HIGH AND LOW INTENSITY EXERCISE: WHAT IS BEST FOR HEALTH AND WHAT IS BEST FOR FITNESS? Filex 2001 Internation Fitness and Healthy Lifestyle Conference, Darling Harbour 2001
Robbie Parker Bed, MEd, PhD Research Fellow
Children's Hospital Institute of Sports Medicine
The Children's Hospital at WestmeadThere is still lack of certainty in the fitness industry regarding the issues of "How much exercise is enough?" and "What type of exercise is best for developing and maintaining fitness, and therefore, supposedly, health?" The term 'physical fitness' is comprised of many characteristics including card iorespiratory fitness (measured by V02max and lactate threshold (LT)), body composition (including total body mass, fat mass and fat free mass), muscular strength and endurance, and flexibility (Pate et al, 1995). These characteristics are often referred to as the health-related components of fitness. It is understood that improvements in one or more of these characteristics may also enhance a number of cardiovascular risk factors such as blood lipid profiles, glucose tolerance and insulin sensitivity, elevated blood pressure levels, postural stability, and markers of bone health (Pescatello, 1999). What is not clearly understood is the doseresponse relationship between exercise duration, frequency and intensity to provide these added benefits. The quantity and quality of exercise needed to obtain healthrelated benefits may differ to what is recommended for fitness benefits.
Physical fitness is defined as the ability to perform moderate to vigorous levels of physical activity without undue fatigue and the capability of maintaining this capacity throughout life (ACSM, 1998). The body's adaptive response to training, irrespective of the training frequency or intensity, is complex and includes central, peripheral, structural and functional factors.
The recommended guidelines (ACSM, 1998) to improve card iorespiratory fitness and body composition is: training 3-5 days per week, at an intensity level of 55-90% of maximum heart rate (HRR,ax), or 40-85% of maximum heart rate reserve (HRR), training 20-60 minutes of continuous or intermittent (minimum of 10-minute bouts of accumulated activity throughout the day) aerobic activity performing an activity that uses large muscle groups.
It is now clear that lower levels of aerobic activity (i.e. with lower intensity levels) than that recommended by ACSM (1998) may reduce the risk for certain chronic degenerative and cardiovascular diseases and improve metabolic fitness but may not be of sufficient quantity or quality to improve V02max (or fitness).
Exercise for health and fitness is therefore best understood in the context of a dosecontinuum. That is, there is a dose-response to exercise by which health benefits are gained through varying quantities of exercise ranging from 7002000 plus kilocalories of effort per week. Training volume, rather than training intensity, may therefore, be a more important factor when health-related fitness outcomes are desired. The ACSM (1998) guidelines would, therefore, appear to be aimed at the middle-to-higher end of the exercise continuum.
Aerobic exercise prescription for fat loss has been questioned recently in the context of this dose-response continuum. In the unfit, fat individual, where the fitness level is very poor, use of the ACSM guidelines would appear to be inappropriate, because the training intensity would be too severe causing a high level of discomfort during exercise (largely due to a lower LT) and posing an increased risk of injury.
There is strong evidence however to show that high intensity exercise (e.g 85% HRmax) in non-obese subjects has been shown to provide better fat loss results than training at a lower intensity level (Tremblay, 1994). High intensity aerobic exercise has also shown to increase exercise and resting energy expenditure separate from any change in muscle mass (Hunter et al 1998). High intensity exercise has resulted in greater fat loss despite less total energy expenditure when compared to a higher level of energy expenditure achieved in a lower intensity exercise session (Tremblay, 1994). High intensity exercise has also been shown to reduce the postexercise energy intake compensation (Tremblay, 1999). Fat has been demonstrated to be the dominate substrate used during high-intensity exercise and during the brief post-exercise period of "pay-back" when compared to low intensity exercise (Kriketos et al, 2000). On the other hand, when total exercise-induced energy deficit is the same, intensity of exercise training has been reported to have no influence on the size of fat loss in men or women (Ballor, 1990).
These high-intensity induced benefits, however, should be weighed against the potential risk of injury and level of exercise discomfort, and hence, exercise compliance over time. It is therefore recommended that in the unfit, obese market, low intensity exercise (i.e. 50-60% of HRmax) should be performed on a daily basis for longer duration (e.g. - 60 minutes) with a view of expending as much energy as possible. This recommendation would account for an energy expenditure of around 400kcal in a realistic program aiming for a total energy deficit of 700-800kcal per day. If total body mass and fat mass are not important considerations in an exercise program, shorter duration, higher intensity interval-exercise programs are recommended for improvements in V02max for healthy individuals at low risk to injury.
High intensity resistance training has been associated with many positive health benefits including · significant improvements in muscle strength and mass in younger and older adults
· increased resting metabolic rate, and decreased risks of falls in older adults
· a significant reduction in fat mass and improvements in bone strength and density in younger and older adults (Nelson, 1994)
· reduced risks of coronary heart disease and
· a decrease in mental depression states. (Feigenbaum and Pollock, 1997)
The ACSM position stand (1998) for non-athletic populations, recommends that the minimum quality and quantity of resistance training is to complete one set of 8-12 repetitions (or 10-15 for older adults) performed to volitional fatigue, on 2 or three days per week. This has been referred to as moderate intensity training. Higher intensity resistance training is recommended for athletic populations.
References:
American College of Sports Medicine (1998) The recommended quantity and quality of exercise for developing and maintaining card iorespiratory and muscular fitness and flexibility in healthy adults. Position Statement. Med Sci Sports Exerc 30 (6): 975 - 991.
Ballor, d et al., (1990) Exercise intensity does not affect the composition of diet- and exercise-induced body mass loss Am J. Clin Nutr. 51: 142-146.
Feigenbaum, M. and Pollock, M. (1997) Strength training: rationale for current guidelines for adult fitness programs Physician and Sports Med. 25: 44 64.
Hunter, G., Weinsier, R., Bamman, M. and Larson, D. (1998) A role for high intensity exercise on energy balance and weight control. International Journal of Obesity 22: 489493.
Kriketos, A. et al., (2000) Effects of aerobic fitness on fat oxidation and body fatness Med Sci Sports Exerc. 32 (4): 804-811.
Nelson, M., et al., (1994) Effects of high-intensity strength training on multiple risk factors for osteoporotic fractures. JAMA 272 (24): 1909-1914.
Pate, R., Pratt, M. and Blair, S. (1995) Physical activity and public health: a recommendation from the Centres for Disease Control and Prevention and the American College of Sports Medicine. JAMA 273: 402-407.
Pescatello, L (1999) Physical activity, cardiometabolic health and older adults. Sports Med 28 (5): 315-323.
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Tremblay, a. Doucet, E. and Imbeault, P. (1999) Physical activity and weight maintenance. International Journal of Obesity 23, Suppi 3: S50-S54.
Tremblay, A. Simoneau, J. and Bouchard, C. (1994) Impact of exercise intensity on boy fatness and skeletal muscle metabolism. Metabolism 43: 814-818.