Exercise is Medicine

by Jade Teta, ND, CSCS, and Keoni Teta, ND, LAc, CSCS

Exercise and Endothelial Dysfunction

Endothelial dysfunction is a major contributor to cardiovascular disease (CVD) and may be one of the earliest predictors of its development.¹ The endothelium is a key control center for both vascular constriction and relaxation. Dysfunction of the endothelial lining of blood vessels leads to a host of negative consequences including vasoconstriction, platelet aggregation, inflammation, and ultimately atherosclerosis.^1–3 Endothelial dysfunction is closely linked with inflammation, and both are independent risk factors for heart disease.

Aerobic exercise has been studied extensively for its ability to protect the endothelium from damage and is associated with a more reactive and healthy vascular system. It is now well established that aerobic exercise has positive and lasting benefits for the vascular system. As high-intensity exercise protocols such as interval training and resistance training gain in popularity, it is useful to understand their impact on CVD and endothelium-related mechanisms. Recent reports have shown high-intensity exercise protocols to provide lasting benefits in cardiovascular risk factors.⁵

Interval Exercise

Interval training is a cardiovascular training modality characterized by short bursts of intense activity followed by a recovery period before the burst is repeated. In general, this modality employs a work to rest ratio of 1 to 2, meaning that for every minute of intense activity, there are 2 minutes of recovery. An article published last year in the Journal of the American College of Cardiology (January 2009) adds to the growing evidence that high-intensity interval training is highly beneficial and may provide extra benefit compared with continuous moderate intensity exercise.⁴ In this study, the authors looked at the response of blood vessel function to a high-fat meal. It is a well-established fact that a high-fat meal can create unfavorable changes in the endothelium for several hours.

The researchers studied the effect of doing different types of exercise 16 to 18 hours prior to the challenge meal. In past studies, continuous aerobic exercise prior to a high-fat meal has been shown to blunt some of the negative effects. This study compared a moderate-intensity aerobic protocol of running at 60%–70% of maximum heart rate (MHR) for 47 minutes with an interval-training workout. The interval protocol involved four 4-minute bouts of exercise at 85%–95% of MHR with each bout separated by 3 minutes of rest at 50%–60% MHR. The two exercise sessions were equal in terms of the number of calories burned. There was also a control group that did no exercise. Additional parameters studied in this paper included antioxidant release generated by exercise, arterial diameter studies, and arterial shear rates. By looking at these additional markers, researchers could ascertain how well vessels dilated in response to exercise and what impact vessel shear has on function. The results showed that the control group and the continuous exercise group had decreases in artery diameter and increased shear rates. However, the high-intensity interval training was able to protect the body from these effects causing the arteries to remain open and suffer very low shear. In regard to endothelium-dependent vascular function, the continuous exercise protocol decreased the negative impact of the high-fat meal but could not completely negate the damage. In contrast, the high-intensity interval training not only completely reversed the endothelial dysfunction, but actually improved it. Another novel finding in this article is that high-intensity interval training significantly enhances the production of antioxidants by the body. Again it outperformed continuous aerobic exercise in this regard.

Resistance Exercise

Research on resistance exercise has been mixed, with reports showing damage to endothelial lining as a result of high shear rates from acute weight lifting.¹¹ Despite these findings, it is clear that resistance training provides risk reduction for CVD.^6,7 Newer research hints that vessel damage from shear may be only temporary and that these forces may actually stimulate enhanced endothelial function.¹⁰ Ironically, weight-lifting activities may provide a protective effect over time through novel mechanisms. Varady et al. showed that a resistance-training intervention was able to improve endothelial function similarly to aerobic exercise.⁹ Interestingly, this positive change was directly related to improvements in adipocytokines, including adiponectin and resistin, in the weight-lifters only. The researchers concluded: “In sum, these findings suggest that habitual resistance training may modulate adipokine profiles in a way that is protective against endothelial dysfunction that occurs with acute exertion.”

Stensvold et al. compared resistance exercise with aerobic interval training.⁸ Forty-three subjects with metabolic syndrome were randomized into an aerobic interval-training group, a weight-training group, or a group combining aerobic intervals and weight training over a 12-week period. Endothelial function was increased in all three treatment groups as measurement by flow mediated dilation (FMD) with a slightly better response for resistance exercise, although this did not reach statistical significance.

Prescriptions

Based on the above insights on exercise and endothelial health, it seems prudent to begin to expand exercise prescriptions beyond aerobic exercise modalities. Although more study should be done, both interval training and resistance exercise seem to confer benefits similar to those from aerobic exercise. In the case of resistance training, the mechanisms seem to be fairly specific and point to improving multiple parameters of health. A good starting exercise prescription for optimal blood vessel function based on the above findings should include multiple exercise modalities. Three days of aerobic exercise with one to three days each of resistance exercise and more intense interval training would provide a great cross-training strategy for blood vessel health.

Notes

1. Lavie et al. Exercise training and cardiac rehabilitation in primary and secondary prevention of cardiovascular disease. Mayo Clinic Proc. 2009;84(4):373–383.

2. Widlansky, et, al. The clinical implications of endothelial dysfunction. J Am Coll Cardiol. 2003;42:1149–1160.

3. Halcox et al. Endothelial function predicts progression of carotid intima-media thickness. Circulation. 2009;119:1005–1012.

4. Tyldum et al. Endothelial dysfunction induced by postprandial lipemia: complete protection afforded by high-intensity aerobic interval exercise. J Am Coll Cardiol. January 2009;53(2):200–206.

5. Jones et al. Exercise intensity and blood pressure during sleep. Int J Sports Med. 2009;30(2):94–99

6. Banz et al. Effects of resistance versus aerobic training on coronary artery disease risk factors. Exp Biol Med. 2003;228(4):434–440.

7. Schjerve et al. Both aerobic endurance and strength training programmes improve cardiovascular health in obese adults. Clin Sci. 2008;115(9):283–293.

8. Stensvold et al. Strength training versus aerobic interval training to modify risk factors of the metabolic syndrome. J Appl Physiol. Epub January 2010.

9. Varady et al. Adipokine responses to acute resistance exercise in trained and untrained men. Med Sci Sport Exerc. Epub November 2009.

10. Tinkin et al. Shear stress mediates endothelial adaptations to exercise training in humans. Hypertension. 2010;55(2):312–318.

11. Rakobowchuk et al. Endothelial function of young healthy males following whole body resistance training. J Appl Physiol. 2005;98(6):2185–2190.