Strength Training in Older African-American Women; Exercise Intensity and Breast Cancer Risk; Trans Fats and Type 2 Diabetes
Adams, K. J., et al. 2001. Progressive strength training in sedentary, older African-American women. Medicine & Science in Sports & Exercise, 33, 1567-76.
Study. Exercise physiologists at the University of Louisville in Kentucky, the University of Nebraska at Lincoln and the Southside Regional Medical Center in Petersburg, Virginia, investigated the effects of an eight-week progressive strength training program on the muscular power, strength, endurance and flexibility of African-American women ages 44 to 68 years. The supervised low-frequency, low-volume program included both free-weight (barbell and dumbbell) and machine (plate-loaded) exercises, but the emphasis was on free-weight, multijoint movements. Nineteen sedentary African-American women were randomly assigned to a strength training (ST) group (n = 12; mean age, 51 years) or a nonexercise control (C) group (n = 7; mean age, 52 years). Maximal power, strength, absolute endurance and flexibility were assessed before and after training. The program included two primary exercises (leg press and bench press) and seven “assistance” exercises (dumbbell lunge, hamstring curl, dumbbell incline press, dumbbell row, lat pull, triceps press-down and dumbbell biceps curl). Subjects trained two days per week, performing two to three sets of eight to 10 repetitions for each exercise.
The program elicited the following changes in the ST group: Upper-body power (medicine ball put distance) significantly increased statistically (p = 0.002), but gains possibly lacked practical significance because of measurement variation. Lower-body power (peak watts on a bicycle) showed a small, nonsignificant increase. Significant increases occurred in one-repetition maximum (1 RM) muscle strength (leg press, +99.8%; bench press, +34.4%); absolute endurance (leg press repetitions to failure at 70% pretest 1RM, +221%; bench press repetitions to failure at 50% pretest 1RM, +112%); and flexibility (sit-and-reach test, +8.2%; p = 0.017). No significant changes occurred in power, strength, absolute endurance or flexibility in the C group.
The authors concluded that an eight-week, supervised program of low-frequency, progressive strength training emphasizing free-weight, multijoint movements can safely cause significant gains in muscle strength, absolute endurance and flexibility in older African-American women.
Comments. The strength of this study was that it demonstrated that a two-day-per-week, low-volume resistance training program stimulated very significant changes in dynamic strength in older women. Past research has likewise indicated that two strength training sessions per week are sufficient to stimulate significant changes in muscular strength and endurance. One can also infer from the available research that women in the current study’s ST group very likely improved bone mineral density in the active bone mass as a result of their training program.
Friedenreich, C. M., Courneya, K. S., & Bryant, H. E. 2001. Relation between intensity of physical activity and breast cancer risk reduction. Medicine & Science in Sports & Exercise, 33, 1538-45.
Study. Epidemiologists from the Alberta Cancer Board in Calgary, Alberta, in collaboration with the faculty of the University of Alberta in Edmonton, examined the influence of physical activity on breast cancer risk reduction. They also compared the risk reduction data obtained when activity intensity values (i.e., low, moderate and vigorous intensity) were self-reported with the data obtained when these values were assigned.
The researchers conducted a population-based study of 1,233 women diagnosed with breast cancer and 1,241 controls in Alberta between 1995 and 1997. The team measured the frequency, duration and intensity of the subjects’ lifetime occupational, household and recreational activities using the Lifetime Total Physical Activity Questionnaire (Friedenreich, Courneya & Bryant 1998) and cognitive, in-person interviews. An advanced statistical analysis method was used to estimate odds ratios (calculated by dividing the odds of developing breast cancer for women reporting a certain level of activity by the odds for women reporting less or more activity) and to assess the effects of confounding factors, such as body mass index, diet and so on. Odds ratios for self-reported and assigned levels of activity were compared for lifetime total activity and for each type of activity (i.e., occupational, household and recreational). MET values were assigned to each reported activity in accordance with the Compendium of Activities Classification (Ainsworth et al. 1993).
The greatest breast cancer risk reductions were associated with moderate-intensity occupational activity (3-6 METs), with some risk decreases also attributable to moderate-intensity household activity. Women in the highest activity quartile (25%) who undertook ≥ 32 hours of household activity each week per year had a 31 percent reduction in risk. Recreational activity, at any intensity level, did not contribute to risk reduction. Self-reported and assigned intensity values were found to provide comparable results.
The authors concluded that the breast cancer risk reductions found in this study were associated primarily with activities of moderate rather than light or vigorous intensity. They also determined that risk reductions were more evident when only frequency and duration of activity (not intensity) were factored in. Among the three types of activity considered, occupational and household activities were associated with the greatest risk reductions.
Comments. Of the studies that have evaluated the risk of developing breast cancer over an entire lifetime, this is the first to measure all types and components of activity. It is noteworthy that low- and vigorous-intensity activities, with the exception of occupational activity, were not found to be related to breast cancer risk. Previous research has shown that excessive exercise adversely affects menstrual function, an outcome that is known to be related to cancer risk; this may partially explain why lifetime vigorous exercise did not significantly reduce breast cancer risk. Readers interested in a comprehensive compendium of estimated energy costs of domestic, recreational and sport activities should refer to the Ainsworth reference above.
Salmerón, J., et al. 2001. Dietary fat intake and risk of type 2 diabetes in women. American Journal of Clinical Nutrition, 73 (6), 1019-26.
Study. The long-term associations between intakes of specific dietary fats and the risk of type 2 diabetes remain unclear. Nutrition scientists from the Harvard School of Public Health and elsewhere examined this topic. Beginning in 1980, they prospectively followed 84,204 women ages 34 to 59 with no diabetes, cardiovascular disease or cancer at the start of the study. The researchers assessed detailed dietary information at baseline and updated their data in 1984, 1986 and 1990 using validated questionnaires. Relative risks of type 2 diabetes were obtained from pooled statistical models adjusted for nondietary and dietary behaviors that might potentially have biased the results.
During 14 years of follow-up, Salmerón and colleagues documented 2,507 cases of type 2 diabetes. Total fat intake, compared with equivalent energy intake (i.e., caloric intake) from carbohydrates, was not associated with the risk of type 2 diabetes; for a 5 percent increase in total energy intake from fat, the relative risk (RR) was 0.98, which was statistically nonsignificant. Intakes of saturated or monounsaturated fatty acids were also not significantly associated with the risk of diabetes. However, for a 5 percent increase in energy from polyunsaturated fat, the RR was 0.63, meaning the risk fell by 37 percent (p < 0.0001); and for a 2 percent increase in energy from trans fatty acids, the RR was 1.39, meaning the risk increased by 39 percent (p = 0.0006). The authors estimated that replacing 2 percent of the energy obtained from trans fatty acids with the same caloric value of polyunsaturated fat would reduce the risk of developing type 2 diabetes by 40 percent.
According to Salmerón and associates, these data suggest that neither total fat intake nor saturated and monounsaturated fatty acid intakes are associated with the risk of type 2 diabetes in women, but that trans fatty acids increase and polyunsaturated fatty acids reduce this risk. The authors concluded that substituting nonhydrogenated polyunsaturated fatty acids for trans fatty acids is likely to substantially reduce the risk of developing type 2 diabetes.
Comments. Of all the fats that may increase the risk for both cardiovascular disease and diabetes, trans fats are proving to be the most detrimental—even more so than saturated fat. Trans fats are partially hydrogenated polyunsaturated vegetable oils found in deep-fried foods, stick margarine, chips, crackers, cookies, donuts, cakes, pastries and processed foods. They are used to increase the shelf life and flavor stability of oils and foods. You can calculate the amount of trans fat in an item by adding the grams of polyunsaturated, monounsaturated and saturated fats and subtracting this sum from the total fat grams listed on the label.