Different visual stimuli affect muscle activation at the knee during sidestepping

Increasing knee stability via appropriate muscle activation could reduce anterior cruciate ligament (ACL) injury risk during unplanned sidestepping. High-level athletes may activate their knee muscles differently from low-level athletes when responding to quasi-game realistic versus non game-realistic stimuli. Eleven high-level and 10 low-level soccer players responded to a non game-realistic arrow-planned condition (AP), a quasi game-realistic one-defender scenario (1DS) and two-defender scenario (2DS), and an arrow-unplanned condition (AUNP), that imposed increasing time constraints to sidestep. Activation from eight knee muscles during sidestepping was measured during pre-contact and weight-acceptance. Knee flexor-extensor co-activation ratios were established. Muscle activation levels increased by approximately 27% solely in the 1DS in both sidestepping phases. In the 2DS, the shift from a flexor dominant co-activation strategy in pre-contact toward extensor dominance in weight-acceptance commenced earlier for the high-level players. Quasi game-realistic information allowed for anticipatory increases in knee muscle activation regardless of expertise levels but only when the time demands to respond were low (1DS). High-level players were better at interpreting complex game-realistic information (2DS) to activate their knee extensors earlier in preparation for single-leg landing during weight-acceptance.     

Searching image in blue jays: Facilitation and interference in sequential priming

Repeated exposure to a single target type (sequential priming) during visual search for multiple cryptic targets commonly improves performance on subsequent presentations of that target. It appears to be an attentional phenomenon, a component of the searching image effect. It has been argued, however, that if searching image is an attentional process, sequential priming should also interfere with performance on subsequent nonprimed targets, and such interference has never been unequivocally demonstrated. In blue jays (Cyanocitta cristata) searching in an operant apparatus for targets derived from images of cryptic moths, detection performance was strongly facilitated in the course of a sequential prime but was relatively unaffected by sequences of mixed target types. Detection accuracy in subsequent probe trials was enhanced by priming with targets of the same type, whereas accuracy on cryptic probes following priming with a more conspicuous target was significantly degraded. The results support an attentional interpretation of searching image.     

Net forces during tethered simulation of underwater streamlined gliding and kicking techniques of the freestyle turn

We assessed the net forces created when towing swimmers while gliding and kicking underwater to establish an appropriate speed for initiating underwater kicking, and the most effective gliding position and kicking technique to be applied after a turn. Sixteen experienced male swimmers of similar body shape were towed by a motorized winch and pulley system. A load cell measured net force (propulsive force - drag force) at speeds of 1.6, 1.9, 2.2, 2.5 and 3.1 m x s(-1). At each speed, the swimmers performed a prone streamline glide, a lateral streamline glide, a prone freestyle kick, a prone dolphin kick and a lateral dolphin kick. A two-way repeated-measures analysis of variance revealed significant differences between the gliding and kicking conditions at different speeds. The results demonstrated an optimal range of speeds (1.9 to 2.2 m x s(-1)) at which to begin underwater kicking to prevent energy loss from excessive active drag. No significant differences were found between the prone and lateral streamline glide positions or between the three underwater kicking techniques. Therefore, there appears to be no significant advantage in using one streamlining technique over another or in using one kicking style over another.