The leading health-related cause of mortality for men and women in the U.S. is a cardiovascular disease (ACSM 2006). Meaningful cardiovascular health benefits may be attained with long-term participating in the cardiovascular exercise. How much exercise is enough? ACSM sought to address that question properly last year when it updates its stance on the recommended quantity and quality of exercise for developing and maintaining cardiorespiratory and muscular fitness, and flexibility, in healthy adults (ACSM 2006). Higher levels of cardiovascular fitness are associated with a 50% reduction in CVD risk in men (Myers et al. 2004). Myers and colleagues demonstrated that increasing physical activity to a total of at least 1,000 kilocalories per week is associated with a 20% reduction in mortality in men. Hu and colleagues (2004) showed that physically inactive middle-aged women (engaging in less than 1 hour of exercise per week) doubled their risk of mortality from CVD compared with theirphysically active female counterparts. It should be emphasized that Haskell (2003) notes that CVD is a multifactor process and that “not smoking, being physically active, eating a heart-healthy diet, staying reasonably lean and avoiding stress and depression are the major components of an effective CVD prevention program.”
Diabetes, Insulin Sensitivity and Glucose Metabolism
Diabetes has reached endemic proportions, affecting 170 million individuals worldwide (Stumvoll, Goldstein & van Haeften 2005). One unfortunate health consequence of physical inactivity is the weakening of the body’s insulin regulatory mechanisms. Elevated insulin and blood glucose levels are characteristic features involved in the development of non-insulin-dependent diabetes mellitus. When insulin function starts breaking down, the body’s blood sugar levels rise, leading eventually to the onset of “prediabetes” and then type 2 diabetes. Diabetes incidence is growing among youth and adults, largely as a result of obesity and inactivity. Regular aerobic exercise meaningfully increases insulin sensitivity and glucose metabolism, which means the body’s cells can more efficiently transport glucose into the cells of the liver, muscle and adipose tissue (Steyn et al. 2004). Improvements in glucose metabolism with strength training, independent of alterations in aerobic capacity or percent body fat, have also been shown (Pollock et al. 2001). Although the mechanisms for improvement are not fully understood, it appears that both resistance training and aerobic exercise offer a strong protective role in the prevention of non-insulin-dependent diabetes mellitus.
Hypertension is a major health problem. Elevated systolic and diastolic blood pressure levels are associated with a higher risk of developing coronary heart disease (CHD), congestive heart failure, stroke and kidney failure. There is a one-fold increase in developing these diseases when blood pressure is 140/90 millimeters of mercury (mmHg) (Bouchard & Despres 1995). In many cases, clients can reduce elevated blood pressure by decreasing weight and lower alcohol and salt intake in their diet. PFT’s and fitness instructors can also pass along the good word to clients that moderate-intensity aerobic exercise (40% - 50% of VO2max), performed 3-5 times per week for 30-60 minutes per session, appears to be effective in reducing blood pressure (when elevated).
The evidence that higher-intensity exercise is more or less effective in managing hypertension is at present inconsistent, owing to insufficient data. In a recent meta-analysis of 54 clinical aerobic exercise intervention trials, findings (in hypertensive men and women) included a reduction, on average, of 3.84 mmHg for diastolic blood pressure (Whelton et al. 2002). Although routine aerobic exercise usually will not affect the blood pressure of normotensive individuals, habitual aerobic exercise may be protective against the increase in blood pressure commonly seen with increasing age (Fagard 2001). During resistance exercise, systolic and diastolic blood pressures may show steep increases, which indicates that caution should be observed with persons with known CVD or CVD risk factors. These increases in blood pressure are dependent on the intensity of the contraction, the length of time the contraction is held and the amount of muscle mass involved in the contraction. More dynamic forms of resistance training, such as circuit training, that involve moderate resistance loads and high repetitions with short rests are safe and associated with reductions in blood pressure (Pollack et al. 2001). Although there is relatively little research on blood pressure and resistance exercise as compared to aerobic training/blood pressure studies, one recent meta-analysis of resistance exercise intervention trials found decreases of 3.2 mmHg and 3.5 mmHg for systolic and diastolic blood pressures, respectively (Cornelissen & Fagard 2005).