Concussed Neural Signature is Substantially Different than Fatigue Neural Signature in Non-concussed Controls.

Traumatic brain injuries can result in short-lived and long-lasting neurological impairment. Identifying the correct recovery timeframe is challenging, as balance-based metrics may be negatively impacted if testing is performed soon after exercise. Thirty-two healthy controls and seventeen concussed individuals performed a series of balance challenges, including virtual reality optical flow perturbation. The control group completed a backpacking protocol to induce moderate fatigue. Concussed participants had lower spectral power in the motor cortex and central sulcus when compared to fatigued controls. Moreover, concussed participants experienced a decrease in overall theta band spectral power while fatigued controls showed an increase in theta band spectral power. This neural signature may be useful to distinguish between concussed and non-concussed fatigued participants in future assessments.

A Six-Year Review of the Biomedical Engineering in Simulations, Imaging, and Modeling Undergraduate Research Experience.

Undergraduate research continues to serve as an effective strategy for mitigating the effects of a leaky pipeline. Significant funding from institutions and government agencies has increased the number of students participating in undergraduate research. In this paper, we report on the six-year experience of a National Science Foundation funded Research Experiences for Undergraduates (REU) Site: Biomedical Engineering in Simulations, Imaging, and Modeling (BME-SIM). The operation and evaluation of the program are both described. We report on the results from 55 students over six summers from 2014 to 2019. Our program was successful in attracting a diverse group of participants including 46% under-represented minority students and 53% women. Based on evaluation results, students reported significant gains in technical skills, communication skills, and knowledge of graduate school. Our findings indicate baseline gender differences for several learning outcomes, where women and nonbinary students report lower levels of mastery. These gaps are closed by the end of the program except for confidence in skills, which is still significantly lower than those reported by male counterparts. The impact of the experience on ultimate career path is difficult to determine due to underlying biases and other motivating factors; however, 67.6% of graduates have entered graduate programs. Finally, we have provided lessons learned for those who are interested in building a summer research program. In conclusion, we have described the successful implementation of an REU site and the positive learning outcomes of the student participants.

Anterior-Posterior Balance Perturbation Protocol Using Lifelike Virtual Reality Environment.

Virtual reality (VR) paradigms have proved to be a valid method to challenge and perturb balance. There is little consensus in the literature on the best protocol design to perturb balance and induce postural sway. Current VR interventions still lack a well-defined standardized metric to generate a virtual environment that can perturb balance in an efficacious, lifelike, and repeatable manner. The objective of this study was to investigate different configurations of amplitude and frequency in an anterior-posterior translation VR environment, that is, lifelike and scaled. Thirteen young adults with no conditions affecting balance were recruited. Balance was challenged by anterior-posterior sinusoidal movement of the lab image within the VR headset. Four different amplitudes of the sinusoidal movement were tested: 1, 5, 10, and 20 cm, with each amplitude being presented at 2 test frequencies : 0.5 and 0.25 Hz. Mean center of pressure velocity was significantly greater than baseline at 0.5 Hz and amplitudes of 10 and 20 cm. Mean center of pressure at approximate entropy was greater than baseline at 0.5 Hz and amplitude of 20 cm. The results suggest that sinusoidal movement of a realistic VR environment produces altered balance compared with baseline quiet standing, but only under specific movement parameters.

Measurement of intrinsic foot stiffness in minimally and traditionally shod runners using ultrasound elastography: A pilot study.

Running is an activity with a consistently high injury rate. Running footwear design that mimics barefoot running has been proposed to reduce injury rate by increasing the strength of foot structures. However, there is little evidence to support this. The purpose of the current study is to use shear wave ultrasound elastography to examine material properties (shear modulus) of intrinsic foot structures in experienced minimally and traditionally shod runners. It is hypothesized that minimalist runners will exhibit increased stiffness compared to controls demonstrating the strengthening of these structures. Eighteen healthy runners (8 minimalist and 10 traditionalist), running a minimum of 10 mi · wk-1, participated. Elastography scans were performed on the left foot of each participant. There is no apparent stiffening of foot structures associated with wearing minimalist shoes. Only the FHB tendon is different between shoe types and, contrary to the hypothesis, was stiffer in traditionalist compared to minimalist runners (257.26 ± 51.64 kPa vs 160.88 ± 27.79 kPa, respectively). A moderate positive (r = 0.7) relationship between training load and tendon stiffness suggests strengthening of tendon when running in traditional shoes. If running in minimalist shoes increases loading on these structures without resulting in stronger tissues, it is possible that minimalist footwear may increase injury risk.

Practice day may be unnecessary prior to testing knee extensor strength in young healthy adults.

A practice session is common prior to strength testing. However, the benefits of practice have not been previously reported. The purpose of this study was to determine the effect of a practice session on peak torque, mean torque and between trial variability across three test days. We hypothesized that peak and mean torque would be higher and less variable the second and third test days than the first. Twenty-five healthy, young participants completed 3 maximal voluntary isometric and isokinetic knee extensions on three separate days. No difference in isometric torque was found between days 1 and 2, but there was a significant decrease in isokinetic torque (8.45 Nm). There was a significant decrease in both mean isometric and isokinetic torque from day 1 to day 3 (12.67 and 13.59 Nm). Contrary to our hypothesis, no benefit from a practice session was found. Healthy, young adults are able to produce peak knee extensor torques on the first day of testing and do not demonstrate any benefit from additional testing. Thus, a practice day preceding isometric and isokinetic knee extensor strength testing may not be necessary when testing healthy, young participants, and may, in fact, negatively impact subsequent strength measurements.

The effect of Nordic hamstring strength training on muscle architecture, stiffness, and strength.

PURPOSE: Hamstring strain injury is a frequent and serious injury in competitive and recreational sports. While Nordic hamstring (NH) eccentric strength training is an effective hamstring injury-prevention method, the protective mechanism of this exercise is not understood. Strength training increases muscle strength, but also alters muscle architecture and stiffness; all three factors may be associated with reducing muscle injuries. The purpose of this study was to examine the effects of NH eccentric strength training on hamstring muscle architecture, stiffness, and strength. METHODS: Twenty healthy participants were randomly assigned to an eccentric training group or control group. Control participants performed static stretching, while experimental participants performed static stretching and NH training for 6 weeks. Pre- and post-intervention measurements included: hamstring muscle architecture and stiffness using ultrasound imaging and elastography, and maximal hamstring strength measured on a dynamometer. RESULTS: The experimental group, but not the control group, increased volume (131.5 vs. 145.2 cm3, p < 0.001) and physiological cross-sectional area (16.1 vs. 18.1 cm2, p = 0.032). There were no significant changes to muscle fascicle length, stiffness, or eccentric hamstring strength. CONCLUSIONS: The NH intervention was an effective training method for muscle hypertrophy, but, contrary to common literature findings for other modes of eccentric training, did not increase fascicle length. The data suggest that the mechanism behind NH eccentric strength training mitigating hamstring injury risk could be increasing volume rather than increasing muscle length. Future research is, therefore, warranted to determine if muscle hypertrophy induced by NH training lowers future hamstring strain injury risk.

Simulations, Imaging, and Modeling: A Unique Theme for an Undergraduate Research Program in Biomechanics.

As the reliance on computational models to inform experiments and evaluate medical devices grows, the demand for students with modeling experience will grow. In this paper, we report on the 3-yr experience of a National Science Foundation (NSF) funded Research Experiences for Undergraduates (REU) based on the theme simulations, imaging, and modeling in biomechanics. While directly applicable to REU sites, our findings also apply to those creating other types of summer undergraduate research programs. The objective of the paper is to examine if a theme of simulations, imaging, and modeling will improve students' understanding of the important topic of modeling, provide an overall positive research experience, and provide an interdisciplinary experience. The structure of the program and the evaluation plan are described. We report on the results from 25 students over three summers from 2014 to 2016. Overall, students reported significant gains in the knowledge of modeling, research process, and graduate school based on self-reported mastery levels and open-ended qualitative responses. This theme provides students with a skill set that is adaptable to other applications illustrating the interdisciplinary nature of modeling in biomechanics. Another advantage is that students may also be able to continue working on their project following the summer experience through network connections. In conclusion, we have described the successful implementation of the theme simulation, imaging, and modeling for an REU site and the overall positive response of the student participants.

Assessing the accuracy of subject-specific, muscle-model parameters determined by optimizing to match isometric strength.

Biomechanical models are sensitive to the choice of model parameters. Therefore, determination of accurate subject specific model parameters is important. One approach to generate these parameters is to optimize the values such that the model output will match experimentally measured strength curves. This approach is attractive as it is inexpensive and should provide an excellent match to experimentally measured strength. However, given the problem of muscle redundancy, it is not clear that this approach generates accurate individual muscle forces. The purpose of this investigation is to evaluate this approach using simulated data to enable a direct comparison. It is hypothesized that the optimization approach will be able to recreate accurate muscle model parameters when information from measurable parameters is given. A model of isometric knee extension was developed to simulate a strength curve across a range of knee angles. In order to realistically recreate experimentally measured strength, random noise was added to the modeled strength. Parameters were solved for using a genetic search algorithm. When noise was added to the measurements the strength curve was reasonably recreated. However, the individual muscle model parameters and force curves were far less accurate. Based upon this examination, it is clear that very different sets of model parameters can recreate similar strength curves. Therefore, experimental variation in strength measurements has a significant influence on the results. Given the difficulty in accurately recreating individual muscle parameters, it may be more appropriate to perform simulations with lumped actuators representing similar muscles.

Maximum height and minimum time vertical jumping.

The performance criterion in maximum vertical jumping has typically been assumed to simply raise the center of mass as high as possible. In many sporting activities minimizing movement time during the jump is likely also critical to successful performance. The purpose of this study was to examine maximum height jumps performed while minimizing jump time. A direct dynamics model was used to examine squat jump performance, with dual performance criteria: maximize jump height and minimize jump time. The muscle model had activation dynamics, force-length, force-velocity properties, and a series of elastic component representing the tendon. The simulations were run in two modes. In Mode 1 the model was placed in a fixed initial position. In Mode 2 the simulation model selected the initial squat configuration as well as the sequence of muscle activations. The inclusion of time as a factor in Mode 1 simulations resulted in a small decrease in jump height and moderate time savings. The improvement in time was mostly accomplished by taking off from a less extended position. In Mode 2 simulations, more substantial time savings could be achieved by beginning the jump in a more upright posture. However, when time was weighted more heavily in these simulations, there was a more substantial reduction in jump height. Future work is needed to examine the implications for countermovement jumping and to examine the possibility of minimizing movement time as part of the control scheme even when the task is to jump maximally.

The relationships between muscle force steadiness and visual steadiness in young and old adults.

Since vision is used in studies of muscle force control, reduced muscle force control might be related to reduced visual ability. We investigated relationships between steadiness in eye movements and quadriceps muscle torque (a surrogate for force) during isometric contractions of constant and varying torques. Nineteen young adults with an average age of 20.7 years and 18 old adults with an average age of 71.6 years performed three vision tasks, three vision and torque tasks at 40% maximal voluntary contraction (MVC), and three vision and torque tasks at 54 nm. Age groups had identical torque steadiness (CV) in 40%-MVC and 54-nm conditions (p > .05). Old had similar vertical (p > .05) but decreased horizontal visual steadiness (SD) (p < .05) compared with young. Correlations between visual steadiness and muscle torque steadiness failed to show a significant relationship (p > .05). We were unable to identify a substantial relationship between muscle torque steadiness and eye movement, as a component of visual steadiness, and conclude that reduced visual steadiness does not contribute to reduced muscle torque steadiness.

Heterogeneous fascicle behavior within the biceps femoris long head at different muscle activation levels.

Magnetic resonance and ultrasound imaging have shown hamstring strain injuries occur most often in the biceps femoris long head (BFLH), and particularly in the proximal vs. distal region of this muscle. Animal research and musculoskeletal modeling (MSK) have detected heterogeneous fascicle behavior within muscle regions, and within fascicles. Understanding architectural behavior differences during muscle contractions may help to discern possible mechanisms behind proximal BFLH injuries. The purpose of our study was to assess the magnitude of shortening of the proximal and distal fascicles of the BFLH under a range of muscle activation levels under isometric conditions using ultrasound imaging (US). Thirteen healthy adults performed targeted sustained isometric contractions while US were taken of the entire BFLH. Measurements of fascicle lengths in both muscle regions were compared at 20%, 30%, 50%, and 67% MVIC. The results showed that while both regions shortened significantly with activation, the proximal fascicles were significantly longer, regardless of activation level (~38%), and shortened significantly more than the distal fascicles overall (~40%), and cumulatively at higher activation levels (30% and above). No significant strain differences were found between the two regions. These data suggest heterogeneous fascicle behavior exists in an absolute sense; however, differences in behavior are eliminated when normalized (strain). Coupled with MSK literature, the absence of regional fascicle strain differences in this study may indicate strain heterogeneity is not detectable at the whole fascicle level. Further knowledge of this commonly strained muscle's regional behavior during dynamic movements could provide evidence of proximal hamstring strain predisposition.

An examination of possible quadriceps force at the time of anterior cruciate ligament injury during landing: A simulation study.

Anterior cruciate ligament (ACL) rupture is a common and traumatic injury. Although, identifying the mechanism of ACL injury has received considerable research attention, there are still many unanswered questions. One proposed mechanism asserts that the ACL is injured due to an aggressive quadriceps muscle contraction. However, recently it has been questioned if the magnitude of quadriceps force needed to tear the ACL is physiologically realistic under the conditions where injury occurs during landing (e.g. near full knee extension and within 50ms after impact). To answer this question, a simple simulation model was developed to examine the upper bounds of quadriceps force that can be developed under these conditions. The model included force-length, and force-velocity properties as well as activation dynamics. Model parameters were chosen to provide a high estimate for possible quadriceps force in a young healthy man. The effects of varying quadriceps pre-activation levels were also examined. When using realistic pre-activation levels, the simulated quadriceps force was less than half of what has been shown to cause ACL injury. Even when using maximum pre-activation, the quadriceps force still did not reach close to the level shown to cause injury. Therefore, we conclude that quadriceps force alone seems to be an unlikely mechanism for ACL injury.

Evaluation of muscles affected by myositis using magnetic resonance elastography.

INTRODUCTION: Idiopathic inflammatory myopathies (IIMs, or myositis) represent a group of autoimmune diseases that result in decreased muscle strength and/or endurance. Non-invasive tools to assess muscle may improve our understanding of the clinical and functional consequences of myopathies and their response to treatment. In this study we examine magnetic resonance elastography (MRE), a non-invasive technique that assesses the shear modulus (stiffness) of muscle, in IIM subjects. METHODS: Nine subjects with active myositis completed the MRE protocol. Participants lay in a positioning device, and scans of the vastus medialis (VM) were taken in the relaxed state and at two contraction levels. Manual inversion was used to estimate the stiffness. RESULTS: A significant reduction in muscle stiffness was seen in myositis subjects compared with healthy controls during the "relaxed" condition. DISCUSSION: The use of non-invasive technologies such as MRE may provide greater understanding of the pathophysiology of IIM and improve assessment of treatment efficacy.

An induced energy analysis to determine the mechanism for performance enhancement as a result of arm swing during jumping.

Arm swing during a jump can enhance performance. This study examined the mechanisms via which arm swing contributes to maximum vertical jump height. Two mechanisms have been proposed to explain how jump height can be increased by arm swing: production of additional energy or slow leg extension which may permit muscles to work on a more favorable region of the force-velocity curve. A simulation model of the vertical jump and an induced energy analysis were used to determine the contribution of each of these mechanisms. The results from the model suggest that both mechanisms for the role of arm swing in enhancing jump performance are at play. Arm swing did slow the hip extensors allowing for more force production from these muscles. The work done and the energy induced in the vertical direction by these muscles were greater in the jump simulated with arm swing. However, these increases were not sufficient to explain the entire improvement in jumping performance. The shoulder musculature generated a considerable amount of work and energy induced and is directly responsible for approximately one-third of the performance enhancement associated with arm swing.

Measurement of stiffness changes in immobilized muscle using magnetic resonance elastography.

BACKGROUND: The isolated evaluation of changes in muscle following immobilization and disuse is a challenge in living subjects. The purpose of this study was to determine whether magnetic resonance elastography is capable of detecting these changes. METHODS: An animal model was created to produce a mild joint contracture following 42 days of one forelimb immobilization in a maximally flexed position with twice-daily passive exercise. Eight pairs of dog forelimbs were harvested. Magnetic resonance elastography scans were performed on the experimental limb in an extended elbow position with a torque of 0.6 N m. Scans of the contralateral limb were performed in two conditions, position matching and torque matching. Furthermore, wet weight, cross sectional area, resting muscle length, and range of elbow joint motion were measured. FINDINGS: The muscle from the experimental limb showed significant reduction in muscle mass, cross sectional area, slack length, and range of elbow motion. When comparing limbs in position matching condition, the muscle lengths were similar, and the experimental muscle had a significantly higher shear modulus (79.1 (SD 12.0)kPa) than the contralateral muscle (31.9 (SD 24.4)kPa). When comparing limbs in torque matching conditions, the muscle strains were similar, and the experimental muscle had a significantly lower shear modulus than the contralateral muscle (113.0 (SD 24.8)kPa). INTERPRETATION: These findings suggest that following immobilization, magnetic resonance elastography has the potential to be used as a clinical tool to guide rehabilitation and as a research tool to study the loss of passive elastic components of muscle.

A critical examination of the maximum velocity of shortening used in simulation models of human movement.

The maximum velocity of shortening of a muscle is an important parameter in musculoskeletal models. The most commonly used values are derived from animal studies; however, these values are well above the values that have been reported for human muscle. The purpose of this study was to examine the sensitivity of simulations of maximum vertical jumping performance to the parameters describing the force-velocity properties of muscle. Simulations performed with parameters derived from animal studies were similar to measured jump heights from previous experimental studies. While simulations performed with parameters derived from human muscle were much lower than previously measured jump heights. If current measurements of maximum shortening velocity in human muscle are correct, a compensating error must exist. Of the possible compensating errors that could produce this discrepancy, it was concluded that reduced muscle fibre excursion is the most likely candidate.

Elbow strength and endurance in patients with a ruptured distal biceps tendon.

BACKGROUND: Patients with complete distal biceps tendon ruptures complain of fatigability with repeated elbow flexion and forearm supination. Some studies have documented changes in strength, but limited information is available about the effects of biceps tendon rupture on endurance. HYPOTHESIS: A ruptured distal biceps tendon results in decreased strength and enducance. MATERIALS AND METHODS: Isokinetic strength and endurance in elbow flexion and forearm supination were measured in both arms of 9 patients with an untreated unilateral complete distal biceps tendon rupture. One additional patient underwent isokinetic testing only. Tests were conducted using a dynamometer at 60 degrees per second for isokinetic strength and 240 degrees per second for endurance. Paired t tests were used for statistical analysis. RESULTS: The peak torque was significantly lower in involved limbs for both flexion (involved, 26.5+/-11.1Nm; uninvolved, 41.0+/-12.6Nm, P < .001) and supination (involved, 4.5+/-2.4Nm; uninvolved, 8.3+/-2.9Nm; P < .001). No significant differences were found in the fatigue index between involved and uninvolved limbs for flexion (involved, 43.2+/-14.1; uninvolved, 45.9+/-13.5; P=.659) or supination (involved, 58+/-17.0; uninvolved, 54.3+/-14.8; P=.592). DISCUSSION: Complete rupture of the distal biceps tendon results in substantial reductions in elbow flexion and forearm supination strength. Endurance of the remaining intact musculotendinous units does not seem to increase or decrease over time. Nonoperative treatment is rarely recommended, but when selected, rehabilitation should concentrate on improving strength, not endurance. CONCLUSION: A ruptured distal biceps tendon results in a substantial decrease in flexion and supination strength.

Effect of collagen digestion on the passive elastic properties of diaphragm muscle in rat.

Effects of collagen digestion have been defined up to the fibril level. However, the question remains as to whether the alteration of skeletal muscle extracellular matrix (ECM) affects a muscle's passive elastic response. Various elastography methods have been applied as tools for evaluating the mechanical properties and ECM content of skeletal muscle. In an effort to develop an ECM altered skeletal muscle model, this study determined the effect of collagen digestion on the passive elastic properties of skeletal muscle. Passive mechanical properties of rat diaphragms were evaluated in various degrees of collagen digestion. Between cyclic loading tests, muscle strips were immersed in various concentrations of clostridium histolyticum derived bacterial collagenase. All samples were later viewed via light microscopy. Cyclic testing revealed linear relationships between passive muscle stiffness and digestion time at multiple concentrations. These results demonstrate that collagenase digestion of the ECM in skeletal muscle could be used as a simple and reliable model of mechanically altered in vitro tissue samples.

The effect of triangular fibrocartilage complex injury on extensor carpi ulnaris function and friction.

BACKGROUND: It has been previously shown that injury to the triangular fibrocartilage complex increases the moment arm of the extensor carpi ulnaris. This will reduce the force producing capacity of the muscle in some situations, but will also increase its mechanical advantage. It is also possible that the change in the tendon path may increase tendon friction, predisposing the patient to future repetitive motion injury. It is the purpose of this study to determine the effects of triangular fibrocartilage complex injury on extensor carpi ulnaris moment producing capacity and tendon friction. METHODS: A simple simulation was used to examine muscle moment producing capacity throughout the range of motion, at varying speeds and in both injured and healthy states. Six fresh frozen human cadaveric wrists were used to determine the effect of injury on tendon friction. A custom made device was used to move the wrists through a range of motion, while a constant force was applied to the proximal tendon and force was recorded at the distal tendon. Friction was measured before and after the creation of injury. FINDINGS: The decreases in muscle force following injury were small, even in the worse case. The moment producing capacity of the muscle was increased following injury. Tendon friction during flexion-extension was decreased following injury. The friction during radial-ulnar deviation was unchanged. INTERPRETATION: When making surgical decisions about triangular fibrocartilage complex repair, it is not necessary to consider extensor carpi ulnaris moment producing capacity or tendon friction.

Feasibility of using magnetic resonance elastography to study the effect of aging on shear modulus of skeletal muscle.

A common complication associated with aging is the stiffening of skeletal muscles. The purpose of this study was to determine the ability of magnetic resonance elastography (MRE) to study this phenomenon in vivo. Twenty female subjects were included in the study with an age range of 50 to 70 years. Shear modulus was calculated for the tibialis anterior of each subject. There was not a significant relationship between age and shear modulus. However, three subjects had abnormally high values and were among the oldest subjects tested. There was a significant relationship between age and tissue stiffness homogeneity. More research is needed to determine whether the changes seen here are reflective of increased tissue cross-linking or related to reduced muscle quality. However, MRE shows promise as a tool to study aging-related muscle stiffness changes or to evaluate treatments to counteract these changes.