Government health bodies and sports medicine organizations agree: Exercise is good for us. They issue recommendations for how much and what type of exercise to get, and even the intensity and frequency required to keep us fit, healthy and free from lifestyle diseases like heart disease, osteoporosis, diabetes and cancer, which are all related to poor physical fitness in some way, for some conditions.
Yet too much exercise to the point of overtraining can impair the immune system, and produce adverse effects in women like loss of menstruation, disordered eating and poor bone health. Professional athletes are in a special category; they often have the guidance of sports medicine and nutrition specialists. But recreational exercisers and athletes have to take more care.
Here are recommendations from the American College of Sports Medicine for aerobic, resistance, flexibility and functional training requirements.
- At least 150 minutes of moderate-intensity exercise per week.
- Either 30 to 60 minutes of moderate-intensity exercise for five days per week, or 20-60 minutes of vigorous-intensity exercise for three days per week.
- Continuous or multiple shorter sessions of at least 10 minutes are acceptable.
- Progressive time, frequency and intensity of exercise is recommended for best results and least injury risk.
- Less exercise than the above is still of benefit.
- Train each major muscle group two or three days each week using a variety of exercises and equipment.
- Light intensity is best for older adults or sedentary adults starting exercise.
- Two to four sets of each exercise for eight to 12 repetitions improve strength and power, 10 to 15 repetitions improve strength in middle-age and older persons starting exercise, and 15 to 20 repetitions improve muscular endurance.
- Include 48 hours between resistance training sessions.
- Flexibility exercises at least two or three days each week to improve range of motion.
- Each stretch should be held for 10 to 30 seconds, two to four times, accumulating 60 seconds per set. Older adults may benefit from up to 60 seconds per individual stretch.
- Flexibility exercise is most effective when muscles are warm. Warm the muscles before stretching with light aerobic movement, or alternatively heat pads or warm shower or bath if convenient..
- Neuromotor exercise is recommended for two or three days each week.
- Exercises should involve balance, agility, coordination and gait, including multifaceted activities like tai chi and yoga to improve physical function and prevent falls in older adults.
- Twenty to 30 minutes per day is appropriate for neuromotor exercise.
More is Not Always Better, and Less Is Not Always Worse
Although these guidelines and similar guidelines from other organizations and other countries describe a level of exercise that aims for a desirable level of fitness, two points emerge:
1. For sedentary people, any increase in physical activity is better than none. The recommendations are not meant to discourage exercise because the target seems unreachable, and illness, work, family and personal commitments can interrupt exercise planning. Fitness is not necessarily lost from week to week. Plan for the long term.
2. Although exercise in addition to that recommended may improve fitness even further, more is not necessarily better. Overtraining can lead to tiredness, injury and even more serious illness.
For weight training, if you follow a progressive model of training, which means slowly increasing the weight load or the volume in a session, it should be possible for fit and conditioned trainers to do well with only 24 hours between sessions, in some circumstances. The 48 hours between sessions as recommended above is probably ideal for most casual trainers, but it need not be a firm rule.
Quantity and Quality of Exercise for Developing and Maintaining Cardiorespiratory, Musculoskeletal, and Neuromotor Fitness in Apparently Healthy Adults: Guidance for Prescribing Exercise. Garber, Carol Ewing; Blissmer, Bryan; Deschenes, Michael R.; Franklin, Barry A.; Lamonte, Michael J.; Lee, I-Min; Nieman, David C.; Swain, David P. Medicine & Science in Sports & Exercise. 43(7):1334-1359, July 2011.