Development of various reaction abilities and their relationships with favorite play activities in preschool children.

This study examines the development of various reaction movements in preschool children and the relationship between reaction times and favorite play activities. The subjects were 167 healthy preschool children aged 4-6 (96 boys and 71 girls). This study focused on the reaction times of the upper limbs (reaction 1: release; reaction 2: press) and the whole body (reaction 3: forward jump). The activities frequently played in preschools are largely divided into dynamic play activities (tag, soccer, gymnastics set, dodge ball, and jump rope) and static play activities (drawing, playing house, reading, playing with sand, and building blocks). The subjects chose 3 of 10 cards picturing their favorite play activities, depicting 10 different activities. All intraclass correlation coefficients of measured reaction times were high (0.73-0.79). In addition, each reaction time shortened with age. Reaction 1 showed a significant and low correlation with reaction 3 (r = 0.37). The effect size of the whole body reaction time was the largest. Whole body reaction movement, which is largely affected by the exercise output function, develops remarkably in childhood. Children who liked "tag" were faster in all reaction times. The children who chose "soccer" were faster in reactions 2 and 3. In contrast, children who liked "playing house" tended to have slower reaction times. Dynamic activities, such as tag and soccer, promote development of reaction speed and agility in movements involving the whole body. Preschool teachers and physical educators should re-examine the effect of tag and use it periodically as one of the exercise programs to avoid unexpected falls and injuries in everyday life.

Relationship between upper-body strength and bat swing speed in high-school baseball players.

This study aimed to clarify the relationship between upper-body strength and bat swing speed in high-school baseball players and to examine the physical characteristics of home run hitters (sluggers). The subjects were 30 male high-school baseball players with national tournament experience at the Koshien Stadium. Bat swing speed exerted by full effort was measured with a microwave-type speed-measuring instrument. One-repetition maximum (1RM) of a bench press (BP), BP power (bench power) using a light load (30 kg), and isokinetic chest press (0.4, 0.8, 1.2 m·s(-1)) were measured as upper-body strength. The relationships between bat swing speed and upper-body strength values were examined. Additionally, the t-test was used to reveal the mean differences between 14 home run hitters (group A) and 16 mediocre hitters (group B) for each measurement value. The bat swing speed showed significant and middle correlations with the 1RM BP (r = 0.59), bench power (0.41), and isokinetic chest press (0.48-0.55). Group A had significantly higher values in bench power and isokinetic chest press (high-speed) per kilogram of body weight than did group B. The swing speed showed significant correlations (r = 0.62) with the 1RM BP in group B but not in group A. In conclusion, to improve the hitting power of high-school baseball players, it may also be important to develop bench power with light loads in addition to 1RM BP.

Influence of restricted vision and knee joint range of motion on gait properties during level walking and stair ascent and descent.

Because elderly individuals experience marked declines in various physical functions (e.g., vision, joint function) simultaneously, it is difficult to clarify the individual effects of these functional declines on walking. However, by imposing vision and joint function restrictions on young men, the effects of these functional declines on walking can be clarified. The authors aimed to determine the effect of restricted vision and range of motion (ROM) of the knee joint on gait properties while walking and ascending or descending stairs. Fifteen healthy young adults performed level walking and stair ascent and descent during control, vision restriction, and knee joint ROM restriction conditions. During level walking, walking speed and step width decreased, and double support time increased significantly with vision and knee joint ROM restrictions. Stance time, step width, and walking angle increased only with knee joint ROM restriction. Stance time, swing time, and double support time were significantly longer in level walking, stair descent, and stair ascent, in that order. The effects of vision and knee joint ROM restrictions were significantly larger than the control conditions. In conclusion, vision and knee joint ROM restrictions affect gait during level walking and stair ascent and descent. This effect is marked in stair ascent with knee joint ROM restriction.

Effectiveness of the 1RM estimation method based on isometric squat using a back-dynamometer.

This study aimed to clarify the relationships between isometric squat (IS) using a back dynamometer and 1 repetition maximum (1RM) squat for maximum force and muscle activities and to examine the effectiveness of a 1RM estimation method based on IS. The subjects were 15 young men with weight training experience (mean age 20.7 ± 0.8 years, mean height 171.3 ± 4.4 cm, mean weight 64.4 ± 8.4 kg). They performed the IS with various stance widths and squat depths. The measured data of exerted maximum force and the action potential of the agonist muscles were compared with the 1RM squat data. The exerted maximum force during IS was significantly larger in wide stance (140% shoulder width) than in narrow stance (5-cm width). The maximum force was significantly larger with decreased knee flexion. As for muscle activity, the % root mean square value of muscle electric potential of the rectus femoris and the vastus lateralis tended to be higher in wide stance. As for exerted maximum force, wide stance and parallel depth in IS showed a significant and high correlation (r = 0.73) with 1RM squat. Simple linear regression analysis revealed a significant estimated regression equation [Y = 0.992X + 30.3 (Y:1RM, X:IS)]. However, the standard error of an estimate value obtained by the regression equation was very large (11.19 kg). In conclusion, IS with wide stance and parallel depth may be useful for the estimation of 1RM squat. However, estimating a 1RM by IS using a back dynamometer may be difficult.

The difference in output properties between dominant and nondominant limbs as measured by various muscle function tests.

Recently, right and left output properties exerted from specific muscle groups have been evaluated using special measurement devices such as an isokinetic dynamometer. However, it remains unclear whether the coach can properly evaluate muscle function corresponding to lateral specificity in athletes. This study aimed to examine the different output properties between the dominant (D) and nondominant (ND) upper limbs as measured by muscle function tests with various muscle contraction patterns. Fifteen right-handed young men participated in this study. Each subject carried out isometric, isokinetic, and isotonic muscle power tests by elbow flexion with right and left arms. When calculating the laterality index, the laterality of the isotonic test (1.17) was the highest. In all tests, significant correlations were found between the measurements of the D and ND limbs. The isometric test was the highest (r = 0.93), followed by the isokinetic test (r = 0.66-0.83) and the isotonic test (r = 0.55). To examine the ratio of the laterality of measurements provided by each muscle function test, each measurement was converted to a standard score (Z-score). There were significant differences between D and ND limbs in the isometric (D:ND = 55.0:45.0) and the isotonic (54.1:45.9) tests but not in the isokinetic test (60°·s⁻¹, 51.4:48.6; 180°·s⁻¹, 50.7:49.2; 300°·s⁻¹, 51.8:48.2). Particularly, the D (right) limb exerted greater muscle power in the isometric and the isotonic tests than in the isokinetic test. Occupational therapists or strength and conditioning professionals should understand that the D-ND differences shown by these muscle function tests may differ because of measurement conditions.

Relationship between the step test with stipulated tempos and gait ability in the elderly.

This study aimed to examine the performance characteristics of a step test with stipulated tempos, used to evaluate the dynamic balance ability of the elderly, as well as the relationship between this step test and walking ability. Ninety-two healthy older women (age 70.9+/-6.1 yr) who could walk independently, twice performed a 10 m walk at maximum speed and a step test for 20 sec with varying metronome tempos (40 bpm, 60 bpm, and 120 bpm). Subjects were divided into three groups (G1-G3) based on their 10 m gait time. Group 3 (G3), with the longest gait time, experienced the most falls.One evaluation parameter was the total time difference between the metronome sound and the time when the subject's foot hit the ground. The gait time was significantly related to the time difference in the 40 bpm and 60 bpm tempos (r=0.22-0.59). In step tests with slower tempos (40 bpm and 60 bpm), group G3 had a significantly larger time difference than the other two groups. In conclusion, a step test with slow tempos has a close relationship with the walking ability of the elderly and may be useful in evaluating their dynamic balance ability related to locomotion.