Speed refers to how quickly muscles can move joints. It can be measured using a 30m sprint test. To improve speed, one should do interval training with short high-intensity intervals followed by longer rest periods. Examples of speed in activities include an attacker needing leg speed to outrun defenders in football and a badminton player needing arm speed for smashes. Factors affecting running speed include leg/arm speed, stride length, hip range of movement, and leg-arm coordination.