Tuesday, 26 July 2011

Arterial Stiffness and Exercise


Stiff arteries or hardened arteries are a serious risk factor for ill health but they can be improved by exercise. It doesn't have to be long and boring and the results can be seen in just a few weeks. People with diabetes, with high blood pressure, and those with chronic obstructive pulmonary disease have experienced a reduction in arterial stiffness after taking up exercise. Healthy middle-aged and older men and women, who were previously physically inactive have gained the same artery-improving benefits from fairly moderate aerobic exercise.

Exercising and keeping fit are important because even in healthy individuals there is a gradual loss of compliance in the aorta and carotid arteries as we age (these are usually referred to as the central arteries). Compliance is the ability of the arteries to expand and contract again in response to the beating of the heart as it pumps blood through them. As this ability is lost, the artery becomes stiffened or hardened. This makes the heart work harder to pump blood through them, putting a strain on the heart. Over time, this will weaken the heart.

This age-related stiffening has been know about since 1881. It seems to be a normal part of ageing in otherwise healthy people, but those who are very active exhibit reduced stiffening or even an absence of it. The peripheral arteries (such as arteries of the arms and legs) can also become stiff but significant stiffening of the peripheral arteries is not normally seen in healthy people, and is usually a sign of an underlying disease.

This loss of compliance in the central arteries due to ageing was largely restored in previously sedentary healthy middle-aged and older men who took up regular aerobic-endurance exercise. This was shown in a study of 151 healthy men aged from 18-77.(1) For at least the previous 2 years, the men were in one of the following categories of activity: sedentary - no physical exercise; recreationally active - light to moderate exercise 3 or more times a week; or endurance-trained - vigorous exercise 5 or more times a week, and active in local road running races. In all 3 activity groups, the arterial compliance was lower in the older men than in the younger ones. No significant differences were found between the recreationally active and the sedentary men at any age - although there was a 10%-17% greater arterial compliance in the recreationally active middle-aged and older men compared with their sedentary peers. The researchers might not think this is significant but it seems quite significant to me. It could be the difference that makes the difference between fairly active and sedentary people.

A much greater difference was seen in the endurance-trained middle-aged and older men's arterial compliance, however. This was 20%-35% higher than in the 2 groups who were less active. Age-related differences in arterial compliance were smaller in the endurance-trained men than in the other 2, less active, groups. The endurance trained middle-aged and older men had arteries that were more like their younger counterparts than the arteries of less active men of their ages.

The researches also studied 20 middle-aged healthy sedentary men aged from 51-55 to see if taking up exercise would change the condition of their arteries. After 3 months of mainly walking aerobic exercise their central arterial compliance increased to levels similar to those of the middle-aged and older endurance-trained men studied previously. The men gradually built up their fitness and the intensity of their exercise until at the end of the 3 months they were walking very briskly or jogging for 40-45 minutes a day, for 4-6 days a week, and at an intensity of 70%-75% of their maximal heart rate.

The Same Effects of Exercise on Arterial Compliance in Women

A study was done to discover if physical activity protects women from age-related arterial stiffening.(2) There were 28 healthy sedentary women (10 premenopausal and 18 postmenopausal) and 25 healthy physically active women (9 premenopausal and 16 postmenopausal). The physically active women had been performing endurance exercise training for at least 2 years prior to the study and they competed in running road races. They exercised on average for about 6 hours a week.

Amongst the sedentary women, there was more central arterial stiffening (in the aorta and carotid arteries) in the postmenopausal than in the premenopausal ones, showing that they were affected by age-related stiffening. There was no significant difference in peripheral arteries, though (in the leg or arm), which is not surprising as those arteries usually only stiffen because of some disease.

There were no differences in central arterial stiffness amongst the physically active premenopausal or postmenopausal women, indicating that physical activity offers protection against arterial stiffening in postmenopausal women.

There was about an equal number of both sedentary and active postmenopausal women who used hormone replacement therapy (10 sedentary, 8 active), which ruled out the effects from that source in this study.

Diabetes Type-2, Aerobic Training and Arterial Compliance

Older adults with type-2 diabetes can get the arterial compliance-improving benefits of aerobic training. Thirty-six people, both men and women, in their early 70s with diet-controlled or oral hypoglycaemic–controlled type 2 diabetes, hypertension, and hypercholesterolaemia took part in a study(3) which showed that 3 months of vigorous aerobic training resulted in a reduction in radial (arm) and femoral (groin/leg) arteries stiffness. Half of the subjects did no exercise and the other half took part in training sessions 3 times a week. These lasted for 60 minutes. Only 40 minutes was spent training, the remainder of the time was devoted to a warm up and a cool down.

In this study only the peripheral arteries were measured rather than the central (aorta and carotid) arteries. Type-2 diabetes often results in stiffening of the peripheral arteries so this is a particularly interesting result.

Similar findings, but in a younger population, came from an earlier study which assessed the reduction in arterial stiffness in 23 people with type-2 diabetes after only 3 weeks of exercise training. Even this short period of exercise resulted in a significant reduction of stiffness in both the carotid and femoral arteries.(4)

Exercise Reduced Arterial Stiffness in Chronic Obstructive Pulmonary Disease

A study was designed to see if endurance training could help to reduce carotid arterial stiffening in 17 patients with chronic obstructive pulmonary disease (COPD).(5) They ranged in age from 55 to 69. They were put into two groups, 10 in the training group and 7 in the group that did no training. After 4 weeks, the untrained patients' arterial stiffness was unchanged. The trained patients achieved a reduction in their carotid artery stiffness.

Interval Training and Arterial Stiffness

If you don't want to spend up to an hour a day in exercise, you could try interval training.

Interval training is a very efficient method of keeping fit in much less time than it takes with the traditional endurance training method. Recently, some studies have found that interval training is as effective as endurance training in coping with high blood pressure and arterial stiffness.

To test its effects on arterial stiffness, 20 healthy but previously untrained men and women aged from 20 to 25 took part in a study.(6) They were split into 2 groups of 5 men and 5 women in each group, which trained for 6 weeks. One group did traditional endurance training starting at 40 minutes and gradually increasing to 60 minutes of continuous cycling for 5 days a week at 65% of their peak oxygen uptake.* The other group started with 4 sessions and gradually increased to 6 sessions of all-out cycling effort lasting 30 seconds each. Each 30-second session was separated by 4.5 minutes of recovery during which time they pedalled slowly. They did this training on only 3 days a week.
*Peak oxygen uptake (also known as VO2 max) is the body's maximum capacity to use and transport oxygen.

At the end of the 6 weeks, both groups showed the same amount of improvement in their popliteal (back of the knee) arteries. There was no improvement in carotid artery function. But, as the authors speculate, such young people would not have had any significant stiffening of the carotid arteries as that only happens with ageing in healthy people.

The study shows that the arteries can benefit from training that takes much less time to do than traditional endurance training. The interval trainers did a total of 2-3 minutes of actual exercise 3 times a week, with 13.5-22.5 minutes of recovery time. Those doing the traditional endurance training did 40-60 minutes of actual exercise, 5 days a week.

One recent study, which had people who have high blood pressure as its subjects, found that both continuous exercise and interval training reduced blood pressure in the subjects but only the interval training reduced their arterial stiffness.(7) This lasted for 16 weeks and had 3 groups - 26 who did interval training exercise, 26 who did continuous exercise, and 13 who did no exercise. The exercisers did 2 40-minute sessions a week. Those in the continuous group kept to the same moderate pace for the 40 minutes, and those in the interval group alternated between 1 minute of very hard work and 2 minutes of much easier work for the full 40 minutes.

Because of all the studies that have shown continuous aerobic exercise to be of great benefit to the arteries of people of all ages with various conditions and in healthy people, I am surprised that this one didn't. The problem could lie in the level of hypertension the patients had, in the treatments they were receiving or the intensity of their exercise. But at least one form of exercise -- interval training -- did help to reduce arterial stiffness.

Interval training comes in many forms, from the brutal Tabata method to less intense but still effective methods. In the Tabata method - which is only for those who are already very fit - you would do as many repetitions of a particular exercise that you can do in 20 seconds. Then rest for 10 seconds. Then do it all again another 7 times. Take heart, though. This level of exercising is not necessary for our purposes here, as can be seen by the method that was used in the first interval training study mentioned above where the interval trainers had 4.5 minutes of comparative rest after each maximum effort.

Once someone is fit and has a few sessions of steady state, aerobic exercise under their belt, I would say that 20-30 seconds maximum effort and 40-60 seconds moderate effort interval training should suffice for most people. Probably 6-12 sets/cycles - so you would go hard for 20 seconds and then more easily for 40 seconds. This is one set or cycle. To be on the safe side, it might be better to start off with 10-20 seconds of max effort and 30-60 seconds of moderate effort. One way of incorporating this type of exercise into your life would be to sprint from one lamp post to the next, and then walk to the next one. Or even walk for 2 lamp post distances. Be your own judge about how hard to push yourself. Juggle the max effort and moderate effort timings but don't make it too easy. Don't make it too hard, either, so that you collapse in a gasping, quivering heap on the floor after a frenzied bout of self-torture.

Exercise has been shown in these and other studies to offer protection against age-related stiffening of the arteries and to help people regain most or all of the compliance that was lost by being physically inactive or through the normal ageing process. So, if you want healthy arteries - and you really can't be healthy unless your arteries are healthy - you will do well to take up fairly vigorous exercise. You know it makes sense. I'm sure you know that being fit has more to offer than just healthy arteries.

Seek advice from an appropriately qualified person if there may be any medical reason for caution before starting an exercise programme.

References

1. Circulation. 2000 Sep 12;102(11):1270-5.
Aging, habitual exercise, and dynamic arterial compliance.

2. Arteriosclerosis, Thrombosis and Vascular Biology. 1998 Jan;18(1):127-32.
Absence of age-related increase in central arterial stiffness in physically active women.

3. Diabetes Care. 2009 Aug;32(8):1531-5.
Short-term aerobic exercise reduces arterial stiffness in older adults with type 2 diabetes, hypertension, and hypercholesterolemia.

4. Diabetes Research and Clinical Practice. 2004 Aug;65(2):85-93.
Short-term aerobic exercise improves arterial stiffness in type 2 diabetes.

5. Chest. 2010 Mar;137(3):585-92.
Significant improvement in arterial stiffness after endurance training in patients with COPD.

6. American Journal of Physiology. Regulatory, Integrative and Comparative Physiology. 2008 Jul;295(1):R236-42.
Sprint interval and traditional endurance training induce similar improvements in peripheral arterial stiffness and flow-mediated dilation in healthy humans.

7. Hypertension Research. 2010 Jun;33(6):627-32.
Effects of continuous vs. interval exercise training on blood pressure and arterial stiffness in treated hypertension.