Reduced Muscle Activity Research Articles

Immediate Effects of the Mandibular Muscle Energy Technique in Adults with Chronic Temporomandibular Disorder

Background/Objectives: Temporomandibular disorders affect the muscles used for chewing, the temporomandibular joint, and other related tissues, resulting in pain, limited mobility, and dysfunction of the masticatory muscles. Physical therapy plays a critical role in treatment. Manual therapy can trigger neurophysiological mechanisms that contribute to pain relief and a reduction in muscle activation. Evaluations of different manual therapy techniques are needed on this topic. The main objective of this study was to evaluate the effects of a specific manual therapy technique (the mandibular muscle energy technique) in adults with temporomandibular disorders. Methods: A randomized, parallel clinical trial was conducted, and 31 participants were recruited into an experimental group and 30 were recruited into a control group in order to analyze its effects on outcomes such as pain, pain threshold to pressure, mandibular mobility, and kinesiophobia. Pre- and post-intervention assessments were performed, followed by statistical analyses to verify the intra- and intergroup changes. Results: The results showed that the mandibular muscle energy technique produced positive effects with significant differences in the intra- and intergroup comparisons for pain threshold to pressure, mandibular mobility, and kinesiophobia, demonstrating its efficacy and safety as a treatment option for adults with temporomandibular disorders, with proven effects in the short term. Conclusions: The effects obtained and the absence of side effects showed that this technique can be integrated into multimodal treatment along with other types of interventions in patients with temporomandibular disorders.

Effects of the IronHand® Soft Exoskeleton on Forearm Muscle Activity During in Field Automotive Assembly Tasks

OCCUPATIONAL APPLICATIONS When compared to not using a soft-hand exoskeleton, the IronHand® caused both increases and decreases in forearm muscle activity while completing automotive assembly tasks. Surprisingly, although there were reductions in muscle activity when wearing the IronHand®, only a few of these decreases resulted in muscle activity changing such that they fell to below recommended ergonomic thresholds. Despite this, some individuals in our study clearly benefited from the device, and this suggests that there is potential for widespread use of such a device if fine tuned to the individual and task demands. Much work is still required for a design that will allow for optimal physical benefit.

Development and evaluation of a novel self-contained breathing apparatus pack to reduce musculoskeletal loads and enhance firefighter comfort

Self‑Contained Breathing Apparatus (SCBA) is an essential piece of personal protective equipment for firefighters, providing essential respiratory support and protection. A major challenge in SCBA research is to reduce musculoskeletal disorders and enhance firefighter comfort while carrying the SCBA. In this study, a novel SCBA pack was designed to reduce SCBA‑related musculoskeletal stress. Ten volunteer firefighters were recruited to participate in the test protocol equipped with a novel SCBA (SCBANovel) and a traditional SCBA (SCBATrad) pack. Surface electromyography and pressure data were collected, and subjective ratings of discomfort using a visual analog scale. The results showed that the SCBANovel significantly reduced trapezius and erector spinae muscle activity. Shoulder and waist pressure were reduced by 19.73%‑32.83% and 18.46%‑41.55%, respectively. In addition, the SCBANovel pack reduced lower back discomfort scores by 59.1%, all compared to the SCBATrad pack. The SCBANovel pack showed a significant reduction in musculoskeletal stress and discomfort in firefighters. Practitioner Summary SCBAs are known to be critical in protecting the health of firefighters, but are often associated with firefighter discomfort and musculoskeletal disorders. We developed the SCBANovel pack and explored the effects on the upper body musculoskeletal system and comfort during walking and running compared to carrying the SCBATrad pack. The SCBANovel pack reduced muscle activity in the trapezius and erector spinae muscles and significantly reduced pressure on the shoulders and lower back.

Limb dominance influences landing mechanics and neuromuscular control during drop vertical jump in patients with ACL reconstruction.

The purpose of this study was to compare the interlimb biomechanical differences in patients who had undergone anterior cruciate ligament reconstruction (ACLR) in either dominant (ACLR-D) or nondominant (ACLR-ND) limbs and healthy controls (CON) during drop vertical jump (DVJ) task. To investigate whether the dominant or nondominant limb influences the risk of re-injury in ACLR patients. Thirty-three ACLR patients were divided into ACLR-D and ACLR-ND groups according to whether the surgical limb was dominant or nondominant. Seventeen healthy individuals were selected as the CON group. Three-dimensional kinematic data, ground reaction force (GRF) data, and surface electromyographic (EMG) data from the bilateral lower limbs of all participants were collected during the DVJ task. Two-way repeated-measures ANOVAs (limb × group) were performed on the variables of interest to examine the main effects of limb (dominant vs. nondominant) and group (ACLR-D, ACLR-ND, and CON), as well as the interaction between limb and group. The nonsurgical limbs of ACLR group had significantly greater knee valgus angles, knee extension and valgus moments, peak posterior GRF (PPGRF), and peak vertical GRF (PVGRF) compared to the surgical limbs. The nonsurgical limbs of ACLR-ND patients demonstrated significantly greater knee extension and valgus moments, greater PPGRF and PVGRF, and reduced muscle activity in the vastus medialis and vastus lateralis compared to the CON group. The ACLR patients had reduced muscle activity in the quadriceps of the surgical limb and the hamstrings of the bilateral limbs compared to controls. The nonsurgical limbs of ACLR patients may suffer an increased risk of ACL injury due to altered landing mechanics and neuromuscular control strategies compared to the surgical limbs. Additionally, limb dominance influences movement patterns and neuromuscular control during DVJ task, the nonsurgical limbs of the ACLR-ND might be at higher risk of ACL injury compared to the ACLR-D group.

Relationship between the flexion relaxation phenomenon and kinematics of the multi-segmental spine in nonspecific chronic low back pain patients

The flexion relaxation phenomenon (FRP) is characterized by the reduction of paraspinal muscle activity at maximum trunk flexion. FRP is reported to be altered (persistence of spinal muscle activity) in more than half of nonspecific chronic low back pain (NSCLBP) patients. Little is known about how the multi-segmental spine affects FRP. The aim of this observational study was to investigate the relationship between FRP and kinematic parameters of the multi-segmental spine in NSCLBP patients. Forty NSCLBP patients and thirty-five asymptomatic participants performed a standing maximal trunk flexion task. Surface electromyography was recorded along the erector spinae longissimus. The kinematics of the spine were assessed using a 3D motion analysis system. The investigated spinal segments were upper thoracic, lower thoracic, thoracolumbar, upper lumbar, lower lumbar, and lumbopelvic. Upper lumbar ROM, anterior sagittal inclination of the upper lumbar relative to the lower lumbar in the upright position, and ROM of the upper lumbar relative to the lower lumbar during full trunk flexion were significantly correlated with the flexion relaxation ratio (Rho 0.42 to 0.58, p < 0.006). The relative position and movement of the upper lumbar segment seem to play an important role in the presence or absence of FRP in NSCLBP patients.

Muscular, temporal, and spatial responses to shoulder exosuit assistance during functional tasks.

Shoulder exosuits are a promising new technology that could enable individuals with neuromuscular impairments to independently perform activities of daily living, however, scarce evidence exists to evaluate their ability to support such activities. Consequently, it is not understood how humans adapt motion in response to assistance from a shoulder exosuit. In this study, we developed a cable-driven shoulder exosuit and evaluated its effect on reaching and drinking tasks within a cohort of 18 healthy subjects to quantify changes to muscle activity and kinematics as well as trial-to-trial learning in duration and actuator switch timing. The exosuit successfully reduced mean muscle activity in the middle (reaching: 23.4 ± 26.3%, drinking: 20.0 ± 25.1%) and posterior (reaching: 12.8 ± 10.3%, drinking: 4.0 ± 7.2%) deltoid across both functional tasks. Likewise, the exosuit reduced integrated muscle activity in the middle deltoid (reaching: 22.2 ± 22.7%, drinking: 14.9 ± 27.0%). Exosuit assistance also altered kinematics such that individuals allowed their arms to follow forces applied by the exosuit. In terms of learning, subjects reduced movement duration by 15.6 ± 11.9% as they practiced using the exosuit. Reducing movement duration allowed subjects to reduce integrated muscle activity in the anterior (15.2 ± 10.3%), middle (14.7 ± 9.7%), and posterior (14.8 ± 9.7%) deltoids. Similarly, subjects activated the actuator switch earlier over the course of many assisted trials. The muscle activity reductions during both reaching and drinking demonstrate the promise of shoulder exosuits to enable independent function among individuals with neuromuscular impairments. The kinematic response to assistance and learning features observed in movement duration provide insight into human-exosuit interaction principles that could inform future exosuit development.NEW & NOTEWORTHY Shoulder exosuits assist arm function, but it is not understood how assistance affects motion. We evaluated spatiotemporal movement features and muscle activity during assisted and unassisted arm motions. Introducing the exosuit caused individuals to let their arms follow assistive forces. Furthermore, individuals learned to use the exosuit with practice by moving more quickly to reduce cumulative effort and by activating assistance earlier. These results demonstrate that individuals adapt exosuit-assisted motion to reduce effort.

Comparison of muscle activity in school students while carrying backpacks and trolley bags.

Trolley bags have gained popularity among students, but there is limited research comparing them to backpack-style school bags. This study aimed to compare how carrying a backpack versus a trolley bag affects the activity of trunk and lower limb muscles in secondary school students. Electromyographic activity was measured in 25 students (13.4±1.1 years) as they walked on level ground and up/down stairs while carrying both types of bags. The activity of the gastrocnemius, tibialis anterior, semitendinosus, rectus femoris, lumbar erector spinae, and rectus abdominis muscles was assessed on both the dominant and non-dominant sides. The study found significantly reduced muscle activation in most of the targeted muscles when walking on level ground with the trolley bag and when going up/down stairs with the backpack. Lifting a trolley bag depends on the slope of the walking surface and is more efficient on level ground, while carrying a backpack is more efficient when going up and down stairs. Since it is not practical to switch bags when encountering stairs in schools, a bag with a mixed model design incorporating features of both trolley and backpack may be more beneficial and practical for students to use. Students, parents, and teachers should be aware of the injury risks associated with carrying different types of bags.

Assessment of Sleep Quality and Duration of Medical Students in Enugu State College of Medicine

Sleep is a physiological behaviour that occurs in all animal species forming about one – third of human life and is essential for survival. Prolonged sleep deprivation leads to severe physical impairment usually accompanied by cognitive loss and can even lead to death. Sleep is a naturally recurring state of mind and body, characterized by relatively inhibited sensory activity and reduced interactions with surroundings, altered consciousness, reduced muscle activity and inhibition of nearly all voluntary eye muscles. Therefore, this study is aimed at investigating the impact of various sleep duration among students and the effect on their academic performance. Using a simple random method of sampling, questionnaires were physically distributed among medicine and surgery students of ESUT College of medicine and 265 students participated. Statistical analysis was done using the Statistical Package for the Social Sciences (SPSS) version 23 (SPSS Inc., Chicago, IL) with a value of &lt;0.05 considered significant. From the analysis of the data retrieved from the questionnaire, it was observed that during a regular school week, majority of students (27.5%) obtained 6 hours of sleep, while the night prior to an examination, of students (27.9%) obtained 4 hours of sleep. Also, 68.7% of students believe that insufficient sleep has a negative impact on memory consolidation, while 31.3% believes otherwise. In conclusion from the results, the study suggests that students should be educated regarding good sleep hygiene practices as this has a positive effect on their academic performance. Keywords: Sleep Quality, Duration and Medical Students

Threshold and Standard Error of Measurement for Relative Rest Time of Pericervical Muscles During Prolonged Computer-Typing Tasks in Individuals With Neck Symptoms.

Introduction The most common work-related musculoskeletal disorder worldwide is neck pain, especially among individuals who extensively use computers in a seated position. One biomedical cause of this neck pain is the prolonged activity of the muscles around the neck. Electromyography (EMG) has been used to evaluate the frequency and intensity of muscle activity. "Relative rest time (RRT)" is an index derived indicating the proportion of time below a certain threshold to the total task time. This study aimed to investigate the measurement errors and minimum detectable change (MDC) of RRT of the pericervical muscles during prolonged typing tasks in individuals with neck symptoms and to examine the differences in measurement errors at 3 µV and 6 µV thresholds. Methods This test-retest reliability study was conducted twice with a one-week interval to examine measurement errors of the RRT using surface EMG. The number of participants was set to 30 subjects who had neck symptoms with a Neck Disability Index of 16% or higher. The primary outcome measure was RRT of the following: the pericervical muscles of the right side during a 60-minute typing task; the splenius capitis muscle, upper trapezius (UT) muscle, middle trapezius muscle, sternocleidomastoid muscle, serratus anterior muscle, longissimus muscle, and pectoralis major muscle. RRT was calculated as the percentage of time that muscle activity was below the threshold for more than 0.250 seconds continuously during a 60-minute typing task. The standard error of measurement (SEM) and MDC were calculated with the two thresholds of 3 µV and 6 µV. The SEMs of the two thresholds were compared using a paired method. Results Ultimately, the data of 26 participants were analyzed. The SEM (MDC) values of the RRT at the 3 µV and 6 µV thresholds were 19.22 (53.27) and 9.52 (26.39) for the splenius capitis muscle, 3.24 (8.97) and 0.38 (1.05) for the sternocleidomastoid muscle, 15.47 (42.88) and 18.79 (52.08) for the UT muscle, 21.28 (58.99) and 2.28 (6.32) for the middle trapezius muscle, 13.67 (37.90) and 11.64 (32.27) for the serratus anterior muscle, 16.81 (46.60) and 3.32 (9.20) for the longissimus muscle, and 8.97 (24.87) and 4.24 (11.74) for the pectoralis major muscle, respectively. The SEMs of the RRT with the 6 µV threshold were statistically significantly lower than those with the 3 µV threshold in all pericervical muscles, except for the UT muscle. Conclusion This study identified the SEM and MDC of the RRT for the pericervical muscles during prolonged typing tasks in individuals with neck symptoms. Except for the UT muscle, the SEMs of the RRT with the 6 µV threshold were statistically smaller than those with the 3 µV threshold. Therefore, when using the RRT in intervention studies that aim to reduce muscle activity during typing in those with neck symptoms, the 6 µV threshold measurement would be recommended for the RRT of the pericervical muscles except for the UT muscle.

An Ergonomic Golf Grip Leads to Lower Forearm Muscle Activity - A Prospective Case Series of 30 Right-Handed Amateur and Professional Golfers

BackgroundThe elbow is a common site for overuse injuries in golfers. Tendinopathies, such as medial and lateral epicondylitis, are frequently diagnosed in amateur and professional golfers. The aim of our study was to determine the effect of an ergonomic golf grip on forearm muscle activity during the five phases of the golf swing.MethodsThirty right-handed golfers with a mean age of 32 years (range, 18–70 years) and a mean handicap of 15 (range, 0–43) performed 10 golf swings with a standard and ergonomic golf grip respectively. The mean and maximum muscle activity of the Musculus (M.) extensor carpi radialis brevis (ECRB), M. flexor carpi ulnaris (FCU), M. pronator teres (PT) and M. biceps brachii (BB) of the lead and trail arms were assessed during the five phases of the golf swing using surface electromyography (EMG). Subgroup analyses were performed regarding sex, playing ability (handicap < 10 vs. ≥10), weekly playing time (≤ 5 h, 5–20 h, > 20 h) and preexisting elbow pain during golfing (VAS < 2 vs. VAS ≥ 2). Significance was set at p < 0.05.ResultsAn ergonomic golf grip resulted in a reduction in muscle activity in at least one but up to three consecutive phases of the golf swing for the ECRB, FCU and PT of the lead arm and for the PT of the trail arm. Amateurs, a playing time < 20 h per week and golfers without preexisting elbow pain were factors that were associated with greater reductions in muscle activity.ConclusionForearm muscle activity can be decreased using an ergonomic golf grip, indicating the possible role of an ergonomic golf grip as a preventive measure against overuse syndromes such as medial and lateral epicondylitis.Trial registration numberThis study was retrospectively registered at the German Clinical Trials Register DRKS-ID: DRKS00033732 (01/03/2024).

EMG Activity of Lower Limb Muscles during Anti-Gravity Treadmill Running with Different Loads and Speeds

The study’s objective was to identify the features of internal movement structure that depend on speed and the importance of unloading when jogging on an anti-gravity treadmill. The aim was to investigate whether the internal structure of running changes under unloaded conditions, using an anti-gravity treadmill. Twenty male competitive middle- and long-distance runners with the following characteristics participated in the study: age, 25 ± 5 years; body weight, 67.2 ± 8.9 kg; body height, 177 ± 11 cm; and training experience, 9 ± 5 years. The gastrocnemius (GC), tibialis anterior (T), quadriceps femoris (Q), biceps femoris (B), and gluteus (G) were the five lower limb muscles whose muscle activity was evaluated. Surface electromyography (sEMG) was used to measure muscle activation while jogging and running on the AlterG Anti-Gravity Treadmill. The study method involved capturing the examined muscular activity at four different speeds: 6, 10, 14, and 18 km/h. At each of these speeds, four two-minute measurements were taken with varying body weight relief: 100%, 75%, 50%, and 25% of body weight. Repeated measures multivariate analysis of variance (RM-MANOVA) [F = 3.4663 p = 0.0001] showed that as running speed increases, the muscular activity of each muscle, expressed as a percentage of maximum muscle tension (%MVIC), decreases significantly. Results indicate that running pace affects the dynamics of the reduction in muscle activity in every examined muscle. As one runs faster, the decline in dynamics becomes more intense. At the slowest jogging pace (6 km/h), the variations were almost negligible (±4 percentage points between 25% and 100% body weight relief) as unloading increased. However, the discrepancies reached up to 14 percentage points at the fastest running speed (18 km/h). In every muscle studied, distinctive patterns and significant dynamics at high speeds were observed. The study’s findings suggest that using an anti-gravity treadmill for training can be beneficial, yet it is important to consider the significant relationships between speed and relief, as these variables could impact maintaining a proper movement pattern and running style. This knowledge may be useful when choosing the right training regimens and loads for runners recovering from injuries.

The Antigravity Treadmill as a Postoperative and Injury Rehabilitation Tool: Reduction in Contact Forces and Muscle Activity With Reduced Weight Running.

To investigate the effects of reduced weight running on the antigravity (AG) treadmill on maintenance of normal muscle activation and reduction of plantar forces in healthy subjects. Descriptive laboratory study. Clinical sports medicine center. Twenty healthy subjects (10 male and 10 female) aged 18 to 29 years. Subjects running at 6.5 miles per hour on a standard treadmill and on the AG treadmill at 100%, 90%, 80%, 70%, 60%, and 50% of bodyweight levels. Dynamic plantar loading data were recorded using pressure insoles. Surface electromyography electrodes with imbedded accelerometers were used to estimate timing and magnitude of muscle activity, stride length, and cadence. There was a significant, sequential reduction in peak pressure, maximum force, and force time integral (FTI) with decreasing bodyweight. A 50% bodyweight reduction resulted in a 51% reduction in maximum force and a 59% reduction in FTI in the heel, as compared with 19% to 28% at the metatarsal heads. There was reduced contact area in the heel and midfoot at and below 70% BW. Lower limb muscle activity decreases with reduced bodyweight while maintain normal muscle recruitment timing. The AG treadmill provides a reduction in loading forces while maintaining normal muscle recruitment patterns. Decreased BW running preferentially unloads the hindfoot. The AG treadmill can be an effective rehabilitation tool following foot or ankle injury and may prove superior to other limited weight-bearing methods.

Sex differences in cervical disc height and neck muscle activation during manipulation of external load from helmets.

Neck pain associated with helmet-wear is an occupational health problem often observed in helicopter pilots and aircrew. Whether aircrew helmet wearing is associated with physiological and biomechanical differences between sexes is currently unknown. This study investigated neuromuscular activation patterns during different helmet-wearing conditions. The helmet load was manipulated through a novel Helmet Balancing System (HBS) in healthy, non-pilot male and female participants (n=10 each, age 19-45years) in two phases. Phase A assessed the acute effects of helmet-wear on neck muscles activation during head movements. Phase B examined changes in muscle activity and cervical disc height after wearing a helmet for 45 min. In Phase A, muscle activity was similar between sexes in many movements, but it was higher in female participants when wearing a helmet than in males. The HBS reduced muscle activity in both sexes. In Phase B, female participants exhibited a greater level of muscular fatigue, and male participants' cervical disc height was significantly decreased [5.7 (1.4) vs. 4.4 (1.5)mm, P<0.001] after continuous wearing. Both sexes showed no significant change in muscle fatigue and disc height [male: 5.0 (1.3) vs. 5.2 (1.4)mm, P=0.604] after applying HBS. These findings demonstrate sex-specific physiological and biomechanical responses to wearing a helmet. They may indicate different postural and motor control strategies, associated with different neck pain aetiologies in male and female aircrew, the knowledge of which is important to reduce or prevent musculoskeletal injuries associated with helmet wearing.

Evaluation of a passive back-support exoskeleton during in-bed patient handling tasks

This study evaluated the effects of a back-support exoskeleton on the trunk and hip joint angles, lower back muscle activity and heart rate during four patient handling tasks: assisting a patient from sitting to lying, laterally repositioning the patient and turning the patient in two directions. Eight participants performed these tasks with and without the exoskeleton. Results demonstrated a significant reduction in the lower back muscle activity, but less pronounced effects for other tasks involving minimal trunk flexion. Hip flexion angles were reduced for all tasks when the exoskeleton was worn. The amount of reduction in the muscle activity and changes in the trunk and hip angles varied by task. The exoskeleton did not affect the heart rate across all tasks. The exoskeleton appeared to be more effective in tasks requiring substantial trunk flexion, indicating its potential benefits for reducing lower back muscle strain during such activities.

Conditional nmy-1 and nmy-2 alleles establish that nonmuscle myosins are required for late Caenorhabditis elegans embryonic elongation.

The elongation of Caenorhabditis elegans embryos allows examination of mechanical interactions between adjacent tissues. Muscle contractions during late elongation induce the remodeling of epidermal circumferential actin filaments through mechanotransduction. Force inputs from the muscles deform circumferential epidermal actin filament, which causes them to be severed, eventually reformed, and shortened. This squeezing force drives embryonic elongation. We investigated the possible role of the nonmuscle myosins NMY-1 and NMY-2 in this process using nmy-1 and nmy-2 thermosensitive alleles. Our findings show these myosins act redundantly in late elongation, since double nmy-2(ts); nmy-1(ts) mutants immediately stop elongation when raised to 25°C. Their inactivation does not reduce muscle activity, as measured from epidermis deformation, suggesting that they are directly involved in the multistep process of epidermal remodeling. Furthermore, NMY-1 and NMY-2 inactivation is reversible when embryos are kept at the nonpermissive temperature for a few hours. However, after longer exposure to 25°C double mutant embryos fail to resume elongation, presumably because NMY-1 was seen to form protein aggregates. We propose that the two C. elegans nonmuscle myosin II act during actin remodeling either to bring severed ends or hold them.

Evaluation of a passive wearable arm ExoNET.

Wearable ExoNETs offer a novel, wearable solution to support and facilitate upper extremity gravity compensation in healthy, unimpaired individuals. In this study, we investigated the safety and feasibility of gravity compensating ExoNETs on 10 healthy, unimpaired individuals across a series of tasks, including activities of daily living and resistance exercises. The direct muscle activity and kinematic effects of gravity compensation were compared to a sham control and no device control. Mixed effects analysis revealed significant reductions in muscle activity at the biceps, triceps and medial deltoids with effect sizes of -3.6%, -4.5%, and -7.2% rmsMVC, respectively, during gravity support. There were no significant changes in movement kinematics as evidenced by minimal change in coverage metrics at the wrist. These findings reveal the potential for the ExoNET to serve as an alternative to existing bulky and encumbering devices in post-stroke rehabilitation settings and pave the way for future clinical trials.

The effect of clear aligner treatment on masticatory muscles (masseter, temporalis) activity in adults: a systematic review and meta-analysis.

The use of clear aligners is becoming more common for aesthetic orthodontic treatment, but there are still concerns about how they affect mastication biomechanics in the short and long term. The clear aligners treatment (CAT) mechanism changes the position of the mandible and maxilla, especially impacting the masseter muscle. Surface electromyography (sEMG) proves to be a useful method to evaluate masticatory muscle activity (MMA). To analyze the effect of clear aligners treatment on alterations in masticatory muscles (masseter, temporalis) using surface electromyography. Five databases (PubMed, Web of Science, SCOPUS, Cochrane Library, and Google Scholar) were searched up to March 2024. Studies in which MMA was evaluated after the installation of orthodontic clear aligners. Screening, data extraction, and quality assessments were performed by four investigators independently. The data, which evaluated temporalis and masseter muscle characteristics during CAT using surface electromyography, was extracted, and the quality of the studies was evaluated. The risk of bias was assessed using the Newcastle-Ottawa Scale (NOS). Six studies (two prospective cohort studies, three observational longitudinal studies, and one observational longitudinal case-control study) with low and moderate risk of bias were included in the qualitative synthesis. Six of these were also included in the meta-analysis. Our study investigated the dynamics of masseter and temporalis muscle activity during CAT. The results show that during maximal voluntary clenching, the masseter muscle demonstrated a significant initial increase (P < .05) followed by a subsequent non-significant decrease. It also showed that submaximal voluntary clenching consistently exhibited a significant reduction in muscle activity throughout the study period (P < .01). Assessment of muscle activity at the mandibular resting position revealed a variety of responses, with some participants showing a significant increase while others exhibited non-significant changes (P < .05, P > .05, respectively). However, the meta-analysis showed a non-significant difference in measuring masseter and temporalis muscles activity during CAT. Based on existing evidence, it is reasonable to conclude that CAT affected MMA. During maximal voluntary clenching, masseter muscle activity initially increased but later decreased, while temporalis muscle activity showed mixed results. Submaximal voluntary clenching revealed a consistent decrease in muscle activity over time. Mandibular resting position assessments showed both increases and no significant changes in muscle activity. However, the existing literature is insufficient to draw concrete conclusions; therefore, well-conducted further research is needed to confirm this statement. This systematic review and meta-analysis were registered in the International Prospective Register of Systematic Reviews (PROSPERO CRD42024522231).

A portable inflatable soft wearable robot to assist the shoulder during industrial work.

Repetitive overhead tasks during factory work can cause shoulder injuries resulting in impaired health and productivity loss. Soft wearable upper extremity robots have the potential to be effective injury prevention tools with minimal restrictions using soft materials and active controls. We present the design and evaluation of a portable inflatable shoulder wearable robot for assisting industrial workers during shoulder-elevated tasks. The robot is worn like a shirt with integrated textile pneumatic actuators, inertial measurement units, and a portable actuation unit. It can provide up to 6.6 newton-meters of torque to support the shoulder and cycle assistance on and off at six times per minute. From human participant evaluations during simulated industrial tasks, the robot reduced agonist muscle activities (anterior, middle, and posterior deltoids and biceps brachii) by up to 40% with slight changes in joint angles of less than 7% range of motion while not increasing antagonistic muscle activity (latissimus dorsi) in current sample size. Comparison of controller parameters further highlighted that higher assistance magnitude and earlier assistance timing resulted in statistically significant muscle activity reductions. During a task circuit with dynamic transitions among the tasks, the kinematics-based controller of the robot showed robustness to misinflations (96% true negative rate and 91% true positive rate), indicating minimal disturbances to the user when assistance was not required. A preliminary evaluation of a pressure modulation profile also highlighted a trade-off between user perception and hardware demands. Finally, five automotive factory workers used the robot in a pilot manufacturing area and provided feedback.

Preliminary Testing of a Passive Exoskeleton Prototype Based on McKibben Muscles

Upper-limb exoskeletons for industrial applications can enhance the comfort and productivity of workers by reducing muscle activity and intra-articular forces during overhead work. Current devices typically employ a spring-based mechanism to balance the gravitational torque acting on the shoulder. As an alternative, this paper presents the design of a passive upper-limb exoskeleton based on McKibben artificial muscles. The interaction forces between the exoskeleton and the user, as well as the mechanical resistance of the exoskeleton structure, were investigated to finalize the design of the device prior to its prototyping. Details are provided about the solutions adopted to assemble, wear, and regulate the exoskeleton’s structure. The first version of the device weighing about 5.5 kg was manufactured and tested by two users in a motion analysis laboratory. The results of this study highlight that the exoskeleton can effectively reduce the activation level of shoulder muscles without affecting the lumbar strain.

Lower face contouring through botulinum toxin therapy: an overview

Botulinum toxin (Botox) has been used cosmetically to reduce and prevent wrinkles since 1989, but its application has since expanded to include treatment of other patient concerns, including masseter muscle hypertrophy. Abnormal enlargement of the masseter, a muscle located in the jaw, can give patients a larger or squarish facial appearance; the injection of Botox, through causing temporary paralysis of the masseter and a resultant reduction in muscle activity, can lead to a slimmer and less square jawline. However, careful patient selection is required, and approaches to injection technique and dosage vary. Francesca Ramadan provides an overview.