Shozo Tsubakimoto

Effect of inclination and position of new swimming starting block's back plate on track-start performance

This study investigated the effects of both anterior–posterior position and inclination of a back plate positioned on a starting platform on swimming start performance. Ten male college swimmers performed eight starts with varying combinations of take-off angle (normal and lower), inclination angle (10°, 25°, 45°, and 65°) and position (0.29, 0.44, and 0.59 m from the front edge of the starting block). Two-way repeated measures analysis of variance (ANOVA; take-off angle × back plate) for four conditions with take-off angles (normal and lower) and inclinations (10° and 45°), and one-way ANOVA for comparisons between four inclinations and three positions were carried out. Multiple comparisons were made using Bonferronis method. The main effects of the take-off angle were on the vertical and resultant take-off velocities [F(1,18) = 36.72, p < 0.001 and F(1,18) = 9.58, p = 0.013, respectively]. Comparisons between the plate positions showed that the 5 m time of the 0.29 m condition was significantly longer, the take-off angle and vertical take-off velocity of the 0.59 m condition were significantly lower, and horizontal and resultant take-off velocities of the 0.29 m condition were significantly less. Rear foot take-off times were significantly longer in the ascending order: 0.29, 0.44, and 0.59 m.

Do differences in initial speed persist to the stroke phase in front-crawl swimming?

Abstract The purpose of the study was to determine the extent to which differences in initial speed persist to the stroke phase in front-crawl swimming. Ten male college swimmers performed trials for three types of start that produced different initial speeds: maximal-effort dive, submaximal-effort dive, and maximal-effort wall push. The submaximal effort was determined by the swimmer himself. Participants swam 25 m for each trial, and their motions were recorded by five fixed cameras positioned lateral to the direction of swimming. The horizontal velocity of the greater trochanter of the femur was used to define swimming speed. Mean swimming speed, evaluated from the initial-speed phase to the stroke phase, differed across trials. The effect sizes of the initial-speed phase were 3.15 between maximal-effort dive and submaximal-effort dive (P < 0.001), 5.00 between maximal-effort dive and maximal-effort wall push (P < 0.001), and 2.71 between submaximal-effort dive and maximal-effort wall push (P < 0.001). However, differences in speed at the stroke phase were small (maximal-effort dive: 1.91 ± 0.07 m · s−1; submaximal-effort dive: 1.88 ± 0.06 m · s−1; maximal-effort wall push: 1.88 ± 0.07 m · s−1), indicating that differences in initial speed do not persist to the stroke phase in front-crawl swimming.

Kinematic analysis of the backstroke start: differences between backstroke specialists and non-specialists

Abstract The purpose of this study was to clarify factors to perform the hole-entry technique in the backstroke start. A total of 16 well-trained Japanese competitive swimmers were divided into two groups (backstroke specialists and non-specialists) to compare their backstroke start motions. Their backstroke motions were videotaped, and two-dimensional co-ordinates for the swimmers were obtained from the video images using direct linear transformation methods. A non-paired t-test and Mann–Whitney U-test were used to analyse the statistical difference of the kinematic variables between the groups. Backstroke specialists showed a significantly shorter 5 m time (P = 0.009, effect size = –1.54), a significantly higher position of the toe (P = 0.010, effect size = 1.47) at signal and of the hip at toe-off (P = 0.002, effect size = 1.94), a significantly larger hip joint angle at toe-off (P = 0.007, effect size = 1.60) and a significantly higher angular velocities of the hip joints (45–85%; P < 0.05) for the normalised time as compared to that of non-specialists. An earlier initiation of the extension and the maintenance of a higher extension speed at the hip joints were important factors in achieving an arched-back posture, which facilitated and water entrance with a small entry range.

Contribution of vitamin D receptor genotypes to bone mineral density in young male athletes with different impact loading

Bone adaptation to exercise relies on exposures to impact loading in sports, but the ability of skeletal change seems to be highly variable among individuals. The present study was designed to investigate the association between a poly-morphism in the vitamin D receptor (VDR) gene at the translation initiation site and impact loading on bone mineral density (BMD). Analysis of the VDR genotypes detected by endonuclease FokI (FF, Ff, and ff) and measurement of total body BMD (TBMD) were performed in 212 young males; 84 athletes were involved in weight-bearing sports, 48 in competitive swimming, and 80 non-athletic controls. The differences in TBMD between athletes and controls de-pended on the VDR genotypes; enhanced BMD in weight-bearing athletes was found in FF (7.7%, p

Effect of imposing changes in kick frequency on kinematics during undulatory underwater swimming at maximal effort in male swimmers

Undulatory underwater swimming (UUS) is an important swimming technique after a start and after turns. It was considered that a higher swimming velocity (U) resulted from a higher kick frequency (f), and greater propelling efficiency, i.e., Strouhal number (St) and Froude efficiency (ηF), resulted from a lower f. The aim of this study was to investigate whether changing f affected U and St, ηF plus other kinematics of UUS. Ten national-level male swimmers participated in the study. First, the swimmers performed maximal UUS (Pre; this f was defined as 100% F). Second, the swimmers synchronized their f with the sound of a metronome and with six frequencies (85% F, 90% F, 95% F, 105% F, 110% F, and 115% F) randomly presented. During the higher f sessions, kick amplitude (A) significantly decreased from Pre (115% F: -10.8%, p<.05); however, U was unchanged. In contrast, in lower f sessions, St and ηF were unchanged, but the wavelength per body length (λBL), which indicates UUS mode, significantly decreased (90% F: -1.3%, p<.05). In conclusion, these results suggest that increasing f for UUS would not affect U, but a decrease in f may be suitable for human undulation training.

Glucose Response after a Ten-Week Training in Swimming

The present study investigated the difference in blood glucose concentration (Glu) response during an incremental swimming test before and after a ten-week training period and verified whether blood glucose threshold (GT) could be determined in competitive swimmers. 7 elite male university swimmers participated in this study. 2 incremental swimming tests were conducted in a swimming flume before and after a ten-week training period. Blood lactate concentration (Bla) and Glu were measured after each swimming step, and the velocities of the lactate threshold (VLT) and glucose threshold (VGT) were analyzed. VLT increased significantly after training (1.21±0.06 m x s(-1) pre-training, 1.31±0.10 m x s(-1) post-training, p<0.05), while Glu did not increase at the higher swimming intensity steps. GT was not determined at each trial. Our results show that lactate threshold (LT) improved significantly after the ten-week training period, while the Glu response during incremental swimming tests did not change. Therefore, GT could not be determined in elite competitive swimmers before and after training.

Contribution of hand and foot force to take-off velocity for the kick-start in competitive swimming

ABSTRACT This study examines the hand and foot reaction force recorded independently while performing the kick-start technique. Eleven male competitive swimmers performed three trials for the kick-start with maximum effort. Three force platforms (main block, backplate and handgrip) were used to measure reaction forces during starting motion. Force impulses from the hands, front foot and rearfoot were calculated via time integration. During the kick-start, the vertical impulse from the front foot was significantly higher than that from the rearfoot and the horizontal impulse from the rearfoot was significantly higher than that from the front foot. The force impulse from the front foot was dominant for generating vertical take-off velocity and the force impulse from the rearfoot was dominant for horizontal take-off velocity. The kick-start’s shorter block time in comparison to prior measurements of the grab start was explained by the development of horizontal reaction force from the hands and the rearfoot at the beginning of the starting motion.

Effect of increased kick frequency on propelling efficiency and muscular co-activation during underwater dolphin kick

In this study, we investigated the effects of increased kick frequency on the propelling efficiency and the muscular co-activation during underwater dolphin kick. Participants included eight female collegiate swimmers. The participants performed seven 15-m underwater dolphin kick swimming trials at different kick frequencies, which is 85, 90, 95, 100, 105, 110, and 115% of their maximum effort. The Froude (propelling) efficiency of the dolphin kick was calculated from the kinematic analysis. The surface electromyography was measured from six muscles (rectus abdominis, erector spinae, rectus femoris, biceps femoris, tibialis anterior, and gastrocnemius). From the EMG data, the co-active phase during one cycle in the trunk, thigh, and leg was evaluated. Our results show that the Froude efficiency decreased at the supra-maximum kick frequency (e.g. 100%F: 0.72±0.03 vs. 115%F: 0.70±0.03, p<.05). The co-active phase in the trunk, thigh, and leg increased with increasing the kick frequency (e.g. 85%F vs. 115%F, p<0.05). Furthermore, it was observed that there was a negative relationship between the trunk co-active phase and the Froude efficiency (r=-0.527, p<0.05). Therefore, both the propelling efficiency and the muscular activation pattern became inefficient when the swimmer increased their kick frequency above their maximum effort.

Kinematic and EMG data during underwater dolphin kick change while synchronizing with or without synchronization of kick frequency with the beat of a metronome

We investigated the effects of synchronizing kick frequency with the beat of a metronome on kinematic and electromyographic (EMG) parameters during the underwater dolphin kick as a pilot study related to the research that entitled “Effect of increased kick frequency on propelling efficiency and muscular co-activation during underwater dolphin kick” (Yamakawa et al., 2017) [1]. Seven collegiate female swimmers participated in this experiment. The participants conducted two underwater dolphin kick trials: swimming freely at maximum effort, and swimming while synchronizing the kick frequency of maximum effort with the beat of a metronome. The kinematic parameters during the underwater dolphin kick were calculated by 2-D motion analysis, and surface electromyographic measurements were taken from six muscles (rectus abdominis, erector spinae, rectus femoris, biceps femoris, tibialis anterior, and gastrocnemius). The results revealed no significant differences in the kinematic and EMG parameters between trials of the two swimming techniques. Therefore, the action of synchronizing the kick frequency with the beat of a metronome did not affect movement or muscle activity during the underwater dolphin kick in this experiment.

Effect of having floats on cardiorespiratory response during eggbeater kick

The eggbeater kick is used to tread water during emergency situations (e.g. boat capsize) and becomes necessary skill for those without a self-floatation device to prevent primary and secondary drowning. Utilizing floating debris or objects to minimize the metabolic cost of performing this technique is essential during such emergencies. However, no study has investigated the effects of having floats on the physiological demands of performing the eggbeater kick, and quantifying these effects forms the focus of the current experiment.