The fitness movement that began in the late 1960s and early 1970s centered around aerobic exercise(有氧操). Millions of individuals became engaged in a variety of aerobic activities, and literally thousands of health spas developed around the country to capitalize(获利) on this emerging interest in fitness, particularly aerobic dancing for females. A number of fitness spas existed prior to this aerobic fitness movement, even a national chain with spas in most major cities. However, their focus was not on aerobics, but rather on weight-training programs designed to develop muscular mass, strength, and endurance in their primarily male enthusiasts. These fitness spas did not seem to benefit financially from the aerobic fitness movement to better health, since medical opinion suggested that weight-training programs offered few, if any, health benefits. In recent years, however, weight training has again become increasingly popular for males and for females. Many current programs focus not only on developing muscular strength and endurance but on aerobic fitness as well. Historically, most physical-fitness tests have usually included measures of muscular strength and endurance, not for health-related reasons, but primarily because such fitness components have been related to performance in athletics. However, in recent years, evidence has shown that training programs designed primarily to improve muscular strength and endurance might also offer some health benefits as well. The American College of Sports Medicine now recommends that weight training be part of a total fitness program for healthy Americans. Increased participation in such training is one of the specific physical activity and fitness objectives of Healthy People 2000, National Health Promotion and Disease Prevention Objectives. The word 'spas'(Line 3, Para. l) most probably refers to ______.