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George Vagenas and T. Blaine Hoshizaki

The sprint starts of 15 skilled sprinters were filmed and their sprinting times recorded while they were performing four 20-meter sprinting trials. They employed their natural hand-block spacings with alternative leg placements in the front starting block. The subjects were tested for dynamic strength on a force platform and their stronger leg was determined. Selected qualitative variables concerning certain perceived characteristics of lateral dominance and preferred leg for some basic motor skills were identified using a questionnaire. Significantly greater takeoff velocities and faster sprinting times were found when the stronger leg was placed in the front block. Previous empirical methods used in determining the best front leg in the start were found unreliable. Even some experienced sprinters fail to use their optimal leg in the forward position. Dynamic lower limb strength asymmetry was established as the key determinant in optimizing leg placement in the sprint start.

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Vassilis Vardaxis and T. Blaine Hoshizaki

This paper describes and interprets joint and segmental power patterns as functional characteristics of the leg movement in terms of generation, absorption, and transfer of power during the recovery phase of the sprinting stride. In addition, a comparison of the power patterns between advanced and intermediate sprinters was undertaken. Two advanced and two intermediate sprinters, each executing six trials of a 100-m dash, served as subjects. The results revealed that the power patterns for both the advanced and intermediate sprinters were similar in shape, depicting the same number of power phases. The hip joint musculature acted primarily as a power generator in comparison to the knee muscles, which acted mainly as absorbers (controllers) during the recovery phase of the sprinting stride. Differences between ability levels were identified using peak power values, with the advanced sprinters producing higher peak powers earlier in the recovery phase.

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Janie Cournoyer, David Koncan, Michael D. Gilchrist, and T. Blaine Hoshizaki

Understanding the relationship between head mass and neck stiffness during direct head impacts is especially concerning in youth sports where athletes have higher proportional head mass to neck strength. This study compared 2 neck stiffness conditions for peak linear and rotational acceleration and brain tissue deformations across 3 impact velocities, 3 impact locations, and 2 striking masses. A pendulum fitted with a nylon cap was used to impact a fifth percentile hybrid III headform equipped with 9 accelerometers and fitted with a youth American football helmet. The 2 neck stiffness conditions consisted of a neckform with and without resistance in 3 planes, representing the upper trapezius, the splenius capitis, and the sternocleidomastoid muscles. Increased neck stiffness resulted in significant changes in head kinematics and maximum principal strain specific to impact velocity, impact location, and striking mass.