Medio-lateral acceleration of female athletes with an ACL reconstruction in comparison with a healthy population

We assessed change of direction abilities in team sport female athletes. Ten participants returned to full activity from ACL reconstruction (ACLR) for longer than one year and 10 healthy controls (CON) were compared. Twelve maximal effort 45° cutting manoeuvres from the reconstructed side (ACLR) or a random selection of both sides (CON) were analysed for each individual using a motion capture system. CON showed greater medio-lateral centre of mass (COM) acceleration between 51 and 75 % of ground contact. CON reported increased ankle plantar flexor power from 94 to 98 % of foot contact, with also a higher peak. Although cleared to return to full activity, biomechanical differences associated with performance were still present in the ACLR group, which may have implications for better targeting rehabilitation practice

Medio-lateral acceleration of female athletes with an ACL reconstruction in comparison with a healthy population

We assessed change of direction abilities in team sport female athletes. Ten participants returned to full activity from ACL reconstruction (ACLR) for longer than one year and 10 healthy controls (CON) were compared. Twelve maximal effort 45° cutting manoeuvres from the reconstructed side (ACLR) or a random selection of both sides (CON) were analysed for each individual using a motion capture system. CON showed greater medio-lateral centre of mass (COM) acceleration between 51 and 75% of ground contact. CON reported increased ankle plantar flexor power from 94 to 98% of foot contact, with also a higher peak. Although cleared to return to full activity, biomechanical differences associated with performance were still present in the ACLR group, which may have implications for better targeting rehabilitation practice

SAGITTAL HIP - KNEE COORDINATION DURING A 45 DEGREE CUTTING TASK

Concurrent extension at the hip and flexion at the knee has been suggested as a high risk coordination pattern for the anterior cruciate ligament (ACL). Nine elite female athletes performed ten 45" cutting tasks before and alter a multi-directional fatiguing protocol. Force and kinematic data were captured. Vector coding was used to calculate sagittal hip - knee coordination for the first 40 ms of foot contact of the dominant limb and percentage time spent in each coordination pattern was extracted. Hip extension - knee flexion was the dominant coordination pattern pre- and post-fatigue ( P less than 0.05)t the time spent in this coordination pattern did not change as a result of fatigue. The hypothesised high risk hip extension - knee flexion was the dominant coordination pattern during the 45' cutting task

INTERPRETATION OF VECTOR CODING VARIABILITY MEASURES: WITHINDAY REPEATABILITY AND BETWEEN-SUBJECT VARIATION IN TREADMILL RUNNING

This study investigated the within-day repeatability and between-subject variation of vector coding variability during treadmill running. The lower-limb kinematics of eight male triathletes running at 12 km/h were captured twice on the same day. Mean coupling angle variability across the stride cycle was computed for 20 couplings using the modified vector coding technique. Between-subject variation was calculated from the first data collection and data from both sessions were used to calculate systematic and typical error. Between-subject variation ranged from 1.4° to 3.7°. Systematic errors between sessions were observed for two couplings and typical errors were between 0.6° and 1.9°. The between-subject variation and within-day repeatability of the measures reported will aid the interpretation of vector coding variability in cross-sectional and intervention studies

Within-day repeatability of coordination variability measures across the running gait cycle

The purpose of this study was to identify the within-day repeatability of coordination variability calculated using a velocity ellipse area method. Twenty participants attended two data collection sessions within 6 hours. At each session, a marker based motion capture system measured kinematics whilst participants ran at 12 km/h on a treadmill. The minimum detectable change in coordination variability was calculated for four commonly researched joint/segment couplings. Of the couplings investigated, thigh flexion/extension – shank flexion/extension and hip flexion/extension – knee flexion/extension were most repeatable. But in the most repeatable coupling, an average change of 75% across the gait cycle would be required between sessions to detect a meaningful change. This indicated poor repeatability and possible causes are discussed

Sagittal hip-knee coordination during a 45 degree cutting task

Background Hashemi et al. (2011) put forward a new theory of ACL injury mechanism, named the ‘hip extension knee flexion paradox’ that attempted to integrate itself with the most convincing findings in ACL research. This theory of mechanism stated that non-contact ACL injury would occur when the following four criteria are simultaneously met: 1) the tibial plateau has a posterior slope 2) the knee is near full extension upon application of a dynamic ground reaction force 3) activation of musculature about the knee is delayed and 4) hip extension and knee flexion occur concurrently. In their paper, Hashemi et al. (2011) also suggest that fatigue may play an important role in increasing the risk of non-contact ACL injury by delaying activation of musculature about the knee joint. Hip-knee coordination and the effect of fatigue on it, have however not previously been investigated. Purpose The purpose of this study was to quantify hip – knee coordination in the sagittal plane during a 45° cutting movement. Methods Nine female team sports players with experience at international or national level and no history of ACL injury were recruited. Written consent was obtained at the time of testing. Cutting was assessed under pre and post fatigue conditions, whilst motion capture data were collected for the lower limbs using QTM (Qualysis AB, Göteburg, Sweden). In each condition, ten successful 45° cuts were captured for the dominant leg. The fatiguing protocol comprised drop maximal vertical jumps and a multi-directional short sprint exercise. Hip and knee sagittal joint angles were extracted between the time of foot contact to 40 ms, the window in which ACL injury is believed to occur. A coordination pattern of 1) hip flexion – knee flexion, 2) hip extension – knee flexion, 3) hip extension – knee extension, 4) hip extension knee flexion was determined for each time point. The average time that each participant spent in each coordination pattern was calculated and the median coordination pattern was determined for each participant at each time point. Wilcoxon tests were executed in SPSS (IBM SPSS Version 22, Armonk, NY) to determine the effect of fatigue on the percentage time spent in hip extension – knee flexion and hip extension – knee extension. Results The average modal coordination pattern of the group, both pre- and post-fatigue, was to extend the hip and knee for the first 10 ms after foot contact. By 25 ms, all participants had changed coordination pattern to flex at the knee whilst continuing to extend at the hip. Both pre- and post-fatigue, a greater percentage of time (p<0.05) was spent in hip extension – knee flexion than in hip extension – knee extension. No change was seen in the percentage time spent in hip extension – knee flexion after fatigue. Practical Applications Most players adopted a hip extension – knee extension pattern at foot contact before switching to hip extension – knee flexion. The initial observation of hip extension – knee extension was interesting as it represents stiffness at both the hip and knee joint, which has been suggested as high risk for non-contact ACL injury (Pollard et al., 2010). The latter coordination pattern has also been hypothesised as high risk for non-contact ACL injury and was dominant both pre- and post-fatigue. The absence of change in coordination patterns after fatigue suggests this risk factor was not accentuated as a result of a short duration fatiguing protocol in an elite, healthy population

A Simple Model to Predict Scalar Dispersion within a Successively Thinned Loblolly Pine Canopy

Bark beetles kill millions of acres of trees in the United States annually by using chemical signaling to attack host trees en masse. As an attempt to control infestations, forest managers use synthetic semiochemical sources to attract beetles to traps and/or repel beetles from high-value resources such as trees and stands. The purpose of this study was to develop a simple numerical technique that may be used by forest managers as a guide in the placement of synthetic semiochemicals. The authors used a one-dimensional, one-equation turbulence model (k–lm) to drive a three-dimensional transport and dispersion model. Predictions were compared with observations from a unique tracer gas experiment conducted in a successively thinned loblolly pine canopy. Predictions of wind speed and turbulent kinetic energy compared well with observations. Scalar concentration was predicted well and trends of maximum observed concentration versus leaf area index were captured within 30 m of the release location. A hypothetical application of the numerical technique was conducted for a 12-day period to demonstrate the model’s usefulness to forest managers