Coordination is the ability to produce smooth, efficient movement patterns, often under uncertain conditions. It involves the ability of the athlete's nervous system to communicate with the relevant muscles to synchronize the network of movement units involved in performing a skill. Movement unit sequencing depends on a well-established nervous system pathway, and this takes many, many years of practice. Coordination under time pressure includes conditions under which the athletes must complete a movement within a certain controlled or uncontrolled time frame. This causes both physical and nervous system fatigue, resulting in a deterioration of the athlete's performance of the skill. For example, while dribbling a ball in soccer, the player would prefer to do this using a comfortable time rhythm. However, an opponent can quickly force the player, whose dribbling the ball, to begin moving within a more restricted space and use muscles on both the left and right side of the body, depending on how the opponent behaves. Further demands on the athlete's coordination occurs while controlling the implement and changing direction almost instantaneously. In other words, the constant changing directions and conditions require quick nervous system adaptation. Training under coordination under time pressure, especially when the environmental conditions are uncertain, involve the use of both agility and mobility drills. Agility is the ability to move quickly and easily, and it requires the ability to think and draw conclusions quickly, in addition to maintaining good balance under changing conditions and speed. All agility training is designed to fine-tune body awareness, reaction time, and nervous system muscular control. Most agility drills are based on very fast stop and start actions that place considerable demand on the body. Good muscular endurance is, therefore, needed to maintain the quality of the movement. Mobility permits the unrestricted dynamic movement of joints, so that skills can be performed within the correct time frame. It reflects how the joints, the tendons, and the ligaments, and lungs, and the body moves while using the types of movements critical to reaching the desired posture. And this requires good core body control to maintain the stability of some joints, while other joints move into a desired position. Mobility is somewhat similar to dynamic flexibility, but it has a specific movement purpose, so the skill can be effectively accomplished. Lack of hip mobility is a common problem among athletes. Coordination under precision requires precisely optimizing the body control in time and space, using muscle strength to maintain certain body positions for a period of time. And this is commonly seen in gymnastics and diving. Coordination under precision occurs when the limbs must be moved precisely in both time and space to maximize the successful outcome of the skill. And finally, flexibility. The word flexibility, itself, is derived from the latin flexibilus, meaning to bend without breaking. The static component involves moving the muscles or the limbs slowly into the stretch position. And the dynamic component involves moving a muscle quickly into a stretch position using high amplitudes of motion. Dynamic flexibility works within the confines of the sensors within the muscle that monitor the tension and length of the muscle, and also within the confines of the senses that measure unsafe stresses on the tendon. Together, all the senses form the stretch reflex mechanism. And one goal of flexibility training is to train and delay or minimize activation of the stretch reflex, thus permitting much higher amplitudes of motion. We're going to come back and discuss all the complexities involved in flexibility in module 15.