Muscle Activation Levels Research Articles

Effects of Various Muscle Disuse States and Countermeasures on Muscle Molecular Signaling.

Skeletal muscle is capable of changing its structural parameters, metabolic rate and functional characteristics within a wide range when adapting to various loading regimens and states of the organism. Prolonged muscle inactivation leads to serious negative consequences that affect the quality of life and work capacity of people. This review examines various conditions that lead to decreased levels of muscle loading and activity and describes the key molecular mechanisms of muscle responses to these conditions. It also details the theoretical foundations of various methods preventing adverse muscle changes caused by decreased motor activity and describes these methods. A number of recent studies presented in this review make it possible to determine the molecular basis of the countermeasure methods used in rehabilitation and space medicine for many years, as well as to identify promising new approaches to rehabilitation and to form a holistic understanding of the mechanisms of gravity force control over the muscular system.

Combined Effects of External Moments and Muscle Activations on ACL Loading during Numerical Simulations of a Female Model in OpenSim

Background: Anterior cruciate ligament (ACL) injuries have been studied using a variety of methods and tools. However, each is hindered by specific limitations with respect to its application. Aim: To assess the combined effects of external moments and muscle activations on ACL loading using serial, forward dynamics (FD) simulations of single leg, hyperextension landings in OpenSim. Methods: The FD tool of OpenSim was iteratively run using different combinations of knee-spanning muscle activation levels, internal rotation and valgus knee moment magnitudes. A regression was conducted on the data in order to predict ACL loading under different conditions. Results: A purely abduction moment leads to greater mean ACL loading than a purely internal rotation moment or any combination of the two. Additionally, the generalized boosted regression model using both external moments and certain knee muscles identified the internal rotation moment as the most important variable in predicting the ACL load (R2 = 0.9; p < 0.0001). Conclusion: This study demonstrated a novel and practical application of an OpenSim musculoskeletal model that supports the ACL injury mechanism of landing with low knee flexion angles, high muscle forces of the Quadriceps muscles and an external knee valgus moment, though further investigation is needed.

Alternative to Reduced Stresses on the Upper Extremity in a Standing Workstation.

This study evaluated a standing armrest to provide more acceptable ergonomic guidelines that may reduce the cost of standing computer workstations. Of the many advantages of standing workstations, there have been no efforts to minimize the biomechanical cost, such as larger wrist extension and greater forearm muscle activity than sitting. Sixteen participants were asked to perform a typing task under a combination of the following factors: (1) desk shape (rectangular and concave); (2) desk height (0, +5, -5cm from 90° elbow flexion); and (3) monitor height (0, -10cm from the eyes). During the trials, the trunk kinematics, muscle activation levels, and CoP were recorded. Both arms were further away from the upper body under the concave and +5 desk height than under the normal condition, but significant decreases in the extensor carpi radialis (8.6%), anterior deltoid (28.8%), and L4 paraspinals (5.5%) were observed. Similarly, the wrist extension angle decreased by 10.5° (42%) under this condition, but the posture required a 2.2° (19%) increase in wrist adduction angle. The CoP irregularity was greater under the concave workstation, indicating more complex motion. A higher and concave desk can provide an armrest effect while engaged in a standing workstation by reducing the wrist extension and related muscle activation level, but at the cost of a larger wrist adduction angle. Providing a standing armrest (+5cm height and concave desk) could reduce the stresses on the upper extremities, but a split keyboard should be considered to minimize wrist adduction.

Biomechanical Effects on Lower Extremities in Human-Robot Collaborative Agricultural Tasks

The present study pertains to a key aspect of human-robot collaborative systems which is usually underestimated, namely occupational health prolepsis. The aim of this investigation was to assess the biomechanical effects of manual symmetric load lifting related to a synergistic agricultural task that utilizes an unmanned ground vehicle to undertake the carriage of loads. Towards that goal, kinetic and kinematic data were collected from the lower extremities of thirteen experienced workers, by testing three different deposit heights (70, 80, 90 cm) corresponding to possible adjustments of the available agricultural robot. Moreover, the muscle activation levels of three lower extremity muscles and one trunk muscle were evaluated via a wireless electromyography system. Overall, the experimental findings revealed that the lower examined load height was associated with larger knee flexion moments and hip extension moments. Nevertheless, this height was related to lower activation mainly of the erectus spinae muscles. Finally, insignificant alterations were observed for the ankle joint as well as the activation levels of the other muscles. Consequently, a height equal to 90 cm is suggested, however, by avoiding extreme lumbar postures. The current results can be exploited for possible ergonomic interventions concerning the optimal deposit height of a robotic platform when a similar case is designed.

The Relationship of Trunk Muscle Activation and Core Stability: A Biomechanical Analysis of Pilates-Based Stabilization Exercise.

Pilates is an effective exercise method for rehabilitating musculoskeletal disorders as its principles are based on the activation of local muscles. This study aimed to compare the subjects with and without Pilates experience to find out the effect of the experience on the core muscle activity and muscle co-contraction, and to examine the relationship between the core muscle activation level and the kinematic data. This study involved 32 subjects, including 16 experienced Pilates practitioners and 16 non-experienced subjects. The knee stretch on the reformer was performed in three different positions: flat back with a neutral pelvis, round back with posteriorly tilted pelvis (RPP), and extended back anteriorly tilted pelvis (EAP). The electromyography of the internal oblique (IO), rectus abdominis (RA), multifidus (MU), and iliocostalis lumborum (IL) muscles were measured, as well as kinematic data from a 3D motion analysis system. Compared to the non-experienced subjects, the experienced subjects activated the IO muscles more than the RA muscles, and the most significant difference was seen in the RPP position (p < 0.05). The experienced patients activated the MU muscles more often than the IL muscles, with the most significant difference observed in the RPP position and the least significant in the EAP position (p < 0.05). All kinematic data and muscle activity (IO, IO/RA ratio, MU/IL ratio) showed significant differences between the experienced and non-experienced subjects (p < 0.05). The subjects presented a moderate correlation between muscle activation and core stability. It was confirmed that the experienced Pilates practitioners activated the abdominal and low back core muscles effectively, and the stability of the pelvis and trunk were better than that of the non-experienced participants. In addition, the better the trunk stability was maintained, the larger and more accurate movement of the mobility segment was observed.

Kinetic and Kinematic Features of Pedestrian Avoidance Behavior in Motor Vehicle Conflicts.

The active behaviors of pedestrians, such as avoidance motions, affect the resultant injury risk in vehicle–pedestrian collisions. However, the biomechanical features of these behaviors remain unquantified, leading to a gap in the development of biofidelic research tools and tailored protection for pedestrians in real-world traffic scenarios. In this study, we prompted subjects (“pedestrians”) to exhibit natural avoidance behaviors in well-controlled near-real traffic conflict scenarios using a previously developed virtual reality (VR)-based experimental platform. We quantified the pedestrian–vehicle interaction processes in the pre-crash phase and extracted the pedestrian postures immediately before collision with the vehicle; these were termed the “pre-crash postures.” We recorded the kinetic and kinematic features of the pedestrian avoidance responses—including the relative locations of the vehicle and pedestrian, pedestrian movement velocity and acceleration, pedestrian posture parameters (joint positions and angles), and pedestrian muscle activation levels—using a motion capture system and physiological signal system. The velocities in the avoidance behaviors were significantly different from those in a normal gait (p < 0.01). Based on the extracted natural reaction features of the pedestrians, this study provides data to support the analysis of pedestrian injury risk, development of biofidelic human body models (HBM), and design of advanced on-vehicle active safety systems.

Computer Vision for Facial Analysis Using Human-Computer Interaction Models

A facial recognition device is a technology that can be used for authenticating a human face by ID verification and for calculating facial features from a single image using a visual image or a video to a facial database. Computer vision’s main objective enables identifying images, detecting speech, the concentration of attention, facial expressions, and recognition of emotions. Face identification is an important part of the understanding of audiovisual speech. In this paper, Intelligent Schemes for human-computer interaction (IS-HCI) provides a broader and more expressive range of computer-based vision features for processing data from one or more sensors. In particular cases of impairment, alternative interaction methods dependent on computer vision can be effectively modified. Facial identification is a biometric safety category. This paper aims to help technology-based concepts, allowing a child with a debilitating neuromuscular disorder to communicate with the robot by recognizing facial expressions. The proposed model was suggested to test in photographs taken from children’s videos, and the preliminary findings show that computational interactions with children through facial expression would break down barriers to their relationship with machines with people with limited mobility. Thus the experimental results show the proposed method IS-HCI to enhance facial expression and effectively interact with the children to achieve sensitivity (94.12%), specificity (96.84%), recognition rate (94.23%), probability (21.78%), accuracy (96.69%), expression prediction rate (98.14%), muscle activity level (79.84%) compared to other methods.

Feasibility of Using a Portable MyotonPRO Device to Quantify the Elastic Properties of Skeletal Muscle.

BackgroundThe aims of this study were to (1) calculate the correlation between different tensile force levels and corresponding muscle stiffness both in vitro and in vivo; (2) determine whether muscle stiffness assessed using a MyotonPRO myotonometer can be used to accurately estimate muscle activity level; and (3) evaluate the inter-operator reliability of MyotonPRO-based measurement in assessing biceps brachii muscle (BBM) stiffness.Material/MethodsIn Experiment I, muscle stiffness, as measured using the MyotonPRO, was obtained at 0 N, 2 N, 4 N, 6 N, 8 N, and 10 N of applied force on 6 fresh medial gastrocnemius muscle specimens. In Experiment II, 11 healthy subjects were recruited. BBM stiffness, assessed by the same device, was obtained at different tensile force levels, from 0 to 50% of maximal voluntary contraction (MVC). For the reliability test, the score for each subject was quantified by 2 operators (I and II), thrice, at 30-minute intervals on the same day.ResultsA strong correlation was found between the different tensile force levels, which corresponded to muscle stiffness in vitro (r=0.71–0.95, all P<0.05). In vivo, muscle stiffness increased linearly with an increase of the tensile force levels from 0 to 50% of MVC (r=0.99, P=0.00) and there was a significant difference in BBM stiffness among the incremental isometric tasks (F [1.76, 17.60]=91.52, P=0.00). The inter-operator reliability for the measurement of BBM stiffness was good (ICC=0.86).ConclusionsOur findings indicate that muscle stiffness measured using the MyotonPRO is strongly related to muscle activity level and that the MyotonPRO is a feasible tool for quantifying BBM stiffness as well as for quantifying changes in MVC levels.

Mechanomyogram amplitude vs. isometric ankle plantarflexion torque of human medial gastrocnemius muscle at different ankle joint angles

The purpose of this study was to investigate the influence of changes in ankle joint angle on the mechanomyogram (MMG) amplitude of the human medial gastrocnemius (MG) muscle during voluntary isometric plantarflexion contractions. Ten healthy individuals were asked to perform voluntary isometric contractions at six different contraction intensities (from 10% to 100%) and at three different ankle joint angles (plantarflexion of 26°; plantarflexion of 10°; dorsiflexion of 3°). MMG signals were recorded from the surface over the MG muscle, using a 3-axis accelerometer. The relations between root mean square (RMS) MMG and isometric plantarflexion torque at different ankle joint angles were characterized to evaluate the effects of altered muscle mechanical properties on RMS MMG.We found that the relation between RMS MMG and plantarflexion torque is changed at different ankle joint angles: RMS MMG increases monotonically with increasing the plantarflexion torque but decreases as the ankle joint became dorsiflexed. Moreover, RMS MMG shows a negative correlation with muscle length, with passive torque, and with maximum voluntary torque, which were all changed significantly at different ankle joint angles.Our findings demonstrate the potential effects of changing muscle mechanical properties on muscle vibration amplitude. Future studies are required to explore the major sources of this muscle vibration from the perspective of muscle mechanics and muscle activation level, attributable to changes in the neural command.

Motor slacking during resisted treadmill walking: Can visual feedback of kinematics reduce this behavior?

Functional resistance training is frequently applied to rehabilitate individuals with neuromusculoskeletal injuries. It is performed by applying resistance in conjunction with a task-specific training, such as walking. However, the benefits of this training may be limited by motor slacking, a phenomenon in which the human body attempts to reduce muscle activation levels or movement excursions to minimize metabolic- or movement-related costs. While kinematic feedback could reduce one's tendency to minimize effort during training, this has not been verified experimentally. Does functional resistance training during walking lead to motor slacking, and can techniques such as visual feedback be used to reduce these effects? Fourteen able-bodied individuals participated in this experiment. Participants were trained by walking on a treadmill while a bidirectional resistance was applied to the knee using a robotic knee exoskeleton. During training, participants were either instructed to walk in a manner that felt natural or were provided real-time visual feedback of their kinematics. Electromyography and knee kinematics were measured to determine if adding resistance to the limb induced slacking and if feedback could reduce slacking behavior. Kinematic aftereffects were measured after training bouts to gauge adaptation. Functional resistance training without feedback significantly reduced knee flexion when compared to baseline walking, indicating that participants were slacking. This reduction in knee flexion did not improve with continued training. Providing visual feedback of knee joint kinematics during training significantly increased knee muscle activation and kinematic aftereffects. The findings indicate that individuals are susceptible to motor slacking during functional resistance training, which could affect outcomes of this training. However, motor slacking can be reduced if training is provided in conjunction with a feedback paradigm. This finding underscores the importance of using additional methods that externally motivate motor adaptation when the body is not intrinsically motivated to do so.

Effects of initial foot position on postural responses to lateral standing surface perturbations in younger and older adults.

An age-related decline in standing balance control in the medio-lateral direction is associated with increased risk of falls. A potential approach to improve postural stability is to change initial foot position (IFP). In response to a lateral surface perturbation, how are lower extremity muscle activation levels different and what are the effects of different IFPs on muscle activation patterns and postural stability in younger versus older adults? Ten younger and ten older healthy adults participated in this study. Three IFPs were tested [Reference (REF): feet were placed parallel, shoulder-width apart; Toes-out with heels together (TOHT): heels together with toes pointing outward; Modified Semi-Tandem (M-ST): the heel of the anterior foot was placed by the big toe of the posterior foot]. Unexpected lateral translations of the standing surface were applied. Electromyographic (EMG) activity of the lower extremity muscles, standard deviation (SD) of the body's CoM acceleration (SD of CoMAccel), and center of pressure (CoP) sway area were compared across IFPs and age. Activation levels of the muscles serving the ankle and gluteus medius were greater than for the knee joint muscles and gluteus maximus in the loaded leg across all IFPs in both groups. TOHT showed greater EMG peak amplitude of the soleus and fibularis longus compared to REF, and had smaller SD of CoMAccel and CoP sway area than M-ST. Compared to younger adults, older adults demonstrated lower EMG peak amplitude and delayed peak timing of the fibularis longus and greater SD of CoMAccel and CoP sway area in all IFPs during balance recovery. During standing balance recovery, ankle muscles and gluteus medius are important active responders to unexpected lateral surface perturbations and a toes-out IFP could be a viable option to enhance ankle muscle activation that diminishes with age to improve postural stability.

Trunk and Lower Extremity Muscle Activation in Children in Various Seated Positions on Horseback

<h3>Research Objectives</h3> To investigate muscle activation of trunk and lower extremity muscles in children in six positions on horseback commonly used by therapists during hippotherapy sessions. <h3>Design</h3> Comparison of muscle activation levels within and between six different riding positions. <h3>Setting</h3> Data collection took place in the general community at a local equestrian facility. <h3>Participants</h3> Convenience sample of fifteen healthy children aged between 4 and 12 years old with no previous horseback riding experience. <h3>Interventions</h3> Surface EMG readings were collected for eight trunk and lower extremity muscles while children were seated in six positions on horseback. Positions were: facing forward, backwards, and sitting sideways on the horse. Upper extremity positions were also manipulated for each seated position and included: hands resting in laps vs. arms abducted to 90°. <h3>Main Outcome Measures</h3> Mean amplitudes of the EMG data for each muscle in each position were normalized by converting to a percentage of average activity of the same muscles during a walking trial of each subject. The resulting percent muscle activity was compared across subjects and positions. <h3>Results</h3> Higher levels of activation for the erector spinae were found for forward arms abducted (FAA) compared to forward hands in lap (FHL) (p= 0.001), sideways arms abducted (SAA) compared to FHL (p= 0.006), and SAA compared to sideways hands in lap (SHL) (p= 0.005). Rectus abdominis demonstrated higher activation with SHL as compared to FHL (p= 0.005), SAA (p= 0.001), and FAA (p= 0.005). Significant differences for gluteus medius activity were found in comparing SHL and SAA to FHL (p= .023 and .027). <h3>Conclusions</h3> Different positions on horseback result in changes in muscle activation of the rider. For therapists wanting to encourage activation of the erector spinae in clients during hippotherapy sessions, all positions with arms abducted resulted in higher activation levels. If activation of the rectus abdominis or gluteus medius is desired, clients may benefit most from a sideways position vs. sitting forwards or backwards. <h3>Author(s) Disclosures</h3> I declare no conflicts of interest.

Constant Resistance During Proportional Speed Provoked Higher Lower Limb Proximal Musculature Recruitment than Distal Musculature in Young Healthy Adults

The lack of exercise in society today often leads to severe muscle loss and poor physical performance. Training methods targeting specific weakened muscle groups can help prevent or counteract muscle loss. This study aimed to analyze how the lower extremity muscles are activated when pushing a sled with constant resistance at two different speeds. Twenty-six participants with an average age of 23.77 years consented to having electromyography surface electrodes placed along the gluteus maximus (GMax), gluteus medius (GMed), tibialis anterior (TA), and gastrocnemius (GA) of their dominant leg. Muscle activation levels were then measured while the participant walked and ran with and without sled resistance. The study results showed that muscle activation was comparable during all trials and was not influenced by speed or constant resistance. However, the muscle activation for GMax and GMed was significantly higher than the activation levels exhibited by GA and TA. While pushing a sled has been shown to impact all studied musculature similarly, adding resistance to the movement can affect gait parameters such as stride length and cadence. Our findings support the use of sled training in patients with hip pathologies who are seeking to strengthen their GMax and GMed.

Effects of using a whole-body powered exoskeleton during simulated occupational load-handling tasks: A pilot study

Whole-body powered exoskeletons (WB-PEXOs) can be effective in reducing the physical demands of heavy occupational work, yet almost no empirical evidence exists on the effects of WB-PEXO use. This study assessed the effects of WB-PEXO use on back and leg muscle activities during lab-based simulations of load handling tasks. Six participants (4M, 2F) completed two such tasks (load carriage and stationary load transfer), both with and without a WB-PEXO, and with a range of load masses in each task. WB-PEXO use reduced median levels of muscle activity in the back (∼42–53% in thoracic and ∼24–43% in lumbar regions) and legs (∼41–63% in knee flexors and extensors), and mainly when handling loads beyond low-moderate levels (10–15 kg). Overall, using the WB-PEXO also reduced inter-individual variance (smaller SD) in muscle activities. Future work should examine diverse users, focus on finding effective matches between WB-PEXO use and specific tasks, and identify applications in varied work environments.

Air pistol shooting: upper limb muscle activation between training and simulated competition

ABSTRACT Heightened stress during air pistol competitions may impair shooters’ abilities to maintain gun stability, resulting in inferior performance. This study aimed to compare the pre-trigger muscle activation levels of upper muscles in 10-m air pistol shooters between training and simulated competition conditions. Seven sub-elite shooters from the Singapore National Youth Air Pistol Team shot 30 shots in a training versus simulated competition condition in randomised orders on separate days. Muscle activation for the forearm and shoulder muscles, namely extensor carpi radialis, flexor carpi ulnaris, anterior deltoid, and posterior deltoid, were recorded using electromyography (EMG). Shooting performance was evaluated by total shot scores. Stress level was monitored via heart rate and the Mental Readiness Form-3. No statistically significant differences were found in EMG, performance, or stress-related variables between conditions, although moderate-to-large effect sizes were observed in some muscle activation and self-reported stress indicators. Analysis of individual performances using smallest worthwhile change showed that two participants improved under the simulated competition condition, while two declined, and three remained unaffected. In conclusion, sub-elite youth air pistol shooters were able to exhibit good neuromuscular control under high anxiety situations and thus their performance was largely unaffected.

Multi-modal gait: A wearable, algorithm and data fusion approach for clinical and free-living assessment

Gait abnormalities are typically derived from neurological conditions or orthopaedic problems and can cause severe consequences such as limited mobility and falls. Gait analysis plays a crucial role in monitoring gait abnormalities and discovering underlying deficits can help develop rehabilitation programs. Contemporary gait analysis requires a multi-modal gait analysis approach where spatio-temporal, kinematic and muscle activation gait characteristics are investigated. Additionally, protocols for gait analysis are going beyond labs/clinics to provide more habitual insights, uncovering underlying reasons for limited mobility and falls during daily activities. Wearables are the most prominent technology that are reliable and allow multi-modal gait analysis beyond the labs/clinics for extended periods. There are established wearable-based algorithms for extracting informative gait characteristics and interpretation. This paper proposes a multi-layer fusion framework with sensor, data and gait characteristics. The wearable sensors consist of four units (inertial and electromyography, EMG) attached to both legs (shanks and thighs) and surface electrodes placed on four muscle groups. Inertial and EMG data are interpreted by numerous validated algorithms to extract gait characteristics in different environments. This paper also includes a pilot study to test the proposed fusion approach in a small cohort of stroke survivors. Experimental results in various terrains show healthy participants experienced the highest pace and variability along with slightly increased knee flexion angles (≈1°) and decreased overall muscle activation level during outdoor walking compared to indoor, incline walking activities. Stroke survivors experienced slightly increased pace, asymmetry, and knee flexion angles (≈4°) during outdoor walking compared to indoor. A multi-modal approach through a sensor, data and gait characteristic fusion presents a more holistic gait assessment process to identify changes in different testing environments. The utilisation of the fusion approach presented here warrants further investigation in those with neurological conditions, which could significantly contribute to the current understanding of impaired gait.

Immediate Effects of Acupuncture on Explosive Force Production and Stiffness in Male Knee Joint.

Acupuncture can improve explosive force production and affect joint stiffness by affecting muscle activation levels. This study aims to explore the effects of true acupuncture (TA) compared with sham acupuncture (SA) on the explosive force production and stiffness of the knee joint in healthy male subjects. Twenty subjects were randomly divided into the TA group (n = 10) and SA group (n = 10) to complete isokinetic movement of the right knee joint at a speed of 240°/s before and after acupuncture. Futu (ST32), Liangqiu (ST34), Zusanli (ST36), Xuehai (SP10), and Chengshan (BL57) were selected for acupuncture. The intervention of SA is that needles with a blunt tip were pushed against the skin, giving an illusion of insertion. The results showed that acupuncture and the intervention time had a significant interaction effect on knee joint explosive force and joint stiffness (p < 0.05). The average maximum (max) torque, average work, average power, average peak power and total work of the TA group increased significantly after acupuncture (p < 0.05), while the SA group did not (p > 0.05). Therefore, true acupuncture can immediately improve the explosive force and joint stiffness of the male knee joint by inducing post-activation potentiation (PAP) and/or De-Qi.

Declines in muscle contractility and activation during isometric contractions of the knee extensors vary with contraction intensity and exercise volume.

What is the central question of this study? Is there a critical threshold beyond which the loss of muscle contractility is regulated by the level of muscle activation during single-limb exercise of differing intensities and volumes? What is the main finding and its importance? Plateaus in the decline in muscle contractility during single-limb knee extension depended on both exercise volume and contraction intensity. A plateau was only evident with an increase in exercise volume. Muscle activation increased and did not decline despite substantial reductions in contractility. The findings indicate that the decrease in muscle contractility exhibited by resistance-trained men during the performance of submaximal isometric contractions with the knee extensors was not regulated by the level of muscle activation. Our study examined the influence of contraction intensity and exercise volume on changes in muscle contractility and activation of the knee extensor muscles. Maximal voluntary torque (MVT) and rate of change in torque, surface electromyograms, voluntary activation, V-waves and quadriceps resting twitch measures were assessed in 10 resistance-trained men during two experimental sessions. Each session began with an initial baseline series of contractions at a fixed intensity of 40% or 80% MVT. The 40%-only session continued with five contractions to task failure at 40% MVT. The 80% session continued with five contractions to failure each at 80%, 60% and 40% MVT. Greater reductions in MVT were observed during the baseline contractions of the 40%-only session compared with the 80% session at each matched-volume time point (P<0.05), with similar changes in twitch values (P<0.001). MVT and twitch values plateaued at each intensity during the 80% session and were significantly different across intensities: 80% > 60% > 40% (P<0.001). There were no differences for measures during the five contractions at 40% MVT performed on the different days, despite a greater volume of exercise performed prior to the 40% MVT during the 80% session. At each contraction intensity, a plateau in contractility loss was observed as more contractions were performed. We found that initial increases in muscle activation were maintained in the presence of increases in exercise volume and, in contrast to the critical-threshold hypothesis, did not decline in parallel with reductions in muscle contractility.

Reflexive Response of Neck Muscle to Sudden Perturbation after Prolonged Smartphone Use

Prolonged smartphone use induces passive stretch of neck tissues and muscle fatigue, affecting spinal stability and pain. It is necessary to evaluate the effect of smartphone use on the reflexive response to detect the changes in neck tissues and head stability. A laboratory experiment (n=10) was conducted to investigate the reflexive response of neck muscle to perturbation after 30 minutes of smartphone use. Neck extensor muscle activation and its activation timing to perturbation were investigated before and after smartphone use. Head angle and muscle activation level were collected during smartphone use. During smartphone use, muscle activation gradually increased. After smartphone use, neck muscles showed a higher activation level and significantly delayed onset to perturbation. Smartphone use changed the reflexive response of the neck muscle. Further study is needed to investigate the association between smartphone use and neuromuscular changes to the tissues of the cervical spine.

Neuromuscular Analysis Of Various Release Mechanisms In Archery: A Study Of The Preparatory Response Between Trigger And Back-Tension Releases

Archery was originally a tool for hunting but since has been transformed into a sport. Archery technology has evolved with little focus as to its effect on humans. Archery requires high levels of concentration and static muscle activity, which has not been analyzed to be successful. By observing the muscle activity in the bow arm and measuring the vibration effects from the bow, it was determined a presence of an impact to the human arm, which the human then creates anticipation for and braces against. To mitigate this anticipation, another technology was introduced to create a surprise factor in the shooting. To reduce the frequency of archers bracing up for the shot, knowledge of when the shot is going off was taken away. It was observed that the new technology did introduce a surprise factor, but it did not reduce the occurrences of preparatory muscle activation in the human arm.