David R. Mullineaux

Research design and statistics in biomechanics and motor control

Biomechanics and motor control researchers measure how the body moves and interacts with its environment. The aim of this review paper is to consider some key issues in research methods in biomechanics and motor control. The review is organized into four sections: proposing, conducting, analysing and reporting research. In the first of these, we emphasize the importance of defining a worthy research question and of planning the study before its implementation to prevent later difficulties in the analysis and interpretation of data. In the second section, we cover selection of trial sizes and suggest that using three trials or more may be beneficial to provide more ‘representative’ and valid data. The third section on analysis of data concentrates on effect size statistics, qualitative and numerical trend analysis and cross-correlations. As sample sizes are often small, the use of effect size is recommended to support the results of statistical significance testing. In using cross-correlations, we recommend that scatterplots of one variable against the other, with the identified time lag included, be inspected to confirm that the linear relationship assumption underpinning this statistic is met and, if appropriate, that a linearity transformation be applied. Finally, we consider important information related to the issues above that should be included when reporting research. We recommend reporting checks or corrections for violations of underpinning assumptions, and the effect of these checks or corrections, to assist in advancing knowledge in biomechanics and motor control.

Biomechanical predictors of retrospective tibial stress fractures in runners

Both kinematics and kinetics of the lower limb have been shown separately to be related with a history of tibial stress fractures (TSFs) in female runners. However, it is likely that these factors interact together to increase the risk of a TSF. This study was conducted to determine which combination of kinematic and kinetic factors are the best predictors of retrospective TSF in female distance runners. Total 30 female runners who had previously sustained a TSF were recruited, along with an age and mileage matched control group (n=30). Subjects ran overground at 3.7m/s while kinematic and kinetic data were recorded. Five trials from each subject were used for data analysis and ensemble means were calculated for both groups. The kinematic variables of peak hip adduction (HADD), peak knee internal rotation (KIR) and knee adduction (KADD), peak rearfoot eversion (RFEV) were entered into a binary logistic regression along with the kinetic variables of vertical instantaneous load rate (VILR) and absolute free moment (FM). The variables HADD, FM and RFEV were able to correctly predict a history of TSF in 83% of cases. Increases in HADD, FM and RFEV (odds ratios of 1.29, 1.37 and 1.18) were associated with an elevated risk of having a history of TSF. The addition of VILR, KIR and KADD did not improve the ability to predict previous injury. Based on these results, HADD, FM and RFEV appear to be the most important of the variables of interest in terms of predicting retrospective TSF in female runners.

Two-Week Joint Mobilization Intervention Improves Self-Reported Function, Range of Motion, and Dynamic Balance in Those with Chronic Ankle Instability

We examined the effect of a 2‐week anterior‐to‐posterior ankle joint mobilization intervention on weight‐bearing dorsiflexion range of motion (ROM), dynamic balance, and self‐reported function in subjects with chronic ankle instability (CAI). In this prospective cohort study, subjects received six Maitland Grade III anterior‐to‐posterior joint mobilization treatments over 2 weeks. Weight‐bearing dorsiflexion ROM, the anterior, posteromedial, and posterolateral reach directions of the Star Excursion Balance Test (SEBT), and self‐reported function on the Foot and Ankle Ability Measure (FAAM) were assessed 1 week before the intervention (baseline), prior to the first treatment (pre‐intervention), 24–48 h following the final treatment (post‐intervention), and 1 week later (1‐week follow‐up) in 12 adults (6 males and 6 females) with CAI. The results indicate that dorsiflexion ROM, reach distance in all directions of the SEBT, and the FAAM improved (p < 0.05 for all) in all measures following the intervention compared to those prior to the intervention. No differences were observed in any assessments between the baseline and pre‐intervention measures or between the post‐intervention and 1‐week follow‐up measures (p > 0.05). These results indicate that the joint mobilization intervention that targeted posterior talar glide was able to improve measures of function in adults with CAI for at least 1 week.

Greater vertical impact loading in female runners with medically diagnosed injuries: a prospective investigation

Background Running has been critical to human survival. Therefore, the high rate of injuries experienced by modern day runners is puzzling. Landing on the heel, as most modern day shod runners do, results in a distinct vertical impact force that has been shown to be associated with running-related injuries. However, these injury studies were retrospective in nature and do not establish cause and effect. Objective To determine whether runners with high impacts are at greater risk for developing medically diagnosed injuries. Methods 249 female runners underwent a gait analysis to measure vertical instantaneous loading rate, vertical average loading rate (VALR), vertical impact peak (VIP) and peak vertical force. Participants then recorded their mileage and any running-related injuries monthly in a web-based, database programme. Variables were first compared between the entire injured (INJ; n=144) and uninjured (n=105) groups. However, the focus of this study was on those injured runners seeking medical attention (n=103) and those who had never injured (n=21). Results There were no differences between the entire group of injured and uninjured groups. However, all impact-related variables were higher in those with medically diagnosed injuries compared with those who had never been injured. (effect size (ES) 0.4–0.59). When VALR was >66.0 body weight (BW)/s, the odds of being DX_INJ were 2.72 (95% CI 1.0 to 7.4). Impact loading was associated with bony and soft-tissue injuries. Conclusions Vertical average loading rate was lower in female runners classified as ‘never injured’ compared with those who had been injured and sought medical attention.

Coordination-variability and kinematics of misses versus swishes of basketball free throws

Abstract Magnitudes and timings of kinematic variables have often been used to investigate technique. Where large inter-participant differences exist, as in basketball, analysis of intra-participant variability may provide an alternative indicator of good technique. The aim of the present study was to investigate the joint kinematics and coordination-variability between missed and successful (swishes) free throw attempts. Collegiate level basketball players performed 20 free throws, during which ball release parameters and player kinematics were recorded. For each participant, three misses and three swishes were randomly selected and analysed. Margins of error were calculated based on the optimal-minimum-speed principle. Differences in outcome were distinguished by ball release speeds statistically lower than the optimal speed (misses −0.12 ± 0.10m · s−1; swishes −0.02 ± 0.07m · s−1; P < 0.05). No differences in wrist linear velocity were detected, but as the elbow influences the wrist through velocity-dependent-torques, elbow–wrist angle–angle coordination-variability was quantified using vector-coding and found to increase in misses during the last 0.016s before ball release (P < 0.05). As the margin of error on release parameters is small, the coordination-variability is small, but the increased coordination-variability just before ball release for misses is proposed to arise from players perceiving the technique to be inappropriate and trying to correct the shot. The synergy or coupling relationship between the elbow and wrist angles to generate the appropriate ball speed is proposed as the mechanism determining success of free-throw shots in experienced players.

Spatial postural control alterations with chronic ankle instability

Postural control deficits have been identified among individuals with chronic ankle instability (CAI) compared to healthy controls. Although deficits in static balance have previously been reported using center of pressure (COP) and, more recently, time to boundary (TTB) measures, the underlying mechanism behind these deficits warrants further investigation. It is unclear if there are differences in the spatial distribution of COP and TTB minima data points under the foot. Our purpose was to determine if there are differences in the location of the distribution of the COP and the TTB minima data points between groups with and without CAI. Fifty healthy and 61 CAI subjects participated in this case-control study. The subjects performed three successful 10-s trials of quiet single limb stance on a force plate with eyes-open and -closed conditions. Results showed that during eyes-open trials, the CAI group exhibited more COP and TTB minima data points on the anterolateral aspect of the foot compared to controls. With eyes-closed single limb balance, the CAI group demonstrated significantly more COP and TTB minima data points anterior to the horizontal midline of the foot compared to controls. Overall, the CAI group showed a greater anterior displacement of COP and TTB minima during single limb static stance compared to controls. This alteration may result from the CAI subjects adopting a more dorsiflexed position in an effort to keep the ankle in a more stable, closed pack position and limiting the available degrees of freedom in the distal lower extremity.

Comparison of Isokinetic Hip Abduction and Adduction Peak Torques and Ratio Between Sexes

Objective:To evaluate hip abductor and adductor peak torque outputs and compare their ratios between sexes. Design:A cross-sectional laboratory-controlled study. Setting:Participants visited a laboratory and performed an isokinetic hip abductor and adductor test. All participants performed 2 sets of 5 repetitions of concentric hip abduction and adduction in a standing position at 60 degrees per second. Gravity was determined as a function of joint angle relative to the horizontal plane and was corrected by normalizing the weight of the limb on an individual basis. Participants:A total of 36 collegiate athletes. Independent Variables:Sex (20 females and 16 males). Main Outcome Measures:Bilateral peak hip abductor and adductor torques were measured. The 3 highest peak torque values were averaged for each subject. Results:Independent t tests were used to compare sex differences in hip abductor and adductor peak torques and the abductor:adductor peak torque ratios. Males demonstrated significantly greater hip abductor peak torque compared with females (males 1.29 ± 0.24 Nm/kg, females 1.13 ± 0.20 Nm/kg; P = 0.03). Neither hip adductor peak torque nor their ratios differed between sexes. Conclusions:Sex differences in hip abductor strength were observed. The role of weaker hip abductors in females deserves further attention and may be a factor for higher risk of knee pathologies.

Real-time biomechanical biofeedback effects on top-level rifle shooters

The aim was to examine the effects of training with real-time biomechanical biofeedback on technique and performance of rifle shooters. Top-level shooters were randomly assigned to biofeedback- (n = 5) and control- (n = 4) groups. Bi-weekly training of 20 shots air-rifle for 4 weeks, with pre- and post-tests of 20 shots air-rifle and smallbore, were performed. The biofeedback group received individualized real-time auditory biofeedback on postural- and barrel-stabilities. Results revealed a technique of reducing postural- and barrel-stabilities towards triggering (e.g. barrel speed 8.0 ± 1.2 mm/s at 3.0-1.0 s reducing to 5.4 ± 0.8 mm/s at 0.3-0.1 s). There were no changes pre- to post-tests and no differences between groups in these measures of stability. The biofeedback group showed meaningful improvements in performance measures, whereas the control group showed no improvement (e.g. smallbore shot group diameter change: biofeedback group -2.6 mm; control group 0.1 mm). Biomechanical biofeedback is proposed to have improved performance, possibly through training better decision making, but the actual cause requires further research.

Whole-body and multi-joint kinematic control strategy variability during backward rotating dismounts from beam

Abstract The aim of this study was to develop insight into the whole-body and multi-joint kinematic control strategy variability associated with the execution of fundamental backward rotating dismounts from beam. Two-dimensional joint centre coordinate data were obtained for ten backward piked and backward tucked somersault dismount skills performed by four female gymnasts (N = 80 trials). Gymnast-specific and group variability in whole-body and multi-joint discrete kinematic measures were compared for the aerial and impact phase of backward piked and backward tucked skills. The backward tucked skill was executed using a more variable knee joint angular velocity at take-off (mean difference in standard deviation ± SD: −2.6 ± 1.0 rad · s−1; P < 0.01) than the backward piked skill. The variability in the whole-body and multi-joint kinematic responses produced between the impact phases of each skill was gymnast-specific. The greater variability in the localized knee joint action at take-off was considered indicative of the diverse shape element demands and key performance outcomes of the two skills. Self-selected modulations to the multi-joint kinematic strategy used in the impact phase suggested customization of the joint loading adjustments in executing the fundamental dismount skills.

Pediatric anthropometrics are inconsistent with current guidelines for assessing rider fit on all terrain vehicles

BACKGROUND/PURPOSE This study sought to establish objective anthropometric measures of fit or misfit for young riders on adult and youth-sized all-terrain vehicles and use these metrics to test the unproved historical reasoning that age alone is a sufficient measure of rider-ATV fit. METHODS Male children (6-11 years, n=8; and 12-15 years, n=11) were selected by convenience sampling. Rider-ATV fit was quantified by five measures adapted from published recommendations: (1) standing-seat clearance, (2) hand size, (3) foot vs. foot-brake position, (4) elbow angle, and (5) handlebar-to-knee distance. RESULTS Youths aged 12-15 years fit the adult-sized ATV better than the ATV Safety Institute recommended age-appropriate youth model (63% of subjects fit all 5 measures on adult-sized ATV vs. 20% on youth-sized ATV). Youths aged 6-11 years fit poorly on ATVs of both sizes (0% fit all 5 parameters on the adult-sized ATV vs 12% on the youth-sized ATV). CONCLUSIONS The ATV Safety Institute recommends rider-ATV fit according to age and engine displacement, but no objective data linking age or anthropometrics with ATV engine or frame size has been previously published. Age alone is a poor predictor of rider-ATV fit; the five metrics used offer an improvement compared to current recommendations.