Yasushi Ikuta

This study aimed to estimate the factors that cause differences in competition level based on the competition performance structure among university student decathletes in Japan. The results of factor analysis using the maximum likelihood method (Oblimin rotation), assuming a five-factor structure estimated from parallel analysis and the information criterion, revealed the following competitive performance structures: "running speed and body projection,” "running endurance,” "rotational throwing power,” "translational throwing power,” and "vertical leaping power.” Some of these were similar to the competitive performance structures of the world’s top athletes, but they were found to have a unique structure: two throwing powers. The analysis results using latent rank theory allowed us to evaluate them on a seven-point scale. The calculated item reference profile, difficulty index, and discrimination index for each rank indicated that shot put and 100 and 400 m performance formed the basis of decathlon performance. In addition, high jump and pole vault, which fall under the category of "vertical leaping power," retained high difficulty and discrimination and were revealed to affect the stage of achievement of overall performance in the decathlon.

The study aims to test three hypotheses: (a) the rotation of the upper trunk consists of roll, pitch and yaw of frequencies harmonic to the stroke frequency of the front crawl stroke, (b) the rotation of the upper trunk generates back-and-forth movements of the shoulders, which enhances the movements of the stroking arms, and (c) the angular velocities of roll, pitch and yaw are associated with hand propulsion (HP). Front crawl strokes performed by twenty male swimmers were measured with a motion capture system. The roll, pitch and yaw angles about the three orthogonal axes embedded in the upper trunk were determined as three sequential Cardan angles and their angular velocities were determined as the three respective components of the angular velocity. HP and the drag and lift components of HP (HPD and HPL) were estimated by the hand positions and the data from twelve pressure sensors attached on hands. The roll, pitch, and yaw angles were altered in frequencies harmonic to the stroke frequency during the front crawl stroke. Shoulders alternately moved back and forth due to the upper trunk rotation. In the pull phase the angular velocity of roll was correlated with HPL (r = -0.62, p = 0.004). Based on the back-and-forth movements of the shoulders and roll motion relative to a hand movement, the arm-stroke technique of the front crawl swimming was discussed in terms of increasing the hand velocity and HP.

高アミロース米の血糖上昇抑制効果に関する報告は複数あるが、日本人を対象とした報告は少ない。そこで、日本人を対象に、高アミロース米「越のかおり」米飯摂取後の血糖応答について検討した。また、加水量を増やし柔らかく炊き上げた高アミロース米飯を用意し、水分量の違いが血糖応答に与える影響についても検証した。試験は健常成人を対象とした二重盲検の無作為化クロスオーバー試験とし、糖質50gを含む3種の米飯(通常加水コシヒカリ、通常加水越のかおり、高加水越のかおり)を用いた。通常加水越のかおりは通常加水コシヒカリと比較し、食後の血糖上昇を有意に抑えた。一方、高加水越のかおりには血糖上昇抑制効果が認められなかった。越のかおりは食後血糖値の急激な上昇を抑えることから糖尿病食事療法等に有用である可能性が示唆されたが、食味と機能性のバランスを両立させた調理方法については更なる検証が必要である。(著者抄録)

The purpose of this study was to examine the difference in muscle activation pattern and co-contraction of the rectus and biceps femoris in flutter-kick swimming between competitive and recreational swimmers, to better understand the mechanism of repetitive kicking movements during swimming. Ten competitive and 10 recreational swimmers swam using flutter kicks at three different velocities (100%, 90%, and 80% of their maximal velocity) in a swimming flume. Surface electromyographic signals (EMG) were obtained from the rectus (RF) and biceps femoris (BF), and lower limb kinematic data were obtained at the same time. The beginning and ending of one kick cycle was defined as when the right lateral malleolus reached its highest position in the vertical axis. The offset timing of muscle activation of RF in the recreational swimmers was significantly later at all velocities than in the competitive swimmers (47-48% and 26-33% of kick time of one cycle for recreational and competitive swimmers, respectively), although the kinematic data and other activation timing of RF and BF did not differ between groups. A higher integrated EMG of RF during hip extension and knee extension induced a higher level of muscle co-contraction between RF and BF in the recreational swimmers. These results suggest that long-term competitive swimming training can induce an effective muscle activation pattern in the upper legs. (c) 2015 Elsevier B.V. All rights reserved.

The aim of this study was to examine whether the intracyclic velocity variation (IVV) was lower in elite swimmers than in beginner swimmers at various velocities, and whether differences may be related to arm coordination. Seven elite and nine beginner male swimmers swam front crawl at four different swimming velocities (maximal velocity, 75%, 85%, and 95% of maximal swimming velocity). The index of arm coordination (IDC) was calculated as the lag time between the propulsive phases of each arm. IVV was determined from the coefficient of variation of horizontal velocity within one stroke cycle. IVV for elite swimmers was significantly lower (26%) than that for beginner swimmers at all swimming velocities (p< 0.01, 7.28 1.25% vs. 9.80 1.70%, respectively). In contrast, the IDC was similar between elite and beginner swimmers. These data suggest that IVV is a strong predictor of the skill level for front crawl, and that elite swimmers have techniques to decrease IVV. However, the IDC does not contribute to IVV differences between elite and beginner swimmers.

The aims of this study were (1) to evaluate changes in muscle activity associated with physiological fatigue and decreased swimming velocity (SV) during 200 m of front crawl swimming, and (2) to examine the relationship between the decreased SV and changes in kinematic or electromyogram parameters. Twenty swimmers participated in a 4 × 50-m swim test. The surface EMG of 11 muscles (7 in the upper limbs and 4 in the lower limbs) was measured and the mean amplitude value (MAV) for one stroke cycle was obtained. The SV and arm angular velocity (AAV) of shoulder flexion during the first (early stroke) and second (late stroke) half of the underwater arm stroke were analyzed using an underwater camera. The AAV, the MAV of flexor carpi ulnaris (FCU), biceps brachii (BB), and triceps brachii during the early stroke, and the MAV of rectus femoris decreased along with a decrease in SV. In contrast, the MAV of the pectoralis major (PM) increased significantly in the final 50 m. The rate of change in MAVs (ΔMAVs) of FCU, BB and latissimus dorsi during the early stroke, and ΔMAV of biceps femoris were significantly correlated with ΔSV and/or ΔAAV. Positive correlations were identified between ΔMAVs of several muscles. However, no negative correlations were observed between ΔMAVs. These results suggest that the decrease in SV was related to decreases in the activities of several muscles that coordinated with each other, and that a compensating strategy occurred between PM and other muscles in the final 50 m.

The purposes of this study were as follows: 1) to classify competitive swimmers on the basis of their stroke rate (SR) and stroke length (SL) by applying a factor analysis and a cluster analysis, 2) to derive discriminant functions by applying a multiple discriminant analysis of the stroke characteristics, and 3) to compare the race patterns of groups classified according to the results of the cluster analysis. 94 male swimmers who had participated in 100-m freestyle events held at the All Japan Swimming Championship from 2000 to 2004 were selected as subjects. The average value of their swimming velocity, SR, and SL in four swimming phases (15-25 m, 25-45 m, 57.5-75 m, and 75-95 m) were measured from videos captured. The subjects were classified according to their SR and SL by applying a factor analysis and a cluster analysis. Results showed that the competitive swimmers could be classified into Type1-4. Type1 showed high values of SR throughout the race, Type2 showed high values of SR in the first half and high values of SL in the second half, Type3 showed high values of SL in the first half and high values of SR in the second half, and Type4 showed high values of SL throughout the race. Although there was no difference in swimming records among the four groups, each group had different race patterns. These results suggest that the knowledge of race patterns might be useful to swimmers or coaches for planning race strategies. (Jpn. J. Phys. Fitness Sports Med. 2010, 59 : 465 similar to 474)

The purpose of this investigation was to determine how swimming velocity (SV), stroke rate (SR), stroke length (SL) and blood lactate concentration change as adaptations to six months of aerobic swim training. Subjects were trained male college swimmers (n = 8). Measurements were obtained following specially designed 400 m freestyle swim tests, pre- and post-intervention. The swim test consisted of 4 x 400 m freestyle over two days. On day 1, subjects performed a maximal effort 400 m freestyle swimming trial maximal mean velocity (V̇max) for each swimmer was calculated from this effort. On the next day, subjects were instructed to perform three 400 m freestyle swims at constant velocities equal to 85%, 90% and 95% of V̇max, respectively. Subjects rested one hour between swims. During each 400 m trial, lap time and time to complete 10 mid-pool strokes 50 m) were measured to determine SV (m·s-1), SR (stroke·min-1) and SL (m·stroke-1). Mixed arterial blood samples were taken at the end of each 400 m trial to evaluate blood lactate concentration. Results indicated that post-maximal swimming velocity (V̇postmax) increased significantly from pre-intervention measures (p &lt 0.05). Blood lactate concentration decreased significantly relative to SV and absolute lactate concentration following V̇postmax was significantly lower than that at V̇premax (p &lt 0.05). Six of seven subjects increased V̇max due to increases in SL. Mean SL during the second test was significantly higher (p &lt 0.05). Also, during the 400 m maximal test, SL increased significantly after sixth lap (p &lt 0.05). There was no significant difference between SRs. The results of this study suggest that swimming performance improvements as a result of aerobic training are due to increases in SL rather than SR.