Body-Worn IMU-Based Human Hip and Knee Kinematics Estimation during Treadmill Walking.

Traditionally, inertial measurement unit (IMU)-based human joint angle estimation techniques are evaluated for general human motion where human joints explore all of their degrees of freedom. Pure human walking, in contrast, limits the motion of human joints and may lead to unobservability conditions that confound magnetometer-free IMU-based methods. This work explores the unobservability conditions emergent during human walking and expands upon a previous IMU-based method for the human knee to also estimate human hip angles relative to an assumed vertical datum. The proposed method is evaluated (N=12) in a human subject study and compared against an optical motion capture system. Accuracy of human knee flexion/extension angle (7.87∘ absolute root mean square error (RMSE)), hip flexion/extension angle (3.70∘ relative RMSE), and hip abduction/adduction angle (4.56∘ relative RMSE) during walking are similar to current state-of-the-art self-calibrating IMU methods that use magnetometers. Larger errors of hip internal/external rotation angle (6.27∘ relative RMSE) are driven by IMU heading drift characteristic of magnetometer-free approaches and non-hinge kinematics of the hip during gait, amongst other error sources. One of these sources of error, soft tissue perturbations during gait, is explored further in the context of knee angle estimation and it was observed that the IMU method may overestimate the angle during stance and underestimate the angle during swing. The presented method and results provide a novel combination of observability considerations, heuristic correction methods, and validation techniques to magnetic-blind, kinematic-only IMU-based skeletal pose estimation during human tasks with degenerate kinematics (e.g., straight line walking).

Body-Worn IMU Human Skeletal Pose Estimation Using a Factor Graph-Based Optimization Framework.

Traditionally, inertial measurement units- (IMU) based human joint angle estimation requires a priori knowledge about sensor alignment or specific calibration motions. Furthermore, magnetometer measurements can become unreliable indoors. Without magnetometers, however, IMUs lack a heading reference, which leads to unobservability issues. This paper proposes a magnetometer-free estimation method, which provides desirable observability qualities under joint kinematics that sufficiently excite the lower body degrees of freedom. The proposed lower body model expands on the current self-calibrating human-IMU estimation literature and demonstrates a novel knee hinge model, the inclusion of segment length anthropometry, segment cross-leg length discrepancy, and the relationship between the knee axis and femur/tibia segment. The maximum a posteriori problem is formulated as a factor graph and inference is performed via post-hoc, on-manifold global optimization. The method is evaluated (N = 12) for a prescribed human motion profile task. Accuracy of derived knee flexion/extension angle (4.34∘ root mean square error (RMSE)) without magnetometers is similar to current state-of-the-art with magnetometer use. The developed framework can be expanded for modeling additional joints and constraints.

Correction: McGrath, T., et al. An Auto-Calibrating Knee Flexion-Extension Axis Estimator using Principal Component Analysis with Inertial Sensors. Sensors 2018, 18(6), 1882.

The authors wish to make the following revisions to this paper [...].

An Auto-Calibrating Knee Flexion-Extension Axis Estimator Using Principal Component Analysis with Inertial Sensors.

Inertial measurement units (IMUs) have been demonstrated to reliably measure human joint angles—an essential quantity in the study of biomechanics. However, most previous literature proposed IMU-based joint angle measurement systems that required manual alignment or prescribed calibration motions. This paper presents a simple, physically-intuitive method for IMU-based measurement of the knee flexion/extension angle in gait without requiring alignment or discrete calibration, based on computationally-efficient and easy-to-implement Principle Component Analysis (PCA). The method is compared against an optical motion capture knee flexion/extension angle modeled through OpenSim. The method is evaluated using both measured and simulated IMU data in an observational study (n = 15) with an absolute root-mean-square-error (RMSE) of 9.24∘ and a zero-mean RMSE of 3.49∘. Variation in error across subjects was found, made emergent by the larger subject population than previous literature considers. Finally, the paper presents an explanatory model of RMSE on IMU mounting location. The observational data suggest that RMSE of the method is a function of thigh IMU perturbation and axis estimation quality. However, the effect size for these parameters is small in comparison to potential gains from improved IMU orientation estimations. Results also highlight the need to set relevant datums from which to interpret joint angles for both truth references and estimated data.

The effect of limb dominance on lower limb functional performance--a systematic review.

Lower limb dominance (or lateral preference) could potentially effect functional performance. Clinicians are often asked to make judgements as to when a patient has sufficiently "recovered" from an injury, typically using strength and dynamic performance outcome measures. The primary purpose of this study was to systematically review the literature in relation to limb dominance within active adult populations and discuss some limitations to current methods and relate this to current clinical practice. A search of MEDLINE and CINAHL and EMBASE databases and reference lists of those articles identified was performed. Eleven articles were selected for meta-analysis. There was no statistical effect of limb dominance for any of the functional tests: isokinetic quadriceps and hamstring tests, hamstring:quadriceps ratios, single-leg hop for distance, single-leg vertical jump and vertical ground reaction force following a single-leg vertical jump. Pooled symmetry values varied from 94.6% to 99.6% across the tests, above the clinically accepted benchmark of 90% used in clinical practice. Although the results of this study must be used with discretion, asymmetries in the tasks described in this analysis should be viewed as undesirable and remedied accordingly. Further research is needed to quantify asymmetries, particularly in relation to sport-specific contexts.

Normative Values for Grip and Pinch Strength for 6- to 19-Year-Olds.

OBJECTIVES: To provide current normative data for grip and pinch strength in children and young adults aged 6 to 19 years as well as to examine the effect of age, sex, and hand dominance on grip and pinch strength. DESIGN: Descriptive cross-sectional. SETTING: Two grade schools, 2 high schools, and 1 university. PARTICIPANTS: Participants (N=1508; 741 male students and 767 female students) aged 6 to 19 years. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Means and SDs were calculated for each strength measurement (grip, tip pinch, lateral pinch, palmar pinch) and stratified by age and sex. Analysis of covariance and 2-sample t tests were used to analyze the data. RESULTS: The analyses demonstrated that age and sex had a significant effect on hand strength values, as evidenced by increasing hand strength with age as well as greater hand strength in males than in females. Hand dominance was not shown to have a significant effect on hand strength. The results of this study were statistically significantly different from previously published normative values, with most hand strength values being lower than those published 28 years ago. CONCLUSIONS: Having updated normative data are paramount for rehabilitation practitioners to compare the grip and pinch strength of their clients with the average values to objectively assess impairment and tracking progress. The statistical significance observed for most data collected in this study as compared with those previously published supports the need for continually updating normative data.

Investigation of Listeria, Salmonella, and toxigenic Escherichia coli in various pet foods.

The Veterinary Laboratory Investigation and Response Network (Vet-LIRN), in collaboration with the Food Emergency Response Network (FERN) and its Microbiology Cooperative Agreement Program (MCAP) laboratories, conducted a study to evaluate the prevalence of selected microbial organisms in various types of pet foods. The goal of this blinded study was to help the Center for Veterinary Medicine prioritize potential future pet food-testing efforts. The study also increased the FERN laboratories' screening capabilities for foodborne pathogens in animal feed matrices, since such pathogens may also be a significant health risk to consumers who come into contact with pet foods. Six U.S. Food and Drug Administration FERN MCAP laboratories analyzed approximately 1056 samples over 2 years. Laboratories tested for Salmonella, Listeria, Escherichia coli O157:H7 enterohemorrhagic E. coli, and Shiga toxin-producing strains of E. coli (STEC). Dry and semimoist dog and cat foods purchased from local stores were tested during Phase 1. Raw dog and cat foods, exotic animal feed, and jerky-type treats purchased through the Internet were tested in Phase 2. Of the 480 dry and semimoist samples, only 2 tested positive: 1 for Salmonella and 1 for Listeria greyii. However, of the 576 samples analyzed during Phase 2, 66 samples were positive for Listeria (32 of those were Listeria monocytogenes) and 15 samples positive for Salmonella. These pathogens were isolated from raw foods and jerky-type treats, not the exotic animal dry feeds. This study showed that raw pet foods may harbor food safety pathogens, such as Listeria monocytogenes and Salmonella. Consumers should handle these products carefully, being mindful of the potential risks to human and animal health.

Determinants of hamstring fascicle length in professional rugby league athletes.

OBJECTIVES: Investigate the determinants of hamstring fascicle length in professional rugby league players. DESIGN: Retrospective cohort study METHODS: Thirty-three elite male athletes underwent testing in the pre-season and in-season periods. Fascicle length measurements of the biceps femoris long head, 3D kinematics and elapsed time-periods at thigh angular velocities between 20°/s to peak velocity during a single-leg Nordic hamstring strength test, GPS-derived running loads, age and previous injury history were all recorded. Fixed effect determinants for fascicle length were analyzed using multiple linear regression. RESULTS: Significant determinants of hamstring fascicle length were observed. Multivariate regression analysis showed modifiable factors including chronic (56 days) running volumes >80% of measured peak velocity and maximum velocity itself collectively explained 43% of the variability in the fascicle length data, whilst peak eccentric strength and elapsed time under load from 20°/s to peak thigh angular velocity collectively contributed an additional 44%. Chronic running volumes >90% of individually measured peak velocity and the 'break angle' during a Nordic eccentric contraction were not significant contributors to the final model. Non-modifiable risk factors (age and previous injury) contributed the remaining 13%. CONCLUSIONS: Managing high velocity running exposure as well as eccentric strength allows for ˜90% of the controllable determinants in fascicle length within elite athlete populations. An important contributor to the explained variability within fascicle length (superseded only by chronic velocity exposure and peak eccentric strength) was an athletes ability to achieve a prolonged contraction at long lengths during eccentric strength training rather than the angle of failure during the contraction in itself.

Objective Metrics Quantifying Fit and Performance in Spacesuit Assemblies.

INTRODUCTION: Human-spacesuit fit is not well understood, especially in relation to operational performance and injury risk. Current fit decisions use subjective feedback. This work developed and evaluated new metrics for quantifying fit and assessed metric sensitivity to changes in padding between the human and hip brief assembly (HBA).METHODS: Three subjects donned the Mark III (MKIII) spacesuit with three padding thicknesses between the lower body and HBA. Subjects performed a walking task with inertial measurement units on the thigh and shin of both the human and suit. For each step, cadence, human knee task range of motion (tRoM), difference in human and suit tROM (ΔtRoM), and the relative coordination metric (ρ) between the human-suit femur and tibia were computed.RESULTS: The MKIII significantly reduced user cadence by 20.4% and reduced tRoM by 16.5% during walking with subject-dependent changes due to added padding. In general, the addition of padding significantly altered ΔtRoM; however, variability did exist between subjects. Mixed-effect regressions of dynamic fit (ρ) reflect distinct positive spikes in ρ around heel strike (human-dominated motion) and negative dips following toe off (suit-dominated motion).DISCUSSION: There were mixed effects of padding on gait performance and dynamic fit measures. Differences in dynamic fit between subjects may be more reliant on alternate aspects of fit, such as suit component sizes and designs, than padding level. Subjective feedback supported quantitative observations, highlighting metric utility. Future work will explore the effects of suit sizing components on measures of fit and performance.Fineman RA, McGrath TM, Kelty-Stephen DG, Abercromby AFJ, Stirling LA. Objective metrics quantifying fit and performance in spacesuit assemblies. Aerosp Med Hum Perform. 2018; 89(11):985-995.

Rapid detection of the Vibrio cholerae ctx gene in food enrichments using real-time polymerase chain reaction.

A real-time polymerase chain reaction (qPCR) assay for the detection of the ctxA gene of toxigenic Vibrio cholerae (Vc) was validated against standard culture techniques. The first experimental phase determined optimal enrichment conditions for detection by culture and qPCR of Vc in shrimp, bottled water, milk, and potato salad. The conditions tested included temperature (35 and 42 degrees C), time (6 and 18 h), and effect of shaking (0 and 100 rpm). No definitive trends were found with enrichment temperature or shaking on Vc isolation frequency or detection by qPCR. Generally, Vc was detected by qPCR more frequently than Vc was isolated, but this difference was significant only in the 35 degrees C 6 h enrichment without shaking. In the second phase of experiments, shrimp, bottled water, milk, potato salad, and oysters were inoculated with each of 3 toxigenic Vc strains (Latin American O1 strain, an O139 strain, and an O1 strain from the U.S. Gulf Coast) and enriched under static conditions at 42OC for 6 and 18 h. Overall, detection frequency of ctx by qPCR was 98% (88/90) and 100% (90/90) after 6 and 18 h enrichments, respectively, while Vc isolation frequency was 87% (78/90) and 83% (75/90) after 6 and 18 h, respectively. Toxigenic Vc can be detected by qPCR within an 8 h work day using the 6 h enrichment procedure, assuming an initial level of at least 1-2 colony-forming units/g; however, overnight enrichment may be necessary to detect lower levels. These data indicate that the qPCR assay for ctx is a more reliable, sensitive, and rapid alternative to standard Vc culture methods and is applicable to diverse food products.

An Ecological Study of Anterior Cruciate Ligament Reconstruction, Part 2: Functional Performance Tests Correlate With Return-to-Sport Outcomes.

BACKGROUND: Additional high-quality prospective studies are needed to better define the objective criteria used in relation to return-to-sport decisions after anterior cruciate ligament (ACL) reconstruction in active populations. PURPOSE: To investigate prospectively the relationship between functional performance test results at 24 weeks postoperative and return-to-sport activity (Tegner activity score) at 12 and 24 months, respectively, after synthetic (ligament advanced reinforcement system [LARS]) and autograft (doubled semitendinosus/gracilis [2ST/2GR]) ACL reconstructions. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: A total of 64 patients who underwent ACL reconstruction (32 LARS, 32 2ST/2GR autograft; mean age, 27.9 years; body mass index [BMI], 24.9 kg/m2) were assessed preoperatively and at staged intervals postoperatively up to 24 weeks for isokinetic testing of quadriceps and hamstring average power per repetition at 60 deg/s and 180 deg/s, a battery of hop tests, peak vertical ground-reaction force (vGRF), and time to peak vGRF (in seconds) during a step- and jump-down task onto a force platform and peak speed (m/s) using a global positioning system (GPS unit) during a running task. A cohort of 32 healthy matched participants (mean age, 26.31 years; BMI, 25.7 kg/m2) were also tested to act as reference. Pearson correlation was calculated to assess correlation of each performance measure at 24 weeks postoperative with activity outcomes (Tegner score) at 12 and 24 months. RESULTS: The strongest correlation between physical performance tests and return-to-sport outcomes was observed with peak speed during running. Large correlations were also observed for hamstring isokinetic power and hop test for distance. Moderate correlations were observed for timed hop, peak vGRF during a jump-down task, and quadriceps isokinetic power. No statistical correlations were observed for time to peak vGRF during a step-down and jump-down task as well as peak vGRF during a step-down task. When the performance tests were pooled together, mean postoperative improvements of 24% were observed from preoperative to 24 weeks within the surgical cohort. For each performance test, preoperative level of function strongly correlated with performance levels on the same test at 24 weeks. DISCUSSION: The results of this study indicate that clinicians might seek to prioritize these tests and the rehabilitation themes they imply when seeking to maximize postoperative ACL activity outcomes. The observed strength between pre- and postoperative performance tests and return-to-sport outcomes within this study highlights the potential value of preoperative conditioning before undergoing ACL reconstruction. Future research should examine absolute predictive criterion thresholds for functional performance-based tests and reinjury risk reduction after ACL reconstruction.

An Ecological Study of Anterior Cruciate Ligament Reconstruction, Part 1: Clinical Tests Do Not Correlate With Return-to-Sport Outcomes.

BACKGROUND: Additional high-quality prospective studies are needed to better define the objective criteria used in relation to return-to-sport decisions after synthetic (ligament advanced reinforcement system [LARS]) and autograft (hamstring tendon [2ST/2GR]) anterior cruciate ligament (ACL) reconstruction in active populations. PURPOSE: To prospectively investigate and describe the recovery of objective clinical outcomes after autograft (2ST/2GR) and synthetic (LARS) ACL reconstructions, as well as to investigate the relationship between these clinimetric test outcomes and return-to-sport activity (Tegner activity scale [TAS] score) at 12 and 24 months postoperatively. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: A total of 64 patients who underwent ACL reconstruction (32 LARS, 32 2ST/2GR autograft) and 32 healthy reference participants were assessed for joint laxity (KT-1000 arthrometer), clinical outcome (2000 International Knee Documentation Committee [IKDC] knee examination), and activity (TAS score) preoperatively and at 12, 16, 20, and 24 weeks and 12 and 24 months postoperatively. RESULTS: There was no significant correlation observed between clinical results using the 2000 IKDC knee examination and TAS score at 24 months (rs = 0.188, P = .137), nor were results for side-to-side difference (rs = 0.030, P = .814) or absolute KT-1000 arthrometer laxity of the surgical leg at 24 months postoperatively (rs = 0.076, P = .553) correlated with return-to-sport activity. Nonetheless, return-to-sport rates within the surgical cohort were 81% at 12 months and 83% at 24 months, respectively. No statistically significant differences were observed between physiological laxity of the uninjured knee within the surgical group compared with healthy knees within the reference group (P = .522). CONCLUSION: The results indicate that although relatively high levels of return-to-sport outcomes were achieved at 24 months compared with those previously reported in the literature, correlations between objective clinical tests and return-to-sport outcomes may not occur. Clinical outcome measures may provide suitable baseline information; however, the results of this study suggest that clinicians may need to place greater emphasis on other outcome measures when seeking to objectively promote safe return to sport.