With the greying of America and increased interest in walking as exercise, Dynastride! is a timely publication. Vigorous walking or dynastriding, LaLanne suggests, provides the health, fitness, and psychological benefits of more intense exercise. Part I covers correct shoes, clothing, and walking routes and gives instructions on how to determine fitness and measure vital signs. Part II describes one-month starter, 90-day, one-year, and lifetime plans. The crux of these programs is the working heart rate, the basis for measuring activity and progress. LaLanne gives instruction on how to determine the necessary numbers, but this reviewer found application of the numbers confusing. Otherwise, a worthwhile program also of appeal to the ``under 50s.''Susan M. Unger, Madison P.L., N.J.