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Interval Training Reduces Arterial Stiffness

Continuous and Interval Training Improve Blood Pressure, But Only Intervals Improve Flexibility

It seems logical that alternating hard and easy exercise in interval training would be more effective than steady-state exercise in improving blood vessel flexibility. And that’s what was shown in a new study performed by researchers at the University of Sao Paulo in Brazil. Dr.Guilherme Veiga Guimaraes and his colleagues reported their findings in the April 9, 2010 online edition of Hypertension Research.

Exercise has been shown to lower blood pressure and reduce arterial stiffness, but it has not been established which type of exercise does this best. Steady-state continuous exercise is the most common form of exercise, and is most frequently recommended for people with high blood pressure.

“Studies have found that interval training can improve endurance and fitness better that moderate-intensity workouts at a steady pace, and in less time,” the UC, Berkeley Wellness Letter stated in the June 2010 issue. “And it can help…lower blood pressure...”

See also our articles Sprints Build Endurance http://www.cbass.com/Sprintendurance.htm and Intervals for Everyone http://www.cbass.com/IntervalsEveryone.htm 

“Interval training promotes greater gradients of shear stress because patients fluctuate between high and low intensities,” Dr. Guimaraes and his colleagues wrote in introducing their study. “We have recently shown that interval exercise acutely decreases blood pressure in hypertensive patients,” they added. “We therefore hypothesized that interval exercise has a better effect on arterial stiffness and blood pressure control than continuous exercise does on hypertensive subjects.”

The aim of the study was to test that hypothesis. Here’s how they went about it and what they found.

Straightforward Design

The study design was clean and simple.

Sixty-five sedentary patients with controlled hypertension were randomly assigned to three different regimens for 16 weeks: continuous exercise (26), intervals (26), or a sedentary control routine (13). The exercise groups performed two supervised sessions a week consisting of 10 minutes warm-up, 40 minutes on a treadmill (continuous or interval), 20 minutes of submaximal strength training, and 10 minutes of cooldown exercise. The control group was advised to maintain their daily activities without exercise.

Exercise intensity was determined based on results of maximum treadmill testing prior to the study regimen. Continuous exercise was 40 minutes at 60% of reserve heart rate.  (Reserve heart rate is the difference between peak and resting heart rate.) Interval exercise was 40 minutes with intensity alternating between 50% (two minutes) and 80% (one minute). Intensity was calculated to produce the same cardiovascular workload; average heart rate was 60% under both routines. The only difference was the up-and-down intensity in the interval group.

Twenty-four hour blood pressure and arterial stiffness were measured before and after the 16 weeks of training. Carotid-femoral pulse wave velocity (PWV) was used to measure arterial stiffness. (The carotid artery is in the neck and the femoral artery is in the groin.) An automatic device measured the transit time for pulse waves to travel from the neck to the groin. Slower indicates more stiffness; faster more flexibility.

Results 

All participants began the study with similar age, body mass, blood pressure, PWV values, and current medications. Drop-outs were evenly distributed between the groups; 43 completed the 16-week protocol—16 in the continuous exercise group, 16 in the interval group, and 11 controls.

At the end of the 16-week study, training method (continuous or interval) made no significant difference in blood pressure; both forms of exercise reduced blood pressure, especially in the daytime. There was, however, a distinction in the effect on arterial stiffness.

Blood pressure declined most in subjects with higher readings at the beginning of the study. Training protocol, continuous or interval, made no difference.

This result is consistent with previous research showing that people with high blood pressure benefit most from aerobic exercise, especially during the day.

Sixteen weeks of interval training significantly decreased—speeded up—the time for pulse waves to travel from the neck to the groin. (Transit time also improved after 16 weeks of continuous training, but the change was not statistically significant.)

Guimaraes and his colleagues concluded: “Continuous and interval exercise training were beneficial for blood pressure control, but only interval training reduced arterial stiffness.”

As usual, the researchers discussed their findings at the end of the study. I’ll comment as well.

Slam Dunk for Intervals

I was a little surprised there was no difference in drop-out rate between the two protocols. Walking on a treadmill at a fixed speed for 40 minutes can only be described as boorrrring. Time would pass faster and it would be more interesting to change speed every few minutes. I can’t prove it, but I’d bet that more people in the continuous training group would’ve quit—if the workouts had been unsupervised. Having a trainer or technician there to observe every step and heart beat would keep most anyone training longer than they would on their own.

What's more, I believe it would be more challenging—and fun—to do fewer intervals and do them harder. As noted above, the researchers made both protocols the same length and average intensity to make alternating intensity the sole variable. You or I would be free to choose the protocol we prefer. (I would cut the time in half and do the intervals harder.)

It would be instructive to know the compliance rate 16 weeks after the study ended. This is no trivial musing. Motivation is essential to the long-term success of any fitness regimen.

The fact that intervals reduced arterial stiffness more than steady state exercise would also provide encouragement. Knowledge is power and improvement is the best motivator. 

The researchers gave their finding more punch by explaining that aging typically leads to a progressive increase in arterial stiffness, especially in larger arteries. Not surprisingly, increase in stiffness is more pronounced in those with high blood pressure.

“Aerobic exercise training seems to attenuate arterial stiffness in healthy subjects, but the results in hypertensive patients are controversial,” the researchers related. That, of course, makes their finding regarding the effect of interval training on stiffness in hypertensive patients more meaningful.

“Arterial stiffness has been shown to be an independent predictor of cardiovascular and all-cause mortality in hypertensive patients,” the researchers observed. “Sedentary lifestyle and anti-hypertensive treatment resulted in an increase [slowing] of 0.8ms (millisecond) of pulse wave velocity [PWV] in 6 years,” they added.

Our study shows that only 16 weeks of interval training caused a drop in PWV of 0.41ms in a similar population.” (Emphasis mine)

In other words, interval training halved 6 years of arterial stiffening in only 16 weeks. Impressive, to say the least.

The researchers also provided a similar statistic for blood pressure: “It has been documented that a reduction of only 2mmHg in systolic blood pressure [the top number] decreases mortality from cerebral accidents by 10% and cardiovascular disease by 7%.”

In their study, the drop in systolic pressure was 7mmHg and 6mmHg for continuous and interval training, respectively.

To recap briefly, continuous and interval training reduced blood pressure about the same, but only intervals significantly improved arterial stiffness. Add that intervals improve fitness in less time and are more appealing, and it’s a slam dunk for intervals.

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