Brian K. V. Maraj

A kinematic analysis of high-speed treadmill sprinting over a range of velocities

INTRODUCTION The purpose of this study was to measure changes in stride characteristics and lower-extremity kinematics of the hip and knee as a function of increasing treadmill velocity, at velocities ranging from submaximal to near maximal. METHODS Six power/speed athletes experienced at sprinting on a treadmill performed trials at 70%, 80%, 90%, and 95% of their previous individual maximum velocity, with video data collected in the sagittal view at 60 Hz. RESULTS Significant differences were seen in stride frequency (70%, 80%, P < 0.01; 90%, P < 0.05), stance time (70%, 80%, P < 0.01; 90%, P < 0.05) flight time (70%, P < 0.01; 80%, P < 0.05), hip flexion angle (70%, P < 0.01), hip flexion angular velocity (70%, P < 0.01), hip extension angular velocity (70%, 80%, P < 0.01), knee flexion angular velocity (70%, 80%, P < 0.01), and knee extension angular velocity (70%, P < 0.01), as compared with the near maximum (95%) velocity. Coefficient of variation (CV) values showed that the positional variables at the hip and knee were more variable at faster test conditions, indicating that kinematic changes occur as a function of increased treadmill velocity. CONCLUSIONS The results indicated that at slower velocities, there were differences in the stride characteristics and lower-extremity kinematics while sprinting on a treadmill. As the velocity approached near maximum mechanical breakdown was seen, suggesting that velocities greater than 90% should be used selectively during treadmill training.

Movement Coordination in Ball Catching: Comparison between Boys with and without Developmental Coordination Disorder.

This investigation examined the catching coordination of 12 boys (M age = 9.9 years, SD = .8) with and without Developmental Coordination Disorder (DCD; M age = 10.5 years, SD = .8), under different task constraints. Participants attempted a total of 60 catches in central and lateral locations, under blocked and randomized conditions. No effect of randomization was found for the number of balls caught, but a significant Group x Location interaction effect (p < .0001) showed that typically developing boys had nearly perfect scores. Boys with DCD caught more balls in central (73%) than lateral trials (47%). During the latter, grasping and positional errors were also evident. Due to pronounced functional difficulties in the lateral trials, and coinciding differences in the arm and leg actions, it was concluded that intersegmental coordination constituted the organizational limits for boys with DCD.

The Effect of Nonregulatory Stimuli on the Triple Jump Approach Run

The purpose of this experiment was to examine the approach run of the triple jump. Specifically, we examined the effect of nonregulatory stimuli (Gentile, 1972) on two different ability levels in performing the triple jump approach run. These nonregulatory constraints (situational factors such as those seen in actual competition) were employed in three jumping conditions: Control (to obtain baseline performance measures), Distance (where participants attempted to obtain as great a jump as possible), and Accuracy (participants attempted to be as accurate as possible on takeoff without sacrificing distance). The results showed that the footfall position variability for all conditions was similar to those previously reported for the long jump approach run. However, in compliance with the nonregulatory constraints, participants altered other performance parameters in executing the approach run. The situational factors created changes that revealed themselves in foot placement on the takeoff board at the end of the approach run (foot position constant error and number of fouls increased for the Distance condition) and decreased horizontal velocity at takeoff in the Accuracy condition. Changes in performance parameters were related to the context in which the skill was performed and may further reflect changes made by jumpers in the course, such as a visual-motor task in competition. We suggest that the characteristics of the approach run may not be fully revealed by the pattern of footfall variability only, as has been suggested in previous work (e.g., Lee, Lishman, & Thomson, 1982), but that the situation under which the jump is performed may have a significant effect on the performance parameters that emerge in executing this type of motor skill.

Variance and invariance in expert and novice triple jumpers.

The purpose of this study was to examine relative timing, relative distance, and effector independence characteristics of the triple jump. We videotaped expert and novice triple jumpers using standing and running starts. On some trials, the triple jumpers were required to take off from their nondominant leg. Gentners (1987) interaction test was used to assess the proportional duration model in describing the timing of the component submovements. For both experts and novices, the proportional durations varied with the type of start. For experts, the relative timing of the jump components was independent of the take-off leg. The findings were mixed for the novices. Similar results were obtained when relative distance was examined. These results are discussed with respect to constructs related to variability in skilled performance.

Influence of Spatial Mapping on Manual Aiming Asymmetries

Two experiments were conducted to examine manual asymmetries in a one-dimensional aiming task. In Exp. 1, 10 right-handed adults slid a computer mouse 13 cm on a graphics tablet with both the right and left hands to targets of 3 different diameters. Under these conditions, the movement time for the right hand was significantly faster as expected. In Exp. 2, subjects performed similar movements to move a cursor 13 cm on a computer monitor. Thus the study was identical except the stimulus-response mapping was indirect. In this situation, there were no significant differences for either movement time or movement error between hands despite these performance measures indicating that target aiming was more difficult in Exp. 2. Because increases in task difficulty generally result in a greater advantage for the right hand, as indicated by Todor & Smiley, 1985, the present studies suggest that superiority of the right hand in aiming tasks may be diminished when spatial translation is required. Perhaps the spatial translation requires greater involvement of the right hemisphere, a process associated with manual advantage for the left hand, previously suggested by Roy and MacKenzie.

Perspectives on Coaching Pace Skill in Distance Running: A Commentary

INTRODUCTION Bradley Young’s paper presents an insightful challenge to the dominant conception of coaching distance runners, whereby training a runner to race is best done as a repetitive practice, e.g., repeating intervals at a specific pace. This widely held belief dates back to early experiments in interval training conducted by Woldemar Gerschler and Dr. Hans Reindell of the University of Freiburg in Germany in the late 1930’s.

Standing Distance in Climbability of Stairs

The purpose of this experiment was to make a preliminary examination of the distance one needs to stand from a stair to successfully climb up without using arms for support. Using an adjustable stair structure to create different heights of risers, a group of 10 tall and of 10 short participants made perceptual judgments and physical attempts at heights that represented 83% and 93% of each groups mean leg length. Choice of maximum and minimum distance from the stair was measured for each participant. Analysis showed that perceptual judgments and physical capabilities were highly correlated (tall: Pearson r = .92); short: Pearson r = .93). Moreover, the ability to climb the two heights depended on the standing distance from the stair. The findings suggest that standing distance may be a consideration in stair climbing and that stair height alone may not be sufficient to specify climbability.

The effect of concurrent hand movement on estimated time to contact in a prediction motion task

In many activities, we need to predict the arrival of an occluded object. This action is called prediction motion or motion extrapolation. Previous researchers have found that both eye tracking and the internal clocking model are involved in the prediction motion task. Additionally, it is reported that concurrent hand movement facilitates the eye tracking of an externally generated target in a tracking task, even if the target is occluded. The present study examined the effect of concurrent hand movement on the estimated time to contact in a prediction motion task. We found different (accurate/inaccurate) concurrent hand movements had the opposite effect on the eye tracking accuracy and estimated TTC in the prediction motion task. That is, the accurate concurrent hand tracking enhanced eye tracking accuracy and had the trend to increase the precision of estimated TTC, but the inaccurate concurrent hand tracking decreased eye tracking accuracy and disrupted estimated TTC. However, eye tracking accuracy does not determine the precision of estimated TTC.