Reliability of variables in the kinematic analysis of spring hurdles

Implications of sample size and acquired number of steps to investigate running biomechanics

Low reproducibility and non-optimal sample sizes are current concerns in scientific research, especially within human movement studies. Therefore, this study aimed to examine the implications of different sample sizes and number of steps on data variability and statistical outcomes from kinematic and kinetics running biomechanical variables. Forty-four participants ran overground using their preferred technique (normal) and minimizing the contact sound volume (silent). Running speed, peak vertical, braking forces, and vertical average loading rate were extracted from > 40 steps/runner. Data stability was computed using a sequential estimation technique. Statistical outcomes (p values and effect sizes) from the comparison normal vs silent running were extracted from 100,000 random samples, using various combinations of sample size (from 10 to 40 runners) and number of steps (from 5 to 40 steps). The results showed that only 35% of the study sample could reach average stability using up to 10 steps across all biomechanical variables. The loading rate was consistently significantly lower during silent running compared to normal running, with large effect sizes across all combinations. However, variables presenting small or medium effect sizes (running speed and peak braking force), required > 20 runners to reach significant differences. Therefore, varying sample sizes and number of steps are shown to influence the normal vs silent running statistical outcomes in a variable-dependent manner. Based on our results, we recommend that studies involving analysis of traditional running biomechanical variables use a minimum of 25 participants and 25 steps from each participant to provide appropriate data stability and statistical power.

Number of trials necessary to achieve performance stability in a reaching kinematics movement analysis game

STUDY DESIGN

A cross-sectional design was used.

INTRODUCTION

Motion analysis is commonly used to analyze reaching movements of individuals, but how many trials are necessary to provide stable data?

PURPOSE OF THE STUDY

The purpose of this study was to determine the number of trials necessary to obtain stable kinematic variables during reaching movements in a virtual environment.

METHODS

Thirty children (10.39 ± 1.68 years) and 20 adults (26.55 ± 3.12 years) participated. All participants interacted with a virtual reality evaluation game called Super Pop VR to collect their reaching kinematics. The players were instructed to pop several sets of virtual bubbles at a self-selected pace and their upper-body coordinates were recorded and reaching kinematics were computed. Two methods (sequential averaging techniques, SAT, and intraclass correlation coefficient, ICC) were carried out to assess performance stability of each kinematic variable.

RESULTS

For the SAT method, children exhibited 3.11 to 5.96 trial range to achieve stability in the dominant hand and 2.7 to 5.96 trial range in the nondominant hand, whereas adults exhibited 2.65 to 6.16 trial range in the dominant hand and 3.40 to 6.05 range in the nondominant hand. For the ICC method, to reach the "excellent" value of ICC, children's dominant hand required 4.20 trials and their nondominant hand required 2.5 trials, whereas adults' dominant hand required 3.00 trials and their nondominant hand required 2.80 trials.

DISCUSSION AND CONCLUSIONS

Our findings supported the importance of determining the minimum number of trials required to obtain stable movements regardless of how familiar the movement seems to participants or how sensitive the apparatus is.

Reliability of estimating active drag in swimming using the assisted towing method with fluctuating speed

The reliability of active drag values was examined using a method that compared free swim speed with measurements taken by towing swimmers slightly faster than their maximum swim speed, while allowing their intra-stroke speed fluctuations. Twelve national age and open level swimmers were tested on two alternate days (Day 1 and Day 2). All participants completed four maximum swim speed, three passive drag and five active drag trials on each of the days. The reliability was determined using within-participant intra-class correlation coefficients (ICC) within each day and between the days. The ICCs for Day 1 and Day 2 were 0.82 and 0.85, respectively, while the comparison of the mean active drag values between days was 0.93. The data showed that the assisted towing method (ATM) with fluctuating speed was only moderately reliable within a single test. However, this method was more reliable when using the average value of active drag from both days (ICC = 0.93). This study identified that the ATM method with fluctuating speed had moderate reliability within-participant trials on values in a single day but high reliability for the average active drag values across different days.

Intersession reliability of kinematic and kinetic variables during vertical jumps in men and women

PURPOSE

To investigate the intersession reliability of selected kinematic and kinetic variables during countermovement vertical jumps (CMJs).

METHODS

Thirty-five men and 35 women performed CMJs on a force platform during four testing sessions each separated by 1 wk. Kinematic variables included time in the air (TIA), take-off velocity (TOV), total vertical displacement of the center of mass (TJH), and countermovement depth, whereas kinetic variables included positive impulse, negative impulse, vertical stiffness, and rates of force development. Systematic bias was assessed by calculating the 90% confidence interval of the change in the mean between consecutive testing sessions and between the first and final testing session for each variable. Coefficients of variation (CV) and intraclass correlation coefficients (ICC) were also calculated.

RESULTS

Systematic bias was observed only for peak rate of force development during the concentric phase of the movement. For TIA, TOV, and TJH, CV values ranged from 1.7% to 6.6%, with ICC values ranging from 0.82 to 0.97. The other variables showed greater variation (CV range: 1.7% to 39.9%; ICC range: 0.04 to 0.99). Only slight gender differences were found in the reliability statistics, and the reliability of most of the variables was diminished as the time between the testing sessions was increased.

CONCLUSION

Even though practitioners can expect good reliability for jump height measured from a force platform in men and women, other kinematic and kinetic variables often assessed during vertical jumps may not be reliable.

The impact of computer display height and desk design on 3D posture during information technology work by young adults

Computer display height and desk design to allow forearm support are two critical design features of workstations for information technology tasks. However there is currently no 3D description of head and neck posture with different computer display heights and no direct comparison to paper based information technology tasks. There is also inconsistent evidence on the effect of forearm support on posture and no evidence on whether these features interact. This study compared the 3D head, neck and upper limb postures of 18 male and 18 female young adults whilst working with different display and desk design conditions. There was no substantial interaction between display height and desk design. Lower display heights increased head and neck flexion with more spinal asymmetry when working with paper. The curved desk, designed to provide forearm support, increased scapula elevation/protraction and shoulder flexion/abduction.

Changes in technique within a sprint hurdle run

The aim of this study was to understand changes in technique within an athlete's own performance during a sprint hurdles run. Four athletes performed a training session containing four trials each over 10 hurdles. Clearances at hurdles three and nine were videotaped from a side view and manually digitised. All athletes in this study yielded a lower running speed over the hurdle at the ninth hurdle in comparison to the third hurdle in each run. All athletes also showed further signs of potential tiredness in the clearances of the ninth hurdle. Interestingly, these changes in technique varied among the athletes. This poses challenges to coaches, as they need to evaluate individually what changes in training should be introduced to keep the quality of clearances as high as possible throughout training. To match more closely the velocities to those in competitions, consideration could be given in training to shorten gradually the distances between the hurdles more during the latter part of the run, although this should be individually checked, based on the athlete. This way, athletes could learn to clear the hurdle with a higher horizontal velocity, even when fatigue is potentially influencing the performance.

Rehabilitation of reaching after stroke: Task-related training versus progressive resistive exercise11No commercial party having a direct interest in the results of the research supporting this article has or will confer a benefit on the author(s) or on any organization with which the author(s) is/are associated

OBJECTIVE

To evaluate the effectiveness of 2 rehabilitative approaches for improving paretic limb reaching by chronic stroke subjects.

DESIGN

Pre- and posttest reaching to targets ipsilateral, midline, and contralateral to the impaired side.

SETTING

Training in subjects' homes; testing in a laboratory setting.

PARTICIPANTS

Twelve poststroke volunteers were matched using the Motor Assessment Scale (MAS) and then were randomly assigned to 1 of 2 training conditions. Subjects were subsequently categorized as at a high or low functional level, using the reaching pretest movement time scores.

INTERVENTIONS

Training (trunk unrestrained) using the paretic limb was 4 weeks (12 sessions). Task-related training (TRT) involved reaching to objects placed across the workspace. Progressive resistive exercise (PRE) involved whole-arm pulling against resistive therapeutic tubing in planes and distances similar to that in TRT. Main outcome measures Kinematic analysis of arm trajectory and trunk motion using the Peak Performance System, as well as scores on the MAS and the Rivermead Motor Assessment (RMA).

RESULTS

For low-level groups, TRT resulted in increased substitutive trunk use at the target ipsilateral to the moving arm, and for midline and contralateral targets after PRE. Only low-level, TRT subjects straightened hand paths, which suggested better coordination of elbow-shoulder motion, and improved on the RMA. High-level subjects decreased trunk use at ipsilateral target after PRE, which was not observed after TRT. No significant differences between training conditions were found for other kinematic variables.

CONCLUSIONS

Training benefits appear to depend on initial level of functioning. Although compensatory trunk use was evident, low-level subjects seemed to benefit most from TRT. High-level subjects, whose kinematics showed fairly normal movement organization, demonstrated less compensatory movement after PRE.

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.

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.

An Examination of Kinematic Variability of Motion Analysis in Sprint Hurdles

Eight trials each of 7 athletes (4 women and 3 men) were videotaped and digitized in order to investigate the variation sources and kinematic variability of video motion analysis in sprint hurdles. Mean coefficients of variation (CVs) of individuals ranged from 1.0 to 92.2% for women and from 1.2 to 209.7% for men. There were 15 and 14 variables, respectively, in which mean CVs revealed less than 5% variation. In redigitizing, CVs revealed <1.0% for 12 variables for the women's trials and 10 variables for the men's trials. These results, together with variance components (between-subjects, within-subject, and redigitizing), showed that one operator and the analysis system together produced repeatable values for most of the variables. The most repeatable variables by this combination were displacement variables. However, further data processing (e.g., differentiation) appeared to have some unwanted effects on repeatability. Regarding the athletes' skill, CVs showed that athletes can reproduce most parts of their performance within certain (reasonably low) limits.