Task Specific and General Patterns of Joint Motion Variability in Upright- and Hand-Standing Postures.

The preservation of static balance in both upright- and hand-stance is maintained by the projection of center of mass (CM) motion within the region of stability at the respective base of support. This study investigated, from a degrees of freedom (DF) perspective, whether the stability of the CM in both upright- and hand-stances was predicted by the respective dispersion and time-dependent regularity of joint (upright stance-ankle, knee, hip, shoulder, neck; hand stance-wrist, elbow, shoulder, neck) angle and position. Full body three-dimensional (3D) kinematic data were collected on 10 advanced level junior female gymnasts during 30 s floor upright- and hand-stands. For both stances the amount of the dispersion of joint angle and sway motion was higher than that of the CM and center of pressure (CP) with an inverse relation to time-dependent irregularity (SampEn). In upright-standing the variability of neck motion in the anterior-posterior direction was significantly greater than that of most joints consistent with the role of vision in the control of quiet upright posture. The findings support the proposition that there are both task specific and general properties to the global CM control strategy in the balance of upright- and hand-standing induced by the different active skeletal-muscular organization and the degeneracy revealed in the multiple distributional variability patterns of the joint angle and position in 3D.

Altered levels of plasma neuron-derived exosomes and their cargo proteins characterize acute and chronic mild traumatic brain injury.

Neuron-derived exosomes (NDEs) were enriched by anti-L1CAM antibody immunoabsorption from plasmas of subjects ages 18-26 yr within 1 wk after a sports-related mild traumatic brain injury (acute mTBI) ( n = 18), 3 mo or longer after the last of 2-4 mTBIs (chronic mTBI) ( n = 14) and with no recent history of TBI (controls) ( n = 21). Plasma concentrations of NDEs, assessed by counts and levels of extracted exosome marker CD81, were significantly depressed by a mean of 45% in acute mTBI ( P < 0.0001), but not chronic mTBI, compared with controls. Mean CD81-normalized NDE levels of a range of functional brain proteins were significantly abnormal relative to those of controls in acute but not chronic mTBI, including ras-related small GTPase 10, 73% decrease; annexin VII, 8.8-fold increase; ubiquitin C-terminal hydrolase L1, 2.5-fold increase; AII spectrin fragments, 1.9-fold increase; claudin-5, 2.7-fold increase; sodium-potassium-chloride cotransporter-1, 2.8-fold increase; aquaporin 4, 8.9-fold increase (3.6-fold increase in chronic mTBI); and synaptogyrin-3, 3.1-fold increase (1.3-fold increase in chronic mTBI) (all acute mTBI proteins P < 0.0001). In chronic mTBI, there were elevated CD81-normalized NDE levels of usually pathologic ß-amyloid peptide 1-42 (1.6-fold, P < 0.0001), P-T181-tau (2.2-fold, P < 0.0001), P-S396-tau (1.6-fold, P < 0.01), IL-6 (16-fold, P < 0.0001), and prion cellular protein (PRPc) (5.1-fold, P < 0.0001) with lesser or greater (IL-6, PRPc) increases in acute mTBI. Increases in NDE levels of most neurofunctional proteins in acute, but not chronic, mTBI, and elevations of most NDE neuropathological proteins in chronic and acute mTBI delineated phase-specificity. Longitudinal studies of more mTBI subjects may identify biomarkers predictive of and etiologically involved in mTBI-induced neurodegeneration.-Goetzl, E. J., Elahi, F. M., Mustapic, M., Kapogiannis, D., Pryhoda, M., Gilmore, A., Gorgens, K. A., Davidson, B., Granholm, A.-C., Ledreux, A. Altered levels of plasma neuron-derived exosomes and their cargo proteins characterize acute and chronic mild traumatic brain injury.

Centre of pressure velocity shows impairments in NCAA Division I athletes six months post-concussion during standing balance.

Sport-related concussion return to play (RTP) decisions are largely based on the resolution of self-reported symptoms and neurocognitive function. Some evaluators also incorporate balance; however, an objective approach to balance that can detect effects beyond the acute condition is warranted. The purpose of this study is to examine linear measures of biomechanical balance up to 6 months post-concussion, and to present preliminary diagnostic thresholds useful for RTP. Each concussed athlete participated in instrumented standing balance tasks at 4 timepoints post-concussion. The measures from concussed athletes were compared to the sport-matched non-concussed athlete group at each timepoint. Centre of pressure (COP) mediolateral (ML) velocity in double-leg stance on a hard surface discriminated well between non-concussed and concussed athletes. COP anterior-posterior (AP) velocity in tandem stance on foam showed sensitivity to concussion. Sixty per cent of athletes at 6 months post-concussion did not recover to within the proposed COP ML velocity threshold in double-leg stance on a hard surface. Seventy-one per cent of athletes at 6 months post-concussion did not recover to within the COP AP velocity threshold in tandem stance on foam. This lack of recovery potentially indicates vestibular and motor control impairments long past the typical period of RTP.

Fully automatic tracking of native glenohumeral kinematics from stereo-radiography.

The current work introduces a system for fully automatic tracking of native glenohumeral kinematics in stereo-radiography sequences. The proposed method first applies convolutional neural networks to obtain segmentation and semantic key point predictions in biplanar radiograph frames. Preliminary bone pose estimates are computed by solving a non-convex optimization problem with semidefinite relaxations to register digitized bone landmarks to semantic key points. Initial poses are then refined by registering computed tomography-based digitally reconstructed radiographs to captured scenes, which are masked by segmentation maps to isolate the shoulder joint. A particular neural net architecture which exploits subject-specific geometry is also introduced to improve segmentation predictions and increase robustness of subsequent pose estimates. The method is evaluated by comparing predicted glenohumeral kinematics to manually tracked values from 17 trials capturing 4 dynamic activities. Median orientation differences between predicted and ground truth poses were 1.7∘ and 8.6∘ for the scapula and humerus, respectively. Joint-level kinematics differences were less than 2∘ in 65%, 13%, and 63% of frames for XYZ orientation DoFs based on Euler angle decompositions. Automation of kinematic tracking can increase scalability of tracking workflows in research, clinical, or surgical applications.

Lower body energy generation, absorption, and transfer in youth baseball pitchers.

An efficient baseball pitch will produce a high-velocity ball while minimizing the risk of injury to the pitcher. This study quantified ground reaction forces and lower body power during the entire pitching motion of youth baseball pitchers to investigate how developing athletes generate and transfer energy from lower limbs to the throwing arm. These data provide a foundation for comparing youth pitching strategy and mechanics to optimal throwing mechanics and may aid in developing appropriate training suggestions for this age group. Full-body three-dimensional (3D) motion capture and force platform data were collected on 23 youth pitchers performing fastballs thrown for strikes. Youth pitchers within this study used a "controlled drop" strategy in which the COM was lowered during the stride phase followed by a weak forward drive motion. Ground reaction forces (GRFs) indicate that the drive leg propels the center of mass (COM) toward the home plate while the stride leg braking force contributes to power generation up the kinetic chain. The stride hip generates energy assisting in energy flow up the kinetic chain as well as the creation of a stable base to rotate the trunk about. The lumbosacral joint generates the most energy of any joint studied, facilitating energy flow up the kinetic chain and underscoring the importance of core strength and coordination in proper pitching mechanics.

Assessment of Long-Term Effects of Sports-Related Concussions: Biological Mechanisms and Exosomal Biomarkers.

Concussion or mild traumatic brain injury (mTBI) in athletes can cause persistent symptoms, known as post-concussion syndrome (PCS), and repeated injuries may increase the long-term risk for an athlete to develop neurodegenerative diseases such as chronic traumatic encephalopathy (CTE), and Alzheimer's disease (AD). The Center for Disease Control estimates that up to 3.8 million sport-related mTBI are reported each year in the United States. Despite the magnitude of the phenomenon, there is a current lack of comprehensive prognostic indicators and research has shown that available monitoring tools are moderately sensitive to short-term concussion effects but less sensitive to long-term consequences. The overall aim of this review is to discuss novel, quantitative, and objective measurements that can predict long-term outcomes following repeated sports-related mTBIs. The specific objectives were (1) to provide an overview of the current clinical and biomechanical tools available to health practitioners to ensure recovery after mTBIs, (2) to synthesize potential biological mechanisms in animal models underlying the long-term adverse consequences of mTBIs, (3) to discuss the possible link between repeated mTBI and neurodegenerative diseases, and (4) to discuss the current knowledge about fluid biomarkers for mTBIs with a focus on novel exosomal biomarkers. The conclusions from this review are that current post-concussion clinical tests are not sufficiently sensitive to injury and do not accurately quantify post-concussion alterations associated with repeated mTBIs. In the current review, it is proposed that current practices should be amended to include a repeated symptom inventory, a cognitive assessment of executive function and impulse control, an instrumented assessment of balance, vestibulo-ocular assessments, and an improved panel of blood or exosome biomarkers.