2D Video Analysis Research Articles

Technical and Morphometric Comparisons Between Vertical and Horizontal Functional Hemispherotomies-A Juxtaposed 2D Video Analysis: 2-Dimensional Operative Video.

Technical and Morphometric Comparisons Between Vertical and Horizontal Functional Hemispherotomies-A Juxtaposed 2D Video Analysis: 2-Dimensional Operative Video.

Smartphone Assessment of the Sitting Heel-Rise Test.

The study presents a new approach for assessing plantarflexor muscles' function using a smartphone. The test involves performing repeated heel raises for 60 s while seated. The seated heel-rise test offers a simple method for assessing plantarflexor muscles' function in those with severe balance impairment who are unable to complete tests performed while standing. The study aimed to showcase how gyroscopic data from a smartphone placed on the lower limb can be used to assess the test. Eight participants performed the seated heel-rise test with each limb. Gyroscope and 2D video analysis data (60 Hz) of limb motion were used to determine the number of cycles, the average rise (T-rise), lowering (T-lower), and cycle (T-total) times. The number of cycles detected matched exactly when the gyroscope and kinematic data were compared. There was good time domain agreement between gyroscopic and video data (T-rise = 0.0005 s, T-lower = 0.0013 s, and T-total = 0.0017 s). The 95% CI limits of agreement were small (T-total -0.1118, 0.1127 s, T-lower -0.1152, 0.1179 s, and T-total -0.0763, 0.0797 s). Results indicate that a smartphone placed on the thigh can successfully assess the seated heel-rise test. The seated heel-rise test offers an attractive alternative to test plantarflexor muscles' functionality in those unable to perform tests in standing positions.

High Agreement Between 3D Motion Capture and 2D Video Analysis Systems and Raters for Knee Flexion Range of Motion During A Single Leg Drop Landing Task

OBJECTIVE: To determine the agreement between a 2-dimensional (2D) and 3-dimensional (3D) video capture system and between multiple raters during a single leg drop landing task. DESIGN: Cross-sectional observational study METHODS: Single leg drop landing trials of twenty-three males (n=12) and females (n=11) were recorded using the 2D and 3D systems. Reliability and agreement were quantified through intraclass correlation coefficients (ICC2, k), standard error of the measurement (SEM), and Bland-Altman plots. Analysis of variance (ANOVA) assessed systematic error between the 2D raters and 3D system. RESULTS: A one-way ANOVA on 35 drop-landing trials across raters detected a difference across the 3 estimates of knee flexion range of motion (p<0.001) where rater 1 did not differ (mean difference ± standard error: 1.15±0.48°, p=0.54) from the 3D system, rater 2 > 3D system (3.30±0.76°, p<0.001), and rater 1 and 2 differed (2.14±0.82°, p=0.04). There was high reliability between the two 2D raters (ICC2, k=0.89; SEM=3.44°). Rater 1 completed analyses on 87 additional trials (total n=117) and was comparable to the 3D system (0.87±0.47°, p=0.06; ICC2, k=0.90; SEM=3.52°). CONCLUSION: 2D video analysis can be used in a clinical setting where 3D capture of movement mechanics is not feasible.

Automating Video-Based Two-Dimensional Motion Analysis in Sport? Implications for Gait Event Detection, Pose Estimation, and Performance Parameter Analysis.

Two-dimensional (2D) video is a common tool used during sports training and competition to analyze movement. In these videos, biomechanists determine key events, annotate joint centers, and calculate spatial, temporal, and kinematic parameters to provide performance reports to coaches and athletes. Automatic tools relying on computer vision and artificial intelligence methods hold promise to reduce the need for time-consuming manual methods. This study systematically analyzed the steps required to automate the video analysis workflow by investigating the applicability of a threshold-based event detection algorithm developed for 3D marker trajectories to 2D video data at four sampling rates; the agreement of 2D keypoints estimated by an off-the-shelf pose estimation model compared with gold-standard 3D marker trajectories projected to camera's field of view; and the influence of an offset in event detection on contact time and the sagittal knee joint angle at the key critical events of touch down and foot flat. Repeated measures limits of agreement were used to compare parameters determined by markerless and marker-based motion capture. Results highlighted that a minimum video sampling rate of 100 Hz is required to detect key events, and the limited applicability of 3D marker trajectory-based event detection algorithms when using 2D video. Although detected keypoints showed good agreement with the gold-standard, misidentification of key events-such as touch down by 20 ms resulted in knee compression angle differences of up to 20°. These findings emphasize the need for de novo accurate key event detection algorithms to automate 2D video analysis pipelines.

Little associations exist between the three commonly used functional screening tests in collegiate athletes

Although an abundant number of studies have investigated the predictability of the commonly used functional screening tests and despite their popularity and applicability, the relationships between these tests have rarely been studied and have not been well established. This study aimed to examine the potential association between the Functional Movement Screen (FMS), Y Balance Test (YBT), and Landing Error Scoring System (LESS). Six hundred twenty-seven Iranian collegiate athletes (347 males, age = 22.63 ± 4.07, weight = 75.98 ± 13.79, height = 181.99 ± 10.15, BMI = 22.84 ± 3.16; and 280 females, age = 22.22 ± 3.37, weight = 60.63 ± 9.58, height = 166.55 ± 6.49, BMI = 21.81 ± 2.84) participated in this study. Following a 5-min warm-up, each participant underwent a standardized screening battery including the FMS, YBT, and LESS, and the scores were recorded and live coded for the statistical analysis, except for the LESS. The LESS tests were video recorded and scored by one expert examiner using an open-source 2D video analysis software (Kinovea- version 0.9.5), afterwards. The Spearman correlation was utilized as a measure for the correlation, and the Mann‒Whitney U test with a significance level of 0.05 was used to check the differences between male and female athletes. The statistical analysis was performed with RStudio 2023.03.0 using R 4.3.1. A small correlation (0.364) was observed between the FMS composite score and the YBT in male athletes. All other pairwise correlations were negligible among male and female athletes, ranging from − 0.096 to 0.294. Reducing the FMS to the component scores targeting the lower extremities did not alter the correlation to the other screening scores. The median FMS composite score in female athletes was significantly higher than that in males (p < 0.001). Negligible correlations exist between the FMS, LESS, and YBT; they do not measure the same values and therefore are irreplaceable with one another. A combination of these tests as a standardized screening battery may potentially better identify injury-predisposed athletes than the application of each test as a stand-alone screening test. Females outperformed males in the FMS test significantly, so sex must be considered a key variable in the FMS studies. Males had slightly higher LESS scores (median difference = 0.5) than females, but this difference is not clinically meaningful. Future research should continue to explore the relationships between various functional screening tests and identify the most effective combinations for comprehensive assessment in different populations and sports disciplines.

Kinematics of 90° change of direction in young football players: Insights for ACL injury prevention from the CUTtheACLstudy on 6008 trials.

To investigate the 90° change of direction (COD) task in an extensive cohort of competitive healthy football players within the CUTtheACLstudy and to provide normative values and differences between males and females for full-body kinematics based on two-dimensional (2D) video analysis and scoring system. One-thousand-and-two competitive football (soccer) players (age 16.3 ± 2.8 years, 264 females) were prospectively enroled. Each player performed three preplanned 90° COD tasks per limb. The 2D evaluation was performed through objective measures (collected through three high-speed cameras) of frontal and sagittal plane joint kinematics at the cut initial foot contact (IC) and maximum knee flexion angle. A previously published scoring system was adopted to measure the movement quality of the COD task. The scoring system included five criteria (limb stability [LS], pelvis stability [PS], trunk stability [TS], shock absorption [SA], movement strategy [MS]) ranked from 0/2 (nonadequate) to 2/2 (adequate) with a maximum score of 10/10. Normative data were provided for all the variables; statistical differences between male and female players were investigated (p < 0.05). A total of 6008 valid attempts were included. Frontal plane knee projection angle (FPKPA) at initial contact was 24.4 ± 9.8° (95thpercentile: FPKPA > 40°). The total score was ≤4/10 in 71.2% of the trials, the lowest subscores were LS and PS. Female players showed different movement patterns with lower hip and trunk flexion both at IC and maximum knee flexion angle (p < 0.01, ES = 0.41-0.64). Female players also showed worse scores than males in SA, MSand total score (p < 0.01). Female players seem more prone to stiffer lower limb strategy and greater pelvis-trunk frontal plane instability than males. Clinicians could adopt normative data and sex-specific differences in players' movement techniques to improve ACL injury risk mitigation protocols. Level IV.

A comprehensive two-dimensional scoring system to assess the single-leg squat task in football players

BackgroundThe single-leg squat (SLS) is a safe and widespread functional test commonly performed in the mid-stages of rehabilitation after severe knee injuries. The use of reliable objective measures has been advocated to improve the quality of SLS assessment. The aim of this study was to describe a qualitative whole-body scoring system based on two-dimensional (2D) video analysis during SLS test and validate it against three-dimensional (3D) kinetics and kinematics. MethodsThirty-four competitive football (soccer) players performed a series of SLS tasks. 3D kinematics and kinetics were collected through infrared cameras, and 2D video analysis was performed through a scoring system with sub-scores ranging from 0/2 (non-adequate movement) to 2/2 (adequate movement) based on frontal and lateral planes objective measurements. 3D kinematics and kinetics were grouped according to the results of the 2D evaluation and compared through the analysis of variance (P < 0.05). ResultsHigher hip adduction, hip internalrotation, and knee valgus collapse were found in trials rated 0/2 or 1/2 compared with theone rated 2/2 in the limb stability score. Hip flexion and hip/knee moment ratio were lower in those scoring 0/2 comparedwith those scoring 2/2 in the movement strategy criterion. A low total score was associated with higherknee valgus collapse and lower hip/knee extensor moment ratio. Compensatory strategieswere found in frontal plane scores. ConclusionsThe 2D scoring system described was strongly associated with kinematics and kinetics from gold-standard 3D motion capture and might represent a valid tool to describe the movement quality of an SLS task.

Normative Running Kinematics in Healthy Adolescent Runners: A 2-Dimensional Video Analysis.

The literature on the running kinematics of youth distance runners is limited. We sought to describe 2-dimensional (2D) video analysis of running kinematics in healthy adolescent distance runners, which has not been previously described. We conducted an observational study of healthy, competitive runners between the ages of 14 and 18 years, prospectively recruited through local running clubs and our hospital's outreach between August 2019 and July 2023. Participants ran on a treadmill at a self-selected speed with markers attached to the thorax, pelvis, and lower extremities. A high-definition video camera recorded the runners in the sagittal and frontal planes. Kinematic measurements were completed using Dartfish software and reported as means and standard deviations. Of the 53 participants (51% boys, mean age: 16.0 ± 1.4 years) included in the 2D running analysis, 91% ran with a rearfoot strike pattern, with a mean foot inclination angle of 10.2° ± 6.2°. Knee flexion angle at initial contact was 13.2° ± 3.8°, tibia inclination angle was 8.5° ± 3.2°, and peak knee flexion was 44.5° ± 3.6°. Cadence was 168.7° ± 8.6°. Contralateral pelvic drop was 6.0° ± 2.2° and peak rearfoot eversion was 11.8° ± 3.6°. This study is the first to describe running kinematics as captured by 2D video in healthy adolescent runners and to identify kinematic variables that may differ from those of adult runners. Further research is required to determine if adult recommendations are applicable to adolescent populations.

Smartphone-Based Video Analysis for Guiding Shoulder Therapeutic Exercises: Concurrent Validity for Movement Quality Control

Neuromuscular re-education through therapeutic exercise has a determinant role in chronic shoulder pain rehabilitation. Smartphones are an interesting strategy to extend the rehabilitation to a home-based scenario as it can increase the attraction and involvement of users by providing feedback. Objective: To analyze the concurrent validity of a smartphone’s application based on 2D video analysis against the gold-standard 3D optoelectronic system for assessing movement quality during upper limb therapeutic exercises. Methods: Fifteen young adults were evaluated while executing two different shoulder exercises with a smartphone’s 2D video and a 3D optoelectronic system simultaneously in two conditions: (1) with the supervision and instructions of a physiotherapist (guided exercise), and (2) without the feedback of the physiotherapist (non-guided exercise). The data obtained during the guided and non-guided exercises were compared to calculate the movement quality index based on the approximation of the non-guided exercise to the guided exercise for the head, trunk, and shoulder’s range of movement. The agreement of the movement quality index assessed with the smartphone application and the optoelectronic system was carried out through Bland–Altman analysis. Results: The Bland–Altman analysis indicates the range of agreement and bias tendency. This tendency demonstrates that the percentage of difference between the two methods increases as the movement quality index decreases. Conclusions: There is agreement between the movement quality evaluated by a gold-standard method and the developed application, although the proposed method appears to have less sensitivity for evaluating movements with lower quality index.

Two-Dimensional and Three-Dimensional Biomechanical Factors During 90° Change of Direction are Associated to Non-Contact ACL injury in Female Soccer Players.

The two-dimensional (2D) video-analysis of the change of direction (COD) technique has never been used to attempt to predict the risk of ACL injury in female football players. The purpose of the present pilot study was to prospectively investigate the biomechanical predictors of ACL injury during a COD task in female football players using both gold standard 3D motion capture and a qualitative scoring system based on 2D video-analysis. Prospective cohort study. Sixteen competitive female football (soccer) players (age 21.4 ± 4.3) performed a series of pre-planned 90° COD tasks. 3D motion data was recorded through 10 stereophotogrammetric cameras and a force platform. 2D frontal and transverse plane joint kinematics were computed through video-analysis from three high-speed cameras. A scoring system based on five criteria was adopted: limb stability, pelvis stability, trunk stability, shock absorption, and movement strategy. The players were prospectively followed for the next two consecutive football seasons and the occurrence of severe knee injuries was registered. Four players (25%) experienced an ACL injury. In 3D analysis, ACL-injured players showed greater knee valgus, knee internal rotation, and lower knee flexion (p= 0.017 - 0.029). Lower hip flexion coupled with greater external rotation (p= 0.003 - 0.042), ankle eversion, and contralateral pelvic drop (p<0.001) were also noted. In 2D analysis, ACL-injured players showed greater internal foot rotation, contralateral pelvic drop, lower knee flexion, and contralateral trunk tilt (moderate-to-large effect size). Pelvis stability and trunk stability showed the highest predictive value towards ACL injury. Total score was significantly lower in ACL-injured players with a moderate effect size (d=0.45). Both 3D and 2D methodologies depicted biomechanical risk factors and offered predictive insights towards the ACL injury risk. Awareness should rise in women's football regarding the high risk of ACL injury and the strategies to assess and mitigate it. 3©The Author(s).

Reliability of 2D video analysis assessing running kinematic variables in patients with exercise-related leg pain in a primary care practice

BackgroundSuboptimal lower limb and trunk positionings is known to influence exercise-related leg pain (ERLP). It is unknown whether simple 2D video analysis is useful for recording and interpreting running variables in a primary care practice. Research questionIs 2D video analysis a reliable instrument to assess running variables in patients with ERLP in a primary care practice? MethodsParticipants undergoing an evaluation for ERLP in two primary care practices were studied. In this reliability study, analysis of running variables was performed by 4 blinded raters on one-stride videos captured with non-high speed cameras (30 fps). Intraclass correlation coefficients (two-way random; ICC 2,1) were calculated to determine the inter-rater reliability. The intra-rater reliability was presented by ICC type two-way mixed (3,1). Footstrike pattern was analyzed by calculating the Fleiss’ kappa for inter-rater agreement and Cohen’s kappa for intra-rater agreement. Sample size calculation indicated that 16 participants would be required for answering the research question. ResultsData of all 16 participants (9 males, age 31 ± 10 yr) were of sufficient quality for analysis. The 2D video analysis demonstrated excellent inter-rater reliability with an overall ICC value of 0.999 (95 % CI = 0.998–0.999). The ICC value of the eversion was 0.384 (95 % CI = 0.148–0.66) and after correction of the systematic error, 0.817 (95 % CI = 0.664–0.922). The agreement on footstrike was substantial with a Fleiss kappa of 0.737. The overall intra-rater reliability was excellent with an ICC value of 0.997 (95 % CI = 0.996–0.997). The intra-rater agreement of the footstrike was excellent with a Cohen’s kappa of 0.868. Significance2D video analysis provides a highly reliable, relative inexpensive, feasible and suitable measuring instrument for determining running variables in patients ERLP in a primary care setting. This simple technique may identify possible running variables associated with different types of ERLP and may serve as an instrument for tailor-made gait retraining programs.

Crossover gait in running and measuring foot inversion angle at initial foot strike: a front-view video analysis approach.

Introduction: Foot inversion angle at initial foot strike is associated with various running-related injuries. Traditionally, video analysis of foot inversion angle has been accomplished by positioning a camera to record from the back view, but complications arise when a crossover gait obscures the area of measurement. This study aims to investigate the viability of measuring foot inversion angles at initial foot strike of running from the front view as an alternative to using the back view in 2D video analysis. Methods: Forty-four healthy runners (20 females, 24 males) ran at their self-selected speeds on a treadmill with their gait recorded from front and back camera views. Foot inversion angles at initial foot strike were analyzed using Kinovea. A 2 × 2 (Camera × Foot) ANOVA with repeated measures was performed on the foot inversion angle data. Subsequently, correlation and linear regression were performed to determine the relationship between the back and front-view measurements. Results: Thirteen runners (29.5%) displayed crossover gait within 18 gait cycles. ANOVA revealed a significant main effect on Camera (p < .001) only, where foot inversion angle was greater from the front camera view. Correlation analysis showed a significant positive correlation between the front and back camera views (r = 0.388, p < .001). Regression analyses yielded an equation, = 0.42 + 0.53 , where and were the foot inversion angle measured from the back and front camera views, respectively. Discussion: With a linear regression conversion equation, front-view foot inversion angles at initial foot strike can be used to determine rearfoot inversion angles when crossover gait obstructs the back camera view.

Foot rotation and pelvic angle correlate with knee abduction moment during 180° lateral cut in football players

BackgroundLateral movements are challenging for 2D video-analysis and are therefore often omitted in functional tests for Anterior Cruciate Ligament (ACL) injury risk assessment. The purpose of the present study was to investigate the association between frontal and transverse plane angles obtained from 2D video-analysis and knee abduction moment (KAM) from gold standard 3D motion capture in a 180° lateral cut task. The hypothesis was that 2D angles other than the knee joint effectively explain variations in KAM. MethodsThirty-four healthy football players (age 22.8 ± 4.1 years) performed a series of 180° lateral cut (lateral shuffles) tasks. The peak KAM was collected through a 3D motion capture system. A 2D video-analysis movement assessment identified frontal and transverse plane joint kinematics: foot projection angle (FPA), Frontal Plane Knee Projection Angle (FPKPA), Pelvis tilt angle (PA), and Trunk tilt angle (TA). A forward stepwise regression model was used to assess significant 2D predictors of KAM (p < 0.05). ResultsFPA and PA were the only significant predictors (R2-ajdusted = 9.2%, p < 0.001), with external foot rotation and contralateral pelvic drop associated with higher KAM. Based on the regression model, the “High FPA & PA group” was defined and showed higher KAM than the rest of the cohort (p = 0.012, ES = 0.71). ConclusionsThe external foot rotation and the contralateral pelvic drop from 2D video-analysis were associated with higher peak KAM during the 180° lateral cut. A qualitative assessment of the 180° lateral cut could offer precious insights on ACL injury risk mitigation. Level of EvidenceDescriptive Laboratory Study.

Reliability and validity of 2D-video analysis to objectively assess hamstring performance during the H-test

ABSTRACT The H-test is commonly used during return-to-sport decisions after hamstring muscle injury. The primary aim was to evaluate the reliability of two-dimensional (2D) video analysis for the H-Test. The second aim was to assess its validity compared to an electronic gyroscope (gold standard), and the third aim was to establish normative values. We conducted a cross-sectional study including 30 healthy individuals. Mean, maximal velocities (VMean and Vmax) and range of motion (ROM) of hip flexion were captured during the H-test to evaluate inter-rater and test-retest reliability using intraclass correlation coefficient (ICC2,1) and standard error of measurement (SEM). Correlation analysis (r) and as typical error of estimate (TEE) were used to assess the validity between the video and the gyroscope. Reliability was excellent for ROM (ICC:0.91, [95% CI:0.83–0.95]), moderate for VMean (ICC:0.57; [95% CI:0.32–0.74]) and VMax (ICC:0.64, [95% CI:0.43–0.79]). Strong positive correlations were found between video and gyroscope for VMean (r = 0.79, [95% CI:0.71–0.86]) and VMax (r = 0.84, [95% CI:0.77–0.89]) and very strong for ROM (r = 0.89, [95% CI:0.85–0.93]). Males exhibited a higher VMax (p < 0.001) than females, while females had a higher ROM (p < 0.001). 2D-video analysis is a valid and reliable method to assess ROM during the H-Test and could easily be implemented in clinical practice.

Adaptive Regulation in a Stable Performance Environment: Trial-To-Trial Consistency in Cue Sports Performance.

This study aimed to investigate individual trial-to-trial performance in three tests to define adaptive regulation as a key feature of expertise in nine-ball. Thirty-one male players were assigned into the low-skilled (n = 11), intermediate (n = 10), or high-skilled groups (n = 10). The power control, cue alignment, and angle tests were selected to assess participants' ability to control the power applied in shots, strike the ball straight, and understand the ball paths, respectively. Error distance and correction of error distance were identified for each shot using 2D video analysis. Results of one-way analysis of variance showed that the high-skilled group performed better in two out of the three tests than the other two groups (p = .010 for the cue alignment test; p = .002 for the angle test). However, the adaptation effect represented by the decreased error distances across trials was not observed. Pearson correlation revealed only a few significant correlations between the error distance and its correction within each participant in all tests (p < .05), and hence, the hypothesis that "low correction happened after small error and vice versa" is not supported.

Foot Morphology and Running Gait Pattern between the Left and Right Limbs in Recreational Runners

Previous studies generally selected one foot to classify participants into groups with different foot types and then analyzed the running or walking biomechanics for one limb. Such approach may have neglected the possible differences in foot morphology and gait between two limbs. This study aimed to compare the foot morphological characteristics and running kinematics of the lower extremities between the left and right limbs among a group of healthy, asymptomatic runners. Forty-four participants [20 females, 24 males; age 25.1 (6.5) years old; height 167.2 (7.0) cm; body mass 62.8 (8.1) kg] were recruited. Foot morphological characteristics were measured for both feet, and bilateral running kinematics were analyzed with 2D video analysis. No significant between-limb differences were found in the foot dimensions, hallux valgus (bunion) angle, or navicular drop (all p &gt; 0.05). On the other hand, several kinematic variables were significantly different between the left and right limbs during running, including the peak foot eversion (p = 0.014), peak knee flexion (p = 0.002), and peak hip adduction (p &lt; 0.001). The results indicate that runners with similar morphological characteristics between the left and right feet can display between-limb gait asymmetry during running. Researchers and practitioners should be aware of the potential between-limb asymmetry in running kinematics and foot morphology. Future studies should avoid arbitrarily analyzing one limb to represent a runner’s gait or foot morphology.

Effects of increasing physical load and fatigue on the biomechanics of elite cyclists

In this study, we propose to expand the research on the biomechanics of cycling, including changes caused by riding at different intensity levels and fatigue, similar to training or competition. Six well-trained, experienced male road cyclists (27.17 ± 3.89 years; 180.41 ± 5.31 cm; 75.23 ± 4.91 kg) with 8.3 ± 4.85 years of (professional) experience in road cycling underwent a lactate test, starting with 100 W and an increment of 20 W every 3 minutes until total exhaustion. Afterward, subjects drove an increment of 50 W every 3 minutes, starting again with 100 W and ending with 250 W (post-test). Changes in position were recorded via 2D video analysis. We found that with higher power output relative to the individual anaerobic threshold (IAT), the joint angles changed. No significant differences were present for the pre–post comparisons of the examined angles, which should map the influence of fatigue (p &gt; .05). Future research should try to observe cycling movement in more realistic settings, such as cycling-specific fatigue or during an outdoor ride, as the biomechanics under these conditions are of particularly high relevance for the athletes. Overall, the results suggest performing bike fitting more individually and in more realistic situations or setting.

Effect of different anthropometry-driven block settings on sprint start performance

Few studies have focused on the effect of individual anthropometrics when considering “set” position posture during the sprint start. This study aimed to measure the effect of different anthropometry-driven block settings on kinetic and kinematic parameters and performance during the start in well-trained and non-trained sprinters. Front block-starting line (FB/SL) distance was manipulated between 50% and 70% of each individual’s leg length at 5% intervals, whilst the inter-block distance was held constant at 45% of leg length. Thirty-six sprinters performed three maximal-effort 10 m sprints in each of the five conditions. Joint angles in the “set” position were quantified though 2D video analysis, the forces generated during block clearance phase were measured by dynamometric starting blocks, and times to 5 m and 10 m were measured with photocells. The effects of the five block setting conditions were largely consistent irrespective of ability level. Shorter FB/SL distances were associated with significantly more flexed hip and knee angles in the “set” position, a significantly more plantar flexed front ankle, and a significantly more dorsiflexed rear ankle. There were no significant effects of FB/SL distance on total block time, and thus the greater rear block peak forces and impulses produced from the shorter FB/SL distances combined with no effects on the resultant front block peak forces and impulses, led to higher levels of sprint start performance from the shorter FB/SL distances. Considering FB/SL distances closer to 50% of leg length may be beneficial for coaches and athletes to explore during sprint start training. Highlights The effects of different front-block starting line distances on “set” position kinematics, block clearance kinetics and sprint start performance are largely consistent irrespective of ability level. When using a medium inter-block distance (45% of leg length), shorter front block-starting line distances (down to 50% of the leg length) led to improved sprint start performance. From shorter front block-starting line distances, sprint start performance was primarily improved through greater force production against the rear block which led to greater impulses due to no change in push durations or resultant front foot forces. Lower-limb length is an important consideration when adjusting anteroposterior block distances.

Accuracy and precision of simpler and lower-cost technologies to measure the initial lean angle, step length and step velocity for forward lean releases

Current technologies to measure the maximum forward lean angle, step length and velocity in a clinical setting are neither simple nor cheap. Therefore, the purpose of this study was to determine the accuracy and precision of four live and one post-processing measurement methods compared to the 3D motion analysis gold standard. Twelve healthy younger adults recovered balance, after being released from six randomly ordered forward initial lean angles, using four different live measurement methods: LabVIEW, load cell, inclinometer and protractor. The initial lean angle, step length and velocity were also calculated in post-processing using 2D video analysis and 3D motion analysis. The LabVIEW method was the most accurate and precise, followed by the protractor, inclinometer and load cell methods. The load cell method was the most complex, followed by the LabVIEW, inclinometer and protractor methods. The LabVIEW method was the most expensive, followed by the load cell, inclinometer and protractor methods. Video analysis was sufficiently accurate and precise, equal in complexity and much less expensive than the gold standard. Simpler and lower-cost technologies to measure the initial lean angle, step length and velocity are sufficiently accurate and precise (live: protractor, post-processing: video analysis) to potentially use in a clinical setting.

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

ABSTRACT 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.