76 STRENGTH Strength is the ability of a muscle or a group of muscles to exert force against resistance. It is the main component of any physical activity, and it is particularly important for athletes. Physical strength is determined by several factors: How to measure strength Testing body strength is important not only to know if we are fit, but also to know if there are any physical issues that can compromise our strength. There are three basic techniques to test body strength: the structure of the muscles ; the quality of muscle fibres; genetic factors; sex. What is a muscle and what is its function? For every 1 square centimetre of cross-sectional area, muscle fibres can exert a maximum force of approximately 30-40 newtons (the weight of a 3-4 kg mass). Types of strength There are seven types of strength. Agile strength refers to the ability to change direction quickly and efficiently while maintaining control and balance. Endurance strength is the ability to continue repeated muscle contractions over an extended period. Do push-ups for three minutes to test your upper body strength: get on your knees, put your hands under your shoulders, and raise your body up with your legs straight and feet together. Your elbows should bend at 90°. A fit 20-year-old man should be able to do at least 20 push ups, a woman at least 15. Speed strength is the ability to exert force quickly during high-speed movements. Explosive strength accounts for releasing a very high amount of strength in a short period of time. Maximal strength refers to the highest amount of force that a muscle or muscle group can generate in a single effort. Relative strength refers to the amount of strength relative to body weight and is usually calculated as how much force per kilo is produced. Starting strength is the ability to generate force at the beginning of a movement. to bend: piegare firmly: saldamente to slide down: scivolare gi 148 SCIENCE AND PHYSICS See how many crunches you can do in one minute to test your endurance: lay down and place your feet firmly on the ground. Place your arms behind your head, raise your shoulders and head without lifting your lower back off the floor. For a 20-year-old man 40 crunches is considered an average result, for a woman 30. Determine how long you can hold a half-squat to test your lower body strength: stand with your back against a wall and slide yourself down until your knees are bent at a 90 angle. A healthy man should be able to keep the position for about 80 seconds, a woman for about 70 seconds.