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People should consult their doctors before beginning competitive sports or an exercise program. Doctors ask about known medical disorders in the person and family members and symptoms the person has. They do a physical examination, including listening to the heart with a stethoscope. This evaluation identifies some of the rare young people who could have a previously unsuspected heart disorder that can lead to serious heart rhythm abnormalities or sudden, unexpected death with 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 (such as tennis and basketball) as well as those that involve impact (such as jogging).
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 pains with walking, palpitations (awareness of heartbeat) or irregular heartbeats, joint pain or swelling, and inability to exercise for long periods (for example, because of weakness, shortness of breath, sweating, or leg pains). Certain drugs may limit the ability to exercise, such as beta-blockers, which slow heart rate, and sedatives, which can cause drowsiness and increase the risk of falling.
Conditions that make exercise too risky to recommend in children include heart inflammation (myocarditis), which is uncommon. It increases the risk of sudden death due to heart dysfunction. Fever is another, because it impairs 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) are also risky, because sweating during exercise can worsen dehydration.
Conditions that make exercise too risky to recommend and that occur mainly in adults include angina pectoris and a heart attack in the previous 6 weeks.
People should take precautions when they have certain other conditions. For example:
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 body mechanics, which helps to prevent future 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. However, some discomfort is necessary for developing stronger, larger muscles. Over time, a person can increase exercise demands as needed or required to achieve fitness goals.
Screening
for Sports Participation:
Most schools and organized sports organizations 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. 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 menarche and presence of the female athlete triad (eating disorders, amenorrhea or other menstrual dysfunction, and diminished bone mineral density), which is becoming more common as more adolescent and young women engage in overly intensive physical activity and overly zealous loss of body fat.
Type
of Exercise
A major distinction among different types of exercise is whether they are aerobic (low intensity, steady state) or strength training (also sometimes called anaerobic exercise). Most forms of exercise have components of both.
Aerobic Exercise:
This term refers to exercise that requires more than the usual amount of oxygen to get to 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 a great deal of calories, improves cardiac function, and decreases slightly the risk of death from cardiac causes. However, it is less effective than strength training at building strength and muscle mass. Too much weight-bearing aerobic exercise causes excessive wear on the joints and surrounding tissues, so trying to improve muscle strength through frequent, repetitive bouts of aerobic activity must be done cautiously if at all.
For aerobic exercise to benefit the heart, oxygen use should be increased to a rate that is within about 15 to 40% of the maximum rate the body can sustain. This maximum rate can be estimated in several ways:
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. It is also probably safer for athletes to exceed the target heart rate, since such targets take into consideration the conditioning of average people. 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. They should discuss with their doctors what target heart rate is desirable.
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| Usual Maximum and Target Heart Rates |
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Age
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Maximum Heart Rate
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Target Heart Rate
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20
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200
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120 to 170
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30
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190
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114 to 162
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40
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180
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108 to 153
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50
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170
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102 to 145
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60
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160
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96 to 136
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70
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150
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90 to 128
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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. Maximum aerobic conditioning can be achieved 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 sprinting (85 to 95% of maximum heart rate or as hard as the person can exercise while maintaining correct exercise form. Sprinting, however, can strain joints and thus should be done for only limited times and perhaps be avoided completely if joint pain occurs or if the person has certain joint disorders. Proper body mechanics 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 daily to avoid injury.
Strength
Training:
Strength training (also called resistance training or anaerobic exercise) involves forceful muscular contraction against resistance, usually using free or machine weights. Depending on how it is done, strength training may be somewhat less beneficial for cardiovascular fitness than aerobic exercise. However, it develops muscle strength, size, endurance, and flexibility and still benefits the heart and lungs. In the long run, increased muscle mass helps a person become leaner and lose weight, 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.
Individual exercises are designed to strengthen particular muscles or muscle groups. Usually, larger muscle groups are exercised first, then smaller ones. Maximum benefit is obtained by exercising at a high workload, but not necessarily to failure (that is, the point at which another repetition in good form is impossible). Traditionally, particular exercises are done in sets. Each set includes 8 to 12 repetitions of the exercise, done continuously (that is, no rest, including joint “locking,” between repetitions). The amount of weight used is the maximum that the person can use and still do 8 to 12 repetitions in a relatively slow and controlled manner, without heaving, throwing, or dropping the weight. Doing one set with steady tension results in about 75 to 85% of the benefit of doing 3 sets, the maximum recommended.
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 is a better way to gauge recommended muscle workload for increasing strength than are sets and repetitions. To continue to increase strength, after 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, since the concurrently heavier loads stimulate superior strength increases, although with less muscle growth and endurance responses.
Frequency of exercise is a critical factor. Muscles start to break down when exercised at sufficient workloads more often than every other day. The day after an adequate workout, bleeding and microscopic tearing occur 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, thus allowing the muscles to heal and to 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. Exercising with less weight but increased numbers 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 more intensely, which requires a high degree of motivation. Once confidence and function increase in the injured person, intensity of effort and work loads should increase in order to optimize results.
In circuit 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 since they require so much energy and are so fatiguing to work. Circuit training of only 15 to 20 minutes 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 important. Jerking or dropping weights can cause minor injury due to sudden starts and stops. Controlled breathing prevents dizziness (and, in extreme cases, fainting), which can occur when forcefully exhaling or bearing down. Specifically, people should exhale while lifting a weight and inhale when 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 should still be coordinated so that a final breath is taken in just before the lifting phase and released during lifting. Blood pressure increases during resistance training, particularly when working the large muscles of the lower body and while gripping very hard with the hands, as can be experienced when doing the leg press exercise. However, blood pressure returns to normal quickly after exercise. And the increase in blood pressure is smaller when breathing technique is correct, no matter how hard a person exerts. 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 body mechanics, and how to breathe during exercises. Having a professional trainer observe the person as the exercise is being done is usually most helpful, so that improper mechanics can be identified and corrected.
Stretching
and Flexibility:
Stretching reduces stiffness of muscles and tendons and thereby improves flexibility. Flexibility is important for comfortable performance of 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 intolerable). These exercises can be done before or after other forms of training or as a program itself, as occurs in yoga and Pilates sessions. Although stretching before exercise enhances mental preparedness, there is no evidence that stretching decreases risk of injury. General warming-up (for example, with low-intensity simulation of the exercise to be performed, 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.
Workload and
Variation
In general, if the intensity of an exercise increases, duration, frequency, or both may need to decrease and vice versa. 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. Exercise that involves too high a workload increases risk of improper mechanics 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.
Last full review/revision September 2007 by Brian D. Johnston
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