Intra-Individual Variability For Basketball Free Throws

Abstract

Several studies have attempted to identify differences between subjects in the performance of basketball free throws. All of these studies have been twodimensional analyses of free throw kinematics and have analyzed only interindividual variability. An analysis of the directional errors for 1042 free throws completed by NCAA Division I varsity basketball players has revealed that 32.8% of missed free throws were off-line to the left, and 19.5% were off to the right. This is indicative of movement outside the sagittal plane. To date, a three-dimensional analysis of free throw shooting has not been reported in the literature, however. Also, since performers do not execute athletic movements in an identical manner each time, intra-individual variability is a component of athletic performance that should be considered. The purpose of this study was to complete a three-dimensional kinematic analysis of the intraindividual variability in basketball free throws. The subjects were members of an NCAA Division I varsity basketball team who attempted a minimum of 30 free throws in games over the course of a season. Five players met this criterion. A total of 648 free throws (FT) were videotaped during games (317 FT) and regular team practices (331 FT) throughout the season. The result of each free throw was classified into one of nine categories--swish, short make, long make, left make, right make, short miss, long miss, left miss, or right miss. A representative sample of free throws was selected that approximated each player's overall performance both in accuracy and error tendency. The number of free throws varied from 10 to 14 for each player. The free throw percentage for the 60 free throws analyzed was 73.3%, compared to an accuracy rate of 73.6% for the 648 free throws recorded. The subjects' free throw percentages ranged from 56.5% to 83.8%. Kinematic variables included range of motion at the wrist, elbow, shoulder, hip, knee, and ankle joints, trunk rotation, arm horizontal abduction/adduction, foot elevation angle, release height, velocity, and angle, and vertical and horizontal center of gravity position. Mean values for kinematic parameters were used to compare inter-individual variability. Intra-individual variability was defined as ± 1 standard deviation from the mean for each subject. Results indicate that intraindividual variability was larger than inter-individual variability for wrist and elbow ROM, and release velocity. Inter-individual variability was greater than intra-individual variability for hip, knee, and ankle ROM. The intra- and inter-individual differences were comparable for other variables. The findings suggest that multiple samples may be required to ensure representative data.