79 Fibre colour is related to the degree of myoglobin present in the fibres. Myoglobin is a protein that both stores oxygen in the muscle and carries oxygen in the blood to the mitochondria. White fibres have a lower amount of myoglobin and mitochondria, so they appear whitish. In track and field events, the actual distance over which acceleration occurs varies per event. For the 100/200m, this is typically the first 30-50m. In the 400m, acceleration may be extended to 40-70m, depending on the athletes strategy. SPEED As a motor skill, speed is the ability to perform one or more movements or cover a distance as fast as possible. Speed is in direct relationship with the nervous system and the muscular system and depends on three main factors: perfect neuromotor synchronisation between agonist (the muscle that is contracting) and antagonist muscles (the one relaxing); correct execution technique, which allows for the conservation of energy and the control of the quality of the movement; genetic factors, which determine the quality of the muscle fibres; white fibres have a greater contraction capacity than red ones , so speed also depends on the amount of white fibres in the muscles. Components of speed Speed is not a linear force but consists of three fundamental components with specific features and functions: reaction speed represents the minimum reaction time between a stimulus and its response (known as kinetic reaction). It depends on the functionality of the central nervous system and the muscles involved in the response; it takes to perform a movement or cover a distance. It has two components: range of motion, which is the extent or limit to which a part of the body can be moved around a joint. It depends on muscle flexibility and elasticity, as well as on the correct execution of the movement; frequency, which is determined by the speed of movement of rhythmic gestures; for example, in running, it is the speed of the sequence of steps. Exercises to increase speed Being partly determined by genetic factors, speed is only partly trainable. The components that can be successfully trained are mobility, resistance, and strength, which are involved in speed. Normally, the typical training for speed comprises exercises performed at maximum execution speed for short durations (10-12 seconds). Since these exercises require a large amount of energy, they should be followed by adequate recovery periods (510 minutes). This type of training is particularly useful to improve reaction speed, concentration, and coordination. acceleration starts immediately after the reaction speed and represents the rate at which velocity increases with time. Acceleration continues until speed can no longer be increased and maximum velocity (called top-end speed) is achieved; movement speed is the combination of reaction speed and acceleration and is determined by the time 152 SCIENCE AND PHYSICS range: ampiezza rate: velocit , ritmo