16. painkilling chemicals that occur naturally in the body are known asa. hormones. b. triglycerides. c. endorphins. d. platelets.17. specificity is important to a fitness program because ita. makes the workout more enjoyable. b. allows you to choose the right types of activities to improve a particular fitness element. c. increases the demands you place on your body. d. you to exercise beyond your regular daily abilities.18. olympic athletes have lower resting heart rates becausea. their lungs tend to be naturally larger. b. they have a lot of muscle mass due to weightlifting. c. they exercise regularly, which improves the efficiency of their heart. d. they tend to eat low-fat diets.19. what does a measure of your cardiorespiratory endurance tell a fitness professional? a. your anaerobic fitness, or how well your leg and arm muscles workb. how long you can sustain a weightlifting programc. what type of exercises you've been doingd. your aerobic fitness, or how efficiently your heart is working20. which type of fat may lower the risk of heart disease? a. saturated fatb. trans fatc. unsaturated fatd. cholesterol