Exploring the Influence of Structured Familiarization to an Adjustable, Passive Load-Bearing Exoskeleton on Oxygen Consumption and Lower Limb Muscle Activation During Walking.

Walking patterns are modified during load carriage, resulting in an increased activation of lower limb muscles and energy expenditure. Negative effects of load carriage could be minimized by wearing an exoskeleton, but evidence on the effects are conflicting. The objectives of this study were to describe the influence of an adjustable, passive load-bearing exoskeleton on the metabolic cost of walking (MCW) and associated muscle activations, and to explore changes in MCW after a familiarization process. Thirteen participants walked on a treadmill with a 22.75 kg payload at six preselected speeds (from 0.67 to 1.56 m/s) under three walking conditions: 1) without exoskeleton (NoExo); 2) with exoskeleton before familiarization (ExoPre); and 3) with exoskeleton after familiarization (ExoPost). Metabolic data was normalized to walking speed to provide MCW. Multi-muscle surface electromyography (EMG) was time and amplitude normalized to the gait cycle to provide muscle activation patterns. The familiarization occurred over three weeks including exposure to the exoskeleton. Differences in MCW and muscle activations were compared using a nonparametric analysis of longitudinal data. There were statistically significant increases in MCW for all speeds in the ExoPre and ExoPost conditions compared the NoExo. The average muscle activation showed an increase during ExoPre and ExoPost for the three speeds evaluated. Post-hoc analysis showed no significant effect of the familiarization period on metabolic data. In conclusion, a first exposure to the adjustable exoskeleton increased MCW and muscle activations, but the familiarization process did not provide any benefits toward a reduction in MCW or reduction in muscle activations at all speeds evaluated.

A data-driven framework for assessing soldier performance, health, and survivability.

Presented is a framework that uses pattern classification methods to incrementally morph whole-body movement patterns to investigate how personal (sex, military experience, and body mass) and load characteristics affect the survivability tradespace: performance, musculoskeletal health, and susceptibility to enemy action. Sixteen civilians and 12 soldiers performed eight military-based movement patterns under three body-borne loads: ∼5.5 kg, ∼22 kg, and ∼38 kg. Our framework reduces dimensionality using principal component analysis and uses linear discriminant analysis to classify groups and morph movement patterns. Our framework produces morphed whole-body movement patterns that emulate previously published changes to the survivability tradespace caused by body-borne loads. Additionally, we identified that personal characteristics can greatly impact the tradespace when carrying heavy body-borne loads. Using our framework, military leaders can make decisions based on objective information for armour procurement, employment of armour, and battlefield performance, which can positively impact operational readiness and increase overall mission success.

Does sitting on a stability ball increase fall risk during ergonomic reaching tasks?

Although sitting on a stability ball has become an alternative to using an office chair, little is known about the increased potential for a fall on the deformable seat. This study examined differences in stability between sitting on a seat pan of a backless office chair and a stability ball during reaching tasks. Sixteen participants performed forward and lateral reaching tasks on a backless and armless office chair and stability ball while whole-body motion and force data under the seat were recorded. Even with participants placing their feet 16.5 cm wider when seated on the ball, the perceived fall risk was significantly greater. Centre of pressure displacement tended to be smaller under the ball for lateral reach directions, but larger during far anterior reaches. While not statistically significant, the medial-lateral margin of stability was on average 3.4 cm smaller on the ball. Despite attempts to increase stability by widening their stance, stability ball fall risk remained higher.

The need for a paradigm shift in the development of military exoskeletons.

An exoskeleton is a body-worn mechanical device designed to work in concert with the user to enhance human capabilities. For the dismounted close combatant, an exoskeleton could be worn whilst performing a variety of complex tasks and duties. As such, there is a requirement for the human and the exoskeleton to readily adapt to different movements in different contexts. There have been many attempts to design an exoskeleton to improve the performance of the complex adaptive human system with limited success. Despite a vast investment in time and resources, exoskeletons have not yet been adopted for operational use by military leadership for use by the dismounted close combatant as they are yet to demonstrate substantive augmentation to individual warfighter and collective team capability. We argue that a major limitation of current exoskeleton systems is their inability to concurrently adapt to the user, task and environment. Unless a device can meet this requirement, it is unlikely to offer a comparative benefit to the dismounted close combatant. This paper will present the state of the art of current exoskeleton technology, and recommend future research necessary to reach an acceptable standard of augmentation and thereby lead to widespread adoption.

Risk factors for musculoskeletal injuries in the military: a qualitative systematic review of the literature from the past two decades and a new prioritizing injury model.

BACKGROUND: Musculoskeletal injuries (MSkIs) are a leading cause of health care utilization, as well as limited duty and disability in the US military and other armed forces. MSkIs affect members of the military during initial training, operational training, and deployment and have a direct negative impact on overall troop readiness. Currently, a systematic overview of all risk factors for MSkIs in the military is not available. METHODS: A systematic literature search was carried out using the PubMed, Ovid/Medline, and Web of Science databases from January 1, 2000 to September 10, 2019. Additionally, a reference list scan was performed (using the "snowball method"). Thereafter, an international, multidisciplinary expert panel scored the level of evidence per risk factor, and a classification of modifiable/non-modifiable was made. RESULTS: In total, 176 original papers and 3 meta-analyses were included in the review. A list of 57 reported potential risk factors was formed. For 21 risk factors, the level of evidence was considered moderate or strong. Based on this literature review and an in-depth analysis, the expert panel developed a model to display the most relevant risk factors identified, introducing the idea of the "order of importance" and including concepts that are modifiable/non-modifiable, as well as extrinsic/intrinsic risk factors. CONCLUSIONS: This is the qualitative systematic review of studies on risk factors for MSkIs in the military that has attempted to be all-inclusive. A total of 57 different potential risk factors were identified, and a new, prioritizing injury model was developed. This model may help us to understand risk factors that can be addressed, and in which order they should be prioritized when planning intervention strategies within military groups.

Validation of an IMU Suit for Military-Based Tasks.

Investigating the effects of load carriage on military soldiers using optical motion capture is challenging. However, inertial measurement units (IMUs) provide a promising alternative. Our purpose was to compare optical motion capture with an Xsens IMU system in terms of movement reconstruction using principal component analysis (PCA) using correlation coefficients and joint kinematics using root mean squared error (RMSE). Eighteen civilians performed military-type movements while their motion was recorded using both optical and IMU-based systems. Tasks included walking, running, and transitioning between running, kneeling, and prone positions. PCA was applied to both the optical and virtual IMU markers, and the correlations between the principal component (PC) scores were assessed. Full-body joint angles were calculated and compared using RMSE between optical markers, IMU data, and virtual markers generated from IMU data with and without coordinate system alignment. There was good agreement in movement reconstruction using PCA; the average correlation coefficient was 0.81 ± 0.14. RMSE values between the optical markers and IMU data for flexion-extension were less than 9°, and 15° for the lower and upper limbs, respectively, across all tasks. The underlying biomechanical model and associated coordinate systems appear to influence RMSE values the most. The IMU system appears appropriate for capturing and reconstructing full-body motion variability for military-based movements.

A Mobile Application to Measure Trunk Flexion Angles in Lifting Tasks.

Occupational Abstract The aim of this project was to develop and test an application capable of quickly and repeatedly measuring trunk flexion angles during sagittal plane lifting tasks. The developed application uses the built-in accelerometer in mobile devices to approximate trunk flexion angle, as the user follows an operator as they perform a lift. A black line is superimposed over the camera feed, allowing the user to approximate the angle of inclination of a line connecting the operator's seventh cervical and first sacral vertebrae-thereby estimating the trunk flexion angle. The magnitude of this angle and its velocity have been linked to the development of occupational low back pain; thus the application provides ergonomists a more refined means of screening tasks beyond currently available survey tools.

TECHNICAL ABSTRACT Background The majority of quantitative postural analysis tools used in biomechanics laboratories are either infeasible or impractical for applied ergonomic field use. Survey tools do exist but are subjective in nature. Purpose To develop an application for handheld mobile devices that can quickly, reliably, and accurately measure the trunk flexion angle in order to afford more detailed and objective ergonomic analyses. Methods The application, Trunk Angle Goniometer (TAG), was programed using Xcode (Apple Inc. Cupertino, CA). Sixteen participants measured the trunk angle of lifts in the sagittal plane using TAG installed on an iPad (Apple Inc., Cupertino, CA). To establish the accuracy of the application, comparisons were made to gold standard (manual anatomical landmark digitization) measures of maximum trunk angle, maximum trunk velocity, and the root-mean square (RMS) difference between trunk angle time histories. Precision was also assessed between raters (inter-rater reliability), between trials assessing the same lift (intra-rater reliability) and between trials assessing similar lifts (test-retest reliability). Results TAG generally underestimated the true magnitude of trunk flexion by 5 ° to 15 °, and overestimated flexion velocity by approximately 10 °/sec. RMS errors were between 8.6 ° and 13.4 °. Performance measures showed fair to good test-retest reliability between 0.631 and 0.709. Overall the application had an excellent inter-rater reliability above 0.95 for all measures; however, suffered from low intra-rater reliability (0.381 to 0.520) but these dramatically increased when averages were taken across multiple trials (from 0.739 to 0.838). Conclusions TAG performed well for quantifying angles in the sagittal plane. The approach has the added benefit of being able to assess lifting tasks in real time, combined with its relatively cheap cost, the approach shows promise for field-work and assessments.

A Pilot Investigation of the Influence of a Passive Military Exoskeleton on the Performance of Lab-Simulated Operational Tasks.

OCCUPATIONAL APPLICATIONSMilitary load carriage increases musculoskeletal injury risk and reduces performance, but is essential for operational effectiveness. Exoskeletons may play a role in reducing soldier burden. We found that wearing a customized passive exoskeleton during a military obstacle course decreased overall performance compared to a mass-matched control condition. Specifically, the "Stairs and Ladder" and "Hatch and Tunnel" obstacles were performed slower while wearing the exoskeleton. In contrast, similar mean completion times in the "Casualty Drag," "Sprint" and "Agility Run" obstacles were found in both the exoskeleton and control conditions. Acceptability of equipment weight and torso stiffness were rated similarly across conditions, whereas the acceptability of overall performance was rated lowest while wearing the exoskeleton. The results of this preliminary investigation suggest that the time to complete operationally-relevant military obstacles was not improved by wearing a passive exoskeleton.

Consensus paper on testing and evaluation of military exoskeletons for the dismounted combatant.

Enhancing the capabilities of the dismounted combatant has been an enduring goal of international military research communities. Emerging developments in exoskeleton technology offers the potential to augment the dismounted combatant's capabilities. However, the ability to determine the value proposition of an exoskeleton in a military context is difficult due to the variety of methods and metrics used to evaluate previous devices. The aim of this paper was to present a standard framework for the evaluation and assessment of exoskeletons for use in the military. A structured and systematic methodology was developed from the end-user perspective and progresses from controlled laboratory conditions (Stage A), to simulated movements specific to the dismounted combatant (Stage B), and real-world military specific tasks (Stage C). A standard set of objective and subjective metrics were described to ensure a holistic assessment on the human response to wearing the exoskeleton and the device's mechanical performance during each stage. A standardised methodology will ensure further advancement of exoskeleton technology and support improved international collaboration across research and industry groups. In doing so, this better enables international military groups to evaluate a system's potential, with the hope of accelerating the maturity and ultimately the fielding of devices to augment the dismounted close combatant and small team capability.

Determination of Orientation and Practice Requirements When Using an Obstacle Course for Mobility Performance Assessment.

OBJECTIVE: Determine effect of orientation (introduction and familiarization) and practice (repeated performance) on human performance under various load conditions as assessed by an obstacle course. BACKGROUND: Obstacle courses are commonly used as screening tools by military, police, and firefighters or to assess human capabilities and the effect of wearing personal protective equipment (PPE) and other occupationally necessary equipment on mobility task performance. Unfortunately, little is formally documented about the effect of orientation and practice on performance outcomes of obstacle or mobility courses being used. METHOD: Forty-eight participants were recruited from the Canadian Army Infantry and Combat Engineer population. Participants either received regular or extensive orientation of the course before completing it. Following orientation, participants completed the course five consecutive times while wearing their PPE with full fighting order (FFO) and five consecutive times while wearing no PPE and non-FFO across a five-day period (maximum two runs per day), with ensemble presentation order counterbalanced. Total course completion time and individual obstacle completion times were measured for each run of the course. RESULTS: While wearing FFO, participants continued to decrease the time required for completing the course; however, while wearing non-FFO, time to course completion did not significantly change over the five runs. There were no differences in course completion times for the regular and extensive course orientation groups. CONCLUSIONS: Considerations required to mitigate orientation and practicing effects can differ depending on type or complexity of load condition. While wearing FFO, practicing effects can introduce undesired confounding factors into data collection. APPLICATION: Any practice runs on an obstacle course prior to its use as an assessment tool should focus on the loaded (e.g., FFO) condition because improvement on loaded runs is likely transferred to unloaded, but this does not apply in the reverse.

Examining the influence of physical size among major league pitchers.

BACKGROUND: Among professional pitchers, anthropometric changes and their effect on statistics are relatively unknown. Bivariate analyses and repeated one-way ANOVA evaluated the impact of physical size on baseball pitching statistics and attributes within an elite talent sample of Major League pitching leaders. METHODS: Body Mass Index (BMI) was calculated from publicly available players' heights and weights to form a statistical database of 1028 pitching leaders from 1950-2010. Repeated measures ANOVAs examined differences in anthropometrics and baseball statistics between decades 1950-2010. Bivariate correlation evaluated BMI as an independent variable of influence on statistics, where all tests applied an a-priori significance level (P<0.05). RESULTS: BMI increased throughout the sixty year period with weight growth greater than height (P<0.001). Increased BMI reported earlier signing age, and age of debut (P<0.05), where larger pitchers showed small positive correlation seen among saves (P<0.001) concurrent to negative correlation with innings pitched and complete games (P≤0.001), as well as shutouts (P<0.05). A contrast between saves and complete games pitched was found where saves increased over time (P<0.001) while complete games pitched declined (P<0.001). CONCLUSIONS: Over time, throwing workloads showed better management for larger starting pitchers with less innings pitched and complete games thrown added to an extra rest day in the pitching rotation. In contrast, paralleled increases in physical size with recorded saves at present requires greater medical and training attention to protecting the throwing arm of the larger relief pitchers, as increased body size can increase force properties and ball velocity owing to greater injury risks.

The Effect of Local Hydration Environment on the Mechanical Properties and Unloaded Temporal Changes of Isolated Porcine Annular Samples.

Preventing dehydration during in vitro testing of isolated layers of annulus fibrosus tissue may require different test conditions than functional spine units. The purpose of the study was twofold: (A) to quantify changes in mass and thickness of multilayer annulus samples in four hydration environments over 120 min; and (B) to quantify cycle-varying biaxial tensile properties of annulus samples in the four environments. The environments included a saline bath, air, relative humidity control, and misting combined with controlled humidity. The loading protocol implemented 24 cycles of biaxial tensile loading to 20% strain at a rate of 2%/s with 3-, 8-, and 13-min of intermittent rest. Specimen mass increased an average (standard deviation) 72% (11) when immersed for 120 min (p < 0.0001). The air condition and the combined mist and relative humidity conditions reduced mass by 45% (15) and 25% (23), respectively, after 120 min (p < 0.0014). Stress at 16% stretch in the air condition was higher at cycle 18 (18 min of exposure) and cycle 24 (33 min of exposure) compared to all other environments in both the axial and circumferential directions (p < 0.0460). There was no significant change in mass or thickness over time in the relative humidity condition and the change in circumferential stress at 16% stretch between cycles 6 and 24 was a maximum of 0.099 MPa and not statistically significant. Implementation of a controlled relative humidity environment is recommended to maintain hydration of isolated annulus layers during cyclic tensile testing.

The Impact of Posture on the Mechanical Properties of a Functional Spinal Unit During Cyclic Compressive Loading.

To assess how posture affects the transmission of mechanical energy up the spinal column during vibration, 18 porcine functional spinal units (FSUs) were exposed to a sinusoidal force (1500 ± 1200 N) at 5 Hz for 120 min in either a flexed, extended, or neutral posture. Force and FSU height were measured continuously throughout the collection. From these data, specimen height loss, dynamic stiffness, hysteresis, and parameters from a standard linear solid (SLS) model were determined and analyzed for differences between postures. Posture had an influence on all of these parameters. In extension, the FSU had higher dynamic stiffness values than when neutral or flexed (p < 0.0001). In flexion, the FSU had higher hysteresis than both an extended or neutral posture (p < 0.0001). Height loss was greatest in a flexed posture and smallest in an extended posture (p < 0.0001). In extension, the series spring element in the SLS model had a stiffness value higher than both flexed and neutral posture conditions, whereas the stiffness in the parallel spring was the same between extension and neutral (p < 0.01), both higher than in flexion. Viscosity coefficients were highest in extension compared to both flexed and neutral (p < 0.01). Based on these results, it was determined that posture had a significant influence in determining the mechanical properties of the spine when exposed to cyclic compressive loading.

Is intervertebral disc pressure linked to herniation?: An in-vitro study using a porcine model.

Approximately 40% of low back pain cases have been attributed to internal disc disruption. This disruption mechanism may be linked to intradiscal pressure changes, since mechanical loading directly affects the pressure and the stresses that the inner annulus fibrosus experiences. The objective of this study was to characterize cycle-varying changes in four dependent measures (intradiscal pressure, flexion-extension moments, specimen height loss, and specimen rotation angle) using a cyclic flexion-extension (CFE) loading protocol known to induce internal disc disruption. A novel bore-screw pressure sensor system was used to instrument 14 porcine functional spinal units. The CFE loading protocol consisted of 3600 cycles of flexion-extension range of motion (average 18.30 (SD 3.76) degrees) at 1Hz with 1500N of compressive load. On average, intradiscal pressure and specimen height decreased by 47% and 62%, respectively, and peak moments increased by 102%. From 900 to 2100 cycles, all variables exhibited significant changes between successive time points, except for the specimen posture at maximum pressure, which demonstrated a significant shift towards flexion limit after 2700 cycles. There were no further changes in pressure range after 2100 cycles, whereas peak moments and height loss were significantly different from prior time points throughout the CFE protocol. Twelve of the 14 specimens showed partial herniation; however, injury type was not significantly correlated to any of the dependent measures. Although change in pressure was not predictive of damage type, the increase in pressure range seen during this protocol supports the premise that repetitive combined loading (i.e., radial compression, tension and shear) imposes damage to the inner annulus fibrosus, and its failure mechanism may be linked to fatigue.

A comparison of trunk biomechanics, musculoskeletal discomfort and productivity during simulated sit-stand office work.

Sedentary office work has been shown to cause low back discomfort and potentially cause injury. Prolonged standing work has been shown to cause discomfort. The implementation of a sit-stand paradigm is hypothesised to mitigate discomfort and prevent injury induced by prolonged exposure to each posture in isolation. This study explored the potential of sit-stand to reduce discomfort and prevent injury, without adversely affecting productivity. Twenty-four participants performed simulated office work in three different conditions: sitting, standing and sit-stand. Variables measured included: perceived discomfort, L4-L5 joint loading and typing/mousing productivity. Working in a sit-stand paradigm was found to have the potential to reduce discomfort when compared to working in a sitting or standing only configuration. Sit-stand was found to be associated with reduced lumbar flexion during sitting compared to sitting only. Increasing lumbar flexion during prolonged sitting is a known injury mechanism. Therefore, sit-stand exhibited a potentially beneficial response of reduced lumbar flexion that could have the potential to prevent injury. Sit-stand had no significant effect on productivity. Practitioner Summary: This study has contributed foundational elements to guide usage recommendations for sit-stand workstations. The sit-stand paradigm can reduce discomfort; however, working in a sit-stand ratio of 15:5 min may not be the most effective ratio. More frequent posture switches may be necessary to realise the full benefit of sit-stand.

Injuries to young professional baseball pitchers cannot be prevented solely by restricting number of innings pitched.

BACKGROUND: The Major League Baseball schedule is longer and more intensive than minor and amateur leagues. As a result, major league pitchers endure a considerably higher cumulative workload throughout the season. Ligament, tendon, muscle, and bone tissues in young pitchers need time to adapt to the workload a major league pitcher must endure. To mitigate the risk of overuse injury, and allow time for tissue adaptation to occur, most teams limit the number of innings a young pitcher may throw. This study examined the relationship between innings pitched and future injury in young professional baseball pitchers. METHODS: All pitchers under 25 years of age that pitched at least one third of an inning in Major League Baseball during the 2002-2007 seasons were included in this study. Total innings pitched were accumulated for each season across three levels of professional baseball (Major League Baseball, and two levels of Minor Leagues). Regression analyses were preformed comparing innings pitched during a single season and difference in innings pitched over consecutive seasons to future injury, as measured by time spent on the disabled list. RESULTS: No significant correlation was found between innings pitched and future injury or consecutive season innings pitched difference and future injury. No significant differences were found when pitchers were split into groups based upon consecutive season innings pitched difference cutoffs. CONCLUSIONS: Based upon the evidence presented, strength and conditioning coaches, sports medicine specialists, and team trainers cannot rely solely on inning counts to accurately measure the tissue demands of professional baseball pitching. Therefore, inning limits alone cannot be used to protect young professional pitchers against the threat of injury.

Evaluating Abdominal and Lower-Back Muscle Activity While Performing Core Exercises on a Stability Ball and a Dynamic Office Chair.

OBJECTIVE: The purpose of this study was to evaluate the ability of a dynamic office chair to activate the core muscles while participants performed exercises sitting on the chair compared to a stability ball. BACKGROUND: Prolonged sitting has become an accepted part of the modern office. However, epidemiological evidence suggests that sedentary postures are linked to many adverse effects on health. The concept of dynamic or active sitting is intended to promote movement while sitting to reduce the time spent in prolonged, static postures. METHODS: Sixteen participants performed four pelvic rotation exercises (front-back, side-side, circular, and leg lift) on both a dynamic office chair and a stability ball. Muscle activity from 12 torso muscles were evaluated with surface electromyography. RESULTS: For all exercises, trunk muscle activity on the chair was comparable to that on a stability ball. The right external oblique was the only muscle to produce greater peak activity (p = .019) when using the ball compared to the chair (21.4 ± 14.0 percent maximal voluntary excitations (%MVE) and 14.7 ± 10.8 %MVE for the ball and chair, respectively). The left thoracic erector spinae produced greater average activity (p = .044) on the chair than on the ball. CONCLUSION: These findings suggest that this dynamic sitting approach could be an effective tool for core muscle activation while promoting movement and exercise while sitting at work. APPLICATION: Muscle activations on the dynamic chair are comparable to those on a stability ball, and dynamic office chairs can promote movement and exercise while sitting at work.

A finite element evaluation of the moment arm hypothesis for altered vertebral shear failure force.

The mechanism of vertebral shear failure is likely a bending moment generated about the pars interarticularis by facet contact, and the moment arm length (MAL) between the centroid of facet contact and the location of pars interarticularis failure has been hypothesised to be an influential modulator of shear failure force. To quantitatively evaluate this hypothesis, anterior shear of C3 over C4 was simulated in a finite element model of the porcine C3-C4 vertebral joint with each combination of five compressive force magnitudes (0-60% of estimated compressive failure force) and three postures (flexed, neutral and extended). Bilateral locations of peak stress within C3's pars interarticularis were identified along with the centroids of contact force on the inferior facets. These measurements were used to calculate the MAL of facet contact force. Changes in MAL were also related to shear failure forces measured from similar in vitro tests. Flexed and extended vertebral postures respectively increased and decreased the MAL by 6.6% and 4.8%. The MAL decreased by only 2.6% from the smallest to the largest compressive force. Furthermore, altered MAL explained 70% of the variance in measured shear failure force from comparable in vitro testing with larger MALs being associated with lower shear failure forces. Our results confirmed that the MAL is indeed a significant modulator of vertebral shear failure force. Considering spine flexion is necessary when assessing low-back shear injury potential because of the association between altered facet articulation and lower vertebral shear failure tolerance.

Localized strain measurements of the intervertebral disc annulus during biaxial tensile testing.

Both inter-lamellar and intra-lamellar failures of the annulus have been described as potential modes of disc herniation. Attempts to characterize initial lamellar failure of the annulus have involved tensile testing of small tissue samples. The purpose of this study was to evaluate a method of measuring local surface strains through image analysis of a tensile test conducted on an isolated sample of annular tissue in order to enhance future studies of intervertebral disc failure. An annulus tissue sample was biaxial strained to 10%. High-resolution images captured the tissue surface throughout testing. Three test conditions were evaluated: submerged, non-submerged and marker. Surface strains were calculated for the two non-marker conditions based on motion of virtual tracking points. Tracking algorithm parameters (grid resolution and template size) were varied to determine the effect on estimated strains. Accuracy of point tracking was assessed through a comparison of the non-marker conditions to a condition involving markers placed on tissue surface. Grid resolution had a larger effect on local strain than template size. Average local strain error ranged from 3% to 9.25% and 0.1% to 2.0%, for the non-submerged and submerged conditions, respectively. Local strain estimation has a relatively high potential for error. Submerging the tissue provided superior strain estimates.

Physical size associations to offensive performance among major league leaders.

Minimal work has studied physical size effects on statistical performance among Major League players. In this study, longitudinal, bivariate, and regression analyses studied the impact of physical size on offensive baseball statistics within a homogeneous talent sample of Major League batting leaders. Body mass index (BMI) was calculated from heights and weights that were publicly available to form a statistical database of 4,360 offense leaders from 1950 to 2010. Repeated-measures analysis of variances examined differences in anthropometrics and baseball statistics between each decade from 1950 to 2010. Bivariate correlation and linear regression analyses evaluated BMI as an independent variable of influence, where all tests applied an a priori significance level (p ≤ 0.05). After 1980, offensive performance increased (p ≤ 0.05) concurrent to body mass and BMI growth (p < 0.001). During the 1960s, only batting average and on-base plus slugging percentages were found statistically decreased (p ≤ 0.05). All baseball statistics were positively correlated and predicted by BMI (p < 0.001). Consideration to covariant factors is required in data interpretation, yet nonetheless, our results showed physical size (BMI) to positively influence Major League offensive statistics. Over the 60-year period, greater body weight-to-height proportions owed to improved competitive performance, which suggests greater emphasis on hypertrophic stimuli in training and nutrition, as well as selection of larger professional baseball prospects.