Recent Key Studies

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Recent Key Studies
By Heidi M. Weingart, M.A. and Len Kravitz, Ph.D.

Introduction
The enthusiasm and interest in the health benefits of resistance training continues to spark compelling new research in this area. In addition, researchers are attempting to determine and explain the mechanisms involved in exercise’s role with weight management, metabolic rate and energy expenditure. Also, using more sophisticated research designs, the role of flexibility and muscle injury is becoming more clear. The following article will review several recent investigations that expound upon the comments above. Much of this information will provide the personal trainer with new education for her/his clients and recommendations for designing more effective exercise prescriptions.

This research review highlights recent research on strength training with postmenopausal women, resistance training with untrained young women, resistance training on blood lipid profiles in women, resistance training versus aerobic training in maintaining resting metabolic rate, detraining, split session workouts and energy expenditure, obesity, weight management maintenance, weight cycling and hypertension risk, exercise and hypertension, exercise and cardiovascular disease risk reduction, flexibility and muscle injury, and one-mile run performance in children. With each investigation a special message section is included that focuses on practical applications for the personal trainer.
The Study:
Resistive Training Maintains Bone Mineral Density in Postmenopausal Women. (1998). A. S. Ryan, G. R. Hunter, and D. Elahi. Calcified Tissue International 62: 295-299.
Loss of bone mineral density is a concern for many postmenopausal women as it may lead to osteoporosis and/or skeletal fractures. Therefore, this study was conducted to determine whether resistance training could prevent loss of bone mineral density in 27 postmenopausal women who were healthy and not on estrogen therapy. The 16-week training program consisted of one-hour sessions on three nonconsecutive days per week. The women performed one set (upper body) and two sets (lower body) of 12-15 reps at 90% 3RM for the following exercises: leg press, chest press, leg curl, latissimus pull down, elbow flexion, elbow extension, leg extension, upper back row, military press, hip abductor, hip adductor, and abdominal curls.
At the end of the program, the women demonstrated a small but significant decrease in body weight (68.4±1.9 to 67.2±1.7 kg) and body mass index (26.0±0.7 to 25.6±0.6 kg/m2). Muscular strength increased significantly (chest press = 65%, latissimus pull down = 36%, leg press = 98%, and leg extension = 32%). There was no significant change in bone mineral density (regional or total body) or bone turnover markers.
The Message:
The findings of this study suggest that it is indeed beneficial for healthy, postmenopausal women to participate in resistance exercise. Although the women in this study did not experience an increase in bone mineral density, it is important to note that they maintained their current bone mineral densities while significantly improving their muscular strength. In addition, this improvement in muscular strength due to resistance training may help reduce the risk of future falls and osteoporotic fractures.

The Study:
Weight Training Increases Fat-free Mass and Strength in Untrained Young Women. (1998). K. Cullinen and M. Caldwell. Journal of the American Dietetic Association 98: 414-418.
It is often recommended that a part of an adult fitness program should include strength training because of the additional benefits it provides. But much of the strength training research has been done on male subjects. Consequently, the purpose of this study was to determine what effects weight training had on untrained healthy, young women. Twenty-three healthy, normal-weight women participated in the weight training program and 10 women served as the control group. The program consisted of two sessions per week and included two sets of 10 reps for each exercise. The exercises performed during Session 1 were dumbbell bench press, seated dumbbell press, latissimus pull down, dumbbell curl, leg extension, and leg curl. Session 2 exercises were chest fly, upright row, latissimus pull down, "EZ" curl (biceps curl), leg extension, and leg curl.
At the end of 12 weeks, the weight-trained group demonstrated no change in body weight. However, percent body fat significantly decreased (29.8±2.8 to 26.9±2.8) and fat-free mass (44.2±5.4 to 46.2±6.0 kg) significantly increased. This represents an impressive 10% loss in percent body fat. Muscular strength also increased for the weight-trained women. Although resting metabolic rate (absolute and standardized to kilograms fat-free mass) did not statistically increase, it did increase 8% in this 12-week training period.
The Message:
This study’s findings of increased strength, fat-free mass, resting metabolic rate and decreased body fat indicate the potential favorable effect of resistance training in weight management programs. It is of interest that these results occurred without a restriction of dietary intake.

The Study:
Effect of 14 Weeks of Resistance Training on Lipid Profile and Body Fat Percentage in Premenopausal Women. (1999). B. Prabhakaran, E. A. Downing, J. D. Branch, D. P. Swain, and B.C. Leutholtz. British Journal of Sports Medicine 33: 190-195.
The aim of this study was to evaluate the effects a resistance training study had on the lipid profiles and body compositions of 12 healthy, sedentary, premenopausal women. Additionally 12 women were assigned to a non-exercising control group. The 14-week resistance training program utilized eight exercises: leg press, leg extension, leg curl, latissimus dorsi pull, bench press, military press, biceps curl, and triceps extension. The intensity was 85% of 1-RM. The duration was 45-50 minutes per session, three times per week. For each exercise, the women performed two sets of eight reps followed by a third set that went to exhaustion. Results demonstrated a 9% decrease in total cholesterol (TC), a 14% decrease in LDL-C, and a 14.3% decrease in TC/HDL ratio. There was no significant change in triglycerides, HDL, body mass, or nutritional intake for the exercise group. This group did demonstrate a significant decrease in percent body fat (5%) and a significant increase in total strength (27%), which was defined as the sum of the estimated 1-RM for eight exercises.
The Message:
The results of this study suggest that sedentary women benefit from high-intensity strength training in terms of their lipid profiles and body composition. However, the vast majority of resistance training studies do not reflect significant changes in the total cholesterol, LDL cholesterol or HDL cholesterol. It is likely, though, that resistance training that results in a significant loss of fat mass will also result in improved lipid profiles

The Study:
Effects of Resistance vs. Aerobic Training Combined with an 800 Calorie Liquid Diet on Lean Body Mass and Resting Metabolic Rate. (1999). R. W. Bryner, I. H. Ullrich, J. Sauers, D. Donley, G. Hornsby, M. Kolar, and R Yeater. Journal of the American College of Nutrition 18: 115-121.
A concern for individuals on very low calorie diets (VLCD) is the loss of fat-free mass and a decrease in resting metabolic rate. Therefore, this study was undertaken in order to determine if resistance training is preferable to aerobic training in terms of favorable changes in body weight, fat-free mass, and resting metabolic rate for individuals on a VLCD. Twenty subjects were randomly assigned to either a resistance exercise group or an aerobic exercise group. All subjects were put on an 800 kilocalorie liquid diet (40% protein, 49% carbohydrates, 11% fat). The respective exercise regimens were as follows:
Strength Training
4 lower body, 6 upper body exercises 3 days/wk
Aerobic Training
Aerobic exercise (walking, biking, stair climbing) 4 days/wk
Weeks 1 and 2 Gradual increase in resistance until 8-12 reps of 8-RM for 2 sets 20 min/day increasing by 10 minutes/day/week until 50-60 min was reached. No exercise intensity was set.
Weeks 2 – 6 2 sets of 8-RM, 8-12 reps
Same as above
Weeks 6 – 9 3 sets of 8-RM, 8-12 reps
Same as above

Weeks 9 – 12 4 sets of 8-RM, 8-12 reps
Same as above

At the conclusion of the 12-week program, both groups had experienced a significant decrease in body weight, percent body fat, body fat, and body mass index. However, the aerobic group demonstrated a significant decrease in lean body weight whereas the resistance group did not. The resistance group also exhibited a slight increase (4%) in resting metabolic rate.
The Message:
For individuals who are on a VLCD, it is beneficial to participate in an intensive resistance-training program instead of only the traditional aerobic exercise regimen. In this study, both groups did experience a loss of body weight. However, unlike the aerobic group, the resistance group’s weight loss was almost entirely due to a loss of fat weight. Therefore, a resistance training program during a VLCD preserved lean body weight and resting metabolic rate while accomplishing the weight loss.

The Study:
Effect of 3 Weeks of Detraining on the Resting Metabolic Rate and Body Composition on Trained Males. (1999). J. LaForgia, R. T. Withers, A. D. Williams, B. J. Murch, B. E. Chatterton, C. G. Schultz, and F. Leaney. European Journal of Clinical Nutrition 53: 126-133.
Resting metabolic rate plays an important role in regulating energy balance and body mass in humans. In the research done on resting metabolic rate, there have been discrepancies as to exactly what effect exercise has on resting metabolic rate. Therefore, this study attempted to examine this effect from a different viewpoint by having 16 healthy males who were exercising regularly for at least two years cease their exercise regimens. The goal was to evaluate if a three-week detraining period would chronically alter resting metabolic rate. After the initial resting metabolic rate measurements, eight of the subjects were asked to stop their training regimens immediately. The other eight subjects formed the control group and were instructed to continue with their normal activities. Results showed that there was no significant changes in maximal oxygen consumption, resting metabolic rate, or fat mass. However, the detraining group did have a significantly greater decrease in fat-free mass after the three-week period, which amounted to a loss of 1.5 lbs. Most important, however, was the result that there was no significant effect for indexed resting metabolic rate.
The Message:
This study suggests that short-term (3 weeks) absence in participation in resistance training exercise has very little effect on fat-free mass and resting metabolic rate in male participants.

The Study:
Effects of Split Exercise Sessions on Excess Postexercise Oxygen Consumption and Resting Metabolic Rate. (1998). K. S. Almuzaini and J. A. Potteiger. Canadian Journal of Applied Physiology 23: 433-443.
It has been reported that after exercise, there is a period where an individual’s oxygen consumption is elevated from normal. This elevated period has been termed excess postexercise oxygen consumption (EPOC) and has also been associated with an increase in metabolic rate. Research results in this area have conflicted as to the EPOC magnitude and duration; how long after exercise the metabolic rate is increased; and what types and lengths of exercise influence EPOC more. The intention of this study was to examine the effects a split exercise session had on EPOC, resting metabolic rate, and energy expenditure. Ten physically active, healthy males performed both a continuous (30 minutes) and a split exercise session (two, 15-minute sessions) aerobic exercise on separate days. Their EPOCs were measured at the end of each exercise session and resting metabolic rate measurements were taken the mornings before and after the exercise sessions.
The combined EPOC for the split exercise periods was significantly greater than the EPOC for the continuous period. However, this is where statistics can be most misleading. The authors presented their results in milliliters of oxygen. When converted to kilocalories, the different in the continuous versus the split exercise sessions is only 10 kcals. There were no significant differences for resting metabolic rate in either exercise protocol.
The Message:
Even though the findings of this study show no major significant differences, this study answers a very important question health and fitness professionals have been seeking. Dividing the workout into split sessions versus one continuous session did not have a practical difference in absolute post-exercise caloric expenditure. Therefore, the decision to split exercise sessions should be made based more on a person’s time schedule, as opposed to any physiological effect.

The Study:
Effects of Exercise-Focused Versus Weight-Focused Maintenance Programs on the Management of Obesity. (1999). Addictive Behaviors 24: 219-227.
This study was undertaken to determine if a weight-loss maintenance program focused on exercise would result in a better maintenance of physical activity and weight loss versus a weight-loss maintenance program focused mainly on weight loss. Both treatment programs included 13 biweekly, supervised group sessions, a restricted dietary intake, and instructions to walk 30 minutes/day, five days/week. The exercise-focused group exercise sessions included monetary rewards for meeting exercise goals, intergroup competitions, and training in exercise relapse prevention strategies. The weight-focused group sessions included discussion sessions on weight-loss maintenance with the major emphasis being on dealing with obstacles to maintaining weight loss.
At the end of the study, the weight-focused group maintained their weight reductions (90.8% of initial weight loss) better than the exercise-focused group (54.4% of initial weight loss). The weight-focused group also had significantly greater reductions in fat consumption than the exercise-focused group. However, both groups did significantly increase their weekly walking amounts.
The Message:
Many individuals who lose weight regain it relatively soon. The key to maintaining the weight loss is diet and exercise. This study suggests that one key to weight-loss maintenance is a group program focused on weight-loss maintenance strategies that also includes exercise. This winning combination helped the subjects in this study to reduce their fat consumption and increased their exercise amounts.

The Study:
Weight Cycling, Weight Gain, and Risk of Hypertension in Women. (1999). A. E. Field, T. Byers, D. J. Hunter, N. M. Laird, J. E. Manson, D. F. Williamson, W. C. Willet and G. A. Colditz. American Journal of Epidemiology 150: 573-579.
This study was performed to evaluate the effect of weight gain and repeated intentional weight loss on the risk of hypertension. A total of 46,224 women were divided into three classes: severe weight cyclers (lost &Mac179; 20 lbs. &Mac179; 3 times), mild weight cyclers (lost &Mac179; 10 lbs. &Mac179; 3 times), and non-weight cyclers. The researchers mailed four questionnaires to the women over a period of six years. These questionnaires inquired about medical history, life-style, health behaviors, maximum and minimum weights (excluding illness and pregnancy), intentional weight loss episodes, methods primarily used for weight loss, weight change, physical activity, average time per week spent exercising during the past year, and if diagnosed with hypertension.
The results of the questionnaires demonstrated that 78% of the women intentionally lost weight at least once, 41% had &Mac179; 2 intentional weight losses of 5 – 9 lbs., 1.4% intentionally lost &Mac179; 20 lbs. &Mac179; 3 times and 18.9% intentionally lost &Mac179; 10 lbs. &Mac179; 3 times. Each 10-lb. change in weight over the six years resulted in a 30% increase in the risk of developing hypertension. However, the results also demonstrated that mild and severe weight cyclers were not appreciably more likely than non-weight cyclers to be diagnosed with hypertension.
The Message:
This study does support the belief that excessive weight and weight gain does lead to health risks. However, weight cycling in and of itself does not increase an individual’s risk for hypertension. The problem with weight cycling is that weight cycling individuals tends to gain even more weight back after they lost the initial weight. It is this additional weight gain that causes a significant increase in the risk of hypertension. The key to solving this problem is to help individuals find a program or plan to keep the lost weight off and then help them stick to this plan.

The Study:
Influence of Age and Gender on Exercise Training-Induced Blood Pressure Reduction in Systemic Hypertension. (1999). The American Journal of Cardiology. 84: 192-196.
Aerobic exercise is often recommended for individuals who have stage 1 or 2 essential hypertension. The purpose of this study was to evaluate what effect age and gender has on the efficacy of aerobic exercise for lowering blood pressure. A sample of 103 men and 35 women were divided into control and treatment groups. These groups were further divided into groups based on age and gender. The control group maintained their normal, sedentary lifestyle. The physical activity group exercised at least 2 days per week at 50% maximal oxygen consumption. Exercises included 30 – 40 minutes of aerobic exercise and 10 – 20 minutes of conditioning/strength exercise.
At the end of eight weeks, the range of reduction in systolic blood pressure for men (-10 to –16 mmHg) and women (-10 to –16 mmHg) was statistically and clinically significant. The range of reduction for diastolic blood pressure for men (-5 to –11 mmHg) and women (-6 to –14 mmHg) was also relevant. Gender did not influence the effect of physical activity. It was noted that the older hypertensive subjects experience the smallest reductions.
The Message:
The results of this study support the benefits of having individuals who are stage 1 or 2 hypertensives perform regular physical activity. Gender did not play a significant role in lowering blood pressure with physical activity. However, age did affect physical activity and blood pressure slightly. The older individuals had a smaller decrease in blood pressure than the younger individuals did. This should not be misinterpreted to mean that older individuals should not exercise because their blood pressure reductions are smaller. Any decrease in blood pressure is beneficial and therefore it would be good for elderly stage 1 or 2 hypertensives to participate in regular physical activity with their physician’s permission.

The Study:
Physical Activity and Cardiovascular Disease Risk in Middle-aged and Older Women. (1999). H. D. Sesso, R. S. Paffenbarger, T. Ha, and I-M Lee. American Journal of Epidemiology 150: 408-416.
Much of the research done on cardiovascular disease (CVD) has involved only male subjects. The studies that have included women have resulted in conflicting findings. Consequently, the present study was performed to determine if physical activity in women during their middle and late years influences the risk of CVD. A sample of 1,564 women who were initially free of CVD were periodically mailed questionnaires over a period of 31 years. The questionnaires assessed physical activity (daily number of stairs climbed and city blocks walked; type and number of hours involved in sports), diagnosis of CVD, and coronary risk factors. There were 181 new cases of CVD reported over the 31 years. There also appeared to be no overall association between higher levels of physical activity and CVD risk. However, walking approximately 6 miles per week was associated with a 33% decreased risk of CVD.
The Message:
The findings of this study support an important health benefit of walking in reducing CVD risk in women.

The Study:
The Role of Passive Muscle Stiffness in Symptoms of Exercise-Induced Muscle Damage. (1999). M. P. McHugh, D. A. J. Connolly, R. G. Eston, I. J. Kremenic, S. J. Nicholas, and G. W. Gleim. The American Journal of Sports Medicine 27: 594-599.
Eccentric exercise often results in muscle damage and soreness. It is unknown why some people are more prone to injury after eccentric exercise. One theory is that flexibility plays a part in this susceptibility. Consequently, this study’s purpose was to determine if passive muscle stiffness had any effect on eccentric exercise-induced muscle damage. Twenty subjects were divided into 3 groups based on passive hamstring stiffness (compliant, normal, and stiff). The testing included isometric strength and eccentric exercises. For the isometric strength tests, the subjects were seated upright with their hips at 90&Mac176; flexion and knees at 45&Mac176; flexion. They then maximally contracted their knee flexors for five-second contractions four times with a ten second rest between. The eccentric exercises were performed immediately after the isometric exercises. The subjects performed these exercises at 90&Mac176; to 0&Mac176; knee flexion. The subjects contracted their muscle group enough to move a dynamometer arm and reach a target set at 60% isometric strength. The eccentric exercises resulted in significant strength loss, pain, muscle tenderness, and increased creatine kinase activity. The stiff subjects had a greater strength loss, pain, muscle soreness, and creatine kinase activity than the compliant subjects.
The Message:
From the results of this study, there appears to be a relationship between flexibility and muscle damage. Subjects, who had less hamstring flexibility showed the greatest loss of strength, more pain and more tenderness. This study indicates that more flexible individuals (at least in the hamstring muscle) are less susceptible to exercise-induced muscle damage. This is one of the few experimentally controlled investigations supporting the improvement of flexibility for the reduction of muscle injury.

The Study:
One-Mile Run Performance and Cardiovascular Fitness in Children. (1999). T Rowland, G. Kline, D. Goff, L. Martel, and L. Ferrone. Archives of Pediactric Adolescent Medicine 152: 845-849.
The purpose of this study was to determine what effects anthropometric and cardiovascular variables have on one-mile run performance in 12-year old boys of a varying range of fitness. A sample of 36 sixth grade boys underwent a graded exercise test on a cycle ergometer to evaluate their fitness levels. Then the children performed a timed, one-mile run outdoors. Results showed the average run time to be 9:07 minutes. Body fat and cardiovascular fitness explained 31% and 28% of running performance. Thus, in a one-mile run, performance may be explained equally by the youth‘s body fat and cardiovascular endurance.
The Message:
A timed one-mile run test is often used in elementary schools to determine a child’s fitness level. This study suggests that this method may not be as good an indicator of cardiovascular fitness levels as was once felt. True cardiovascular fitness only accounts for 28% of the variance in running velocity which was actually lest than percent body fat. This also suggests that other nonaerobic factors (such as running skill, muscle strength, and anaerobic capacity) may contribute to endurance performance in youth.

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