Assessment of movement variability and time in a football reactive agility task depending on constraints

The aims of this study were to (1) analyse time and movement variability in a football (soccer) agility task performed with or without ball, both in the following situations a) reacting to the movement of two players with a single exit gate (R1), b) reacting to the movement of one player with two possible exit gates (R2) and c) not reacting to a stimulus; and, (2) analyse the relationship between time and movement variability. Seventeen semi-professional female football players participated in the study. Acceleration was measured using an inertial measurement unit attached to each player through an elastic belt close to the sacrum. Entropy was calculated from the acceleration signal and time was extracted using a magnet-based timing system. Movement variability was reduced whereas time increased when adding the ball and/or the reaction, finding no differences between R1 and R2. A moderate negative correlation was found between time and movement variability (r = -0.56, p < 0.01). Our findings demonstrate that increasing the difficulty and/or the amount of information from the environment, decreased movement variability and increased the time. The measurement of movement variability in addition to time in an agility task can be used to determine the mastery level of players.