence and optimize CV function in these groups. Two promising interventions that may meet these criteria are interval training and inspiratory muscle strength training (IMST). Limited research suggests these modes of training may improve CV function with time commitments of ≤60 min/wk. This review will summarize the current evidence for interval training and IMST to improve CV function in midlife/older adults and identify key research gaps and future directions.

Blood pressure normalization via pharmacotherapy improves cutaneous microvascular function through NO-dependent and NO-independent mechanisms

Hypertension is associated with endothelial dysfunction and vascular remodeling.

OBJECTIVE

To assess effects of antihypertensive pharmacotherapy on eNOS- and iNOS-dependent mechanisms and maximal vasodilator capacity in the cutaneous microvasculature.

METHODS

Intradermal microdialysis fibers were placed in 15 normotensive (SBP 111±2 mm Hg), 12 unmedicated hypertensive (SBP 142±2 mm Hg), and 12 medicated hypertensive (SBP 120±2 mm Hg) subjects. Treatments were control, iNOS-inhibited (1400w), and NOS-inhibited (l-NAME). Red cell flux, measured during local heating (42°C) and ACh dose-response protocols, was normalized to CVC (flux MAP^-1 ) and a percentage of maximal vasodilation (%CVC_max ).

RESULTS

Compared to normotensives, ACh-mediated vasodilation was attenuated in the hypertensive (P<.001), but not in medicated subjects (P=.83). NOS inhibition attenuated ACh-mediated vasodilation in normotensives compared to hypertensive (P<.001) and medicated (P<.001) subjects. With iNOS inhibition, there was no difference in ACh-mediated vasodilation between groups. Compared to the normotensives, local heat-induced vasodilation was attenuated in the hypertensives (P<.001), but iNOS inhibition augmented vasodilation in the hypertensives so this attenuation was abolished (P=.31). Compared to normotensives, maximal vasodilator capacity was reduced in the hypertensive (P=.014) and medicated subjects (P=.004).

CONCLUSIONS

In the cutaneous microvasculature, antihypertensive pharmacotherapy improved endothelial function through NO-dependent and NO-independent mechanisms, but did not improve maximal vasodilator capacity.

Acute lysyl oxidase inhibition alters microvascular function in normotensive but not hypertensive men and women

The lysyl oxidase (LOX) family of enzymes regulates collagen cross-linking. LOX is upregulated in hypertension, increasing vascular stiffness. In vivo human research is sparse, as long-term LOX inhibition in animals causes vascular instability. Our aim was to evaluate the effects of LOX inhibition on cutaneous microvascular function to determine whether LOX function was upregulated in hypertensive humans. Four intradermal microdialysis fibers were placed in the forearm of 10 young [age: 24 ± 1 yr, mean arterial pressure (MAP): 87 ± 2 mmHg], 10 normotensive (age: 50 ± 2 yr, MAP: 84 ± 1 mmHg), and 10 hypertensive (age: 53 ± 2 yr, MAP: 112 ± 2 mmHg) subjects. Two sites were perfused with 10 mM β-aminopropionitrile (BAPN) to inhibit LOX. The remaining two sites were perfused with lactated Ringer solution (control). A norepinephrine dose response (10-12-10-2 M) was performed to examine receptor-mediated vasoconstrictor function. A sodium nitroprusside dose response (10-8-10-1.3 M) was performed to examine vascular smooth muscle vasodilator function. Red blood cell flux was measured via laser-Doppler flowmetry and normalized to cutaneous vascular conductance (flux/MAP). LogEC50 values were calculated to determine changes in vasosensitivity. Skin tissue samples were analyzed for both extracellular matrix-bound and soluble LOX. LOX inhibition augmented vasoconstrictor sensitivity in young (control: -6.0 and BAPN: -7.1, P = 0.03) and normotensive (control: -4.8 and BAPN: -7.0, P = 0.01) but not hypertensive (control: -6.0 and BAPN: -6.1, P = 0.79) men and women. Relative to young subjects, extracellular matrix-bound LOX expression was higher in hypertensive subjects (young: 100 ± 8 and hypertensive: 162 ± 8, P = 0.002). These results suggest that upregulated LOX may contribute to the vascular stiffness and microvascular dysfunction characteristic in hypertension. NEW & NOTEWORTHY Matrix-bound lysyl oxidase (LOX) and LOX-like 2 expression are upregulated in the microvasculature of hypertensive men and women. Microvascular responsiveness to exogenous stimuli is altered with localized LOX inhibition in healthy men and women but not hypertensive adults. The LOX family differentially affects microvascular function in hypertensive and normotensive men and women.

Menthol-Induced Cutaneous Vasodilation Is Preserved in Essential Hypertensive Men and Women

BACKGROUND

Menthol is a selective transient receptor potential melastatin 8 (TRPM8) channel agonist that induces cutaneous vasodilation in young, normotensive men and women through nitric oxide synthase (NOS)-, endothelium-derived hyperpolarizing factor (EDHF)-, and sensory nerve-mediated mechanisms. Microvascular dysfunction is present in essential hypertension and whether menthol induces vasodilation is men and women with essential hypertension is equivocal.

METHODS

Four intradermal microdialysis fibers were placed in the forearm of 9 essential hypertensive and 10 age-matched normotensive control subjects. Sites were pretreated with lactated Ringer's (control), l-NAME (NOS inhibited), TEA (EDHF inhibited), and lidocaine (sensory nerve inhibited). The microdialysis fibers were then perfused with 7 increasing doses of menthol (0.1-500 mM). Red cell flux in response to menthol was measured with laser Doppler flowmetry. Data were normalized to mean arterial pressure and presented as a percentage of site-specific maximum vasodilation (%CVCmax).

RESULTS

At the control site, menthol caused vasodilation in both the normotensive and hypertensive groups (menthol doses 100, 250, and 500 mM; all P < 0.05 compared to baseline). There were no differences between groups (P = 0.58, main effect). There was no effect of either NOS or sensory nerve inhibition on menthol-induced vasodilation in the normotensive group; however, menthol-induced vasodilation was attenuated with NOS and sensory nerve inhibition in the hypertensive group. EDHF inhibition attenuated menthol-induced vasodilation in both groups.

CONCLUSIONS

Menthol-induced vasodilation has NO, EDHF, and sensory nerve components. Menthol-induced cutaneous vasodilation is preserved in hypertensive subjects. However, the hypertensive subjects exhibited a loss of redundant vasodilator systems.

Effects of vehicle microdialysis solutions on cutaneous vascular responses to local heating

Microdialysis is a minimally invasive technique often paired with laser Doppler flowmetry to examine cutaneous microvascular function, yet presents with several challenges, including incompatibility with perfusion of highly lipophilic compounds. The present study addresses this methodological concern, with an emphasis on the independent effects of commonly used vehicle dialysis solutions to improve solubility of pharmacological agents with otherwise low aqueous solubility. Four microdialysis fibers were placed in the ventral forearm of eight subjects (4 men, 4 women; 25 ± 1 yr) with sites randomized to serve as 1) control (lactated Ringer's), 2) Sodium carbonate-bicarbonate buffer administered at physiological pH [SCB-HCl; pH 7.4, achieved via addition of hydrochloric acid (HCl)], 3) 0.02% ethanol, and 4) 2% dimethyl sulfoxide (DMSO). After baseline (34°C), vehicle solutions were administered throughout a standardized local heating protocol to 42°C. Laser Doppler flowmetry provided an index of blood flow. Cutaneous vascular conductance was calculated and normalized to maximum (%CVC_max, sodium nitroprusside and 43°C local heat). The SCB-HCl solution increased baseline %CVC_max (control: 9.7 ± 0.8; SCB-HCl: 21.5 ± 3.5%CVC_max; P = 0.03), but no effects were observed during heating or maximal vasodilation. There were no differences with perfusion of ethanol or DMSO at any stage of the protocol ( P > 0.05). These data demonstrate the potential confounding effects of some vehicle dialysis solutions on cutaneous vascular function. Notably, this study provides evidence that 2% DMSO and 0.02% ethanol are acceptable vehicles with no confounding local vascular effects to a standardized local heating protocol at the concentrations presented. NEW & NOTEWORTHY This study examined the independent effects of common vehicle solutions on cutaneous vascular responses. A basic buffer (SCB-HCl) caused baseline vasodilation; 2% DMSO and 0.02% ethanol had no effects. This highlights the need for considering potential confounding effects of solubilizing solutions when combined with low aqueous soluble pharmacological agents. Importantly, DMSO and ethanol do not appear to influence cutaneous vascular function during baseline or local heating at the concentrations studied, allowing their use without confounding effects.

Kinesiology tape modestly increases skin blood flow regardless of tape application technique

Kinesiology tape (KNT) is commonly used for injury prevention and as part of rehabilitation to treat muscle and joint pain. KNT is purported to increase local blood flow by lifting the skin and reducing local pressure. Whether or not skin blood flow is increased by KNT is not presently known. We carried out 2 experiments to elucidate the effects of KNT on skin blood flow. Protocol 1: KNT was applied to the skin at 0%, 25%, 50%, and 100% relative tension. Red cell flux, an index of skin blood flow, was measured by laser Doppler flowmetry (LDF) at each site and at a no-tape control site. There was an overall effect of tape on cutaneous vascular conductance (CVC: LDF/MAP) (KNT: 0.12 (95% confidence interval: 0.10, 0.14), control 0.08 (0.07, 0.10) flux•mmHg^-1; p<0.01), but no effect of tension (all p>0.05). Subjects kept KNT on for 3 days then returned for follow-up testing. CVC was not changed after 3 days of KNT application (p=0.07). Protocol 2: KNT was applied to the skin with and without convolutions. There was an overall effect of tape on CVC (KNT: 0.30 (0.21, 0.39), control 0.15 (0.09, 0.21) flux•mmHg^-1; p=0.03), but no difference between KNT applied with or without convolutions (all p>0.05). These data suggest that KNT modestly increases microvascular blood flow, regardless of tension or presence of convolutions.

Ingestion of transient receptor potential channel agonists attenuates exercise-induced muscle cramps

INTRODUCTION

Exercise-associated muscle cramping (EAMC) is a poorly understood problem that is neuromuscular in origin. Ingestion of transient receptor potential (TRP) channel agonists has been efficacious in attenuating electrically induced muscle cramps. This study examines the effect of TRP agonist ingestion on voluntarily induced EAMC and motor function.

METHODS

Study 1: Thirty-nine participants completed 2 trials after ingesting TRP agonist-containing active treatment (A), or vehicle (V) control. Cramping in the triceps surae muscle was induced via voluntary isometric contraction. Study 2: After ingesting A or V, 31 participants performed kinematic and psychomotor tests of manual dexterity.

RESULTS

A increased precramp contraction duration (A, 36.9 ± 4.1 s; V, 27.8 ± 3.1 s), decreased cramp EMG area under the curve (A, 37.3 ± 7.7 %EMG_max ·s; V, 77.2 ± 17.7 %EMG_max ·s), increased contraction force to produce the cramp (A, 13.8 ± 1.8 kg; V, 9.9 ± 1.6 kg), and decreased postcramp soreness (A, 4.1 ± 0.3 arbitrary units (a.u.); V, 4.7 ± 0.3 a.u.). Kinematic and psychomotor tests were not affected.

DISCUSSION

TRP agonist ingestion attenuated EAMC characteristics without affecting motor function. Muscle Nerve 56: 379-385, 2017.

Topical menthol increases cutaneous blood flow

Menthol, the active ingredient in several topically applied analgesics, activates transient receptor potential melastatin 8 (TRPM8) receptors on sensory nerves and on the vasculature inducing a cooling sensation on the skin. Ilex paraguariensis is also a common ingredient in topical analgesics that has potential vasoactive properties and may alter the mechanisms of action of menthol. We sought to characterize the microvascular effects of topical menthol and ilex application and to determine the mechanism(s) through which these compounds may independently and combined alter cutaneous blood flow. We hypothesized that menthol would induce vasoconstriction and that ilex would not alter skin blood flow (SkBF). Three separate protocols were conducted to examine menthol and ilex-mediated changes in SkBF. In protocol 1, placebo, 4% menthol, 0.7% ilex, and combination menthol+ilex gels were applied separately to the skin and red cell flux was continuously measured utilizing laser speckle contrast imaging (LSCI). In protocol 2, seven concentrations of menthol gel (0.04%, 0.4%, 1%, 2%, 4%, 7%, 8%) were applied to the skin to model the dose-response curve. In protocol 3, placebo, menthol, ilex, and menthol+ilex gels were applied to skin under local thermal control (34°C) both with and without sensory nerve blockage (topical lidocaine 4%). Post-occlusive reactive hyperemia (PORH) and local heating (42°C) protocols were conducted to determine the relative contribution of endothelium derived hyperpolarizing factors (EDHFs)/sensory nerves and nitric oxide (NO), respectively. Red cell flux was normalized to mean arterial pressure expressed as cutaneous vascular conductance (CVC: flux·mmHg(-1)) in all protocols. Topical menthol application increased SkBF compared to placebo (3.41±0.33 vs 1.1±0.19CVC: p<0.001). During the dose-response, SkBF increased with increasing doses of menthol (main effect, p<0.05) with an ED50 of 1.0%. Similarly, SkBF was increased after menthol application during PORH (3.62±0.29 vs. 2.50±0.21flux·mmHg(-1); p<0.001), but not local heating (2.98±0.24 vs 2.86±0.32flux·mmHg(-1); p=0.44). Concurrent sensory nerve inhibition attenuated menthol-mediated vasodilation at thermoneutral baseline (1.29±0.19flux·mmHg(-1); p<0.001) and during PORH (2.79±0.28flux·mmHg(-1); p<0.001), but not during local heating (3.45±0.21flux·mmHg(-1); p=0.1). Topically applied menthol, but not ilex, dose-dependently increases blood flow in the cutaneous microvasculature. This increase in blood flow is mediated, in-part by sensory nerves and EDHFs.

A novel running mechanic's class changes kinematics but not running economy

A novel method of running technique instruction, Midstance to Midstance Running (MMR), was studied to determine how MMR affected kinematics and running economy (RE) of recreational runners. An experimental pre-post randomized groups design was used. Participants (n = 18) were recreational runners who ran at least 3 days a week and 5 km per run. All testing was performed on a treadmill at 2.8 m·s. The intervention group (n = 9) completed 8 weeks of instruction in MMR; the control group (n = 9) continued running without instruction. The MMR group showed significant decreases in stride length (SL) (p = 0.02) and maximum knee flexion velocity in stance (p = 0.01), and a significant increase in stride rate (SR) (p = 0.02) after 8 weeks. No significant changes were found in heart rate, rating of perceived exertion, or RE. Midstance to Midstance Running was effective in changing SR and SL, but was not effective in changing other kinematic variables such as foot contact position and maximum knee flexion during swing. Midstance to Midstance Running did not affect RE. Evidence suggests that MMR may be an appropriate instructional method for recreational runners trying to decrease SL and increase SR.

Heat waves, aging, and human cardiovascular health

This brief review is based on a President's Lecture presented at the Annual Meeting of the American College of Sports Medicine in 2013. The purpose of this review was to assess the effects of climate change and consequent increases in environmental heat stress on the aging cardiovascular system. The earth's average global temperature is slowly but consistently increasing, and along with mean temperature changes come increases in heat wave frequency and severity. Extreme passive thermal stress resulting from prolonged elevations in ambient temperature and prolonged physical activity in hot environments creates a high demand on the left ventricle to pump blood to the skin to dissipate heat. Even healthy aging is accompanied by altered cardiovascular function, which limits the extent to which older individuals can maintain stroke volume, increase cardiac output, and increase skin blood flow when exposed to environmental extremes. In the elderly, the increased cardiovascular demand during heat waves is often fatal because of increased strain on an already compromised left ventricle. Not surprisingly, excess deaths during heat waves 1) occur predominantly in older individuals and 2) are overwhelmingly cardiovascular in origin. Increasing frequency and severity of heat waves coupled with a rapidly growing at-risk population dramatically increase the extent of future untoward health outcomes.