Do not leap onto the tennis court like Achilles on a pogo stick. Your enthusiasm may be your "heel." Be sure to warm up slowly and build up a good sweat. Medical evidence pooh-poohs the suggestion that warming up improves performance. But it certainly suggests that the risk of injury during exercise can be greatly reduced by a warm-up. Although unheard of in America, Finnish marathoners often stride vigorously for several hundred yards before running or even jogging.

Warming up usually requires five to ten minutes. Warm up until you begin to perspire. Keep going?slowly. Do not stop during your workout. Endurance cannot increase with sporadic bursts of unbridled energy. If you start slowly, there will be no need to stop in the middle of a workout. If you must halt due to fatigue, you have tackled too much in too short a time.

We can be impetuous. We want to achieve the difficult today and the impossible tomorrow. Take it easy, be leisurely, and be of relaxed mien. To be blunt, do not kill yourself!

During exercise, do not let extra exertion creep up unnoticed. This is a particular hazard in "friendly" games. The first time Fancy Dan is your adversary in a game of tennis he may have you lunging for impossible returns. If you cannot retrieve his shots with an average attempt, forget it. Once you are in shape, you may or may not pin his ears back. With outdoor sports, force yourself to slow down in cold weather.

Low temperatures mean extra clothing, and the weight and wind resistance of added apparel necessarily increase work load and decrease efficiency. A head wind or uphill topography also requires inappropriate "oomph." Rowing against the current is the same. Reserve that impetuous, carefree blast for downstream, downhill, tail-wind, cautious pick-ups.

Save three minutes for the weak areas.

When you are well into a workout and as you finish, a feeling of well-being pervades. This stems partly from a sense of accomplishment and partly from a wholesome release of unresolved tensions and pent-up nerves. Worry, anger, boredom, anxiety, and frustration come back into proper perspective. Things are not quite so bad as they seem.

Into this glow of minor achievement intrudes the only hint of athletic tedium. Although not time-consuming, you must round out your session with calisthenics. Very few sports exercise the whole body. Swimming and weight lifting, while vastly different, are two exceptions. Suppose, however, you walk, bicycle, or run. The legs do most of the work. The arms reap the least benefit. Three minutes o? push-ups and pull-ups after a satisfactory workout is a modest imposition on the time and effort of the hiker, cyclist, or runner, yet ensures a more equal distribution of muscular rehabilitation. Contrariwise, a three-minute rapid jog (half a mile) for the oarsman balances his fitness program. You are the judge of what muscles you have called into play for your own activity. Devote the last three minutes to calisthenics which utilize the rest of your physique.

Calisthenics, while boring and almost totally devoid of fun, are essential for total fitness. Judiciously selected they fill a hiatus inherent in most sports. They also promote flexibility and mobility, your best insurance against creaking joints, bunched-up muscles, and poor posture.

It is how you play the sport, not the sport itself, that counts. Overexertion may mean injury and defeat. Regardless of how refreshed and vigorous you may feel, temper your zeal. Never do so much on one day that you interfere with the next day's program. A two- or three-day layoff because of stiffness, fatigue, and the need for recuperation may well negate the good of the initial workout. Time and experience will very quickly outline your own limitations. If you exercise properly, you should always be able to repeat yesterday's workout today without feeling stiff or tired.