Muscle Coordination During Maximal Butterfly Stroke Swimming: Comparison Between Competitive and Recreational Swimmers.

This study aimed to clarify the differences in muscular coordination during butterfly swimming between high- and low-performance swimmers using muscle synergy analysis. Eight female competitive swimmers and 8 female recreational swimmers participated in this study. The participants swam a 25-m butterfly stroke with maximum effort. Surface electromyography was measured from 12 muscles and muscle synergy analysis was performed from the data using nonnegative matrix factorization algorithms. From the results of the muscle synergy analysis, 4 synergies were extracted from both groups. Synergies 1 and 2 were characterized by coactivation of the upper and lower limb muscles in the recreational swimmers, whereas only synergy 1 was characterized by this in the competitive swimmers. Synergy 3 was involved in arm recovery in both groups. Synergy 4 was only involved in the downward kick in the competitive swimmers. From these results, it can be concluded that muscle synergies with combined coordination of upper and lower limb muscles were extracted more in the recreational swimmers and that the competitive swimmers controlled the downward kick with an independent synergy and that the adjustment of the timing of the downward kick may be an important factor for the efficient performance of butterfly swimming.

Effects of different initial speeds on subsequent glide and underwater undulatory swimming.

This study aimed to investigate the effect of different initial speeds on the performance during underwater undulatory swimming (UUS). The study included 13 female swimmers. Each participant was asked to perform a 15-m maximum UUS, starting with four different push-off speeds. The experiment was recorded using three underwater cameras; subsequently, a two-dimensional motion analysis was conducted. Statistical parametric mapping (SPM) was employed to identify the position where the UUS velocity stabilised. The findings revealed a significant difference in the average swimming velocities during the first cycle of UUS, which was attributed to the variation in initial speed (p < 0.05) while there is no significant difference in the middle and final cycles. The results of SPM analysis suggested that differences in UUS velocity became negligible after approximately 6-m position from the pool wall, regardless of variations in push-off velocity. Furthermore, it was confirmed that swimmers can reach their maximum achievable UUS velocity at approximately 5-m position, even if they fail to execute an effective push-off from the wall. These findings offer valuable insights for future UUS studies, specifically in choosing suitable cycles for analysis.

Changes in Kinematics and Muscle Activity With Increasing Velocity During Underwater Undulatory Swimming.

This study aimed to investigate the changes in kinematics and muscle activity with increasing swimming velocity during underwater undulatory swimming (UUS). In a water flume, 8 male national-level swimmers performed three UUS trials at 70, 80, and 90% of their maximum swimming velocity (70, 80, and 90%V, respectively). A motion capture system was used for three-dimensional kinematic analysis, and surface electromyography (EMG) data were collected from eight muscles in the gluteal region and lower limbs. The results indicated that kick frequency, vertical toe velocity, and angular velocity increased with increasing UUS velocity, whereas kick length and kick amplitude decreased. Furthermore, the symmetry of the peak toe velocity improved at 90%V. The integrated EMG values of the rectus femoris, biceps femoris, gluteus maximus, gluteus medius, tibialis anterior, and gastrocnemius were higher at 90%V than at the lower flow speeds, and the sum of integrated EMGs increased with increasing UUS velocity. These results suggest that an increase in the intensity of muscle activity in the lower limbs contributed to an increase in kick frequency. Furthermore, muscle activity of the biceps femoris and gastrocnemius commenced slightly earlier with increasing UUS velocity, which may be related to improving kick symmetry. In conclusion, this study suggests the following main findings: 1) changes in not only kick frequency but also in kicking velocity are important for increasing UUS velocity, 2) the intensity of specific muscle activity increases with increasing UUS velocity, and 3) kick symmetry is related to changes in UUS velocity, and improvements in kick symmetry may be caused by changes in the muscle activity patterns.

Japanese translation and modification of the Oslo Sports Trauma Research Centre overuse injury questionnaire to evaluate overuse injuries in female college swimmers.

The purpose of the present study was to translate and modify the Oslo Sports Trauma Research Centre (OSTRC) overuse injury questionnaire into Japanese and validate it among Japanese athletes through a longitudinal survey. A modified back-translation method was used to translate the questionnaire from English to Japanese. The longitudinal survey was performed in 29 female college swimmers who were followed up for more than 24 consecutive weeks. The response rate to the 24 weekly questionnaires was 88.8% (95% confidence interval [CI]: 85.2-92.3). Internal consistency was measured by using Cronbach's alpha (0.73 (0.69-0.77)). The anatomical areas most frequently affected by overuse injuries were the lower back (average weekly prevalence: 27.6%, 95% CI: 25.1-30.1), shoulder (16.0%, 95% CI: 13.7-18.2), knee (9.9%, 95% CI: 7.7-12.0), and ankle (9.0%, 7.6-10.5). The severity score showed that knee (22.5, range: 6-65), ankle (21.5, range: 6-67), and lower back (20.7, range: 6-80) injuries had the greatest impact. The Japanese version of the modified OSTRC overuse injury questionnaire demonstrated reliability and validity based on the results of internal consistency and trend of injury of the swimmers. The participants in the present study did not have substantial injuries or time-loss injuries and continued practicing and competing, despite these minor injuries. Although knee and ankle injuries do not occur as often as lower back and shoulder injuries, these injuries often had a greater impact on swimmers when they did occur.

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 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.

Spatial variability of nitrous oxide emissions and their soil-related determining factors in an agricultural field.

To evaluate spatial variability of nitrous oxide (N2O) emissions and to elucidate their determining factors on a field-scale basis, N2O fluxes and various soil properties were evaluated in a 100- x 100-m onion (Allium cepa L.) field. Nitrous oxide fluxes were determined by a closed chamber method from the one-hundred 10- x 10-m plots. Physical (e.g., bulk density and water content), chemical (e.g., total N and pH), and biological (e.g., microbial biomass C and N) properties were determined from surface soil samples (0-0.1 m) of each plot. Geostatistical analysis was performed to examine spatial variability of both N2O fluxes and soil properties. Multivariate analysis was also conducted to elucidate relationships between soil properties and observed fluxes. Nitrous oxide fluxes were highly variable (average 331 microg N m(-2) h(-1), CV 217%) and were log-normally distributed. Log-transformed N2O fluxes had moderate spatial dependence with a range of >75 m. High N2O fluxes were observed at sites with relatively low elevation. Multivariate analysis indicated that an organic matter factor and a pH factor of the principal component analysis were the main soil-related determining factors of log-transformed N2O fluxes. By combining multivariate analysis with geostatistics, a map of predicted N2O fluxes closely matched the spatial pattern of measured fluxes. The regression equation based on the soil properties explained 56% of the spatially structured variation of the log-transformed N2O fluxes. Site-specific management to regulate organic matter content and water status of a soil could be a promising means of reducing N2O emissions from agricultural fields.