People should consult their doctor before beginning competitive sports or an exercise program. Doctors ask about known medical disorders in the person and family members and about symptoms the person may have. They then do a physical examination, including listening to the heart with a stethoscope. This evaluation aims to identify previously unsuspected heart disorders that can lead to serious heart rhythm abnormalities or sudden, unexpected death triggered by strenuous exercise. It also detects conditions that could restrict activities. For example, overweight people are more likely to develop musculoskeletal injuries after activities involving sudden starts and stops (jerking motions of the joints typical of activities like tennis and basketball) as well as those that involve impact (such as jogging). Doctors may recommend safe introductory programs and discuss specific limitations to ensure safety and limit injuries.
People older than age 40 who are starting an exercise program should report any diagnoses of heart disorders or arthritis and describe any symptoms of chest pain, shortness of breath, leg pain during walking, palpitations (awareness of heartbeat) or irregular heartbeats, joint pain or swelling, and inability to exercise for long periods. They should also mention any immediate family members who were younger than 50 when they died suddenly due to a heart problem. Most people do not need an exercise stress test, and many do not need an electrocardiogram (ECG) before they begin exercise if they plan to increase exercise intensity gradually.
Certain drugs may decrease the ability to exercise, such as beta-blockers, which slow heart rate, and sedatives, which can cause drowsiness or reduce mental alertness and muscle control, thereby increasing the risk of falling or injury. Other drugs may affect the body's ability to exercise safely and influence whether exercise is recommended. So, people should review with their doctors any prescription drugs, supplements, or over-the-counter drugs they are taking to review any potential safety concerns.
Generally, exercise in healthy children is safe. Any child who exhibits more fatigue than normal, shortness of breath, light-headedness, or other problems while exercising should see a doctor because these symptoms may indicate an underlying medical problem. Otherwise, exercise in healthy children should be encouraged except for during times of illness. As an example, fever impairs the ability to exercise, may be a sign of serious illness, and may lead to heat-related illness such as heatstroke. Conditions that lead to dehydration (for example, vomiting and diarrhea) also pose an exercise risk because sweating during exercise can worsen dehydration. Children with heart problems (such as heart failure, myocarditis, and other conditions) may be at increased risk of sudden death during exercise and should follow the advice of their doctors before exercising.
Most adults, even those with acute or chronic medical disorders, can benefit from some form of exercise. Recommendations or restrictions are based on the person's specific circumstances. Some general examples include
People who have had several concussions or a recent concussion should avoid contact sports.
People with seizures should avoid swimming and weight lifting while alone to prevent injuring themselves and should avoid riflery and archery to prevent injuring others.
People with an enlarged spleen (for example, after infectious mononucleosis) should avoid contact sports because an injury may rupture the enlarged spleen.
Doctors can provide specific instructions on the type of activity as well as the level of intensity (how hard the exercise should be), the duration of activity (how long the exercise should last), and the frequency (how often the exercise should be done). In some cases, exercise should be supervised by a physical therapist or other health care practitioner or by an experienced, licensed fitness professional.
The safest way to start an exercise program is to do the chosen exercise or sport at a low intensity of effort. Beginning at a low intensity allows time to learn proper technique (body mechanics), which helps to prevent injuries when training at a higher intensity. Beginning at a low intensity also prevents excessive muscle strain. The exercise should be done until the legs or arms ache or feel heavy. If muscles ache after just a few minutes, the first workout should last only that long. As fitness increases, a person should be able to exercise longer without feeling muscle pain. Some discomfort, particularly after weight training, is part of the process of developing stronger, larger muscles. However, the discomfort of intense exercise differs from the pain associated with an injury or overexertion (see Exercising Safely). Over time, a person can increase exercise demands as needed or required to achieve fitness goals.
Most schools and organized sports associations require that people have a doctor evaluate whether they can safely participate before they join the program. Doctors ask questions about general health and do an examination as previously described. Occasionally, additional testing may be needed after this evaluation. Adolescents and young adults are often asked about use of illicit and performance-enhancing drugs. (See also the US Anti-Doping Agency web site.)
In girls and women, doctors look for delays in the onset of menstruation and presence of the female athlete triad (eating disorders, amenorrhea or other menstrual dysfunction, and diminished bone mineral density), which is common among adolescent and young women who engage in overly intensive physical activity, and overly zealous loss of body fat.
A major distinction among different types of exercise is whether they are aerobic (activity that focuses most on heart rate and breathing capacity) or strength training (activity that focuses on muscle tension and lifting, also sometimes called resistance training). All forms of exercise have components of both. Exercise programs provide greater benefits when they encompass multiple dimensions of fitness, including
This term refers to exercise that requires more than the usual amount of oxygen to reach the muscles, thus the heart and lungs are forced to work harder. Running, biking, swimming, skating, and using aerobic exercise machines (such as treadmill, stair-climbing, and elliptical training machines) are activities that people do to experience aerobic exercise. Aerobic exercise tends to expend many calories, improves heart function, and decreases slightly the risk of death due to heart disease. However, it is less effective than strength training at building strength and muscle mass. Too much weight-bearing aerobic exercise (such as running or using a treadmill machine) causes excessive wear on the joints and surrounding tissues, thus contributing to the development of osteoarthritis.
For aerobic exercise to benefit the heart, exercise intensity should be increased until the heart rate is within about 60 to 85% of the maximum rate the body can sustain. This maximum rate can be estimated using a formula. But people should temporarily stop increasing the intensity of exercise if they have trouble breathing or maintaining controlled rhythmic breathing.
The target heart rate is only an estimate. Overweight or deconditioned people reach their target heart rate more quickly and with less effort. Athletic people reach their target heart rate more slowly. Conditioned athletes may exceed the target heart rate, because such targets are based on people of average fitness. People taking drugs that slow heart rate (such as beta-blockers or calcium channel blockers) may not reach their target heart rate despite intense exercise. These people should discuss with their doctor what target heart rate is desirable.
A typical recommendation is to do 30 minutes of aerobic exercise at sufficient intensity about 2 to 3 times per week, with 5-minute warm-up (gradual increase to peak intensity) and 5-minute cool-down (gradual decrease in intensity) periods. However, the 30-minute length of time is arbitrary. Certain people can safely achieve maximum aerobic conditioning by doing as little as 10 to 15 minutes of activity per session 2 to 3 times per week if interval cycling is used.
In interval cycling, moderate aerobic exercise is alternated with intense exertion. For example, about 90 seconds of moderate activity (60 to 80% of maximum heart rate) is alternated with 20 to 30 seconds of all-out effort, such as sprinting (85 to 95% of maximum heart rate or as hard as the person can exercise while maintaining correct exercise form). Proper technique should be maintained to avoid injury. Sometimes aerobic exercise can be done while strength training (for example, if little time is taken to rest between doing strength training exercises).
Different aerobic exercises work different muscle groups. For example, running works primarily the lower leg muscles. Landing on the heels and rising on the toes exerts the greatest force on the ankle. Riding a bicycle works primarily the upper leg muscles because pedaling works the front thigh muscles (quadriceps) and hips. Rowing and swimming work the upper body and the back predominantly. These exercises can be alternated each workout to avoid injury and work different muscle groups.
Strength training (also called resistance training) involves forceful muscular contraction against resistance, usually using free or machine weights or sometimes body weight (such as when a person does push-ups or abdominal crunches). Some people may use elastic bands rather than weights when they begin a strength training program.
Depending on how it is done, strength training may be somewhat less beneficial for cardiovascular fitness than aerobic exercise. However, sustained, high-intensity strength training can be as beneficial for cardiovascular fitness as aerobic exercise. The main goals of strength training are to develop the following in muscle:
In the long run, increased muscle mass helps a person become leaner and lose body fat because muscle uses more calories, even at rest, than do other types of tissues, particularly fat. More muscle mass also means more functional ability into later years, which helps people remain independent as they age. In older adults, particularly the frail elderly such as those living in nursing homes, increased muscle mass improves recovery from critical illness by providing the body with protein stores that are needed for recovery (see also Exercise in the Elderly). Older adults, particularly the frail, also benefit because the increase in muscle mass improves mobility, thus speeding recovery.
Strengthening muscles around an injury (for example, thigh muscles with an injured knee) decreases pain. Thus, a strength training program may help in injury rehabilitation. This approach should be supervised by a rehabilitation physical therapist.
Individual exercises are designed to strengthen particular muscles or muscle groups. Usually, larger muscle groups are exercised first, then smaller ones. Usually a person starts with the legs, then exercises the upper back, chest, shoulders, and then the arms. Maximum benefit is obtained by exercising at a high workload, but not necessarily to failure. Failure is defined as the point at which it is impossible to do another repetition while using the correct technique.
Traditionally, particular exercises are done in sets. Each set includes 8 to 12 repetitions of the exercise, done continuously (that is, no rest, or joint “locking,” between repetitions). The amount of weight used is the maximum that allows the person to do 8 to 12 repetitions in a relatively slow and controlled manner, without heaving, throwing, or dropping the weight. If the first set is done with high, steady tension, each subsequent set provides progressively less value. Three is the maximum recommended number of sets.
Tension time is another way to determine recommended muscle workload (the amount of weight lifted and the amount of work the muscle does). Tension time refers to the total duration of lifting and lowering the weight in one set. Tension time should be briefer if the goal is moderate exercise and building strength than if the goal is more muscular endurance than strength (for example, during rehabilitation from injury). Tension time—rather than number of repetitions—is a better gauge of recommended muscle workload, whether exercising for strength, increases in muscle mass, or endurance.
To continue to increase strength and muscle mass, once the recommended tension time is achieved with good technique, weight should be increased to the maximum at which the person can maintain or be challenged again with the same tension time. Recommended tension time is ideally 40 to 60 seconds for the upper body and, because the lower body has greater endurance, about 60 to 90 seconds for the lower body. If the goal is muscular endurance, tension time is usually about 90 to 120 seconds. Strength athletes, such as power lifters, respond better and favor briefer tension times of 10 to 30 seconds because the concurrently heavier loads stimulate superior strength increases, although with less muscle growth and increases in endurance. However, the average person should avoid such heavy training because heavier loads also increase tissue strain and thus the risk of injury.
Frequency of exercise is a critical factor. Muscles start to break down when exercised heavily more often than every other day. The day after an adequate workout, bleeding and microscopic tears are present in muscle fibers, which is probably why muscles feel sore. This soreness (also called an alarm reaction) stimulates muscles to repair themselves and grow to adapt to a higher state of function. Exercisers should allow about 48 hours for muscles to recover after exercise. After very vigorous exercise, a muscle group may take several days to heal completely and thus become stronger. Hence, in strength training, it is usually best to alternate the muscle groups being exercised. An ideal schedule, for example, alternates exercise for the upper body on one day with exercise for the lower body on the next, with each muscle trained no more than twice per week. The more intense and the more exercise done for a muscle, the less often it should be worked. People who train with a very high level of intensity of effort likely should not train each muscle any more than once a week.
Injury rehabilitation may not aim for development of large muscles initially, although better muscle function and strength strongly correlate with reduced pain. Exercising with less weight but increased number of repetitions can increase strength and endurance, provide some aerobic exercise, and increase blood flow to the area, which accelerates healing. This approach may be tolerated better than exercising muscles with too much weight and fewer repetitions, which requires a high degree of motivation. Exercise form must be strictly maintained because incorrect form risks aggravating the injury. People who are undergoing rehabilitation may limit exercise because of discomfort or pain. Occasionally these people also may be inexperienced with exercise and may not know how much effort they are capable of. Once the injured person's confidence and function increase (and often pain decreases), intensity of effort and workloads should increase in order to optimize results.
In circuit weight training, the large muscles of the legs, hips, back, and chest are exercised followed by the smaller muscles of the shoulders, arms, abdomen, and neck. Some people prefer to train legs last because they require so much energy and are so fatiguing to work. Circuit weight training of only 15 to 20 minutes potentially can benefit the cardiovascular system more than jogging or using aerobic exercise machines for the same time. The workout is often more intense, and heart rate can increase even more as a result.
Safe technique is of paramount importance. Jerking or dropping weights can cause injury due to sudden starts and stops. Controlled breathing prevents light-headedness and fainting, which can occur when forcefully exhaling or bearing down. Specifically, people should exhale while lifting a weight and inhale while lowering a weight. If a movement is slow, such as lowering a weight for 5 seconds or longer, people may need to breathe in and out more than once, but breathing still should be coordinated so that a final breath is taken just before the lifting phase and released during lifting.
Blood pressure increases during resistance training, particularly when the large muscles of the lower body are worked and when gripping very hard with the hands (as when doing the leg press exercise while gripping the machine's handles). However, blood pressure returns to normal quickly after exercise. This temporary increase in blood pressure is minimal when the breathing technique is correct, no matter how hard a person may exert. Most people who intend to lift weights benefit from initial supervision that includes instruction on how to set the weights and seat levels, how to maintain proper technique, and how to breathe during exercises. Having a professional trainer observe as the person exercises is usually most helpful, so that improper techniques can be identified and corrected.
Stretching reduces stiffness of muscles and tendons and thereby improves flexibility. Flexibility is important for comfortable performance of everyday physical activities. Although stretching itself does not strengthen muscles, it can increase the area over which the muscle contracts, which allows muscle force to be exerted more effectively and with less risk of injury. Stretching may help people jump higher, lift heavier weights, run faster, and throw farther.
Specific flexibility exercises involve slowly and steadily stretching groups of muscles without jerking, bouncing, or causing excess pain (minor discomfort is normal when stretching current limits of a joint, but pain should never be severe or intolerable). To achieve maximal flexibility, a stretch should be held for 20 to 60 seconds. A stretch can be held longer than 60 seconds, but doing so has not been proven to further increase flexibility. Stretches are usually repeated 2 to 3 times, each time stretching further than before if possible. These exercises can be done before or after other forms of training or as a program in itself, as occurs in yoga and Pilates sessions.
Although stretching before exercise enhances mental preparedness, there is no conclusive evidence that stretching decreases risk of injury. General warming-up (for example, with low-intensity simulation of the exercise to be done, jogging on the spot, calisthenics, or other light activities that increase core temperature) appears to be more effective than stretching for facilitating safe exercise. Stretching after exercise is preferred because tissues stretch more effectively when warmed. Stretching also can be done between exercises, but stretching between exercises can decrease strength during exercise, thus resulting in the need to decrease the weight or number of repetitions during strength training.
Balance training aims to challenge the center of gravity by exercising in unstable environments, such as standing on one leg or using balance boards. Basic strength training improves balance because it increases muscle size and strength around the joints, improving balance indirectly because the joints are more stable.
In general, if the intensity of an exercise increases, duration, frequency, or both may need to decrease. Similarly, if frequency or duration increases, intensity may need to decrease. For most people who participate in weight training, the amount of weight lifted should continue to increase as they get stronger, whereas duration and frequency typically remain constant once a certain level is reached.
Exercise that involves too low a workload provides fewer rewards, although exercising harder (more exercise intensity) with a lighter load can be as beneficial as exercising with less intensity and a heavier load. Exercise that involves too high a workload increases risk of improper technique and thus injury. Additionally, people should vary the way they train their muscles over time. The body adapts to routine, so that doing the same exercises in the same way over time becomes less effective in building strength, muscle, and cardiovascular fitness. Therefore, people who engage in resistance exercises should alter their routines every few weeks, and aerobic exercisers should alternate among the different forms of aerobic exercise available.
People who exercise at very high intensity levels should consider incorporating breaks from training into their fitness planning to allow for sufficient recovery. One example would be 1 week off every 3 months, perhaps coordinated with holidays or vacations. Signs that suggest a prolonged rest period is needed include
Such a prolonged period of rest should be at least 1 to 2 weeks (possibly longer). People should not return to exercise until all of the symptoms have resolved. People should consult their physician if symptoms are not improving, are prolonged, or are severe, to ensure there is no medical disorder causing their symptoms.