What is the best machine in the gym for developing cardiorespiratory fitness?
What is interval training, and how do I incorporate it into my endurance exercise program?
What's the difference between weight-bearing activity and non-weight-bearing activity? What are the pros and cons of each?
How can I avoid being so sore when I start an exercise program?
What causes muscle cramps and what can I do about them?
How can I develop upper-body endurance?
What is the best training strategy to boost endurance performance?
I'm thinking about getting into an "extreme" sport like marathon running or long-distance biking. Are such sports bad for your heart?

What is the best machine in the gym for developing cardiorespiratory fitness?

Every cardio exercise machine in the gym will build fitness, but not every machine is right for every person. Treadmill running burns plenty of calories but may be unacceptable if you have knee problems. Stationary bikes, elliptical trainers, and stair-climbers are easier on the joints but some people find them boring, and they may require too much muscle power to be effective for some. Rowing machines may trigger back pain and take many weeks to develop effective technique. The ideal cardio machine burns plenty of calories, is easy on the joints, loads the skeleton to build strong bones, builds muscle strength and power, and is fun. No machine scores perfect marks on all factors. The cardio machine report card below rates the most popular cardio machines and will help you choose the best ones for your exercise program. Keep in mind, however, that your personal choice will depend on your own preferences and current level of fitness. The best machine is the one you will use. Choose the machines you like and fulfill your needs, and then exercise on them regularly.

          A few comments about the top-rated machines:

* The overall ratings winner is treadmill running. It builds cardiovascular fitness and burns calories faster than any other form of exercise you can do on cardio equipment. Modern treadmills have knee- friendly surfaces and sophisticated program that allow varied and interesting training routines, but they provide enough shock to build or maintain strong bones.

* The elliptical trainer finishes a close second. While it is less effective than the treadmill for bone development, its easy action makes it an exerciser's joy, and its variable workload can accommodate everyone from a rank beginner to a world-class athlete. The elliptical trainer is particularly good for people with kneecap pain. The motion places minimal stress on the knee, while promoting joint lubrication.

* The rowing machine is best for people who want an upper and lower body workout at the same time. Modern rowing machines take more skill than other cardio machines. Also, poor technique may increase the risk of back pain.

Cardio Machine Report Card
(Assumes typical program for moderately trained people)

Interval training refers to bouts of higher intensity exercise interspersed with periods of lower intensity exercise or rest. You can use interval training for all of your favorite aerobic exercises, including ground or treadmill running, stair climbers, elliptical trainers, tennis, swimming, or cycling. Adding interval training to your program help you reach your fitness goals more quickly.

          Interval training also builds muscle power that will carry over to your fitness and body-shaping program. The strong, shapely muscles you build doing intervals will make it easier to play sports such as skiing and tennis, help you do exercises such as lunges and squats, and give you greater stamina that will help you better cope with your busy schedule. Intervals will also develop sleek, healthy-looking lower body muscles faster and better than almost any other exercise.

          Intervals can be a real time-saver. You know you need to run, work on the elliptical trainer, or ride a bike to cut fat, but perhaps you just can't face the boredom of slogging along on the roads or facing a blank wall for a half-hour—or, you just don't have the time. Interval training not only makes you run faster but also enhances cell enzymes that improve fuel use at rest and during exercise. Previously, scientists thought you needed to run for 45 minutes or more per workout to get these cellular effects. If you train intensely in short bouts, you can get more benefits in less time. An added benefit is that interval training turns up your metabolic furnace so that you continue to burn more calories than normal all day long.

          Interval training involves performing repeated exercises at set distances or times. This type of training helps the body move at faster speeds by training the nervous system to react more quickly, increasing the heart's ability to pump blood, and urging the cells to cope with rapid metabolism.

          You can use interval training techniques for almost any type of exercise and even sports skills. For example, a middle distance runner might do repeated bouts of 400-meter runs at 90-100% of maximum effort. A tennis player might practice volleys against the wall for 30 seconds followed by 30 seconds of rest. A swimmer might swim 100 meters at 90% effort for 15 repetitions with 3 minutes rest in between. People interested in body shaping and improving fitness can choose an interval training activity they enjoy. The sport or exercise you select is unimportant as long as you burn calories rapidly.

          The four components of interval training are distance, repetitions, intensity, and rest. Distance refers to either the distance or time of the exercise interval. Repetition is the number of times the exercise is repeated. Intensity is the speed of the exercise. Rest is the time between exercises.

          Each factor of interval training is related to the others. When you train more intensely, you will do fewer repetitions and rest longer. For example, a runner performing 400-meter runs at 100% of maximum running speed might only manage 4-6 repetitions. A person working at only 75% of maximum intensity might manage 8-15 repetitions.

          Don't practice interval training more than 3 days per week. Intervals are exhausting and easily lead to injury. Let your body tell you how many days you can tolerate. If you are overtired doing 3 days per week, cut back to 1-2 days. Also, if you feel good, try increasing the intensity or volume and see what happens. Begin slowly and progress conservatively. Integrate interval training into your total exercise program. You shouldn't be so tired from doing intervals that you can't function during the day or do other parts of your exercise and shaping program.

          Here are some specific examples of interval training during endurance activities.

          Interval Training for Running

          Intervals range in distance from 15-50 meters for a volleyball or tennis player to several miles for a marathon runner. People interested in building muscle power and cutting fat should do intervals ranging from 100-400 meters (run 400 meters, rest, run another 400 meters, etc.). Do running and walking intervals on a track, field, or treadmill.

          A good beginning interval training program on a standard 400-meter track is to run the straightaways at approximately 80% of maximum speed and walk the turns. Start off by doing two laps (800 meters) running the straightaways and walking the turns. Build up gradually until you can do 8 laps (16 straightaways). As fitness improves, sprint the straightaways at full speed. Later, sprint the straightaways and jog the turns.

          Graduate to 200- (1/2-lap) and 400 (1-lap) meter intervals as fitness improves. Begin by running two 200-meter intervals and progress until you can do 8-10 repetitions. Walk across the infield to the starting position after each 200-meter interval. Finally, progress to 400-meter intervals. These can be extremely exhausting, particularly when run at high intensities. Again, start off running 1-2 400-meter intervals. Build up until you can do 6-8 of them. Try to run each of the intervals in approximately the same time.

          Intervals for Treadmill Walking and Running

          Interval training on the treadmill involves alternating between fast and slow running and walking. You can also vary the exercise intensity by raising and lowering the treadmill grade. Use the built-in programmer (if available) because it will automatically change the speed and elevation of the treadmill during the workout.

          For treadmill walking, begin by exercising at a brisk pace that you can manage easily. For example, set the treadmill speed at 3 mph and the elevation at a 0% grade and walk for 2 minutes. Then, raise the elevation to 10% and walk for 1 minute. Return to a 0% grade and walk for another minute. Alternate each minute between walking up 0% and 10% grades for a total of 10 minutes. As you become more fit, extend the total time of your interval training workout or increase the speed or elevation of the treadmill.

          Running intervals follow the same principles as walking intervals: run at a fast pace for 30-60 seconds, then walk or rest for 30-60 seconds. For example, set the treadmill speed for 7 mph and 0% elevation. Run for 30 seconds, and then straddle the treadmill for 30 seconds of rest. Repeat this exercise-rest interval cycle for 5-10 repetitions. As you become more fit, increase the number of reps, treadmill speed, or repetitions, or shorten the rest interval. There are endless combinations of intensity, repetitions, or rest. Use your imagination and have fun with it.

          Interval Training for Elliptical Trainers

          Elliptical trainers are great for interval training because you can train intensely without beating up your knees, hips, and back. Interval training on this machine varies the striding speed, resistance, and ramp setting. A basic program is to alternate between fast and slow striding rates. For example, set the ramp and resistance at low levels (1-5) and "run" for 2 minutes at 70 strides per minute (spm). Alternate between 1 minute at 110 spm and 1 minute at 70 spm. Begin with 5 intervals and increase the number of intervals as you become more fit. As with the treadmill, you can increase the intensity of your elliptical trainer interval workout by varying spm, resistance, and ramp settings. Remember, the basic principle of interval training is to push harder than you do during normal aerobic workouts.

          Intervals for Stairclimbing Machines

          Stairclimbers provide plenty of ways to cheat so it's easy to get almost no exercise. If you hang onto the rails so hard that your hands turn white, you're robbing yourself of the calorie-burning potential of the machine. Don't take small baby steps; instead, take large steps working through a full range of motion. Studies show that you'll burn far more calories and better work your gluts and quads. Don't hunch over the bar when you climb. Not only do you burn fewer calories than when you stand upright, but you also risk back injury.

          Interval routines for the stairclimber are similar to those of the elliptical trainer—you vary the resistance and stepping rate. An example of a beginning routine is to set the resistance at a low level and work at a step rate of 50-60 steps per minute (spm) for 2 minutes. Alternate between one minute at 80-90 spm and 1 minute at 50-60 spm. Begin with 5 intervals and increase the number of intervals as you become more fit.

          Interval Training for Other Activities

          You can practice interval training in almost any sport or type of exercise. For example, in tennis, you could hit against a wall or tennis ball machine for 2 minutes, rest one minute, then repeat. On the stationary or supine bike, exercise for 1 minute at a high power output, rest 1 minute, then repeat. In basketball, you could run four court lengths, shooting a lay-up at each end, rest, then repeat. You are limited only by your imagination when setting up interval training programs. The bottom line is that interval training is a terrific fat burner and fitness builder that will help you make rapid progress.

Sample Interval Programs

Do one of these workouts 2-3 times a week aside from your normal training program. These are only examples. Design your own program if you want to work harder or need variety.

          Running

          Beginning: On a 440-yard running track, sprint the straightaways and walk the turns. Start with 1 lap and progress to 4-8 laps.
          When you're in shape (pick one workout):

          1) Run 4-8 sets of 200 meters (1/2 lap) at 90-100% of your top sprint speed for that distance. Rest 5 minutes between sets.
          2) Run 4-8 sets of 400 meters (1 lap around standard track). Rest 5 minutes between sets.

          Treadmill

          Beginning: Set speed at 6 mph and the elevation at 0%. Run for 1 minute, then rest for 1 minute. Repeat 4-8 times.
          When you're in shape: Set speed at 10-12 mph. Do 8-12 1-minute intervals with 1-2 minutes of rest between each.

          Swimming

          Beginning : Swim 4-8 sets of 25 meters (1 length of standard health club pool) at 90% pace. Rest 1-4 minutes between swims.
          When you're in shape: Swim 10 sets of 100 meters (4 lengths of a standard pool or 2 lengths of an Olympic pool) at 90-100% pace. Rest 1-6 minutes between sets.

          Cycling

          Beginning : Mark a 1-mile course in a park or on a road. Ride 4 sets of 1 mile at 90% pace.
          When you're in shape: Mark a 2-3-mile course, and ride 4-10 sets of the course at 90-100% pace (for that distance).

          Stationary Bike

          Beginning: Ride at a pedal speed of 90-150 rpm. Set resistance so that you can ride for 30 seconds at a fast rpm. Do 5-10 sets of 30-60 seconds. Rest for 1-5 minutes between sets.
          When you're in shape: Pedal as fast as you can for 1 minute. Set friction as high as you can while pedaling at a speed of at least 120 rpm. Repeat 10-20 times.

What's the difference between weight-bearing activity and non-weight-bearing activity? What are the pros and cons of each?

Bones and muscles work against the force of gravity during weight-bearing exercise. They include exercises in which your body weight is supported by your legs and feet. Weight-bearing exercises include walking, jogging, aerobics, dancing, stair climbing, skating, and resistance exercises done from a standing position. Weight-bearing exercises are best for building bone, balance, coordination, and posture.

          Part or all of the body's weight is supported during non-weight bearing exercises. Examples include swimming, water aerobics, and cycling. Non-weight-bearing exercises minimize the risk of injury in people with joint injuries, people who are obese, and women who are pregnant. While non-weight-bearing exercises contribute to fitness in most people, they should not be your primary form of exercise if you are capable of doing weight-bearing exercises. Serious swimmers and cyclists often have lower bone densities than sedentary people. If you enjoy non-weight bearing activities, also include weight-bearing activities in your exercise program to build bone mass.

How can I avoid being so sore when I start an exercise program?

Post-exercise muscle soreness is caused by muscle injury followed by muscle inflammation. Muscles get stronger and larger in response to muscle tension and injury. However, excessive injury can delay progress. The best approach is to begin conservatively with low volume, low intensity workouts, and gradually increase the severity of the exercise sessions.

          Have you been sedentary for a long time? Leading health organizations recommend at least 60 minutes of exercise per day for people who want to lose weight. Begin with 5 to 10 minutes of exercise and gradually increase the distance and speed you walk, run, ride a bike, or swim.

What causes muscle cramps and what can I do about them?

Muscle cramps are caused by local muscle fatigue that triggers the nervous system to overstimulate the muscles. Until recently, muscle cramps were thought to be caused by dehydration or salt depletion in the muscles, but scientists have found little evidence for this. Muscle cramps can occur during or after exercise performed either in heat or in cold. You can prevent cramps by improving your fitness and making sure you consume enough fluid and electrolytes during exercise and in your diet (low intake of fluid and electrolytes contributes to fatigue). When cramps occur, gently stretch the cramping muscle for 15-30 seconds. Do not overstretch the cramping muscle because this can lead to serious injury.

How can I develop upper-body endurance?

Endurance capacity involves a lot more than increasing the capacity of the heart to pump blood and deliver oxygen to the tissues. Active muscles also adapt by increasing mitochondria (cell energy centers), increasing fuels and enzymes that improve metabolism and clear wastes, and building power output. People usually build endurance and aerobic capacity by doing large muscle lower body exercises, such as jogging, walking, cycling, treadmill exercise, or elliptical training. While lower body exercise is great for building oxygen transport capacity and lower body muscle adaptation, it does little to develop endurance fitness in upper body muscles. Most people who are active on the job need upper body fitness, yet few people do any endurance exercise with their arms. Many gyms and fitness centers have upper body ergometers, which work similarly to stationary cycles except that you "pedal" using your arms. Add exercises sessions with the upper body ergometer to move your exercise program to the next level.

Roger Bannister broke the 4-minute mile in 1952 running about 2 miles during each training session. He used high intensity interval training methods developed by eastern European, Australian, and British coaches. During the 1970s, great distance runners such as Steve Prefontaine and Gerry Lindgren ran as many as 150 miles per week using a training technique called LSD (long, slow distance). Scientists and coaches thought that LSD training was better than intervals for building oxygen transport and muscle metabolic capacity. Coaches are now going back to the high intensity methods of the 1950s and adding plyometrics and weight training programs to improve performance in endurance events. Canadian researchers found that six sessions of sprint interval training (total of 15 minutes in 2 weeks) increased muscle oxidative capacity (citrate synthase) by almost 50 percent, muscle glycogen by 20 percent, and cycle endurance capacity by 100 percent. This study showed the importance of high intensity training for athletes whose training goal is high performance in an endurance activity.

Source: J Appl Physiol. 98: 1985-1990, 2005.

Many people wonder whether too much exercise can be bad for them. In some cases, the answer can be "yes." In a condition known as the female athlete triad, for example, excessive exercise combines with abnormal eating habits to create problems such as amenorrhea (lack of menstrual periods) and premature osteoporosis (loss of bone mass). The female athlete triad usually occurs in young women who are striving to become unrealistically thin, but may also occur in women who are trying