Applying the ACSM Guidelines

While all of the reported studies showed favorable outcomes for improving strength and body composition, there was little consensus regarding a standard training protocol. For example, important strength-training studies conducted at Tufts University typically featured five or fewer exercises, performed two or three days a week, for three sets of eight repetitions each.^9,13,21,11 On the other hand, equally important studies conducted by University of Maryland investigators^29,28,25,23 typically featured seven to 14 exercises, performed three days per week, for one to two sets of 15 repetitions each.

During this same time period, researchers at the University of Florida examined the comparative effects of various strength-training protocols, especially the number of exercise sets^30,15,33 and the number of weekly training sessions.^30,8,16,22

The 1995 ACSM exercise guidelines essentially restated and reinforced the 1990 ACSM Position Stand3 with respect to the recommended training protocols for developing and maintaining cardiorespiratory and muscular fitness in healthy adults. Both of these ACSM publications advised previously sedentary but otherwise healthy men and women to perform one set (eight to 12 repetitions) of eight to 10 resistance exercises for the major muscle groups at least two days a week. These guidelines also recommended a minimum of 20 minutes of aerobic activity, three days a week, at sufficient intensity to attain 60 to 90 percent of maximum heart rate.

The South Shore YMCA, Quincy, Mass., decided to apply the 1995 ACSM minimum requirement exercise guidelines to previously sedentary adults who enrolled in a 10-week introductory fitness program for the primary purposes of improving body composition and reducing resting blood pressure. Because exercise class participants typically perform both muscular strength and cardiovascular endurance activities during the same session, we offered a two-time-per-week training program (consistent with ACSM's minimum strength-training guidelines), and a three-times-per-week training program (consistent with ACSM's minimum endurance exercise guidelines).

Exercise classes were scheduled mornings, afternoons and evenings on a Tuesday/Thursday sequence (twice per week) and on a Monday/Wednesday/Friday sequence (three times a week). All training sessions were completed within one-hour class periods, and included approximately 20 minutes of resistance exercise and 20 minutes of aerobic activity. Participants with low initial fitness levels required more time to complete the strength-training circuit, and began with shorter bouts of aerobic activity. All exercise classes were carefully instructed and closely supervised (maximum of six participants with two instructors) to ensure compliance with the ACSM exercise guidelines.

To provide a controlled training environment, a separate exercise facility was outfitted with 10 standard weightstack machines (leg extension, leg curl, double chest, pullover, lateral raise, biceps curl, triceps extension, abdominal curl, low-back extension and neck flexion/extension) and three common cardiovascular tools (two treadmills and a recumbent cycle).

Strength training consisted of one set of each resistance exercise, from larger to smaller muscle groups, with a weightload that could be lifted between eight and 12 repetitions. When a trainee completed 12 repetitions, the resistance was increased by 5 percent (or less). Each exercise repetition was performed in approximately six seconds, with about two seconds for the concentric muscle action and about four seconds for the eccentric muscle action.

Aerobic training bouts began and ended with three-minute warm-up and cool-down periods, during which participants performed the same aerobic activity at a lower training intensity (slower treadmill speed or reduced cycle resistance). The steady-state aerobic training segment was performed at an exercise heart rate approximately 70 to 80 percent of the participant's age-predicted maximum. However, participants were not allowed to train above level 15 (hard effort) on the Borg (6 to 20) rating scale of perceived physical exertion,⁵ regardless of their exercise heart rate.

Participants also performed a 20-second static stretch for the prime-mover muscle group immediately following each resistance-training exercise. For example, upon completing the leg extension exercise, participants performed a 20-second quadriceps stretch; after completing the leg curl exercise, they performed a 20-second hamstrings stretch, and so on, for all 10 strength exercises.

Program participants

Participants in the 10-week introductory fitness program were 1,644 adults between the ages of 21 and 80 years old from the greater Boston area. Each participant completed a medical history questionnaire, and anyone with possible exercise contraindications was required to provide written physician permission before beginning the program. The mean age for the 892 participants who trained twice a week was 56.2 years, and the mean age for the 752 participants who trained three times a week was 51 years.

Program results

Pre-training and post-training assessment data were collected over an eight-year period from 1996 through 2004, including nine spring, eight summer, eight fall and eight winter exercise sessions of 10 weeks in duration. Ninety-two percent of the previously sedentary adults who enrolled in the exercise program completed all 10 weeks of training. Data for these 1,644 introductory exercise program participants were analyzed by training frequency, gender and age. Beginning values for body weight, body composition and blood pressure are presented in Table 1.

Training frequency. The mean exercise adherence rates (percentage of scheduled training sessions attended) were 83.2 percent for twice-per-week trainees and 79.6 percent for three-times-per-week trainees. Both training frequencies were effective for improving body composition and resting blood pressure in previously sedentary adults (Table 2). Participants who trained three times per week had significantly greater decreases in percent fat (­2.2 vs. ­1.9 percent) and fat weight (­4.4 vs. ­3.2 pounds) than those who trained twice a week, which makes sense because three-day trainees performed 50 percent more exercise. However, both training frequencies produced identical increases in lean weight (+3.1 pounds), indicating that two weekly resistance workouts may be as effective as three weekly strength-training sessions for stimulating muscle development in beginning exercisers. Reductions in resting systolic and diastolic blood pressure were statistically similar for participants who trained three times a week and twice a week.

Based on these findings, it would appear that three exercise sessions a week may be more beneficial overall, but two weekly workouts are effective for improving body composition and reducing resting blood pressure in previously sedentary adults.

Gender. Our program participants included 1,258 women and 386 men, showing a stronger response from women than men to supervised exercise classes (3:1 ratio). The men experienced significantly greater decreases in percent fat (­2.8 vs. ­1.8 percent) and fat weight (­5.9 vs. ­3.0 pounds) than the women. Men also added significantly more lean weight (+4.6 vs. + 2.6 pounds) than women (Table 3). The greater changes in body composition components attained by the men may be due in part to their higher bodyweight (204.7 vs. 171.9 pounds) and lean weight (156.1 vs. 119.2 pounds), compared to the women. Men and women trainees had statistically similar reductions in resting systolic and diastolic blood pressure.

Age. The data were also divided into age groups: 1) 21 to 30 years; 2) 31 to 50 years; 3) 51 to 65 years; and 4) 66 to 80 years. The analyses showed no significant differences among the four age groups in body weight, body composition or blood pressure changes. These findings indicate that the ACSM minimum requirement exercise guidelines produce similar improvements in these health/fitness factors for young, middle-aged and older adults.

Summary and practical application

Based on the results attained by 1,644 adults who completed our 10-week introductory exercise program, the 1995 ACSM minimum requirement exercise guidelines are effective for improving body composition and resting blood pressure in previously sedentary men and women between 21 and 80 years of age. On average, 10 weeks of combined strength and endurance training produced a 2 percent reduction in percent fat, a 3.7-pound loss in fat weight, a 3.1-pound gain in lean weight, a 3.8 mmHg-decrease in resting systolic blood pressure and a 1.8 mmHg-decrease in resting diastolic blood pressure (see sidebar).

The basic and brief 1995 ACSM exercise protocol was apparently well-received by these formerly inactive adults. More than 90 percent of those who enrolled in the fitness program completed it, attending more than 80 percent of their scheduled classes. According to written, anonymous questionnaires administered at the completion of each 10-week training session, more than 95 percent of the participants reported high levels of satisfaction with the overall exercise program, and committed to continuing their training.

Research indicates that both genetic and psychological factors can influence tolerance for and responsiveness to physical training.^6,4 In addition, it would appear that relatively simple and time-efficient exercise protocols may be advantageous for previously inactive adults from an acceptance and compliance perspective. Based on our experiences with beginning exercisers, the 1995 ACSM basic strength and endurance training guidelines provide both a practical and effective approach for improving body composition and resting blood pressure in previously sedentary adults.

Finally, the recently released 7th edition of ACSM's Guidelines for Exercise Testing and Prescription¹ presents essentially the same strength-training recommendations used in this study. The key resistance exercise guidelines in the latest ACSM certification textbook call for the following:

* Full range of pain-free movement.

Clearly, these guidelines are consistent with our research findings, and we agree that new exercisers should begin strength training in this manner. FM