Walking-like swimming，bicycling and running--is an aerobic exercise，(31)___builds the capacity for energy output and physical endurance by increasing the supply of oxygen to skin and muscles.Such exercises may be a primary factor in the(32) ___0f heart and circulatory disease.

　　As probably the least strenuous，safest aerobic activity，walking is the(33) ___acceptable exercise for the largest number of people.Walking(34) ___comfortable speed improves the efficiency of the cardio respiratory system(35) ___stimulating the lungs and heart，but at a more gradual rate(36) ___most other forms of exercise.

　　In one test，a group of men 40 t0 57 years of age，(37) ___at a fast pace for 40 minutes four days a week，showed improvement(38) ___to men the same age on a 30 minute，three—day—a—week jogging program in the same period.Their resting heart rate and body fat decreased(39) ___.These changes suggest(40) ___of the important-even vital--benefits walking can(41) ___about.

　　Walking(42) ___burns calories.It takes 3，500 calories to gain or(43) ___0ne pound.Since a one.hour walk at a moderate pace will(44) ___up 300 t0 360 calories.By walking one hour every other day，you Can burn up a pound—and—a—half monthly，or l8 pounds(45) ___-providing there is no change in your in-take of food.To(46).___weight faster，walk an n hour every day and bum up 3 pounds a month，or 36 pounds a year.

　　(47) ___your age，right now is the time to give your physical well-being as much thought as you(48) ___to pensions or insurance.Walking is a vital defense(49) ___the ravages of degenerative diseases and aging.It is nature’s (50) ___of giving you a tuneup.