scholarly journals Effect of Computer Keyboard Slope on Wrist Position and Forearm Electromyography of Typists Without Musculoskeletal Disorders

2003 ◽  
Vol 83 (9) ◽  
pp. 816-830 ◽  
Author(s):  
Guy G Simoneau ◽  
Richard W Marklin ◽  
Joseph E Berman
Keyword(s):  
Carpal Tunnel ◽  
Physical Therapists ◽  
Maximum Voluntary Contraction ◽  
Slope Angle ◽  
Voluntary Contraction ◽  
Emg Activity ◽  
Electromyographic Activity ◽  
Wrist Extension ◽  
Computer Keyboard ◽  
Downward Slope

Background and Purpose. Positioning a computer keyboard with a downward slope reduces wrist extension needed to use the keyboard and has been shown to decrease pressure in the carpal tunnel. However, whether a downward slope of the keyboard reduces electromyographic (EMG) activity of the forearm muscles, in particular the wrist extensors, is not known. Subjects and Methods. Sixteen experienced typists participated in this study and typed on a conventional keyboard that was placed on slopes at angles of 7.5, 0, −7.5, and −15 degrees. Electromyographic activity of the extensor carpi ulnaris (ECU), flexor carpi ulnaris (FCU), and flexor carpi radialis (FCR) muscles was measured with surface electrodes, while the extension and ulnar deviation angles of the right and left wrists were measured with electrogoniometers. Results. Wrist extension angle decreased from approximately 12 degrees of extension while typing on a keyboard with a 7.5-degree slope to 3 degrees of flexion with the keyboard at a slope of −15 degrees. Although the differences were in the range of 1% to 3% of maximum voluntary contraction (MVC), amplitude probability distribution function (APDF) of root-mean-square EMG data points from the ECU, FCU, and FCR muscles varied across keyboard slopes. Discussion and Conclusion. Wrist extension decreased as the keyboard slope decreased. Furthermore, a slight decrease in percentage of MVC of the ECU muscle was noted as the keyboard slope decreased. Based on biomechanical modeling and published work on carpal tunnel pressure, both of these findings appear to be positive with respect to comfort and fatigue, but the exact consequences of these findings on the reduction or prevention of injuries have yet to be determined. The results may aid physical therapists and ergonomists in their evaluations of computer keyboard workstations and in making recommendations for interventions with regard to keyboard slope angle.

scholarly journals External torque as a factor to modify load in abdominal curl-up exercises

2015 ◽  
Vol 7 (1) ◽  
Author(s):  
Alicja Rutkowska-Kucharska ◽  
Agnieszka Szpala
Keyword(s):  
External Force ◽  
Maximum Voluntary Contraction ◽  
Voluntary Contraction ◽  
Emg Activity ◽  
Electromyographic Activity ◽  
Upper Limbs ◽  
External Torque ◽  
Lever Arm ◽  
Emg Signal ◽  
Ca 50

SummaryStudy aim: the aim of our study was to evaluate electromyography (EMG) activity in exercises where the load to the muscles is determined by the external torque. In a part of the exercises, we changed the value of the external force, while in the other we modified the length of the lever arm at which the force was applied.Material and methods: the study was carried out on a group of 12 subjects (21 ± 2 years, 61 ± 4.8 mass, 172 ± 5 cm height). Electromyographic activity of the rectus abdominis (RA) muscle was evaluated by recording the EMG signal. The length of the lever arm of the external force was changed by using four different positions of the upper limbs, whereas the magnitude of the external force was changed through adding the weights of 0.5, 1.0, and 1.5 kg. The data recorded were normalized with respect to EMG activity measured under maximum voluntary contraction (MVC) conditions.Results: it was found that the change of the lever arm at which the force was applied (any change in the position of the upper limbs) causes a change in EMG activity in each part of the RA muscle from ca. 50% to ca. 100% MVC (p < 0.001). Further, the change in the external load changes statistically significantly the EMG activity only in the left upper part of the RA muscle (p < 0.05).Conclusions: activity in the RA muscle that increased for longer lever arms of the external force, offers opportunities for changing the load used during the exercise in a manner that is safe for the vertebral column.

scholarly journals Electromyographic Activity of Masseter and Temporal Muscles with Different Facial Types

2009 ◽  
Vol 79 (3) ◽  
pp. 515-520 ◽  
Author(s):  
Michelle Santos Vianna-Lara ◽  
Paulo Henrique Ferreira Caria ◽  
Darcyde Oliveira Tosello ◽  
Flávio Lara ◽  
Maise Mendonça Amorim
Keyword(s):  
Statistical Tests ◽  
Maximum Voluntary Contraction ◽  
Voluntary Contraction ◽  
Emg Activity ◽  
Electromyographic Activity ◽  
Anterior Portion ◽  
Temporal Muscle ◽  
Homogeneity Of Variance ◽  
The Right ◽  
Facial Types

Abstract Objectives: To compare the electromyographic (EMG) activity of the masseter and anterior portion of temporal muscles in different vertical facial types. Materials and Methods: Clinical examination, cephalometric analysis, and electromyographic examination were performed in 44 volunteers ranging from 18 to 35 years old. The volunteers were classified on the basis of their vertical facial characteristics into three groups—brachyfacial, mesofacial, and dolicofacial—by the grouping analysis. The EMG records were obtained with three repetitions during mandibular rest, maximum voluntary contraction in intercuspidation, and simultaneous bilateral isotonic contraction. The Kolmogorov-Smirnov and Levene tests were applied to verify the normality and homogeneity of variance. Analysis of variance and the Kruskal-Wallis test identified statistical differences among groups that did not present normality and homogeneity of distribution, respectively. Significance for all statistical tests was set at P &lt; .05. Results: At rest, only the right temporal and masseter muscles presented statistically significant differences among the groups. The differences were observed between groups 1 and 2 (P = .02) and 1 and 3 (P = .038) for the right temporal muscle, and between groups 1 and 2 (P = .029) for the right masseter muscle. Generally, group 1 presented the lowest EMG values for the four muscles evaluated during rest. For isotonic evaluation, none of the groups of muscles presented statistically significant differences. Conclusion: Different vertical facial types do not determine distinct patterns of EMG activity for the masseter and anterior portion of temporal muscles during rest and bilateral mastication.

Reflex Inhibition of Normal Cramp Following Electrical Stimulation of the Muscle Tendon

2007 ◽  
Vol 98 (3) ◽  
pp. 1102-1107 ◽  
Author(s):  
Serajul I. Khan ◽  
John A. Burne
Keyword(s):  
Electrical Stimulation ◽  
Maximum Voluntary Contraction ◽  
Voluntary Contraction ◽  
Muscle Cramp ◽  
Emg Activity ◽  
Reflex Inhibition ◽  
Experimental Conditions ◽  
Inhibitory Feedback ◽  
Two Phases ◽  
Stimulation Of

Muscle cramp was induced in one head of the gastrocnemius muscle (GA) in eight of thirteen subjects using maximum voluntary contraction when the muscle was in the shortened position. Cramp in GA was painful, involuntary, and localized. Induction of cramp was indicated by the presence of electromyographic (EMG) activity in one head of GA while the other head remained silent. In all cramping subjects, reflex inhibition of cramp electrical activity was observed following Achilles tendon electrical stimulation and they all reported subjective relief of cramp. Thus muscle cramp can be inhibited by stimulation of tendon afferents in the cramped muscle. When the inhibition of cramp-generated EMG and voluntary EMG was compared at similar mean EMG levels, the area and timing of the two phases of inhibition (I1, I2) did not differ significantly. This strongly suggests that the same reflex pathway was the source of the inhibition in both cases. Thus the cramp-generated EMG is also likely to be driven by spinal synaptic input to the motorneurons. We have found that the muscle conditions that appear necessary to facilitate cramp, a near to maximal contraction of the shortened muscle, are also the conditions that render the inhibition generated by tendon afferents ineffective. When the strength of tendon inhibition in cramping subjects was compared with that in subjects that failed to cramp, it was found to be significantly weaker under the same experimental conditions. It is likely that reduced inhibitory feedback from tendon afferents has an important role in generating cramp.

Activation varies among the knee extensor muscles during a submaximal fatiguing contraction in the seated and supine postures

2003 ◽  
Vol 95 (4) ◽  
pp. 1515-1522 ◽  
Author(s):  
L Rochette ◽  
S. K. Hunter ◽  
N Place ◽  
R Lepers
Keyword(s):  
Vastus Lateralis ◽  
Maximum Voluntary Contraction ◽  
Knee Extensor ◽  
Voluntary Contraction ◽  
Emg Activity ◽  
Task Failure ◽  
Rate Of Increase ◽  
Extensor Muscles ◽  
Seated Posture ◽  
Knee Extensor Muscles

Ten young men sustained an isometric contraction of the knee extensor muscles at 20% of the maximum voluntary contraction (MVC) torque on three separate occasions in a seated posture. Subjects performed an isometric knee extension contraction on a fourth occasion in a supine posture. The time to task failure for the seated posture was similar across sessions (291 ± 84 s; P > 0.05), and the MVC torque was similarly reduced across sessions after the fatiguing contraction (42 ± 12%). The rate of increase in electromyograph (EMG) activity (%MVC) and torque fluctuations during the fatiguing contractions were similar across sessions. However, the rate of increase in EMG differed among the knee extensor muscles: the rectus femoris began at a greater amplitude (31.5 ± 11.0%) compared with the vastus lateralis and vastus medialis muscles (18.8 ± 5.3%), but it ended at a similar value (45.4 ± 3.1%). The time to task failure and increase in EMG activity were similar for the seated and supine tasks; however, the reduction in MVC torque was greater for the seated posture. These findings indicate that the time to task failure for the knee extensor muscles that have a common tendon insertion did not alter over repeat sessions as had been observed for the elbow flexor muscles (Hunter SK and Enoka RM. J Appl Physiol 94: 108-118, 2003).

scholarly journals Crossfit Practice: An Electromyographic Analysis of Masticatory Muscles

2020 ◽  
Author(s):  
Nayara Soares da Silva ◽  
Marcelo Palinkas ◽  
Evandro Marianetti Fioco ◽  
Edson Donizetti Verri ◽  
Saulo César Vallin Fabrin ◽  
...  
Keyword(s):  
Maximum Voluntary Contraction ◽  
Masticatory Muscles ◽  
Voluntary Contraction ◽  
Control Group ◽  
Electromyographic Activity ◽  
Physical Conditioning ◽  
Striated Muscles ◽  
Functional Changes ◽  
Significant Difference ◽  
The Impact

Abstract Background: CrossFit is a regular high-intensity physical conditioning exercise for skeletal striated muscles, which promotes functional changes in the human body. The aim of this study was to investigate the impact of CrossFit exercise on the electromyographic activity of the masseter and temporalis muscles. Methods: Forty participants were divided into two groups: athletes who practiced CrossFit (n=20) and controls who did not practice sports (n=20). The electromyographic activities of the masseter and temporalis muscles were measured using mandibular tasks at rest, protrusion, right laterality, left laterality, and dental clenching in maximum voluntary contraction and habitual chewing of peanuts and raisins. Both the groups were matched for age, sex, and body mass index. The data were analyzed using the t-test with a 5% significance level. Results: Reduced electromyographic activities were found in all mandibular tasks in the CrossFit group than in the control group, with a significant difference for the right masseter (p=0.01), left masseter (p=0.001), and left temporal muscles (p=0.001) at mandibular rest; right (p=0.001) and left (p=0.001) masseter in chewing of peanuts. Conclusion: The results of this study suggest that CrossFit promotes positive changes in electromyographic activity of the masticatory muscles, especially in the mandibular rest and chewing of hard food. CrossFit exercise practiced within the appropriate technical protocols improves masticatory muscle function.

scholarly journals Effect of Breast Cancer Treatment on the Stomatognathic System

2018 ◽  
Vol 29 (4) ◽  
pp. 368-373
Author(s):  
Danilo Stefani Esposto ◽  
Marcelo Palinkas ◽  
Ligia Maria Napolitano Gonçalves ◽  
Paulo Batista de Vasconcelos ◽  
Vânia Tie Koga Ferreira ◽  
...  
Keyword(s):  
Breast Cancer ◽  
Standard Deviation ◽  
Maximum Voluntary Contraction ◽  
Muscle Thickness ◽  
Voluntary Contraction ◽  
Bite Force ◽  
Electromyographic Activity ◽  
Average Standard Deviation ◽  
Functional Changes ◽  
Unilateral Mastectomy

Abstract Breast cancer is the most common cancer affecting women in the world and provides functional changes in the human body. Evaluate women submitted to unilateral mastectomy, through electromyographic activity (mandibular rest, right and left laterality, protrusion, maximum voluntary contraction with and without Parafilm, habitual and non-habitual mastication) and thickness (rest and maximum voluntary contraction) of the right temporal muscle (RT), left temporal (LT), right masseter (RM) and left masseter (LM), also the molar bite force (right and left) and compare the data with healthy women. Material and Methods: 32 women were divided into two groups: unilateral mastectomy group (MG), average ± standard deviation 56.50±14.50 years (n=16) and without the disease group (CG), average ± standard deviation 56.56±14.15 years (n=16). The normalized electromyographic data, muscle thickness and maximal molar bite force were tabulated and submitted to statistical analysis (SPSS 21.0; student t test, p≤0.05). Significant statistical differences between MG and CG were found in right laterality, for RM (p=0.02); left laterality, for LT (p=0.01); chewing with peanuts, for RM (p=0.04); chewing with raisins, for LM (p=0.04) and right molar bite force (p=0.03). There was no statistically significant difference between MG and CG for muscle thickness. The results of this study suggest that women undergoing unilateral mastectomy may present functional changes, with emphasis on muscular hyperactivity, lower masticatory efficiency and lower maxillary bite force.

scholarly journals El impacto inicial con antepié incrementa la actividad muscular del gastrocnemios durante la carrera. Un estudio cuantitativo de actividad electromiográfica (The initial impact with forefoot increases the muscular activity of gastrocnemius during running)

Retos ◽  
2020 ◽  
pp. 271-275
Author(s):  
Oscar Valencia ◽  
Iver Cristi ◽  
Dario Ahumada ◽  
Keiny Meza ◽  
Rodrigo Salas ◽  
...  
Keyword(s):  
Lower Limb ◽  
Stance Phase ◽  
Maximum Voluntary Contraction ◽  
Neuromuscular Control ◽  
Voluntary Contraction ◽  
Medial Gastrocnemius ◽  
Emg Activity ◽  
Myoelectric Activity ◽  
Initial Contact ◽  
Limb Injuries

Un importante porcentaje de las lesiones de miembros inferiores ha sido vinculado a la técnica de carrera, en particular, al contacto inicial con retropié (RP) o antepié (AP). Sin embargo, existe limitada evidencia de la actividad electromiográfica (EMG) para ambas condiciones. El objetivo de este estudio fue comparar la amplitud EMG en miembros inferiores al utilizar técnicas de RP vs AP durante la carrera. Trece corredores fueron evaluado a una velocidad de trote autoseleccionada en dos condiciones: contacto inicial con RP y AP. Se registró la actividad mioeléctrica del recto femoral (RF), bíceps femoral (BF), tibial anterior (TA), gastrocnemio medial (GM) y lateral (GL). Se consideró la amplitud promedio de la EMG en 10 ciclos de carrera, normalizados a la contracción voluntaria máxima. Los resultados destacan una mayor activación significativa de los músculos GM y GL en el contacto AP durante la fase de apoyo, balanceo y en todo el ciclo de carrera. Adicionalmente, el TA presentó una mayor activación durante la fase de vuelo y el 100% del ciclo de carrera para la condición RP. No se encontraron otras diferencias significativas. En conclusión, el uso de la técnica AP incrementa la actividad muscular de GM y GL, posiblemente asociado a una mayor absorción del impacto durante la fase de apoyo. Por otro lado, el TA incrementa su actividad con RP, lo que podría implicar un mayor control previo al contacto inicial. La técnica de carrera se presenta como una condición modificable según situaciones de rendimiento o patología.Abstract. Running technique has an impact on lower limb injuries, particularly the initial contact pattern such as rearfoot (RF) or forefoot (FF). However, there is limited evidence of the electromyographic (EMG) activity for both conditions. The aim of this study was to compare the lower limb muscles EMG amplitude between RF and FF techniques during running. Thirteen runners were evaluated at a self-selected running speed under two conditions: initial contact with RF and FF. The myoelectric activity of the rectus femoris (RE), biceps femoris (BF), tibialis anterior (TA), medial gastrocnemius (GM) and lateral (GL) were analysed. The EMG amplitudes of 10 running cycles were averaged and normalized to the maximum voluntary contraction. The results included a significantly higher activation of GM and GL muscles for the FF condition during the stance phase, balance and the entire running cycle. In addition, TA showed higher activation during the swing phase and the 100% running cycle for the RP condition. No other significant differences were found. In conclusion, FF technique increases GM and GL myoelectric activity, possibly associated with a higher impact absorption during the stance phase. On the other hand, TA increases its activity for RF condition which may imply a greater neuromuscular control prior to initial contact. Finally, the running technique is presented as a modifiable condition which can be changed to enhance performance or in pathologic circumstances.

scholarly journals Electromyographic activity in patient with an inferior implant/tooth-supported overdenture: Clinical Case Report.

2016 ◽  
Vol 19 (2) ◽  
pp. 139
Author(s):  
Caroline Cotes ◽  
José Benedito Oliveira Amorim ◽  
Vanessa Macedo ◽  
Estevao Kimpara ◽  
Tarcísio Paes-Junior
Keyword(s):  
Case Report ◽  
Clinical Case ◽  
Good Condition ◽  
Maximum Voluntary Contraction ◽  
Voluntary Contraction ◽  
Electromyographic Activity ◽  
Masticatory Efficiency ◽  
Pre Treatment ◽  
Electrical Activities ◽  
Viable Treatment

<p>Clinicians can find patients with one mandibular remaining tooth, and it is difficult to decide if the tooth has to be removed. When a clinician decide to maintaining the tooth, it is common to feel doubts about masticatory load distribution divided between the tooth and implant. This paper reports a clinical case of patient with an implant/tooth-supported overdenture and elucidates the masticatory efficiency by electromyography activity analysis. The objective of this case report was to describe a clinical case of a patient with an implant/tooth-supported overdenture and to discuss the muscle response to this treatment. Electrical activities of the masseter and anterior temporal surfaces at maximum voluntary contraction were evaluated by electromyography during pre-treatment, immediately post-treatment, 15 and 60 days after installation. When patient has one remaining tooth in good condition, the implant/tooth-supported overdenture can be recommended, to preserve the periodontal ligament and proprioception, and to minimize bone loss. Electromyography analysis showed that implant/tooth-supported overdenture is a viable treatment alternative, in muscular standpoint, when the patient has a remaining tooth with good osseous support.</p>

scholarly journals Dependence of EMG Responses Evoked by Imposed Wrist Displacements on Pre-existing Activity in the Stretched Muscles

1984 ◽  
Vol 11 (2) ◽  
pp. 272-280 ◽  
Author(s):  
W. Bedingham ◽  
W.G. Tatton
Keyword(s):  
Background Activity ◽  
Human Subjects ◽  
Maximum Voluntary Contraction ◽  
Voluntary Contraction ◽  
Emg Activity ◽  
Onset Latency ◽  
Normal Human ◽  
Motoneuron Activity ◽  
Movement Parameters ◽  
The Relationship

ABSTRACT:The relationship between the segmented EMG activity in flexor carpi radialis evoked by imposed angular wrist displacement was studied with respect to the level of pre-existing background activity in 30 normal human subjects. Input-output response planes demonstrate that the magnitude of the Ml & M2-3 segments is dependent on both the displacement parameters and the level of pre-existing EMG activity in the stretched muscle. If the level of background activity exceeded 4-5% of the maximum voluntary contraction, the onset latency of the M1 segment and duration of the Ml and the M2-3 segments remained constant (within ± 2 msec) for different magnitudes of step load displacements, despite marked variation in the range of the displacement’s amplitude, duration, velocity, and acceleration. We propose that the dependency of the relationship between reflex magnitude and imposed movement parameters on tonic motoneuron activity, as represented by pre-existing EMG levels, may reflect an automatic adjustment mechanism that could be utilized in servo compensation of movements requiring markedly different force levels.

scholarly journals Electromyographic activity of masticatory muscles in women with osteoporosis

2009 ◽  
Vol 20 (3) ◽  
pp. 237-342 ◽  
Author(s):  
Selma Siéssere ◽  
Luiz Gustavo de Sousa ◽  
Naira de Albuquerque Lima ◽  
Marisa Semprini ◽  
Paulo Batista de Vasconcelos ◽  
...  
Keyword(s):  
Muscle Activation ◽  
Masticatory Muscles ◽  
Voluntary Contraction ◽  
Bite Force ◽  
Emg Activity ◽  
Electromyographic Activity ◽  
Stomatognathic System ◽  
Sample Data ◽  
Clinical Conditions ◽  
Skeletal Bone

The purpose of this study was to analyze the electromyographic (EMG) activity and the maximal molar bite force in women diagnosed with osteoporosis in the maxillary and mandibular regions, considering the habits and conditions that lead to development of generalized skeletal bone loss, including on face bones, can disturb the functional harmony of the stomatognathic system. Twenty-seven women with mandibular and maxillary osteoporosis and 27 healthy controls volunteered to participate in the study. A 5-channel electromyographer was used. Muscle activity was evaluated by means of EMG recordings of the masticatory musculature (masseter and temporalis muscles, bilaterally) during the following clinical conditions: rest (5 s); right and left lateral excursions (5 s); protrusion (5 s); maximal dental clenching on Parafilm™ (4 s) and maximal voluntary contraction (4 s). This latter clinical condition was used as the normalization factor of the sample data. It was observed that individuals with osteoporosis presented greater EMG activity when maintaining mandible posture conditions and less activity during dental clenching and when obtaining maximal molar bite force. It may be concluded that facial osteoporosis can interfere on the patterns of masticatory muscle activation and maximal bite force of the stomatognathic system.

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