Saccades and prefrontal hemodynamics in basketball players.

We investigated saccade performance and prefrontal hemodynamics in basketball players with different skill levels. Subjects were 27 undergraduate basketball players and 13 non-athlete undergraduates (control group: CON). The players were divided into two groups: those who had played in the National Athletic Meet during high school or played regularly (n=13, elite group: ELI) and those who were bench warmers (n=14, skilled group: SKI). Horizontal eye movement and oxy-, deoxy-, and total-hemoglobin (Hb) concentration in the prefrontal cortex during pro- and anti-saccade were measured using electro-oculography and near-infrared spectroscopy, respectively. Only error rate in anti-saccade was less in ELI (4.8+/-4.0%) than SKI (13.7+/-12.6%) and CON (13.9+/-8.3%) (p<0.05). In ELI alone, oxy- (-0.15+/-0.18 mmol*mm) and total-Hb (-0.12+/-0.15 mmol*mm) during anti-saccade decreased significantly compared with that during rest (p<0.05), while those in CON significantly increased (oxy-Hb: 0.17+/-0.15 mmol*mm, total-Hb: 0.14+/-0.14 mmol*mm) (p<0.05). These results suggest that inhibition of eye movement to a visual target changes from voluntary to automatic through the motor learning of basketball.

Sports exercise effect on shortening of saccadic reaction time associated with neck extensor muscle activity.

We investigated sports exercise effect on shortening of saccadic reaction time associated with neck extensor muscle activity. Saccadic reaction time was measured in neck rest position, 20 degrees neck flexion, and 30 % muscle contraction of the shoulder girdle elevators for two groups. These groups were an untrained group that has never belonged to any sports club (UT group) and a group that has belonged to high-speed ball sports clubs (HS group). In the neck flexion and 30 % muscle contraction conditions, there was a significant shortening of the reaction time for the HS group. For the UT group, no significant shortening was found in those conditions, and the reaction time in the 30 % contraction was rather significantly longer than that in the rest position. Sports experience pursuing a high-speed ball will be effective in the shortening of the saccadic reaction time associated with the activity of neck extensors.

Saccadic reaction times during isometric voluntary contraction of the shoulder girdle elevators and vibration stimulation to the trapezius.

We investigated the effect of increases in muscle afferent information from the shoulder girdle elevators on saccadic reaction time. Saccadic reaction time was measured under conditions of isometric voluntary contraction of the shoulder girdle elevators and vibratory stimulation of the trapezius. Saccadic reaction time was defined as the latency until the beginning of eye movement toward the lateral target, which was moved at random time-intervals in jumps of 20 degress amplitude. Eye movement was measured using the electro-oculogram technique. Muscle contraction force was set in 10% increments from 0% to 30% of maximal voluntary contraction (MVC), and vibration frequency was maintained at 100 Hz. Under voluntary contraction, the saccadic reaction time gradually shortened up to 30% MVC. Under vibration stimulation at 0% MVC, the reaction time shortened to the same degree as that under voluntary contraction at 30% MVC. Under conditions of combined vibratory stimulation and voluntary contraction, the reaction time was essentially identical to these values; namely, no additive effect in shortening of the reaction time was recognized. The results demonstrated that saccadic reaction times were remarkably shortened by increases in muscle afferent information from the neck extensors. We have discussed reasons for the lack of an additive effect and factors limiting shortening of reaction times.

Modality of postural movement in men and women with both arms flexed during standing.

We investigated postural movement associated with bilateral arm flexion in response to a light signal during standing in 179 healthy men and women to assess whether individual and sex differences arc evident in the postural movement pattern. The following results were obtained. (a) A correlation of -.87 was noted between movement angles of the foot-leg and leg-trunk. (b) Individual differences in movement angle were approximately twice as large in the hip joint as in the ankle and knee joints, and the movement angle of the leg trunk showed approximately half the number of extension as flexion movements. (c) The postural movement pattern was categorized on the basis of the movement angle of the foot leg and leg trunk into the following three patterns: hip flexion, backward leaning, and hip extension. The percentages of subjects showing these patterns were 59.2%, 33.5%, and 7.3%, respectively. (d) The inclination angle reflecting the righting response showed a gradual increase in size in the order of trunk, head, and neck. However, the righting response was not controlled precisely enough to enable subjects to maintain the inclination angle in a quiet standing posture. (e) We identified a significant sex difference in the relative frequency of subjects in the postural movement pattern.

Changes in saccadic reaction time while maintaining neck flexion in men and women.

We investigated changes in saccadic reaction time in relation to the degree of increase in activity of neck extensor muscles when neck flexion occurred, and assessed the reliability of the measurements. Saccadic reaction time was measured firstly, during neck flexion angles set at 5 degrees increments from 0 degrees (resting position) to 25 degrees, with the chin either resting on a stand or not, and secondly, during shoulder girdle elevator muscles providing a relative muscle force of 30%, with the neck flexion angle maintained at 0 degrees by having the subjects rest their chins on a stand. Saccadic reaction time was evaluated by the latency to the beginning of eye movement toward the lateral target, which was moved at random intervals in 20 degrees amplitude jumps. Muscle activity in the trapezius muscle was evaluated using the mean amplitude of electromyogram recordings. Very high coefficients of reliability in muscle activity and saccadic reaction time were observed between the two sets of tests at 1-h intervals and also among the three trials with a 1-min rest. When their necks were flexed and the subjects rested their chins on a stand, muscle activity increased slightly in accordance with the enlargement of this angle, with no significant change in saccadic reaction time. With the chin not resting on the stand, muscle activity increased gradually, while the saccadic reaction time decreased to that obtained at an average neck flexion angle of 20 degrees. However, the angle where the shortest reaction time was obtained showed considerable individual variation (5-25 degrees ). Activity in the trapezius muscle at a 20 degrees neck flexion angle, with the chin not resting on the stand, was far less than that for 30% maximal voluntary contraction in shoulder girdle elevator muscles. Nevertheless, the saccadic reaction times were roughly equivalent under the two different sets of conditions. No sex differences were observed in terms of saccadic reaction time under any set of conditions.

Starting position of movement and perception of angle of trunk flexion while standing with eyes closed.

The present study attempted to investigate the effect of position on the perception of angle of trunk flexion while standing. For this purpose, the range effect was factored out by setting the constant target angle at 10 degrees, with varied starting positions of trunk flexion. We found that subjects underestimated angle of trunk flexion when the starting position was close to a quiet standing posture, overestimated when close to maximum trunk flexion, and correctly perceived it when at the middle position. Less perceptual distortion was observed at the positions close to maximum trunk flexion in the present study than in our previous one, in which various target angles of trunk flexion were reproduced from a quiet standing posture. The reduced distortion in the present study was believed to have resulted from factoring out the range effect. The flexion angle of the hip joint changed in tandem with that of the trunk, while very little movement was observed in the ankle, knee, and neck joints. Judging from the changing pattern of hip-joint angle, the muscle activity of the erector spinae and biceps femoris increased gradually to 90 degrees trunk flexion. In contrast, the actual increment of muscle activity reached zero or a minimum value at the middle angles as the angle of trunk flexion increased. It was assumed that the abrupt change in kinesthetic information associated with muscle activity exerted a great influence on the perception of trunk flexion.

Perceptibility of body position in anteroposterior direction while standing with eyes closed.

The perception of body position in the anteroposterior direction was investigated by evaluating the reproducibility of the position from a quiet standing posture to forward or backward leaning posture with eyes closed. The subjects were 10 healthy male undergraduates, aged 20 to 28 years. The standing position was represented by the pressure center of the foot, which was shown by the relative distance (%) from the heel to the length of the foot. The reference positions of the pressure center of the foot were set at 10% increments from 20 to 80% of the length of the foot. The subjects attempted to reproduce each reference position 10 times, and the absolute and constant errors of the reproduced position were analyzed. The absolute errors at reference positions of 30 to 60% were distinctly larger than those at the other reference positions. This indicated that the perception of standing positions from 30 to 60% was less accurate. The constant errors at the reference positions of 40 to 60% were significantly positive, which meant that the reproduced position was located farther forward than the reference position.

Relationship between reaction time of eye movement and activity of the neck extensors.

This study investigated the relationship between the reaction time of eye movement (RTEM) and activity of the superficial neck extensor muscles when the shoulder girdle elevator muscles contracted isometrically. The results were compared with those of a previous study in which the subjects's head was fixed and loaded with the neck flexed. When the shoulder girdle elevator muscles contracted isometrically, RTEM decreased significantly in comparison to RTEM at rest. This demonstrated that the reaction time significantly decreased not only as a result of the neck in flexion, which activated the deep and superficial neck extensor muscles, but also from contraction of the shoulder girdle elevator muscles which mainly activated the superficial extensor muscles. The relationship between RTEM and relative muscle load of the shoulder girdle elevator muscles showed that RTEM decreased up to 30% loading, and with loading above 40% the RTEM was longer than with 30%. The relative muscle load for the shortest RTEM demonstrated a subject-to-subject variance ranging from 24.7% to 49.6%. The difference between RTEM at rest and at their shortest reaction time was approximately 20 ms, which was consistent with the data for the neck in flexion. However, the relative muscle load for the shortest RTEM differed between the current and previous studies. The parameters obtained in this study were higher than for those in the previous study.