No abstract

In ball game sports, players demand agility, which is a quick and adequate reaction to various changing stimuli. We developed a "successive choice reaction test" that evaluates such agility. This test requires subjects to be exposed to successive stimuli. Hence, it is very important to select appropriate stimulus tempos. In addition, it is necessary to examine the reliability of a new test. This study examined adequate stimulus tempos and test reliability. Fifteen healthy university students participated in this study. All the subjects conducted a successive choice reaction test with 3 kinds of tempos (1.3, 1.5, and 2.0 seconds). To examine its reliability, the test was conducted again on another day. It was found that any tempo has a high reliability, that their relationships are close, and insignificant time differences exist among the tempos. In conclusion, the successive choice reaction test was judged to be useful with any of the above tempos.

BackgroundStepping over an obstacle is a kind of compound movement that makes walking more difficult, especially for preschool children. This study examines sex and age-level differences in walking time in preschool children on an obstacle frame.MethodsThe participants included 324 healthy preschool children: four-year-old boys (51) and girls (51), five-year-old boys (50) and girls (60), and six-year-old boys (62) and girls (50). A 5 cm- or 10 cm-high obstacle (depth 11.5 cm, width 23.5 cm) was set at the halfway point of a 200 cm × 10 cm walking course.ResultsThe participants walked to the end of the course and back as fast as possible under three conditions: no obstacle, low obstacle and high obstacle. Walking time showed age-level differences in all conditions, but there were no differences in sex. Age levels were divided into two groups, with one group within the first six months of their birthday, and the second group within the last six months of that year. Walking time for children in the first half of their fourth year was longer than that of the five- and six-year-old children. In addition, for children in the last half of their fourth year, walking time was longer than both sexes in the last half of their fifth and sixth years. The children in the latter half of their fifth year had a longer walking time in the high obstacle condition than those in the last half of their sixth year. In the four-year-old participants, walking time was shorter with no obstacles than with a high obstacle frame.ConclusionsIn the above data, obstacle course walking time does not show a gender difference, except that the four-year-old participants needed longer than the five- and six-year-old children. Setting the obstacle 10 cm high also produced a different walking time in the five- and six-year-old participants. The high obstacle step test (10 cm) best evaluated the dynamic balance of preschool children.

The authors examined the effects of the direction (front or lateral) and method (light touch [LT] or support [LS]) of hand help on body sway and muscle activity during 1-leg stance (OLS). Fifteen subjects performed OLS with hand help under 4 conditions (front LT, front LS, lateral LT, lateral LS) after conducting normal OLS. Center of pressure (COP) path length and electromyography (EMG) were recorded. When using the lateral help, the COP and EMG were significantly smaller with LS than with LT. When using the front help, a difference in help methods did not affect the COP, but the EMG of gastrocnemius was significantly smaller with LS than with LT. In conclusion, body sway and muscle activity during OLS markedly decrease with lateral LS.

Conspicuous male sexual traits (e.g. weapons for male-male competition and displays for courting females) may attract predators. Under conditions of high predation risk females typically become less choosy with respect to mates to reduce the time spent on mate selection. However, post-copulatory sexual traits, such as sperm ejaculation for sperm competition and sperm removal for cryptic female choice (CFC), may increase with predation risk because they are more inconspicuous to predators. To examine this hypothesis, we observed the reproductive behaviour in the Japanese pygmy squid, Idiosepius paradoxus, in which the male attaches ejaculated spermatangia to the female's body and the female removes the spermatangia after copulation. Squid from two populations (Ohmura and Oki), with low and high predation levels respectively, were copulated in tanks under controlled presence/absence of predator conditions. Among the Ohmura individuals spermatangia removal was suppressed in the presence of a predator. Females may not be able to remove spermatangia effectively when facing a predator because they feel threatened by the predator; as a result, more spermatangia were retained during trials in which they were exposed to predators. In contrast for squid from the Oki (high predation) population, which is exposed to a higher predation risk, were not strongly affected by the predator presence. While the males ejaculated more spermatangia, the females removed more of them. The effect of sexual conflict may be greater than that of the predation risk in the pygmy squid. This suggests adaptive differences in post-copulatory sexual selection traits linked to predation.