Adam L. Bryant

Validity of the Microsoft Kinect for assessment of postural control

Clinically feasible methods of assessing postural control such as timed standing balance and functional reach tests provide important information, however, they cannot accurately quantify specific postural control mechanisms. The Microsoft Kinect™ system provides real-time anatomical landmark position data in three dimensions (3D), and given that it is inexpensive, portable and simple to setup it may bridge this gap. This study assessed the concurrent validity of the Microsoft Kinect™ against a benchmark reference, a multiple-camera 3D motion analysis system, in 20 healthy subjects during three postural control tests: (i) forward reach, (ii) lateral reach, and (iii) single-leg eyes-closed standing balance. For the reach tests, the outcome measures consisted of distance reached and trunk flexion angle in the sagittal (forward reach) and coronal (lateral reach) planes. For the standing balance test the range and deviation of movement in the anatomical landmark positions for the sternum, pelvis, knee and ankle and the lateral and anterior trunk flexion angle were assessed. The Microsoft Kinect™ and 3D motion analysis systems had comparable inter-trial reliability (ICC difference=0.06±0.05; range, 0.00-0.16) and excellent concurrent validity, with Pearsons r-values >0.90 for the majority of measurements (r=0.96±0.04; range, 0.84-0.99). However, ordinary least products analyses demonstrated proportional biases for some outcome measures associated with the pelvis and sternum. These findings suggest that the Microsoft Kinect™ can validly assess kinematic strategies of postural control. Given the potential benefits it could therefore become a useful tool for assessing postural control in the clinical setting.

Performance on the Single-Leg Squat Task Indicates Hip Abductor Muscle Function

Background: Contemporary clinical expertise and emerging research in anterior knee pain indicate that treatment of hip muscle function will result in greater effects, if such treatments can be provided to those with hip muscle dysfunction. Thus, it is imperative to develop and evaluate a clinical assessment tool that is capable of identifying people with poor hip muscle function. Hypothesis: The clinical assessment of single-leg squat performance will have acceptable inter- and intrarater reliability. Furthermore, people with good performance on the single-leg squat will have better hip muscle function (earlier onset of gluteus medius activity and greater lateral trunk, hip abduction, and external rotation strength) than people with poor performance. Study Design: Cohort study (diagnosis); Level of evidence, 2. Methods: A consensus panel of 5 experienced clinicians developed criteria to rate the performance of a single-leg squat task as “good,” “fair,” or “poor.” The panel rated the performance of 34 asymptomatic participants (mean ± SD: age, 24 ± 5 y; height, 1.69 ± 0.10 m; weight, 65.0 ± 10.7 kg), and these ratings served as the standard. The ratings of 3 different clinicians were compared with those of the consensus panel ratings (interrater reliability) and to their own rating on 2 occasions (intrarater reliability). For the participants rated as good performers (n = 9) and poor performers (n = 12), hip muscle strength (hip abduction, external rotation, and trunk side bridge) and onset timing of anterior (AGM) and posterior gluteus medius (PGM) electromyographic activity were compared. Results: Concurrency with the consensus panel was excellent to substantial for the 3 raters (agreement 87%-73%; κ = 0.800-0.600). Similarly, intrarater agreement was excellent to substantial (agreement 87%-73%; κ = 0.800-0.613). Participants rated as good performers had significantly earlier onset timing of AGM (mean difference, –152; 95% confidence interval [CI], –258 to –48 ms) and PGM (mean difference, –115; 95% CI, –227 to –3 ms) electromyographic activity than those who were rated as poor performers. The good performers also exhibited greater hip abduction torque (mean difference, 0.47; 95% CI, 0.10-0.83 N·m·Bw−1) and trunk side flexion force (mean difference, 1.08; 95% CI, 0.25-1.91 N·Bw−1). There was no difference in hip external rotation torque (P > .05) between the 2 groups. Conclusion: Targeted treatments, although considered ideal, rely on the capacity to identify subgroups of people with chronic anterior knee pain who might respond optimally to a given treatment component. Clinical assessment of performance on the single-leg squat task is a reliable tool that may be used to identify people with hip muscle dysfunction.

Validity of the Microsoft Kinect for providing lateral trunk lean feedback during gait retraining

Gait retraining programs are prescribed to assist in the rehabilitation process of many clinical conditions. Using lateral trunk lean modification as the model, the aim of this study was to assess the concurrent validity of kinematic data recorded using a marker-based 3D motion analysis (3DMA) system and a low-cost alternative, the Microsoft Kinect™ (Kinect), during a gait retraining session. Twenty healthy adults were trained to modify their gait to obtain a lateral trunk lean angle of 10°. Real-time biofeedback of the lateral trunk lean angle was provided on a computer screen in front of the subject using data extracted from the Kinect skeletal tracking algorithm. Marker coordinate data were concurrently recorded using the 3DMA system, and the similarity and equivalency of the trunk lean angle data from each system were compared. The lateral trunk lean angle data obtained from the Kinect system without any form of calibration resulted in errors of a high (>2°) magnitude (mean error=3.2±2.2°). Performing global and individualized calibration significantly (P<0.001) improved this error to 1.7±1.5° and 0.8±0.8° respectively. With the addition of a simple calibration the anatomical position coordinates of the Kinect can be used to create a real-time biofeedback system for gait retraining. Given that this system is low-cost, portable and does not require any sensors to be attached to the body, it could provide numerous advantages when compared to laboratory-based gait retraining systems.

Effects of estrogen on the mechanical behavior of the human Achilles tendon in vivo

The purpose of this study was to elucidate the effect of normal fluctuating [non-monophasic oral contraceptive pill (MOCP) users] and low, consistent (MOCP users) endogenous plasma estrogen levels on the strain behavior of the Achilles tendon in vivo. Twenty women (age 28.0 +/- 4.2 yr, height 1.67 +/- 0.07 m, mass 61.6 +/- 6.8 kg) who had been using the MOCP for at least 12 mo together with 20 matched women who were non-MOCP users (age 31.9 +/- 7.3 yr, height 1.63 +/- 0.05 m, mass 62.5 +/- 5.9 kg) participated in this study. Non-MOCP users were tested at the time of lowest (menstruation) and highest (approximately same as ovulation) estrogen, whereas MOCP users, who exhibited constant and attenuated endogenous estrogen levels, were tested at day 1 and day 14 of their cycle. At each test session, maximal isometric plantarflexion efforts were performed on a calf-raise apparatus while synchronous real-time ultrasonography of the triceps surae aponeurosis was recorded. Achilles tendon strain (%) was calculated by dividing tendon displacement during plantarflexion by resting tendon length. Repeated-measures ANOVA revealed a significant (P < 0.05) main effect of subject group with significantly lower Achilles strain (25.5%) in the MOCP users compared with the non-MOCP users. In conclusion, acute fluctuations in plasma estrogen across the menstrual cycle in non-MOCP users did not alter the strain behavior of the Achilles tendon. Conversely, long-term exposure to attenuated estrogen in MOCP users resulted in a decrease in Achilles tendon strain, which is thought to be attributed to the effects of endogenous estrogen on collagen synthesis. These findings have a number of important functional and clinical implications.

A Prospective Study of the Relationship between Lower Body Stiffness and Hamstring Injury in Professional Australian Rules Footballers

Background Hamstring strains remain one of the most prevalent injuries in Australian Rules football. The authors prospectively examined the relationship between musculotendinous stiffness of the hamstring and leg stiffness with hamstring injury in professional Australian Rules footballers during the 2006 season. Hypothesis Higher hamstring stiffness and leg stiffness are related to noncontact, soft tissue hamstring injury risk in professional Australian Rules footballers. Study Design Case-control study; Level of evidence, 3. Methods Unilateral hamstring stiffness and leg stiffness were assessed in 136 professional footballers in the month before the commencement of the competitive season. This information was then investigated relative to players who suffered noncontact, soft tissue hamstring injuries during either matches or training throughout the season to identify whether preseason stiffness was related to injury occurrence. Results Fourteen tested players recorded acute, noncontact hamstring injuries, resulting in 3.3 ± 2.8 weeks of missed match play per injury. At preseason testing, the players who ended up sustaining a hamstring injury during the season recorded significantly higher mean hamstring stiffness (11%, P = .04) and leg stiffness (5%, P = .03). When considering the injured players, the leg stiffness of the involved limb was significantly higher than the noninjured players (P = .02), whereas hamstring stiffness was significantly higher on the noninvolved limb (P = .01). Further, those players who suffered a hamstring injury were significantly older than the noninjured players (P = .01). Conclusion It appears that a high bilateral hamstring stiffness and leg stiffness may be a determinant in the risk of sustaining a hamstring injury. Further, relatively lower hamstring stiffness in the involved limb of injured players appears to be associated with increased injury and may be related to a lack of strength. The information from stiffness assessment may allow medical staff to determine the hamstring risk status for individual players in team sports.

Mechanical Properties of the Achilles Tendon Aponeurosis Are Altered in Athletes With Achilles Tendinopathy

Background: Achilles tendinopathy is a considerable problem for active people. The degenerative processes associated with tendinopathy may be associated with changes in the inherent mechanical properties of the musculotendinous unit. Purpose: The purpose of this study was to compare Achilles tendon–aponeurosis strain between male athletes with and without Achilles tendinopathy. Study Design: Cross-sectional study; Level of evidence, 3. Methods: Fifteen healthy men (age, 35 ± 9 years; height, 1.78 ± 0.05 m; mass, 79 ± 11 kg) and 14 men with midportion Achilles tendinopathy (age, 40 ± 8 years; height, 1.77 ± 0.06 m; mass, 80 ± 9 kg) who were all running over 20 km per week participated in the study. Each participant was tested in a single session that involved maximal isometric plantar flexion efforts being performed on a calf-raise apparatus while synchronous real-time ultrasonography of the triceps surae aponeurosis was recorded. Achilles tendon–aponeurosis strain (%) was calculated by dividing tendon displacement during plantar flexion by resting tendon length (intrarater reliability: intraclass correlation coefficient = .92). Results: Participants in the Achilles tendinopathy group (5.2% ± 2.6%) had significantly (P = .039) higher Achilles tendon–aponeurosis strain compared with the control group (3.4% ± 1.8%). In contrast, there were no significant between-group differences for maximal isometric plantar flexion force. Conclusion: Achilles tendon–aponeurosis strain is higher in male athletes with tendinopathy than those without. The results of this study provide a rationale for current clinical approaches to management of Achilles tendinopathy, whereby repetitive mechanical loading may impart a positive benefit through reduced compliance of the musculotendinous unit.

Australian football players' Achilles tendons respond to game loads within 2 days: an ultrasound tissue characterisation (UTC) study.

Background/aim The Achilles tendon is a tissue that responds to mechanical loads at a molecular and cellular level. In vitro and in vivo studies have shown that the expression of anabolic and/or catabolic proteins can change within hours of loading and return to baseline levels within 72 h. These biochemical changes have not been correlated with changes in whole tendon structure on imaging. We examined the nature and temporal sequence of changes in Achilles tendon structure in response to competitive game loads in elite Australian football players. Methods Elite male Australian football players with no history of Achilles tendinopathy were recruited. Achilles tendon structure was quantified using ultrasound tissue characterisation (UTC) imaging, a valid and reliable measure of intratendinous structure, the day prior to the match (day 0), and then reimaged on days 1, 2 and 4 postgame. Results Of the 18 participants eligible for this study, 12 had no history of tendinopathy (NORM) and 6 had a history of patellar or hamstring tendinopathy (TEN). Differences in baseline UTC echopattern were observed between the NORM and TEN groups, with the Achilles of the TEN group exhibiting altered UTC echopattern, consistent with a slightly disorganised tendon structure. In the NORM group, a significant reduction in echo-type I (normal tendon structure) was seen on day 2 (p=0.012) that returned to baseline on day 4. Summary There was a transient change in UTC echopattern in the Achilles tendon as a result of an Australian football game in individuals without a history of lower limb tendinopathy.

Reliability and validity of the Microsoft Kinect for evaluating static foot posture.

BackgroundThe evaluation of foot posture in a clinical setting is useful to screen for potential injury, however disagreement remains as to which method has the greatest clinical utility. An inexpensive and widely available imaging system, the Microsoft Kinect™, may possess the characteristics to objectively evaluate static foot posture in a clinical setting with high accuracy. The aim of this study was to assess the intra-rater reliability and validity of this system for assessing static foot posture.MethodsThree measures were used to assess static foot posture; traditional visual observation using the Foot Posture Index (FPI), a 3D motion analysis (3DMA) system and software designed to collect and analyse image and depth data from the Kinect. Spearman’s rho was used to assess intra-rater reliability and concurrent validity of the Kinect to evaluate foot posture, and a linear regression was used to examine the ability of the Kinect to predict total visual FPI score.ResultsThe Kinect demonstrated moderate to good intra-rater reliability for four FPI items of foot posture (ρ = 0.62 to 0.78) and moderate to good correlations with the 3DMA system for four items of foot posture (ρ = 0.51 to 0.85). In contrast, intra-rater reliability of visual FPI items was poor to moderate (ρ = 0.17 to 0.63), and correlations with the Kinect and 3DMA systems were poor (absolute ρ = 0.01 to 0.44). Kinect FPI items with moderate to good reliability predicted 61% of the variance in total visual FPI score.ConclusionsThe majority of the foot posture items derived using the Kinect were more reliable than the traditional visual assessment of FPI, and were valid when compared to a 3DMA system. Individual foot posture items recorded using the Kinect were also shown to predict a moderate degree of variance in the total visual FPI score. Combined, these results support the future potential of the Kinect to accurately evaluate static foot posture in a clinical setting.

Associations of knee extensor strength and standing balance with physical function in knee osteoarthritis.

Knee extensor strength is an important correlate of physical function in patients with knee osteoarthritis; however, it remains unclear whether standing balance is also a correlate. The purpose of this study was to evaluate the cross‐sectional associations of knee extensor strength, standing balance, and their interaction with physical function.

Successful Feed-Forward Strategies Following ACL Injury and Reconstruction

The purpose of this study was to elucidate the most successful feed-forward strategies responsible for enhancing dynamic restraint following anterior cruciate ligament (ACL) injury and ACL reconstruction (ACLR). Ten male ACL deficient (ACLD) subjects (18-35 years) together with 27 matched males who had undergone ACLR (14 using a patella tendon graft and 13 using a combined semitendinosus and gracilis graft) and 22 matched-control subjects were recruited. After their knee functionality (0- to 100-point scale) was rated using the Cincinnati Knee Rating System, each subject performed a maximal, countermovement hop for distance on their involved limb while EMG data were collected from the vastus lateralis (VL), vastus medialis (VM), semitendinosus (ST) and biceps femoris (BF) muscles. Acceleration transients at the proximal tibia were recorded using a uniaxial accelerometer mounted at the level of the tibial tuberosity. Whilst pre-programmed muscle activation strategies and tibial acceleration transients when landing from a single-leg long hop for distance were not contingent upon ACL status, a number of significant correlations were identified between neuromuscular variables and knee functionality of ACLD and ACLR subjects. Increased hamstring preparatory activity together with a greater ability to control tibial motion during dynamic deceleration was associated with higher levels of knee functionality in the ACLD subjects. Successful feed-forward strategies following ACLR were related to graft selection; STGT subjects with superior knee function activated their quadriceps earlier and were better able to synchronise peak hamstring muscle activity closer to initial ground contact whilst more functional PT subjects demonstrated enhanced tibial control despite a lack of evidence supporting modified pre-programmed muscular activation patterns. Our conclusion was that more functional individuals used sensory feedback to build treatment-specific, feed-forward strategies to enhance dynamic restraint when performing a task known to stress the ACL.