Comparative assessment of bone pose estimation using point cluster technique and OpenSim

Estimating the position of the bones from optical motion capture data is a challenge associated with human movement analysis. Bone pose estimation techniques such as the Point Cluster Technique (PCT) and simulations of movement through software packages such as OpenSim are used to minimize soft tissue artifact and estimate skeletal position; however, using different methods for analysis may produce differing kinematic results which could lead to differences in clinical interpretation such as a misclassification of normal or pathological gait. This study evaluated the differences present in knee joint kinematics as a result of calculating joint angles using various techniques. We calculated knee joint kinematics from experimental gait data using the standard PCT, the least squares approach in OpenSim applied to experimental marker data, and the least squares approach in OpenSim applied to the results of the PCT algorithm. Maximum and resultant RMS differences in knee angles were calculated between all techniques. We observed differences in flexion/extension, varus/ valgus, and internal/external rotation angles between all approaches. The largest differences were between the PCT results and all results calculated using OpenSim. The RMS differences averaged nearly 5 for flexion/extension angles with maximum differences exceeding 15 . Average RMS differences were relatively small (< 1.08 ) between results calculated within OpenSim, suggesting that the choice of marker weighting is not critical to the results of the least squares inverse kinematics calculations. The largest difference between techniques appeared to be a constant offset between the PCT and all OpenSim results, which may be due to differences in the definition of anatomical reference frames, scaling of musculoskeletal models, and/or placement of virtual markers within OpenSim. Different methods for data analysis can produce largely different kinematic results, which could lead to the misclassification of normal or pathological gait. Improved techniques to allow non-uniform scaling of generic models to more accurately reflect subject-specific bone geometries and anatomical reference frames may reduce differences between bone pose estimation techniques and allow for comparison across gait analysis platforms

A new perspective on transient characteristics of quiet stance postural control.

Postural control provides insight into health concerns such as fall risk but remains relatively untapped as a vital sign of health. One understudied aspect of postural control involves transient responses within center of pressure (CoP) data to events such as vision occlusion. Such responses are masked by common whole-trial analyses. We hypothesized that the transient behavior of postural control would yield unique and clinically-relevant information for quiet stance compared to traditionally calculated whole-trial CoP estimates. Three experiments were conducted to test different aspects of this central hypothesis. To test whether transient, epoch-based characteristics of CoP estimates provide different information than traditional whole-trial estimates, we investigated correlations between these estimates for a population of young adults performing three 60-second trials of quiet stance with eyes closed. Next, to test if transient behavior is a result of sensory reweighting after eye closure, we compared transient characteristics between eyes closed and eyes open conditions. Finally, to test if there was an effect of age on transient behavior, we compared transient characteristics during eyes closed stance between populations of young and older adults. Negligible correlations were found between transient characteristics and whole-trial estimates (p>0.08), demonstrating limited overlap in information between them. Additionally, transient behavior was exaggerated during eyes closed stance relative to eyes open (p<0.044). Lastly, we found that transient characteristics were able to distinguish between younger and older adults, supporting their clinical relevance (p<0.029). An epoch-based approach captured unique and potentially clinically-relevant postural control information compared to whole-trial estimates. While longer trials may improve the reliability of whole-trial estimates, including a complementary assessment of the initial transient characteristics may provide a more comprehensive characterization of postural control

Lumbopelvic control and pitching performance of professional baseball pitchers

This study assessed the correlation between lumbopelvic control during a single-leg balancing task and in-game pitching performance in Minor-League baseball pitchers. Seventy-five healthy professional baseball pitchers performed a standing lumbopelvic control test during the last week of spring training for the 2008 and 2009 seasons while wearing a custom-designed testing apparatus, the "Level Belt." With the Level Belt secured to the waist, subjects attempted to transition from a 2-leg to a single-leg pitching stance and balance while maintaining a stable pelvic position. Subjects were graded on the maximum sagittal pelvic tilt from a neutral position during the motion. Pitching performance, number of innings pitched (IP), and injuries were compared for all subjects who pitched at least 50 innings during a season. The median Level Belt score for the study group was 7°. Two-sample t-tests with equal variances were used to determine if pitchers with a Level Belt score <7° or ≥7° were more likely to perform differently during the baseball season, and chi-square analysis was used to compare injuries between groups. Subjects scoring <7° on the Level Belt test had significantly fewer walks plus hits per inning than subjects scoring ≥7° (walks plus hits per inning pitched, 1.352 ± 0.251 vs. 1.584 ± 0.360, p = 0.013) and significantly more IP during the season (IP, 78.89 ± 38.67 vs. 53.38 ± 42.47, p = 0.043). There was no significant difference in the number of pitchers injured between groups. These data suggest that lumbopelvic control influences overall performance for baseball pitchers and that a simple test of lumbopelvic control can potentially identify individuals who have a better chance of pitching success

The influence of receiving real-time visual feedback on breathing during treadmill running to exhaustion.

Breathing plays a vital role in everyday life, and specifically during exercise it provides working muscles with the oxygen necessary for optimal performance. Respiratory inductance plethysmography (RIP) monitors breathing through elastic belts around the chest and abdomen, with efficient breathing defined by synchronous chest and abdomen movement. This study examined if providing runners with visual feedback through RIP could increase breathing efficiency and thereby time to exhaustion. Thirteen recreational runners (8F, 5M) ran to exhaustion on an inclined treadmill on two days, with visual feedback provided on one randomly chosen day. Phase angle was calculated as a measure of thoraco-abdominal coordination. Time to exhaustion was not significantly increased when visual feedback was provided (p = 1). Phase angle was not significantly predicted by visual feedback (p = 0.667). Six participants improved phase angle when visual feedback was provided, four of whom increased time to exhaustion. Four participants improved phase angle by 9° or more, three of whom increased time to exhaustion. Participants who improved phase angle with visual feedback highlight that improving phase angle could increase time to exhaustion. Greater familiarization with breathing techniques and visual feedback and a different paradigm to induce running fatigue are needed to support future studies of breathing in runners

Tibiofemoral Osteoarthritis and Varus–Valgus Laxity

The purpose of this study was to systematically review and synthesize the literature measuring varus–valgus laxity in individuals with tibiofemoral osteoarthritis (OA). Specifically, we aimed to identify varus–valgus laxity differences between persons with OA and controls, by radiographic disease severity, by frontal plane knee alignment, and by sex. We also aimed to identify if there was a relationship between varus–valgus laxity and clinical performance and self-reported function. We systematically searched for peer-reviewed original research articles in PubMed, Scopus, and CINAHL to identify all existing literature regarding knee OA and objective measurement of varus–valgus laxity in vivo. Forty articles were identified that met the inclusion criteria and data were extracted. Varus–valgus laxity was significantly greater in individuals with OA compared with controls in a majority of studies, while no study found laxity to be significantly greater in controls. Varus–valgus laxity of the knee was reported in persons with OA and varying degrees of frontal plane alignment, disease severity, clinical performance, and self-reported function but no consensus finding could be identified. Females with knee OA appear to have more varus–valgus laxity than males. Meta-analysis was not possible due to the heterogeneity of the subject populations and differences in laxity measurement devices, applied loading, and laxity definitions. Increased varus–valgus laxity is a characteristic of knee joints with OA. Large variances exist in reported varus–valgus laxity and may be due to differences in measurement devices. Prospective studies on joint laxity are needed to identify if increased varus–valgus laxity is a causative factor in OA incidence and progression

Reducing Core Stability Influences Lower Extremity Biomechanics in Novice Runners

The role of core stability in running and its influence on injury risk in runners is not well understood. The purpose of this study was to investigate the effect of core stability (and core fatigue) on running mechanics. We hypothesized that decreasing core stability in novice runners would result in altered running mechanics previously associated with increased risk for common lower extremity running injuries. Three-dimensional running kinematics and kinetics and seated postural sway on an unstable surface were collected on 25 healthy, novice runners before and after they performed a core stability knockdown protocol (CSKP), designed to temporarily reduce participants' core stability in a single testing session. Linear mixed models demonstrated that the CSKP resulted in an increased peak knee flexion moment (0.51%BW·ht increase, effect size = 0.49, P = 0.021) and a decreased vertical average loading rate (4.5 BW·s decrease, effect size = 0.44, P = 0.037) during running, but no significant changes in peak knee adduction moment, knee adduction impulse, hip adduction moment, hip adduction impulse, or peak vertical ground reaction force (all P > 0.05). Of 25 runners, 20 demonstrated a measurable decrement in their core stability as defined by their seated postural sway center of pressure excursion changing more than the standard error of measurement of 76 mm. An experimentally induced decrement in core stability in novice runners caused an increased peak knee flexion moment during stance, which has previously been associated with increased patellofemoral contact pressure during running. Therefore, these results demonstrate that insufficient core stability in novice runners may be a risk factor for developing patellofemoral pain. Other results did not support a role of core stability in other common overuse running injuries in this population

Association Between Ball-Handling Versus Defending Actions and Acute Noncontact Lower Extremity Injuries in High School Basketball and Soccer

High school-sponsored athletic programs currently provide more than 7.7 million students in the United States with health and societal benefits, but they also inherently increase the risk of students sustaining a sports injury. Understanding risk factors that predict injuries in sports is an essential first step to addressing the problem in this population. To determine the role of offensive versus defensive actions in noncontact lower extremity injury rates in high school basketball and soccer in both boys' and girls' sports. Descriptive epidemiological study. Noncontact lower extremity injury data were collected from academic years 2005-2006 through 2011-2012 for boys' and girls' basketball and soccer through the surveillance tool High School RIO (reporting information online). The injuries in this subset of the database occurred over a total of 6.4 million athlete-exposures. Significant differences in overall lower extremity injury rates were found when comparing ball-handling and defending actions in basketball (rate ratio [RR], 1.36; 95% CI, 1.08-1.73; P = .009), but no appreciable difference was observed in soccer (RR, 0.89; 95% CI, 0.70-1.12; P = .31). Female participants had higher injury rates than did males for both ball-handling and defending actions for both sports (P < .05). Only girls' soccer showed significant differences in the odds ratio (OR) of defending to ball-handling injury rates between competition and practice (OR, 1.88; 95% CI, 1.01-3.48; P = .047). The injury rate differences observed in this study between offensive and defensive actions suggest that investigating potential differences between sport-specific tasks may provide a more complete understanding of injury mechanisms