Sports Biomechanics最新文献

This study aimed to identify the optimal transition velocities between streamlined glide (SL), underwater dolphin kick (DK), and front crawl (FC) during high-speed swimming. Ten elite female swimmers performed front crawl and dolphin kick trials in a long-course pool, and repeated the same motions under tethered conditions in a water flume to measure net force. Power-law fitting was applied to model net force as a function of flow velocity across the three movement conditions. The results revealed distinct patterns in the scaling coefficients $\left(A\right)$ and exponents $\left(n\right)$, following the order: $A_{\mathrm{SL}}>A_{\mathrm{DK}}>A_{\mathrm{FC}}$ and $n_{\mathrm{SL}}<n_{\mathrm{DK}}<n_{\mathrm{FC}}$. The fitted net force curves intersected at two velocities, $U_{\mathrm{SL}-\mathrm{DK}}$ and $U_{\mathrm{DK}-\mathrm{FC}}$, and for most swimmers, these intersection velocities exceeded their respective constant velocities, $V_{\mathrm{DK}\_\mathrm{const}}$ and $V_{\mathrm{FC}\_\mathrm{const}}$. These intersection points indicate the optimal timing for initiating propulsive actions to minimise deceleration during the post-start and post-turn phases. A conceptual model was proposed to explain the phase transition strategy based on velocity-dependent net force profiles. Although individual variation was observed, most swimmers exhibited similar trends, supporting the applicability of the model. These findings provide a fluid mechanical perspective for optimising underwater strategies and may contribute to enhanced start and turn performance in competitive swimming.

The purpose of this study was to examine the effects of handheld dumbbell load on force-time characteristics during countermovement jumps with accentuated eccentric loading (CMJ_AEL). Nineteen youth athletes (9 males and 10 females; age 15 ± 2 years; stature 1.66 ± 0.09 m; body mass 54.8 ± 8.4 kg) performed bodyweight CMJs (CMJ_BW) followed by CMJ_AEL conditions at 20% (CMJ_AEL20) and 30% (CMJ_AEL30) of body mass. Vertical ground reaction force (vGRF) data were analysed using a combined forward and backward integration method to account for changes in system mass. Jump height increased in both CMJ_AEL conditions compared with CMJ_BW, with the greatest improvement during CMJ_AEL20. Propulsion time increased with load, while propulsion mean vGRF decreased, suggesting participants produced force over a longer duration to attain a greater jump height. Propulsion mean velocity and power increased under CMJ_AEL20 but changes were uncertain for CMJ_AEL30. Braking responses were inconsistent, as higher braking vGRF were not accompanied by meaningful changes in braking velocity or power. These findings suggest CMJ_AEL can acutely increase jump height; however, associated changes in force-time characteristics, particularly phase durations and velocities, should be considered, as they provide insight into how jump performance is achieved in response to AEL.

The throwing motion in baseball pitching is the fastest recorded human motion, demanding higher sample frequencies than most human movements. Previous studies have used sample frequencies from 240 to 500 Hz and a wide range of low-pass filter frequencies, although 13.4 and 18.0 Hz are the most common. This study examined the effects of two common sample frequencies (240 and 480 Hz) and three filter frequencies (13.4, 18.0, 27.2 Hz) on pitching data. Fastballs from 28 professional baseball pitchers were collected at 480 Hz with marker motion capture, then down-sampled to 240 Hz; each data set was filtered at the three filter frequencies. Twenty-six common kinematic, temporal and kinetic variables were computed for each pitcher across all sample-filter frequency combinations and compared using two-way repeated measures ANOVA. Differences were interpreted relative to minimal clinically important differences (MCID). Pitching data were more sensitive to filter frequency (significant differences above MCID in 13 of 26 variables) than to sample frequency (4 of 26 variables). Variables involving differentiation (e.g. velocities and torques) were most impacted. Based on these findings and time-series inspection, we recommend a minimum sample frequency of 240 Hz and a Butterworth low-pass filter of 18.0 Hz for marker-based motion capture pitching mechanics.

Eccentric finger movements have been identified as risk factor in the injury mechanism of pulley ruptures during climbing. So far, they have mainly been associated with inadvertent events. Whether eccentric movements also occur as regular motion patterns was not assessed. Main purpose of this study was to examine eccentric finger movements during typical climbing tasks. Therefore, kinematics and interaction force of eleven elite climbers was recorded during a sequence of four climbing moves. Participants were instructed to use crimp, half-crimp, open-hand grip and campusing. Change of flexion angle in the proximal interphalangeal (PIP) joints from the start to the end of the holding phase (ΔPIP_P2) was calculated. Mean ΔPIP_P2 was -1.5° (SD 6.6°), 0.2° (5.1°), -2.9° (3.4°) and -6.0° (9.6°) for the open-hand, half-crimp, crimp and campusing task, respectively, whereby negative values represent eccentric movements. Eccentric finger joint movements (ΔPIP_P2 < 0°) during the holding phase were very common (59-73%) across all grip types. The loading rate was highest during campusing and lowest using the crimp grip. Climbers exhibit eccentric finger movements not only during accidental slips or when fatigued, but also as consistent patterns. Further research is needed to assess whether these differences are associated with an individual's risk of pulley injury.

The objective of this study was to clarify the effects of fatiguing muscle contractions of the m. quadriceps femoris on kicking abilities of experienced soccer players. 16 male professional (n = 5) and amateur players (n = 11) performed kicking tests in two conditions (fatigue and control) on separate days in a randomised crossover design. The fatiguing protocol performed with the kicking leg consisted of 5 sets of 10 maximal voluntary concentric and eccentric knee extensions. Maximal voluntary isometric contraction force (MVIC), 15 hz/50 hz stimulation force ratio (force ratio), and kicking abilities were assessed before and after completion of the fatiguing protocol or rest (control). The fatiguing protocol successfully induced fatigue of 14.0 ± 2.7% (mean ± SE) reduced MVIC and 14.0 ± 3.7% reduced force ratio while no reductions occurred in the control condition. Between group difference showed ball speed declined 2.1 ± 0.95% more following the fatigue protocol compared to control condition. On the control day shooting accuracy improved by 13.3 ± 5.6% and was numerically impaired on the intervention day by 1.0 ± 9.2%. Despite this, no significant between group difference was observed in shooting accuracy (p = 0.18). The study demonstrated that fatigue induced by prior muscle contractions impairs maximal shooting speed, but we observed no significant impairment of shooting accuracy.

In figure skating, achieving higher scores often relies on the successful execution of difficult jumps, e.g., quadruple jumps. According to previous biomechanical studies, jump heights do not change significantly even with more rotational jumps. However, strategies employed by top skaters to acquire new jumps are unclear. Therefore, this study aimed to investigate specific kinematic strategies used by skaters to perform the quadruple axel jump (4A), focusing on two skaters (skaters A and B) who attempted this jump in competitions. Using data from the Ice Scope tracking system, this study analysed the vertical height, horizontal distance, take-off speed, landing speed, and height-to-distance ratio of the jumps. Both skaters achieved higher vertical heights in their 4A attempts than in their triple axel jump (3A) attempts. Notably, Skater A's successful 4A and Skater B's downgraded 4A had significantly greater vertical heights than the average 3As among world-class skaters. This suggests a strategic shift towards increasing the vertical height to master 4As, contrary to previous biomechanical research that did not emphasise vertical height. These findings update existing theories on figure skating research and provide insights into training strategies for mastering difficult jumps.

This paper critically appraises the utility of markerless motion capture in the context of skill development and sports performance enhancement. If markerless motion capture is to be useful in a profiling or monitoring capacity, the amount of measurement error needs to be smaller than the amount of movement variability over iterative performance trials. Current evidence suggests that it is unlikely that any existing markerless system satisfies this requirement. The resolution of this issue would, in principle, enable technical errors to be more easily pinpointed and performance variation to be better explained. However, decomposing movement variability into its functional and dysfunctional components is not only a nontrivial undertaking for most practitioners, the practical consequences of doing so are limited because synergies are self-organising entities and any attempt to micro-manage their constituent degrees of freedom will likely have deleterious effects on performance. Biomechanical measurements technologies, including markerless motion capture, may be best used to support search strategies employed by coaches and athletes.

It is well-known among swimmers and coaches that the swimming speed of the underwater dolphin kick (UDK) is higher than that of the underwater flutter kick (UFK). This study aimed to clarify the differences in swimming performance between the two kicking styles in terms of kinematics, kinetics and muscle activity. Eight male swimmers performed UDK and UFK in a water flume at same effort levels. The three-dimensional motion analysis and measurement of surface electromyography for the left lower limb were performed. The fluid forces acting on the body and joint torques were estimated using Swumsuit simulator. As the results, the kick amplitude and range of joint motion were smaller for the UFK than for the UDK, and the muscle activity and the peak joint torques of the hip and knee were lower for the UFK than for the UDK. Furthermore, the estimated propulsion for both the downward and upward kicks was lower for the UFK than for the UDK. Therefore, our results suggest that the differences in propulsion between the two kicking styles, caused by the differences in movement and muscle activity, may influence the differences in swimming speed.

Pelvic running injuries often require extensive rehabilitation and pelvic girdle pain is a barrier to running engagement in population sub-groups, such as perinatal women. However, exploration into how external pelvic loading may be altered during running is limited. This study assessed which biomechanical variables influence changes in external peak pelvic acceleration during treadmill running, across various stride frequency conditions. Twelve participants (7 female, 5 male) ran (9 km∙h^-1) at their preferred stride frequency, and at ± 5% and ± 10% of their preferred stride frequency. Coordinate and acceleration data were collected using a motion capture system and inertial measurement units. Linear mixed models assessed peak tibial acceleration, displacement from hip to knee and ankle, contact time, and stride frequency as predictors of peak pelvic acceleration. Stride frequency and contact time interacted to predict peak vertical (p = .006) and resultant (p = .009) pelvic acceleration. When modelled, short contact times and low stride frequencies produced higher peak vertical (p = .007) and resultant (p = .016) pelvic accelerations than short contact times and average, or high stride frequencies. Increasing contact time, or increasing stride frequency at shorter contact times, may therefore be useful in reducing pelvic acceleration during treadmill running.

This study aimed to investigate the effect of the flutter kick on the propulsive force generated by a stroke. Eight male swimmers performed 20 m front crawl trials under two conditions: the Whole Condition, involving maximum effort (T100%) and stroke frequencies at 70, 80, and 90% of T100%, and the Arm Condition, which excluded the flutter kick and matched stroke frequencies with the Whole Condition. Various parameters, including swimming velocity, stroke frequency, stroke length, three-dimensional (3D) resultant hand speed, and hand propulsion were calculated based on underwater 3D motion analysis and hand pressure distribution measurements. A two-way repeated-measures ANOVA was conducted to assess differences, considering the conditions and instructed frequencies as the two factors. There was no significant interaction between the condition and intensity for any of the variables. There was a significant main effect of condition on swimming velocity and stroke length, with these variables being 16.9-18.5% higher and 17.3-19.5% longer, respectively, in the Whole Condition compared to the Arm Condition. However, there was no difference in hand propulsion between the conditions, and it was clarified that the flutter kick did not affect hand propulsion at any swimming velocity.