What is an appropriate frequency for a cardiorespiratory endurance program based on moderate-intensity activities?

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Baseline Characteristics of Study Participants

The American College of Sports Medicine (ACSM) has updated its position stand on the quantity and quality of exercise to maintain cardiorespiratory and muscular fitness. The revised ACSM guidelines include for the first time a recommendation for flexibility training as a component in maintaining fitness in addition to aerobic and strength training exercises.

The ACSM position stand is published in the June 1998 issue of Medicine & Science in Sports & Exercise (vol. 30, no. 6). The 17-page position stand also provides the rationale and supportive research for the recommendations. The following information highlights the ACSM recommendations for exercise in healthy adults.

Cardiorespiratory Fitness and Weight Control

To maintain cardiorespiratory fitness and weight control, the recommendations state that aerobic exercise should be performed three to five days a week for 20 to 60 minutes at an intensity that achieves 55 to 90 percent of the maximum heart rate and 40 to 85 percent of the maximum oxygen uptake reserve. In place of one 20- to 60-minute session on a given day, the recommendations state that two to six 10-minute periods of aerobic activity throughout the day can be used to fulfill the requirements for the amount of exercise.

Lower-intensity exercise is recommended for persons who are unfit. Lower-intensity exercise should be performed for 30 minutes or more. Persons training at higher levels should exercise for at least 20 minutes. Moderate-intensity exercise for a longer duration is recommended for most adults.

According to the recommendations, resistance training should be a part of a fitness program and of sufficient intensity to enhance muscular strength and endurance and to maintain a fat-free mass. One set of eight to 10 exercises that work the major muscle groups should be performed two or three days a week. The guidelines advocate for most persons eight to 12 repetitions (or to a near-fatigue level) of each exercise. Persons who are older or frail may benefit from 10 to 15 repetitions.

The recommendations for resistance training are based on three factors: a practical amount of time to perform resistance training, the degree of training that results in improved muscular strength and endurance, and the suitability of the level of resistance training for most adults. With respect to the amount of time, the position stand notes that higher dropout rates occur when more than 60 minutes is required to complete a session. A previous study revealed that only 20 minutes is required to complete one set of weight-training exercises, whereas 50 minutes is required to complete three sets. While more frequent training and additional sets and repetitions may produce larger gains in strength, the difference in improvement is usually small in the average healthy adult, plus the average adult does not have the same goals as an athlete. In addition, more intense resistance training may increase the risk of orthopedic injury or a cardiac event in middle-aged and older participants.

The recommendations state that flexibility exercises two or three days a week should be incorporated into the fitness program. At least four repetitions per muscle group should be completed at each session. Stretching exercises should mobilize the major muscle and tendon groups and may include static, proprioceptive neuromuscular facilitation and ballistic techniques.

With the static technique, the tendons and muscles are slowly stretched and the stretched position is held for a period of time. Static stretches should be held for 10 to 30 seconds. Proprioceptive neuromuscular facilitation stretching consists of alternating isometric muscle contraction and passive stretching. This technique is sometimes described as active/assisted, contract/relax or hold/relax. Proprioceptive neuromuscular facilitation stretching should be maintained for a six-second contraction, followed by a 10- to 30-second assisted stretch. Ballistic stretching involves repetitive bouncing motions in which the tendon is rapidly stretched and relaxed.