Newsletter #274

It’s well established that exercise is associated with lower blood pressure.

But the profound impact of physical activity on blood pressure regulation is probably underappreciated. Especially for people who have hypertension.

For example, a meta-analysis of 391 randomized controlled trials that compared effects of exercise versus anti-hypertensive drugs found that, in individuals with a resting systolic BP over 150 mmHg, exercise interventions resulted in a mean reduction of 11 mmHg, compared to antihypertensive medications with a mean reduction of 9 mmHg.

But there are many different types of exercise — what is the best modality?

Up until fairly recently, aerobic exercise has been the most strongly recommended mode of exercise for reducing blood pressure, and generally with good reason.

However, emerging evidence suggests that other activities may also have powerful anti-hypertensive effects, even when they involve very little actual movement. For example, you might recall a few years ago, we highlighted a trial demonstrating that static stretching was surprisingly effective for lowering blood pressure.

Indeed, exercises in which you basically don’t move at all may have the most potent anti-hypertensive effects — and achieve these benefits in a mere fraction of the time commitment required for aerobic exercise.

Current guidelines on exercise prescriptions for managing blood pressure emphasize traditional aerobic activity, like jogging or cycling. However, this is largely based on old data, and does not include forms of exercise that have become popular more recently (like high intensity interval training).

In an effort to fill in this gap, researchers affiliated with Canterbury Christ Church University in the UK performed a network meta-analysis of randomized controlled trials, published within the past twenty years, which had demonstrated reductions in blood pressure in response to various different exercise interventions.

The final analysis included 270 randomized controlled trials, with a pooled sample size of 15,827 participants. They determined that all of the modes of exercise were effective at significantly lowering systolic and diastolic blood pressure, versus controls. Which in itself is good news. But as you can see, some elicited greater reductions than others:

Isometric exercise emerged as the superior exercise mode for fighting hypertension, producing reductions in blood pressure comparable to standard doses of single anti-hypertensive medications, and which would be expected to lead to a decrease in risk of coronary events of 17%-27% and a decrease in risk of stroke of 33%-48%. When they dug a little deeper into specific exercises, they found that wall sits were the most effective single exercise for lowering systolic blood pressure, and running was best for lowering diastolic blood pressure. Study author Jamie O'Driscoll concluded in a press release, "These findings provide a comprehensive data-driven framework to support the development of new exercise guideline recommendations for the prevention and treatment of arterial hypertension."

The benefits of isometric exercise for blood pressure are clearly established, but underlying physiological mechanisms remain to be elucidated. To gain some insight into mechanistic changes following this exercise modality, researchers performed a systematic review of controlled trials reporting the effects of isometric exercise interventions on resting blood pressure and at least one secondary mechanistic parameter.

The final analysis contained 18 studies, with a pooled sample size of 628 participants. Similar to the previously described meta-analysis, they found that isometric exercise training led to significant decreases in resting systolic and diastolic blood pressure of 9.35 mmHg and 4.30 mmHg respectively. And wall sits emerged as the most effective single exercise.

Mechanistically, the researchers determined that isometric exercise primarily reduces blood pressure by lowering total peripheral resistance — meaning the resistance that blood experiences as it flows through blood vessels throughout the body. However, the way it achieves this is sort of counter-intuitive.

When you hold an isometric position, like a plank or a glute bridge, that muscular contraction temporarily occludes the local vasculature. Then, when you relax, there is a sudden influx in blood flow, resulting in an increase in shear stress (meaning the pressure exerted by blood against the walls of the blood vessels).

Now, so far this actually sounds pretty bad, and it's probably one reason why isometric exercise has been regarded with skepticism in the past. However, we now know that this increase in shear stress triggers a rapid rise in bioavailability of nitric oxide. Nitric oxide causes blood vessels to widen and become less stiff. This translates into chronic improvements in the function of the blood vessels, and thus into long-term reductions in blood pressure. Of course, all exercise modalities are able to stimulate nitric oxide release, but the unique form of stress presented by isometric holds seems to set it apart from other activities, and may explain why it results in greater drops in blood pressure.

🦒 Giraffes have the highest blood pressure in the animal kingdom.

As you can imagine, the staggering height of the giraffe presents a serious cardiovascular challenge. To ensure that the brain gets a steady blood supply, their blood pressure must be exceptionally high, normally hovering around 280/180 mm Hg. This is accompanied by a very rapid resting heart rate (170 bpm).

They appear to tolerate this through a number of anatomical and genetic adaptations. Hopefully further study of these critters can unveil some useful info for managing blood pressure in humans!

Kyolic Aged Garlic Extract Cardiovascular Extra Strength Reserve

Another lifestyle tool for managing blood pressure that may have been underestimated is garlic. One meta-analysis found that garlic supplements lowered systolic and diastolic blood pressure by an average of 8.3 mmHg and 5.5 mmHg respectively. Kyolic aged garlic, specifically, lowered central blood pressure, arterial stiffness, and boosted the richness and diversity of the gut microbiota.

Stress Resilience — From Physical Activity and Daily Performance

This week we’d like to highlight one of the lessons from our Daily Performance Program.

In this micro-lesson, Dan explains the difference between acute and chronic stress, with respect to exercise.

As we’ve seen from the research described above, exercise can be sort of a paradox. In the short term, it acts as a stressor, elevating blood pressure and heart rate. But in the long term, exercise actually buffers stress, and markers associated with stress, thus cultivating stress resilience.

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