PT FAT LOSS INTENSIVE: EXERCISE AND OBESITY FILEX 2001 Fitness and Healthy Lifestyle Convention Darling Harbour Sydney 3 June 2001
Robert J Parker, MEd, FACHPER, PhD Research Fellow, Science Faculty, University of Sydney Head, Children's Hospital Institute of Sports Medicine The Children's Hospital at Westmead
There has been a steady increase in the proportion of overweight and obese adult Australians over the past 15 years. Trend data from the National Heart Foundation Risk Factor Prevalence Survey (1989) and the National Nutritional Survey (1995), show that the proportion of overweight and obese women aged between 25 and 64 years has increased from 27% in 1980 to 43% in 1995. Similarly the proportion of overweight or obese men rose from 48% to 63% over this period. The proportion of obese men has increased from 8% in 1980 to 18% in 1995 and the proportion of obese women has increased from 7% to 16% On average, women in 1995 weighed 4.8 kg more than their counterparts in 1980.
Comparisons of statistics between the 1985 ACHPER survey and more recent data highlight an increasing prevalence of obesity among young populations (Wilcken et al., 1996, Dolman et al. 1998, Wake 1999). Booth et al have recently made a comparison of three recent cross-sectional Australian surveys (the National Nutrition Survey; the Health of Young Victorians survey; and the NSW Schools survey). Using the new Body Mass Index (BMI) for age- international reference values, the authors found that approximately 2022% of Australian children and adolescents are overweight or obese and the trends show that this rate is increasing. While agreement on the criteria to define obesity has been problematic (Rowland, 1990), no matter which criteria are applied, the incidence of children in Australia who can be classified as overweight, is a major concern.
Several theories exist to help explain the aetiology of obesity including genetics (Bouchard, 1994; Caterson 1998; Caro et al., 1996) and birth weight (Rona et al., 1996). Baur (1997) has suggested that while the genetic predisposition to become overweight in the paediatric population has probably not altered over the years, the environments in which these genes can fully express their potential (in Westernised society) has changed markedly. There are a number of environmental factors, which have been linked to the prevalence of obesity both in childhood and adults. These include a decline in the level of energy expenditure and dietary fat intake imbalances.
Effective weight loss strategies in the adult population would appear to be complex. There is sufficient data to indicate that restrictive diet interventions in the adult market can be efficacious in the reduction of body weight. This method however appears to show a greater proportion of fat-free mass loss relative to fat mass loss and often results in a decrease in metabolic rate with a concomitant weight gain with re-feeding. There is also sufficient evidence to show that exercise alone is not an effective method for achieving fat loss when compared to the effects of dietary interventions (Ross et al 2000). Specific exercise modalities have been shown to hold fat-free mass and either attenuate or increase metabolic rate to pre-weight loss levels.
Recent attention has focussed on the importance of exercise intensity on fat loss. It is now clear that a lower level of aerobic activity (ie., 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 dose-continuum. 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 some 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 even higher 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 post-exercise 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 (ACSM, 1998). 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.
Key issues to be discussed in this session will include: the appropriate intensity of exercise needed for fat loss (or weight stability); the impact of exercise intensity on total body weight and fat weight loss; the importance of aerobic exercise and resistance training on energy expenditure, both during and after exercise, the role of exercise in the maintenance of fat-free mass; and the impact of aerobic exercise and resistance training on substrate utilisation and metabolic rate.
Selected 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.
Baur, L.A. (1997) Obesity in childhood - consequences, aetiology and management. (Proceedings) Child Nutrition Today, Health Tomorrow. HINS National Nutrition Symposium, Melbourne, May. pp 36-45
Bailor, et al., (1990) Exercise intensity does not affect the composition of dietand exercise-induced body mass loss Am J. Clin Nutr. 51: 142-146.
Bouchard, C. (1994) Genetics of obesity: Overview and research directions. In: Bouchard, C. (Ed) The Genetics of Obesity CRC Press: Boce Raton, FL, pp223-233.
Caro, J.F., Sinha, M.K., Kolaczynski, J.W., Zhand, P.L. & Considine, R.V. (1996) Leptin: the tale of an obesity gene. Diabetes, 45: 14551462
Dolman J, Olds T, Norton K, and Stuart D. Trends in the health-related fitness of Australian children (Abstract) Australian Conference of Science and Medicine in Sport, Adelaide, 1998 (p100).
Feigenbaum, M. and Pollock, M. (1997) Strength training: rationale for current guidelines for adult fitness programs Physician and Sports Med. 25: 4464.
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: 489-493.
Kriketos, A. et al., (2000) Effects of aerobic fitness on fat oxidation and body fatness Med Sci Sports Exerc. 32 (4): 804-811.
NH&MRC (1997) Acting on Australia's weight: a strategic plan for the prevention of overweight and obesity. National Health and Medical Research Council. Australian Government Printing Service; Canberra.
Ross, R., Jansssen, 1. and Tremblay, A. (2000) Obesity reduction through lifestyle modification. Canadian Journal of Applied Physiology 25(1): 1-18
Rowland, T.W. (1990). Exercise and Children's Health. Human Kinetics, Champaign, II, USA.
Sallis, J.F. (1995) A behavioural perspective on children's obesity. In: L. Cheung and J.B. Richmond (eds) Child Health, Nutrition and Physical Activity. Human Kinetics, Champaign, IL, pp.125-138.
Tremblay, a. Doucet, E. and Imbeault, P. (1999) Physical activity and weight maintenance. International Journal of Obesity 23, Suppl 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.
Wake, M. What's happening to Australian Children? (1999) Australasian Society of the Study of Obesity. Proceedings from the Eight Annual Scientific Meeting, Sydney, Australia, p 55
Wilcken, D.E.L., Lynch, J.F., Marshall, M.D., Scott, R.L. & Wang, X.L. (1996) Relevance of body weight to apo-lipoprotein levels in Australian children. Medical Journal of Australia. 164: 22-25.