ACSM Exercise Recommendations for Healthy Adults
Muscular Strength and Endurance: Resistance Training using one set of 8-10 exercises that condition the major muscle groups should be performed 2-3 days per week. Most people should complete 8-12 repetitions of each exercise. for older (approximately 50-60 years of age and above) and more frail people, 10-15 repetitions may be more appropriate. Multiple-set regimens may provide greater benefits if time allows.
Flexibility Training: Stretches for the major muscle groups should be performed a minimum of 2-3 days per week; at least four repetitions, held for 10-30 seconds, should be completed. Stretching should include appropriate static and/or dynamic techniques.
Source: American College of Sports Medicine. 1998.
Position Stand: The Recommended Quantity of Exercise for Developing and Maintaining Cardiorespiratory and Muscular Fitness, and Flexibility in Healthy Adults. Medicine and Science in Sports and Exercise 30(6): 975-991.