THE DOSE

jacky

THE DOSE

The epidemiological research focused on a range of physical activity and exercise. Are both effective in health?

• How much physical activity is enough?
• Is exercise as effective as physical activity for health benefits?
  

From the epidemiologic work, it appears as though changing from sedentary to the lowest level of physical activity may be enough to prevent modern chronic disease; 150 to 200 calories per day or 1500 to 2000 calories per week.
This translates to an accumulation of 30 minutes of moderate physical activity on most, if not all days of the week.

• Blair, S. N., Y Cheng, and J.S. Holder. Is physical activity or physical fitness more important in defining health benefits? Medicine and Science in Sports and Exercise 33:S379-S399, 2001
• Lee, M.I. and P.J Skerrett. Physical activity and all-cause mortality: what is the dose-response relation? Medicine and Science in Sports and Exercise 33:S459-S471, 2001.
• ACSM: Physical activity and health: dose response. Medicine and Science in Sports and Exercise 33: Supplement 6, 2001.
  

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FITNESS vs. PHYSICAL ACTIVITY
Blair summarized the health outcomes for 49 research articles on physical activity and health, 9 research articles on cardiorespiratory fitness and health, and 9 research articles on physical activity, fitness and health.

There is an inverse dose-response gradient across physical activity There is an inverse dose-response gradient across categories of cardiorespiratory fitness and health outcomes The dose-response gradient for health outcomes is steeper across categories of cardiorespiratory fitness

Is it possible for too much exercise to not provide a health protection?

Probably, however, the upper limit of exercise and disease prevention has not been investigated.

An obvious difference between exercise and physical activity can be found between the physical activity prescription for health and the exercise prescription to improve fitness. The amount of physical activity to produce a health benefit may not produce a fitness benefit.

Rx for Fitness: Mode: Cardiovascular FQ: 3-5/week Dur: 20-60 min Int: >60% intensity

Rx for Health: Mode: Physical activity FQ: most, if not all days of the week Dur: 30 min Int: Moderate (40-60%

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Accumulation vs. Continuous

The recommendations in most of the public policies state the physical activity can be accumulative; it does not need to be a continuous workout. The majority of the research focuses on physical work capacity (VO2max) as the outcome varialbe. Lipids, body mass, blood pressure, and bone mineral content have been the outcome measure in others.

Only 16 studies were found to compare fitness and health outcomes between continuous and accumulative exercise. These 16 studies are summarized to the left. All 16 focused on VO2max; 9 on body mass; 6 on body fat; 8 on blood pressure; and 7 on lipids. The red bar indicates how many of the studies found no difference between continuous and accumulative; the blue bar indicates how many studies found "better" values for continuous; and the green indicates how many studies found "better" values for accumlative exericse. These studies do illustrate that it doesn't matter if the exericse is continuous or accumlative. It is believed that accumulative exericse may be more "accepting" to the public. Thus, acculative is recommended.

An accumlative session must be at least 10 minutes.

• Murphy, M.H., S.N. Blair and E.M. Murtagh. Accumulated versus continuous exercise for health benefit: A review of empirical studies. Sports Medicine 39:29-43, 2009
  
  

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Another of the unknown questions is the kinetics of these health changes. That is, cardiovascular fitness can change in six weeks of training. Do health changes ocurr that fast? Or do they take over shorter or longer periods of time? Blood pressure can reduce in one session of physical activity. On the other hand, how long does it take to reverse atherosclerosis or to lose weight?

• Haskell, WL. Health consequences of physical activity: understanding and challenges regarding dose-response. Medicne and Science in Sports and Exercise 26:649-660, 1994.
  
  

One advantage of targeting fitness, which improves health at the same time, is that the individual can experience the fitness benefits faster, which may be more substantial and rewarding in the long run. The perception of any kind of benefit can enhance motivation to continue to exercise. Health benefits are not exhibited as rapidly or as strong as the fitness benefits and may not promote adherence as well.

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