Measurement of bend sprinting kinematics with three-dimensional motion capture: a test-retest reliability study

Sprint velocity decreases on the bend when compared with the straight, therefore understanding technique during bend sprinting could have important implications for aiding race performance. Few bend sprinting studies have used optoelectronic cameras to investigate kinematic variables. Limited published evidence regarding the reliability of marker sets in conditions representative of elite bend sprinting makes model selection difficult. Therefore, a test-retest protocol was conducted to establish the reliability and minimum detectable difference of a lower limb and trunk marker set during bend sprinting (radius: 36.5 m). Six participants completed five, 60 m trials at maximum effort, with data collected at 38-45 m. This was repeated 2-7 days later. Spatio-temporal (e.g., contact time) and kinematic variables (e.g., peak joint angles) were evaluated. Intra-class correlation coefficients (ICC) were used to determine the between- and within-day reliability. Between-day reliability (ICC 3, k) was fair to excellent for all variables. Compared to between-day, within-day reliability demonstrated stronger agreement for the majority of variables. Thus, same-day data collection is preferable. It has been established that the marker set is reliable for future use. In addition, the minimal detectable difference was calculated which serves as useful reference for future research in bend sprinting.

A Review of the Evolution of Vision-Based Motion Analysis and the Integration of Advanced Computer Vision Methods Towards Developing a Markerless System

BACKGROUND

The study of human movement within sports biomechanics and rehabilitation settings has made considerable progress over recent decades. However, developing a motion analysis system that collects accurate kinematic data in a timely, unobtrusive and externally valid manner remains an open challenge.

MAIN BODY

This narrative review considers the evolution of methods for extracting kinematic information from images, observing how technology has progressed from laborious manual approaches to optoelectronic marker-based systems. The motion analysis systems which are currently most widely used in sports biomechanics and rehabilitation do not allow kinematic data to be collected automatically without the attachment of markers, controlled conditions and/or extensive processing times. These limitations can obstruct the routine use of motion capture in normal training or rehabilitation environments, and there is a clear desire for the development of automatic markerless systems. Such technology is emerging, often driven by the needs of the entertainment industry, and utilising many of the latest trends in computer vision and machine learning. However, the accuracy and practicality of these systems has yet to be fully scrutinised, meaning such markerless systems are not currently in widespread use within biomechanics.

CONCLUSIONS

This review aims to introduce the key state-of-the-art in markerless motion capture research from computer vision that is likely to have a future impact in biomechanics, while considering the challenges with accuracy and robustness that are yet to be addressed.

Cricket

This study investigated the bowling arm kinematics of 21 elite fast bowlers (mean +/- SD; age = 27.8 +/- 3.9 years) while performing in test, tour and one day international matches. Thirty-one of the 34 deliveries analysed exhibited straightening at the elbow joint (straightening min = 3 degrees, max = 22 degrees, mean +/- SD = 9 +/- 5 degrees), which by strict definition in the 2000 laws of cricket made them illegal. Five deliveries from three bowlers exhibited hyperextension of the bowling elbow (19 +/- 5 degrees). When assessed against an arbitrary threshold of 15 degrees for elbow straightening, ball speeds for deliveries above this threshold (39.5 +/- 2.0 m/s) were significantly faster (effect size = 1.4; p = 0.006) than deliveries below it (37.1 +/- 1.4 m/s). When grouped by delivery length, the bouncers and short deliveries recorded more elbow straightening (12 +/- 6.6 degrees) than the good length deliveries (9 +/- 4.4 degrees) and the full deliveries (8 +/- 5.7 degrees), although these were not statistically significant differences. The results of this study support the implementation of a tolerance threshold for assessing the legality of fast bowling actions. Further research is recommended into in-match kinematic modelling, laboratory based assessments of illegal bowling actions, perceptual aspects of bowling actions and remedial methods to reduce elbow straightening in bowling actions.

Movement variability cannot be determined reliably from no-marker conditions

We sought to quantify the proportion of total variability due to movement variability in digitizing marker and no-marker conditions in treadmill running. Manually digitized markers gave variabilities in joint angles within 0.4 degrees of those from auto-tracking. Marker conditions allowed reliable estimation of movement variability by an experienced operator; the contribution of movement variability to total variability, expressed by omega-squared, had averages across the four operators of 97% for the knee angle and 93% for the hip. The no-marker condition did not allow reliable estimation of movement variability-the above figures fell, respectively, to 72% and 48%-and cannot be recommended. The group design in the marker condition produced omega-squared values of 97% knee and 91% hip, showing excellent objectivity (inter-operator reliability). However, without markers, these values fell to 47% and 15%, respectively, indicating that movement variability cannot be assessed objectively in no-marker conditions.

Reproducibility of energy parameters in the pole vault

The purpose of this study was to analyze the reproducibility of kinematic, dynamometric and derived mechanical energy parameters in the pole vault as a main precondition for the practical applicability of the concept of energy exchange in the pole vault. A total of 46 vaults of six experienced vaulters were analyzed. On the basis of 3D kinematic data of the athlete and the pole and ground reaction forces measured at the end of the pole in the planting box the reproducibility of parameters that describe the energy transfer into the pole and the energy exchange between the athlete and the pole during the vault was proofed. Intraclass correlation, mean root mean square and the coefficient of variance were determined, additionally the Wilcoxon Test was applied. Parameters of the athlete's 3D total mechanical energy, e.g. initial energy and final energy, and the pole energy (maximum pole energy, energy of the pole due to compressive force and bending moment) were highly reproducible. The distribution of the energy transferred into the pole due to compressive force and bending moment, the same as the energy gain of the vaulter-pole system during the vault, which indicates the strategy of interacting with the pole, were also reproducible. With this the concept of energy exchange in the pole vault can be used to analyze the impact of training interventions, changes in movement pattern respectively, on the vaulters performance during different phases of the vault. The analysis of one trial of an athlete should be sufficient to identify changes in the athlete's interaction with the elastic pole.

Cricket

We investigated the techniques used by nine right-handed, international batsmen to perform front foot off-side drives in first class and international matches. All strokes were captured using two synchronised high-speed video cameras; nine were selected for kinematic analysis. These movement sequences were then manually digitised at a sampling frequency of 125 Hz using APAS motion analysis software. The results of this study indicated that the batsmen used movement patterns that enabled important aspects of stroke production, such as the front stride and the downswing of the bat, to be delayed so that additional information from ball flight could be assimilated. Front upper limb segments were constrained to work in a unitary fashion, with the peak horizontal end point speed of each segment occurring almost simultaneously just before impact. It has been suggested that these strategies serve to enhance stroke accuracy. Other aspects of their techniques included a distinctively looped bat path, a front foot placement that occurred only just before impact, and a front ankle that was positioned well inside the line of the ball at impact. Various technical parameters, such as the alignment of the trunk relative to ground and the continuous flow of the bat between the backswing and downswing, were similar to findings in previous batting research. Other characteristics of stroke production not previously addressed, including the path of the bat and the timing of the front stride, may challenge some long held beliefs evident in current coaching literature.

Reliability of Biomechanical Variables of Sprint Running

PURPOSE

The purpose of this paper was to report the reliability of variables used in the biomechanical assessment of sprint running and to document how these reliability measures are likely to improve when using the average score of multiple trials.

METHODS

Twenty-eight male athletes performed maximal-effort sprints. Video and ground reaction force data were collected at the 16-m mark. The reliability (systematic bias, random error, and retest correlation) for a single score was calculated for 26 kinematic and 7 kinetic variables. In addition, the reliability (random error and retest correlation) for the average score of 2, 3, 4, and 5 trials was predicted from the reliability of a single score.

RESULTS

For all variables, there was no evidence of systematic bias. The measures of random error and retest correlation differed widely among the variables. Variables describing horizontal velocity of the body's center of mass were the most reliable, whereas variables based on vertical displacement of the body's center of mass or braking ground reaction force were the least reliable. For all variables, reliability improved notably when the average score of multiple trials was the measurement of interest.

CONCLUSION

Although it is up to the researcher to judge whether a measurement is reliable enough for its intended use, some of the lower-reliability variables were possibly too unreliable to monitor small changes in an athlete's performance. Nonetheless, there was a consistent trend for reliability to improve notably when the average score of multiple trials was the measurement of interest. Subsequently, if resources permit, researchers and applied sports-scientists may like to consider using the average score of multiple trials to gain the advantages that improved reliability offers.

Reproducibility of electromyography and ground reaction force during various running techniques

This study examined the validity of the assumption of electromyographic (EMG) and vertical ground reaction force (GRF) parameter reproducibility during running at different velocities and stride frequencies. Each of 12 female long distance runners ran on a treadmill in combinations of three velocities (2.5, 3.0 and 3.5 m/s) and three stride frequencies (preferred, +/-10% from preferred). Seven parameters from the GRF and five parameters from the EMG signals from five muscles of the lower extremity were evaluated (1000 Hz). The GRF was analysed by a pressure measuring insoles. A total number of three trials for each running condition were recorded. GRF parameters during all running conditions showed high intraclass correlation coefficients (ICC average 0.87). The ICC of the EMG parameters of gastrocnemius medialis and lateralis were high (r>0.69 in 73% of the data), while those for vastus lateralis (22%), hamstrings (42%) and tibialis anterior (51%) were clearly lower. The results revealed that GRF parameters were reproducible during all running techniques indicating that a single trial would provide reproducible GRF-data. The reproducibility of the EMG parameters was not influenced by the running technique but dependent on the parameter itself and on the muscle studied.

Assessment of the reliability of a technique to measure postural sway in horses

OBJECTIVE

To assess the reliability of the center-of-pressure (COP) values obtained from a force platform for analysis of postural sway in horses.

ANIMALS

Six 2-year-old horses that were free from lameness and neurologic disease.

PROCEDURE

Horses stood stationary with all 4 hooves on a force platform; COP data were collected at 1,000 Hz and 3-dimensional kinematics collected at 60 Hz for 10 seconds. Five trials were recorded at each of 3 time periods (15-minute intervals) or at 1 time period on 3 separate days. Mean values for each set of 5 trials and actual, normalized, and relative COP variables were calculated. The reliability was quantified by use of agreement boundary.

RESULTS

The COP results within and across days were similar and provided small agreement boundary limits (eg, across days, in order of least relative reliability: area, +/- 62 mm2; mediolateral range, +/- 8 mm; radius, +/- 2 mm; craniocaudal range, +/- 4 mm; and velocity, +/- 3 mm/s). Head height possessed the greatest relative intraday reliability (12%) but a high agreement boundary limit (+/- 0.15 m). CONCLUSIONS AND CLINICAL RELEVANCE; The use of a force platform to analyze postural sway in a group of young healthy horses was found to produce reliable results and may provide a simple and sensitive measure for assessing balance deficiencies in horses. Agreement boundaries provide 95% confidence intervals for use as limits of error and variability in measurements that, if exceeded, may signify meaningful effects.

Symmetry and reproducibility of kinematic parameters during various running techniques

PURPOSE

This study examined the validity of the assumption of lower-extremity kinematic parameter reproducibility and symmetry during running with different velocities and stride frequencies.

METHODS

Each of 12 female long-distance runners ran on a treadmill in combinations of three different velocities (2.5, 3.0, and 3.5 m.s-1) and three different stride frequencies (preferred and +/- 10% from preferred). The left and right sides of the athletes were filmed using video cameras placed orthogonally to the sagittal plane. A total number of three step cycles for each running condition were recorded (250 Hz). For each side of the body, 19 sagittal kinematic parameters from the lower extremity were evaluated.

RESULTS

Intraclass correlation coefficients (ICC) for both legs were high (generally > 0.80). Only the angular velocity parameters demonstrated correlation values below 0.70. The symmetry index for the linear and angular displacement parameters and the contact times during all running techniques were less than 8%, whereas those for the angular velocity parameters and flight times were higher than 15%.

CONCLUSION

The present results suggested that the degree of reproducibility and symmetry of kinematic data do not vary with a deliberate change in running technique but rather depend on the parameter itself. With respect to the economy of data analysis, the present findings indicate that recording a single monolateral trial would provide reproducible and symmetric values for most kinematic parameters.

Changes in coordination during the first 8 months of independent walking

This study assessed the development of coordination during the first 8 months of independent walking and identified potential hypotheses that may be tested by further research. The walking gait of a normal child was recorded on video at the onset of independent walking, and thereafter at monthly intervals over a period of 8 months. Video images were digitized and 3-dimensional coordinates obtained. The coefficient of variation was used to measure variability in the movement. Other variables studied included range of movement, relationships between angles, angular velocties, timing relationships, proportional distance and temporal phasing. By adopting a dynamical systems perspective, this study identified variables that challenged the stability of the locomotor system. Coordinative structures were observed to shift from one state to another from age 18 months; such mutations included decreased range of motion, hip knee angle relationship that resemble mature walking, relative time of peak angular velocity, and stability of angle angular velocity phasing.