Every day millions of people in the United States participate in sports and athletic activities, and the Bay Area is certainly no exception. Exercise can strengthen the cardiovascular (heart and lungs) and musculoskeletal systems while helping to reduce body fat and improve flexibility, balance and coordination. However, sports activities can also result in injuries ranging from minor aches and bruises to more serious ones that typically involve soft tissues (muscles, tendons and ligaments), bones and joints.

This article will discuss steps you can take to prevent injuries resulting from exercise. Part I will address the importance and benefits of heart and lung and muscle conditioning. Part II, in the April issue of To Your Health!, will focus on exercise and sports-related injuries.

Section Index:

• Exercise and Conditioning
• Aerobic Conditioning
• Tips for Aerobic Conditioning
• Cross Training

Exercise and Conditioning

All sports and exercises, even walking, carry a risk of injury, and the anatomic areas most at risk depend on the specific activities involved. Acute injuries are usually caused by a sudden trauma, and commonly include contusions (bruises), sprains (a partial or complete tear of a ligament), strains (a partial or complete tear of a muscle or tendon) and fractures. However, many injuries are caused by overuse rather than by a single, sudden twist, fall, or collision. Cumulative stresses and repetitive microtrauma can also damage bones, joints and the surrounding soft tissues, resulting in pain and other symptoms.
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Aerobic Conditioning

Aerobic conditioning exercises involve activities that increase overall heart rate, thereby strengthening the cardiovascular system, as well as the muscles involved. The term aerobic refers to the method in which energy is generated - it literally means "with oxygen." Cells require oxygen in order to burn fat. Aerobic exercises such as jogging and cycling enable muscle cells to utilize fat as the main energy source.

Anaerobic exercises, on the other hand, involve the generation of energy in the absence of oxygen. Anaerobic activities such as sprinting and weight training require moving at a faster pace and with greater effort as compared to aerobic activities. As a result of the increased effort involved, oxygen cannot be delivered at a sufficient pace to muscle cells, and fat cannot be utilized as the major fuel source. Carbohydrates do not require oxygen as part of the energy-generating pathway. Thus, anaerobic exercises use carbo-hydrates for fuel. However, even though anaerobic exercises do not directly burn fat, they are still important in any conditioning program, since they increase the body's overall metabolic rate and help to indirectly burn fat.

Aerobic exercise strengthens the cardiovascular system by allowing it to function more efficiently. The lungs process more air with less effort, and the heart pumps more blood with fewer beats, which leads to increased blood and oxygen supply to the body's muscles and organs. Other benefits of aerobic exercise include increased overall stamina and energy, improved muscle tone and increased lean body mass, as well as psychological benefits including improvement of overall mood, reduction of anxiety and stress, and better sleeping patterns.

Most experts believe that in order to maximize the health benefits of cardiovascular activity, aerobic exercise should be performed 3-5 times per week for 30-60 minutes per session (excluding warm-up), during which a target heart rate of 60-85% of age-specific maximum heart rate is maintained.

To calculate your maximum heart rate, subtract your age from 220, and then determine your target heart range based upon this value.

For example, for a 30-year old individual, the maximum heart rate would be 190 beats per minute (220-30), and the target heart rate would be between 114-162 beats per minute (60% of 190 equals 114, and 85% of 190 equals 162).

Exercising below the 60% mark has little sustainable aerobic impact, although exercising at lower ranges for prolonged periods helps to burn fat and may be a reasonable place to start for beginners. Conversely, exercising above the 85% mark for prolonged periods may lead to increased strain and injury. Above this level, the heart is simply working too fast for any significant additional benefit, and the body cannot replenish oxygen quickly enough. Anaerobic pathways are used at these levels to generate energy, but cannot be maintained for long.


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Tips for Aerobic Conditioning

Prior to engaging in an aerobic exercise regimen, if you are over the age of 35 or have a personal or family history of heart disease, you may want to consult your medical doctor and undergo a physical examination. Once you are ready to begin your exercise program, it is important to first warm up adequately.

You can easily warm up by running in place, jumping rope or riding an exercise bicycle. Increase your heart rate by about 20 beats per minute, which will help prevent injury during your stretching and workout periods. After you have warmed up briefly for 3-5 minutes, some gentle stretching is also beneficial to help increase flexibility and reduce the risk of muscle soreness and injury. Slowly assume a stretch position for your targeted muscle group until resistance, not pain, is felt and then release gradually after holding the position for 30-60 seconds. Repeat this 3-5 times for each muscle group; once you have completed stretching all the muscle groups involved, you are ready to begin your aerobic workout.

Initially, aim for the lower part of your target heart zone and begin with an activity level equivalent to your current fitness level. A walking program may be a good place to begin if you have been inactive and are just starting out. As you get into better shape, you can gradually work out for longer periods of time and/or at a faster rate. Slowly build up to the higher part of your target heart zone but do not push too hard or too quickly. Exercise at a pace that is comfortable for you and you will find that with time, you will feel more comfortable exercising and can slowly increase your heart rate within your target zone. You should monitor your heart rate during your workout period.

Good places to take your pulse include your wrist and neck. Count your pulse for 15 seconds and multiply by 4 to determine your heart rate per minute. If you fall within your target heart rate range, continue exercising at your current pace. If you are below it, you may increase the intensity of your activity as tolerated. If you are above it, decrease the intensity of your workout. Remember, however, that your target heart rate is only a guide, so listen to your body for signs of injury or overexertion.

Once you have completed your workout, it is important to "cool down." Continue to move for several minutes at low intensity, such as with slow jogging or walking. This allows the oxygen-rich blood to be distributed from the working muscles to the brain and other organs of the body, rather than pooling in muscles that are no longer active. This prevents the dizziness, nausea and muscle cramps that can occur after a workout. Stretching should be repeated after the cool-down period while the muscles are warm in order to enhance muscle strength and flexibility.

During the workout period, it is important to maintain adequate hydration, and the best fluid to replace body losses is water. Electrolyte replacement drinks such as Gatorade and sports drinks are also fine. It is important to drink enough fluid before, during and after your workout. This is of even greater importance during hot weather workouts, as the body loses more water and dehydration can easily result. Caffeinated beverages such as coffee and soda should be avoided, as they will cause your body to lose even more fluid. Alcohol should also be avoided during aerobic activity, as it impairs performance, increases fluid loss and dehydration, decreases coordination and can mask warning signs of fatigue, all of which can lead to further injury.

In addition, you should wait at least 1-2 hours after a meal to exercise to avoid cramps, nausea, or vomiting. It is also appropriate to wait at least 30 minutes after exercising to eat a meal, as this will give your body enough time to recover from the workout. There are unfortunately no miracle foods that improve athletic performance. Choosing a variety of foods from the basic food groups is the best way to ensure a complete and well-balanced diet.


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Cross Training

As the popularity of triathlons and similar multisport events has increased, cross training has also become an increasingly popular training technique. Active individuals have come to realize that lower-impact activities such as cycling and swimming represent great ways to improve fitness in a more "joint-friendly" manner by decreasing the repetitive joint-impact forces that are associated with running. Cross training allows you to condition different muscle groups and to vary stresses placed on muscles and the cardiovascular system.

After months of the same movements the body becomes extremely efficient at performing these activities, thus limiting the extent of overall fitness and conditioning that is gained from training. Rather than continuing to improve, the body maintains a certain level of fitness. Cross training involves multiple activities employing different muscles groups. It transfers the training effects gained with one mode of exercise to another, thereby enabling the body to maintain a high level of overall fitness.

The entire body is conditioned rather than merely specific muscles, and the stresses that are placed on each muscle group are decreased as different activities use various muscles in slightly different ways. In addition, cross training allows certain muscle groups to be conditioned while other groups rest as activities are alternated. As a result, cross training is helpful in reducing the risk of injury from repetitive strain or overuse. Cross training has the additional benefit of reducing the boredom that some people experience with repetition of the same activity.

Cross training entails performing exercises from multiple categories: cardiovascular and aerobic (e.g., running, swimming, cycling, rowing), strength training (e.g., weight-training, calisthenics, martial arts), flexibility training (e.g., yoga, Pilates), sports-specific speed and agility drills, and multiple other forms of conditioning (e.g., circuit training, plyometrics). With cross training, one form of exercise can be performed every day, or more than one may be performed in a single day. If multiple activities are performed daily, the order in which they are performed may be changed to alternate the training regimen.

Cross training can be tailored to each individual's needs and interests, and different sports and activities can be changed on a regular basis. However, the same general guidelines for conditioning apply, as overtraining and overexertion can just as easily occur with cross training and should be avoided in order to prevent injury.


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