Short-term changes in the physiology of the primary motor cortex following head impact exposure during a Canadian football game.

OBJECTIVE: This study investigated the association between head impact exposure (HIE) during varsity Canadian football games and short-term changes in cortical excitability of the primary motor cortex (M1) using transcranial magnetic stimulation (TMS). METHODS: Twenty-nine university-level male athletes wore instrumented mouth guards during a football game to measure HIE. TMS measurements were conducted 24 hours before and 1-2 hours after the game. Twenty control football athletes were submitted to a noncontact training session and underwent identical TMS assessments. Between-group changes in short-interval intracortical inhibition (SICI) ratios over time were conducted using two-way ANOVAs. The relationship between HIE (i.e., number, magnitude, and cumulative forces of impacts) and SICI (secondary outcome) was also investigated using Pearson correlations. RESULTS: Relative to controls, the group of athletes who had played a full-contact football game exhibited a significant intracortical disinhibition (p = 0.028) on the SICI 3-msec protocol (i.e., short interstimulus interval of 3 msec) within hours following the game. Moreover, exposure to ≥ 40g hits positively correlated with SICI disinhibition (p < 0.05). CONCLUSIONS: Athletes exposed to subconcussive hits associated with Canadian football exhibit abnormal M1 corticomotor inhibition function, particularly when the recorded impact magnitude was ≥ 40g. Given the deleterious effects of decreased inhibition on motor control and balance, systematically tracking head impact forces at each game and practice with contacts could prove useful for injury prevention in contact sports.

Methods to analyse the long head of the biceps in the management of distal ruptures of the supraspinatus tendon. Part 1: the concept of the "biceps box": dynamic rotator interval approach. Incidence of lesions of the long head of the biceps tendon.

INTRODUCTION: The area encompassing the long head of the biceps (LHB) can be represented as a rectangular parallelepiped. This geometric view can be likened to a box, the "biceps box", where the sides are the extrinsic structures and the LHB is the intrinsic structure. Since these structures are mobile in relation to each other, a dynamic "biceps box" model can modify assessments of the LHB, in its healthy or pathological state, and make the therapeutic approach to treating LHB lesions less arbitrary. MATERIAL AND METHOD: In order to describe the different sides of the "biceps box", and to understand their possible physiological and pathological consequences, a literature review using PRISMA methodology was used. RESULTS: The supraspinatus (SSP) has expansions on its anterior aspect that project anteriorly and cross the coracohumeral ligament (CHL). The most functionally important expansion is the fasciculus obliquus, which extends perpendicular to the axis of the tendon fibers of the SSP, divides the CHL into a deep and a superficial layer, and terminates on the superficial aspect of the subscapularis. The humeral insertion of the SSP may be binary, making a bridge over the LHB, with a posterior branch inserting on the greater tuberosity and an anterior branch on the lesser tuberosity. The superior glenohumeral ligament (SGHL) has a twisted course, downward and forward, and ends at the proximal opening of the bicipital groove with a flap on which the LHB rests. The bicipital pulley is not an independent structure but an arciform structure resulting from the fusion of several tissues. DISCUSSION: The presence of structures linked together by common expansions in the 3 planes of space validates the relevance of a "biceps box" as a functional geometric model. The structure that acts as a crossroads through which all expansions pass is the CHL. An extrinsic SSP lesion can be compensated for by other "biceps box" structures, whereas an extrinsic SGHL lesion rarely exists without the presence of an intrinsic LHB lesion. The CHL constitutes a connective tissue crossed by a vasculonervous pedicle from the lateral pectoral nerve, which may explain some anterior shoulder pain attributed to the biceps. CONCLUSION: The LHB can be likened to an intrinsic structure contained in a box whose sides are made up of different interconnected stabilizing structures defining the extrinsic structures. The concept of a dynamic "biceps box" allows LHB lesions to be accurately classified, separating extrinsic and intrinsic lesions, and thus potentially modifying therapeutic approaches to the LHB. LEVEL OF EVIDENCE: IV; systematic review.

A New Approach to Quantifying Muscular Fatigue Using Wearable EMG Sensors during Surgery: An Ergonomic Case Study.

(1) Background: Surgeons are exposed to musculoskeletal loads that are comparable to those of industrial workers. These stresses are harmful for the joints and muscles and can lead to musculoskeletal disorders (MSD) and working incapacity for surgeons. In this paper, we propose a novel ergonomic and visualization approach to assess muscular fatigue during surgical procedures. (2) Methods: The activity of eight muscles from the shoulder girdle and the cervical/lumbar spines were evaluated using position and electromyographic wearable sensors while a surgeon performed an arthroscopic rotator-cuff surgery on a patient. The time and frequency-domain variables of the root-mean-square amplitude and mean power frequency, respectively, were calculated from an electromyographic signal. (3) Results: The entire surgical procedure lasted 73 min and was divided into 10 sub-phases associated with specific level of muscular activity and fatigue. Most of the muscles showed activity above 60%, while the middle trapezius muscles were almost constantly activated (>20%) throughout the surgical procedure. (4) Conclusion: Wearable sensors can be used during surgical procedure to assess fatigue. Periods of low-to-high activity and fatigue can be evaluated and visualized during surgery. Micro-breaks throughout surgical procedures are suggested to avoid fatigue and to prevent the risk of developing MSD.

A predictive model to quantify joint torques and support reaction forces when using a smartphone while standing with support.

The present study had a dual objective: (1) to present and validate a predictive model of standing posture in the sagittal plane, joint torques and support forces for a smartphone user built from biomechanical principles; (2) propose risk scales for joint torques and reaction forces based on simulations in order to use them into the musculoskeletal disorders prevention. Comparison of the modelled data with experimental measurements (400 tested postures with sample size verification) for calling and texting tasks highlights the model's ability to correctly estimate posture and reaction forces on the ground. The model was able to provide estimates of the range of variation of each parameter for a wide range of environmental conditions as a function of the user body mass index (setting between 12.5 and 50). Joint torques risk scales have been constructed, especially for shoulder and elbow, to characterise the risks incurred by the users. Practitioner summary: The proposed model enables the postures, joint torques and reaction forces to be estimated from subject's body mass index and environmental configuration without resorting to experimentation, which is relevant in industry. This approach allows the proposition of new scales based on joint torques to reinforce the recommendations for MSDs prevention. Abbreviations: BMI: body mass index; LUBA: postural loading on the upper body assessment; MSDs: musculoskeletal disorders; RULA: rapid upper limb assessment; WHO: World Health Organization.

Identification of generic drilling task phases and height effect: Coupling of kinematic and kinetic data.

BACKGROUND: The prevention of work-related musculoskeletal disorders (MSDs) is an important issue for the health of operators, especially when the workload is heavy, such as in drilling activities. RESEARCH QUESTION: This study aimed to propose an objective identification and description of the different phases that comprise a drilling task as well as a biomechanical and ergonomic evaluation of the subjects' overall posture during its effective part. METHODS: Fourteen healthy subjects performed three successive drillings at two different heights, 130 (H130) and 170 cm (H170) from the ground, of a 3 mm thick steel plate. Kinematic and kinetic data were simultaneously acquired using a Qualisys motion capture system and a force platform. The speed profiles of each body segments and the evolution of the force exerted were analysed to identify the different phases. Then, the average joint angles of the whole body were calculated during the drilling phase for the two heights considered and compared. Finally, the measured postures were qualified through the Rapid Upper Limb Assessment (RULA) score in order to assess the risk of developing MSDs for each condition. RESULTS: The drilling task could be divided into five phases whatever the condition: transport, aiming, repositioning, drilling, and return. The increase in height has doubled the duration of the drilling phase while reducing the force exerted by about 30 %. Similarly, height variation significantly influenced the subjects' posture, mainly in the head, trunk and upper limbs, and the RULA scores obtained for conditions H130 and H170 were 6 and 7 respectively. SIGNIFICANCE: The results indicate, on the one hand, the relevance of coupling kinematic and kinetic data in order to analyse the drilling task and, on the other hand, that operators are exposed to considerable risk of developing MSDs, even at intermediate heights, which increase as the height increases.

Effects of environmental illumination and screen brightness settings on upper limb and axial skeleton parameters: how do users adapt postures?

79% of smartphone users carry their phone 22 hours a day. In this context, the main task worldwide, texting, is performed under a wide range of light and position conditions. The aim of this study was to test the effects of environmental illumination and screen brightness settings on upper limb and axial skeleton parameters. Twelve subjects performed three trials of texting under three experimental positions, two screen luminance settings and three environmental light conditions. 3 D axial skeleton and upper limb angles, smartphone orientation and face-to-smartphone distance were used as dependent variables. High environmental illumination and/or low screen brightness resulted in an increase in interaction time and a reduction in the face-to-smartphone distance by approximately 10%. Subjects attempted to compensate for the unfavourable effects of such light conditions by adopting postures rated 5 in the Rapid Upper Limb Assessment, indicating an increased risk of developing musculoskeletal disorders. Practitioner's summary: The purpose of the study was to quantify the joint angles of the upper body in experimental conditions that represent daily life. Postures were influenced by ambient illumination and display brightness. The most harmful postures were observed when the display brightness was minimum, and the ambient light was similar to a sunny day. Abbreviations: ST: seated with table; SWT: seated without any support; STA: standing; 0L: in the dark, no light; AL: ambient light; SL: strong light; BrightMin: minimum display brightness; BrightMax: maximum display brightness (BrightMax); ISB: International Society of Biomechanics; RULA: rapid upper limb assessment; MSDs: musculoskeletal disorders.