The purpose of this study was to determine the amount of head movement associated with different batter stride lengths, and to determine if the longer stride leads to poorer pitch tracking. Coaches often disagree whether a stride is necessary when hitting, but if they do think a stride is necessary, almost all agree that the stride should be short. They justify this claim because of the presumed negative effect on gaze error associated with a long stride. We hypothesized that when a subject made a long stride toward the pitcher there would be significantly larger amounts of head rotation and translation.
Fourteen subjects with a minimum of one year of high school baseball experience were enrolled in this study. They were tested using a pitching machine called the Flamethrower under three conditions. In the control condition they just tracked the ball, in the stride condition they made a stride of eight inches toward the pitching machine with their front foot, and in the no stride condition they raised their foot and then replaced it in the same location. Each subject viewed 100 pitches at a speed of approximately 80 miles per hour for each of the three conditions. The balls were pitched from a distance of 43.57 feet from the plate. Eye movements were recorded with the ISCAN infrared eye tracker. Head rotation and translation was recorded using the 3DM-GX1 Microstrain gyro head tracker and the Flock of Birds head tracker. Using a software program, head and eye recordings were synchronized.
A total of 2300 pitches were analyzed and the mean absolute gaze errors, head movements, and eye movements were calculated. Mean absolute gaze errors were very similar initially for each of the three conditions. After 250 ms, the no stride condition exhibited a significantly larger gaze error, but gaze errors and standard deviations were very large in all conditions after 250 ms.
Head rotation measured with the Microstrain tracker was initially (at 150 ms) significantly larger for the stride condition, but after 150 ms there was not a significant difference between the conditions. There was a tendency for larger head translations toward the pitching machine to occur in the stride condition. Combining the correlation analysis with the visual graph inspection, these data suggest that a horizontal rotation in the direction of the ball is accompanied by a concomitant horizontal translation in the direction of the ball. Eye movements were initially larger in the stride condition, but after 150 ms the stride and no stride condition were very similar. Both conditions exhibited larger eye movements than the track only control condition.
Overall, tracking performance was not significantly different for subjects who took a stride when compared to subjects who just tracked the ball or subjects who used the no stride hitting approach. The absolute gaze errors were less than 2.5 degrees for the first 250 ms of the pitch for all conditions. After 250 ms, the gaze errors and standard deviations become quite large. Both translational and rotational head movements were similar between the three conditions and it can be concluded from this study that taking a stride does not lead to more head movement as was predicted by many coaches. Eye movement was also very similar between the no stride and stride conditions, although the track only condition did exhibit smaller eye movements. This indicates that taking a stride does not lead to increased eye movement which was also predicted by many coaches.
From this study, it is reasonable to conclude that taking a stride does not significantly impact tracking a pitched ball. A stride also does not cause a batter to have excessive head and eye movements. It is quite possible that the stride can serve as an important timing mechanism of the swing. This study does not indicate which approach is better, but it does show that a stride is not detrimental for successful tracking.