Paddle propulsive force and power balance: a new approach to performance assessment in flatwater kayaking

This study aims to determine the propulsive force (Fp) and its timing of application during the paddle stroke confirming the dynamic balance between propulsive and drag powers (Pp = Pd) in kayaking performance. Ten male sub-elite paddlers participated in the study. The athletes carried out three trials of 50 m at three different velocity ranges: 2.70 - 3.00 m/ s; 3.01 - 3.50 m/s and 3.51 - 4.00 m/ s. A constant velocity during each trial was maintained and the section between 15 and 40 m of the total pool length was considered for further analysis. Data were collected using the E-kayak system provided of an instrumented paddle and 2D video analysis. It was observed that the propulsive force increases in intensity (up to 90% of the peak force) as the velocity increases. The dynamic balance between Pd and Pp was confirmed with a Bland and Altman plot (estimated bias: 0.2; LoA: 12.8 and 13.3 W). The related comparisons between the power parameters showed no significant difference (p > 0.050) in each of the considered velocity. By applying the dynamic balance theory between Pp = Pd on the data obtained from the interaction among GPS, force on the paddle and 2D video analysis, it is possible to acquire essential information (Fp, Pp) to monitor the flatwater kayaking performance.

A Kinematic Analysis of the Basketball Shot Performed with Different Ball Sizes

In youth basketball, the ball’s size is adapted to fit the participants’ physical capacities and improve the development of manipulative skills. The current study compared the kinematic parameters of the basketball shot (BS) performed with two different ball sizes. Twenty-seven adolescent females aged 12.1 ± 0.9 years (height: 153.3 ± 8.0 cm; body mass: 48.8 ± 12.8 kg) completed 10 BS trials from a frontal position at 5.75 m from the basket with two ball sizes: a smaller and lighter ball (size five, 480 g) and the standard ball size for their age (size six, 566 g). No statistically significant differences were observed for ball release variables or efficacy levels. Significantly greater shoulder flexion was detected at release while shooting with a size six ball (F = 2.982, p ≤ 0.01). The shoulder’s angular velocity at release was significantly lower while performing with a size six ball (F = 3.089, p ≤ 0.01). No significant differences were found for the elbow or knee angles or angular velocities. Stature and upper-body strength were significantly correlated with selected kinematic parameters. A change in ball size may be a helpful strategy for coaches seeking to promote optimal shooting patterns, enhancing effectiveness and enjoyment, particularly among young people and more inexperienced players.

Kinematic Analysis of Water Polo Player in the Vertical Thrust Performance to Determine the Force-Velocity and Power-Velocity Relationships in Water: A Preliminary Study

BACKGROUND

To date, studies on muscle force and power-velocity (F-v and P-v) relationships performed in water are absent.

AIM

The goal of this study is to derive the F-v and P-v regression models of water polo players in water vertical thrust performance at increasing load.

METHODS

After use of a control object for direct linear transformation, displacement over the water and elapsed time was measured, by using a high-speed 2D-videoanalysis system, on 14 players involved in the study.

RESULTS

Intra-operator and player's performance interclass correlation coefficient (ICC) reliability showed an excellent level of reproducibility for all kinematic and dynamic measurements considered in this study with a coefficient of variation (CV) of less than 4.5%. Results of this study have shown that an exponential force-velocity relationship seems to explain better the propulsive force exerted in the water in lifting increasing loads compared to the linear one, while the power and velocity have been shown to follow a second-order polynomial regression model.

CONCLUSION

Given the accuracy of the video analysis, the high reliability and the specificity of the results, it is pointed out that video analysis can be a valid method to determine force-velocity and power-velocity curves in a specific environment to evaluate the neuromuscular profile of each water polo player.

Two-Man Bobsled Push Start Analysis

The importance of push start times on bobsled performance was evidenced by some studies, but at this moment there is no article to the authors’ knowledge that describes the bobsled push start. Thus, the objectives of this study were to describe the two-man bobsled push start, analyze the differences between teams, and estimate the most important variable analyzed. We hypothesized that the pilot and brakeman athletes’ movement patterns during a bobsled pushing start can be described. The images used in this study were obtained during the men’s two-man XIV World Championship of Bobsled (2004). Fifteen best teams participating in the championship were recorded, and four start runs for each team were analyzed. The videos were captured by two digital video cameras. The pilot athletes were analyzed during the moment that they touched the lateral push bar of the sled, and the brakemen were analyzed during the first take-off and first landing. The teams were pooled in three groups of five teams using the final ranking of pushing time. We concluded that there was a distinct pattern movement for pilots and brakemen. The initial position of the majority of the pilots was localized slightly behind the bar. After touching the lateral bar, the pilots remained in a semi-squat position, pushing the sled forward in a pattern of marching movement. All brakemen used the board attached to the track as a support for both feet at the start. The brakeman gave the greatest contribution to break the inertia of the sled. There was no significant difference of movement between the three groups analyzed for the pilot and the brakeman.

Equine hoof slip distance during trot at training speed: comparison between kinematic and accelerometric measurement techniques

Longitudinal sliding of horse's hooves at the beginning of stance can affect both performance and orthopaedic health. The objective of this study was to compare two measurement methods for quantifying hoof slip distances at training trot. The right front hoof of four French Trotters was equipped with an accelerometer (10 kHz) and kinematic markers. A firm wet sand track was equipped with a 50 m calibration corridor. A high-frequency camera (600 Hz) was mounted in a vehicle following each horse trotting at about 7 m/s. One of the horses was also trotted on raw dirt and harrowed dirt tracks. Longitudinal slip distance was calculated both from kinematic data, applying 2D direct linear transformation (2D-DLT) to the markers image coordinates, and from the double integration of the accelerometer signal. For each stride, both values were compared. The angle of the hoof with respect to the track was also measured. There was 'middling/satisfactory' agreement between accelerometric and 2D-DLT measurements for total slip and 'fairly good' agreement for hoof-flat slip. The influence of hoof rotation on total slip distance represented <6% of accelerometric measures. The differences between accelerometric and kinematic measures (from -0.5 cm to 2.1cm for total slip and from -0.2 cm to 1.4 cm for hoof-flat slip) were independent of slip distance magnitude. The accelerometric method was a simple method to measure hoof slip distances at a moderate training speed trot which may be useful to compare slip distances on various track surfaces.

Velocity and acceleration before contact in the tackle during rugby union matches

The velocity and acceleration at which the ball-carrier or tackler enters the tackle may contribute to winning the contest and prevailing injury free. Velocity and acceleration have been quantified in controlled settings, whereas in match-play it has been subjectively described. The purpose of this study was to determine the velocity and acceleration of the ball-carrier and tackler before contact during match-play in three competitions (Super 14, Varsity Cup, and Under-19 Currie Cup). Using a two-dimensional scaled version of the field, the velocity and acceleration of the ball-carrier and tackler were measured at every 0.1 s to contact for 0.5 s. For front-on tackles, a significant difference (P < 0.05) between the ball-carrier (4.6 ± 1 m · s⁻¹) and tackler (7.1 ± 3.5 m · s⁻¹) was found at the 0.5 s time to contact interval in the Varsity Cup. For side-on tackles, differences between the two opposing players were found at 0.5 s (ball-carrier: 4.6 ± 1.7 m · s⁻¹; tackler: 3.1 ± 1.2 m · s⁻¹) and 0.4 s (ball-carrier: 6.3 ± 2.3 m · s⁻¹; tackler: 3.7 ± 1.6 m · s⁻¹) at Under-19 level. After 0.4 s, no significant differences (P > 0.05) were evident. Also, the ball-carrier's velocity over the 0.5 s was relatively stable compared with that of the tackler. Results suggest that tacklers adjust their velocity to reach a suitable relative velocity before making contact with the ball-carrier.

Determination of football pitch locations from video footage and official pitch markings

The ability to determine a specific location on a football (soccer) pitch from television footage would provide a cost-effective method of obtaining competition-specific information on many professional and international teams. This study presents the accuracy and reliability of a new method of calculating ball location from simulated television coverage and known pitch markings. The coordinates of 99 markers of known location on a football pitch were digitized from video. An intersection point was determined from the equations of two lines that form pitch markings and the relationship from this point to other known pitch coordinates was calculated using a curve-fitting based method. Average error between known and reconstructed measures was 0.21 m for pitch width and 0.11 m for pitch length from a view simulating television coverage. Inter- and intra-rater reliability analyses showed researchers could consistently reconstruct pitch locations to within less than half a metre. The accuracy and reliability of this method will be sufficient for most practical uses in an applied sport environment, although the level of accuracy required will depend on the specific application. This method could be applied to other sports to determine specific locations on a pitch or court or to improve current competition analysis systems.

Inter-segmental coordination in progressions for the longswing on high bar

This study focused on identifying the most effective skill progression for developing the longswing on high bar in men's artistic gymnastics. Building on previous work by Irwin and Kerwin, in which a method to rank progressions based on their angular kinematics was developed, this study aimed to use the method to quantify similarities in inter-segmental coordination between selected progressions and the longswing on high bar. Video images of four members of the UK men's national gymnastics squad performing three series of five longswings and eight progressions were recorded at 50Hz. Two-dimensional direct linear transformation techniques were used to determine the real-world coordinates from the digitized data. Inter-segmental coordination of the hip and shoulder joints during the functional phases of the longswing was assessed using continuous relative phase. Similarity between the longswing and each progression was represented by a "specificity score", which was also used to rank the progressions. Each progression's specificity score was calculated by combining a "difference score" (root mean squared difference between the continuous relative phase profiles of the longswing and the progression) and a "variability score" (standard deviation of the continuous relative phase profiles for each progression). The progressions that were most similar to the longswing included the looped bar longswing and layaway swing down (ranked 1st and 2nd), with specificity scores of 9% and 10% respectively. In contrast, the least similar progressions were the looped bar "no action" longswing (51%) and pendulum swing (63%) (ranked 7th and 8th). Establishing effective skill learning pathways is recognized as a key component of the coaching process and ranking progressions based on their specificity score provided a mechanism to identify progressions with similar inter-segmental coordination profiles to the key skill on the high bar, the longswing.

A Comparison of Time–Motion Analysis Methods for Field-Based Sports

Purpose:

To assess the validity of a digitizing time–motion-analysis method for field-based sports and compare this with a notational-analysis method using rugby-union match play.

Method:

Five calibrated video cameras were located around a rugby pitch, and 1 subject completed prescribed movements within each camera’s view. Running speeds were measured using photocell timing gates. Two experienced operators digitized video data (operator 1 on 2 occasions) to allow 2-dimensional reconstruction of the prescribed movements.

Results:

Accuracy for total distance calculated was within 2.1% of the measured distance. For intraoperator and interoperator reliability, calculated distances were within 0.5% and 0.9%, respectively. Calculated speed was within 8.0% of measured photocell speed with intraoperator and interoperator reliability of 3.4% and 6.0%, respectively. For the method comparison, two 20-minute periods of rugby match play were analyzed for 5 players using the digitizing method and a notational time–motion method. For the 20-minute periods, overall mean absolute differences between methods for percentage time spent and distances covered performing different activities were 3.5% and 198.1 ± 138.1 m, respectively. Total number of changes in activity per 20 minutes were 184 ± 24 versus 458 ± 48, and work-to-rest ratios, 10.0%:90.0% and 7.3%:92.7% for notational and digitizing methods, respectively.

Conclusion:

The digitizing method is accurate and reliable for gaining detailed information on work profiles of field-sport participants and provides applied researchers richer data output than the conventional notational method.

Effects of light refraction on the accuracy of camera calibration and reconstruction in underwater motion analysis

One of the most serious obstacles to accurate quantification of the underwater motion of a swimmer's body is image deformation caused by refraction. Refraction occurs at the water-air interface plane (glass) owing to the density difference. Camera calibration-reconstruction algorithms commonly used in aquatic research do not have the capability to correct this refraction-induced nonlinear image deformation and produce large reconstruction errors. The aim of this paper is to provide a thorough review of: the nature of the refraction-induced image deformation and its behaviour in underwater object-space plane reconstruction; the intrinsic shortcomings of the Direct Linear Transformation (DLT) method in underwater motion analysis; experimental conditions that interact with refraction; and alternative algorithms and strategies that can be used to improve the calibration-reconstruction accuracy. Although it is impossible to remove the refraction error completely in conventional camera calibration-reconstruction methods, it is possible to improve the accuracy to some extent by manipulating experimental conditions or calibration frame characteristics. Alternative algorithms, such as the localized DLT and the double-plane method are also available for error reduction. The ultimate solution for the refraction problem is to develop underwater camera calibration and reconstruction algorithms that have the capability to correct refraction.

Biomechanical research in artistic gymnastics: a review

Biomechanical research into artistic gymnastics has grown substantially over the years. However, most research is still skill oriented with few tries at generalization. Consequently, our understanding of the principles and bases of the sport, although improved, is still marginal with gaps in knowledge about technique attributes throughout the sport. For that reason, this review begins with an attempt to identify important variables contributing to successful performance. The review is presented in clusters of work in similar apparatuses culminating in Tables offering an 'at a glance' summary of knowledge in each cluster. The last section of the review tries to give some direction to future biomechanical research in gymnastics in issues relating to data collection--two-dimensional or three-dimensional, image size, frame rate--and analysis, such as descriptive or explanatory, simulation and optimization, and statistical issues.

Effects of light refraction on the accuracy of camera calibration and reconstruction in underwater motion analysis

One of the most serious obstacles to accurate quantification of the underwater motion of a swimmer's body is image deformation caused by refraction. Refraction occurs at the water-air interface plane (glass) owing to the density difference. Camera calibration-reconstruction algorithms commonly used in aquatic research do not have the capability to correct this refraction-induced nonlinear image deformation and produce large reconstruction errors. The aim of this paper is to provide a through review of: the nature of the refraction-induced image deformation and its behaviour in underwater object-space plane reconstruction; the intrinsic shortcomings of the Direct Linear Transformation (DLT) method in underwater motion analysis; experimental conditions that interact with refraction; and alternative algorithms and strategies that can be used to improve the calibration-reconstruction accuracy. Although it is impossible to remove the refraction error completely in conventional camera calibration-reconstruction methods, it is possible to improve the accuracy to some extent by manipulating experimental conditions or calibration frame characteristics. Alternative algorithms, such as the localized DLT and the double-plane method are also available for error reduction. The ultimate solution for the refraction problem is to develop underwater camera calibration and reconstruction algorithms that have the capability to correct refraction.

Gymnastics

Based on specificity of training and biomechanical analysis, the aim of this study was to develop a method to rank selected progressions for learning the longswing on high bar. Four members of the Men's National Gymnastics Squad were recorded (50 Hz) performing three series of five longswings and eight progressions. Real world co-ordinates from the digitized data were determined using two-dimensional direct linear transformation. Biomechanical similarity between the functional phases of the longswing and the corresponding phases of the progressions were calculated. The functional phases were described as a hyperextension to flexion of the hip and hyperflexion to extension of the shoulder joints as the gymnast passed underneath the bar. Using a combined score of 'Difference' and movement 'Variability' a 'Specificity score' was calculated for hip and shoulder angular displacements and velocities. An overall score based on the average of the four scores provided a ranked list of progressions based on their similarity to the target skill. The progression that showed the greatest similarity to the biomechanics of the longswing, and was therefore ranked first, was the chalked bar pendulum swing. The least similar progression, and, therefore, eighth ranked, was the chalked bar bent knee longswing. The hip kinematics were found to contribute most to the overall differences because the performance requirements of these progressions emphasize an increase in hip flexion during the ascending phase. The method described provides a means to quantify and rank progressions based on their kinematic similarity to the longswing.