Improving anterior deltoid activity in a musculoskeletal shoulder model - an analysis of the torque-feasible space at the sternoclavicular joint.

Modelling the shoulder's musculature is challenging given its mechanical and geometric complexity. The use of the ideal fibre model to represent a muscle's line of action cannot always faithfully represent the mechanical effect of each muscle, leading to considerable differences between model-estimated and in vivo measured muscle activity. While the musculo-tendon force coordination problem has been extensively analysed in terms of the cost function, only few works have investigated the existence and sensitivity of solutions to fibre topology. The goal of this paper is to present an analysis of the solution set using the concepts of torque-feasible space (TFS) and wrench-feasible space (WFS) from cable-driven robotics. A shoulder model is presented and a simple musculo-tendon force coordination problem is defined. The ideal fibre model for representing muscles is reviewed and the TFS and WFS are defined, leading to the necessary and sufficient conditions for the existence of a solution. The shoulder model's TFS is analysed to explain the lack of anterior deltoid (DLTa) activity. Based on the analysis, a modification of the model's muscle fibre geometry is proposed. The performance with and without the modification is assessed by solving the musculo-tendon force coordination problem for quasi-static abduction in the scapular plane. After the proposed modification, the DLTa reaches 20% of activation.

Electromyographic validation of basic exercises for physical conditioning programmes IV. Analysis of the deltoid muscle (anterior portion) and pectoralis major muscle (clavicular portion) in frontal-lateral cross, dumbbells exercises

The electromyographic activity of the shoulder muscles deltoid - anterior portion (DA) and pectoralis major - clavicular portion (PMC) was tested on 24 male volunteers using a 2 channel TEC A TE4 electromyograph and Hewlett Packard surface electrodes during the execution of four different modalities of frontal-lateral cross, dumbbells exercises. The results showed that all of the tested exercises developed high levels of action potential for both muscles. So, we jusfity the indication of all of them for physical fitness programmes for DA and PMC. Some suggestions to the use of the tested exercises are presented.

Electromyographic validation of basic exercises for physical conditioning programmes V. The comparison of the response in the deltoid muscle (anterior portion) and the pectoralis major muscle (clavicular portion) determined by the frontal-lateral cross, dumbbells and the rowing exercises

The action potential level for shoulder muscles deltoid-anterior portion (DA) and pectoralis major-clavicular portion (PMC) determined by four different modalities of execution of rowing exercises, each one with two different grips, was recorded. These were compared with the action potential level determined for the same muscles by four different modalities of execution of the frontal-lateral cross, dumbbells exercises. Twenty-four male volunteers were examined using a 2 channel TECA TE4 electromyograph and Hewlett Packard surface electrodes. The statistic analysis showed significant (p<0,05) superiority for all the frontal-lateral cross, dumbbells exercises in comparison to all rowing exercises for the PMC, for the DA this generalized supremacy was not observed.

Participation of the deltoid (anterior portion) and pectoralis major (clavicular portion) muscles in different modalities of supine and frontal elevation exercises with different grips

The muscles deltoid-anterior portion (DA) and pectoralis major-clavicular portion (PMC) were analysed to establish the muscular behavior and intensity patterns, as well to evaluate the connected participation of these muscles during supine and frontal elevation exercises. Twenty-four male volunteers were examined using a 2-channel TECA TE4 electromyograph and Hewlett Packard surface electrodes. Our results showed low levels of activity to PMC in frontal elevation exercises, whereas to DA the levels were very high. In the supine exercise, the action potential levels developed by the PMC were always lower than those presented by DA, however, with action simultaneity. Some suggestions to the use of the tested exercises are presented.

Electromyographic validation of the muscles deltoid (anterior portion) and pectoralis major (clavicular portion) in military press exercises with open grip

It was analized the deltoid muscle anterior portion and the pectoralis major clavicular portion in 24 male volunteers using a two-channel electromyograph TECA TE 4, and Hewllet Packard surface electrodes, in 4 modalities of military press exercises with open grip. The results showed high inactivity for PMC in almost all the modalities while DA developed very high levels of action potentials in all the modalities assessed.

Electromyographic validation of the muscles deltoid (anterior portion) and pectoralis major (clavicular portion) in military press exercises with middle grip

With the objective to know the electromyographic activity normal parameters of the deltoid (anterior portion) and pectoralis major (clavicular portion) muscles in the different modalities of military press exercises with middle grip, we analyzed 24 male volunteers using a two-channel electromyograph TECA TE 4, and Hewllet Packard surface electrodes. It was observed high inactivity levels for PMC in almost all the modalities and the concentration in the active cases, mainly, in the weak potential, while DA presented very high levels of much strong action potentials in all the modalities assessed.

Electromyographic validation of the deltoid (anterior portion) and pectoralis major (clavicular portion) in military press exercises with open and middle grips

The deltoid (anterior portion) and pectoralis major (clavicular portion) were evaluated in several execution ways of military press exercises with open and middle grips in order to know their behavior pattern. It was analyzed 24 male volunteers, using a 2-channel TECA TE4 electromyograph and Hewllet Packard surface electrodes. It was observed that the execution variation with open and middle grips does not present any significant difference as for the demanding level neither for the pectoralis major muscle nor the deltoid muscle.

Shoulder Muscular Activity During Isometric Three-Point Kneeling Exercise on Stable and Unstable Surfaces

The purpose of this study was to determine if performing isometric 3-point kneeling exercises on a Swiss ball influenced the isometric force output and EMG activities of the shoulder muscles when compared with performing the same exercises on a stable base of support. Twenty healthy adults performed the isometric 3-point kneeling exercises with the hand placed either on a stable surface or on a Swiss ball. Surface EMG was recorded from the posterior deltoid, pectoralis major, biceps brachii, triceps brachii, upper trapezius, and serratus anterior muscles using surface differential electrodes. All EMG data were reported as percentages of the average root mean square (RMS) values obtained in maximum voluntary contractions for each muscle studied. The highest load value was obtained during exercise on a stable surface. A significant increase was observed in the activation of glenohumeral muscles during exercises on a Swiss ball. However, there were no differences in EMG activities of the scapulothoracic muscles. These results suggest that exercises performed on unstable surfaces may provide muscular activity levels similar to those performed on stable surfaces, without the need to apply greater external loads to the musculoskeletal system. Therefore, exercises on unstable surfaces may be useful during the process of tissue regeneration.

Coactivation of the shoulder and arm muscles during closed kinetic chain exercises on an unstable surface

Introduction: The purpose of this study was to compare the electromyography index of muscle coactivation of the following muscle pairs: posterior deltoid and pectoralis major (PD/PM); triceps brachii and biceps brachii (TB/BB); and serratus anterior and upper trapezius (SA/UT) during three different closed kinetic chain exercises (wall-press, bench-press and push-up) on an unstable surface at the maximal load. Methods: A total of 20 healthy sedentary men participated in the study. Integral linear values were obtained from three sustained contractions of six seconds each for the three proposed exercises. Mean coactivation index values were compared using the mixed-effects linear model, with a five percent significance level. Results: Electromyography indexes of muscle coactivation showed significant differences for the PD/PM and TB/BB muscle pairs. No differences were found between exercises for the SA/UT muscle pair. Conclusion: Our results seem to differ from those of previous studies, which reported that the similarity in exercises performed is responsible for the comparable muscle activation levels.

Neuromuscular activity during bench press exercise performed with and without the preexhaustion method

Brennecke, A, Guimaraees, TM, Leone, R, Cadarci, M, Mochizuki, L, Simao, R, Amadio, AC, and Serrao, J. Neuromuscular activity during bench press exercise performed with and without the preexhaustion method. J Strength Cond Res 23(7): 1933-1940, 2009-The purpose of the present study was to investigate the effects of exercise order on the tonic and phasic characteristics of upper-body muscle activity during bench press exercise in trained subjects. The preexhaustion method involves working a muscle or a muscle group combining a single-joint exercise immediately followed by a multi-joint exercise (e. g., flying exercise followed by bench press exercise). Twelve subjects performed 1 set of bench press exercises with and without the preexhaustion method following 2 protocols (P1-flying before bench press; P2-bench press). Both exercises were performed at a load of 10 repetition maximum (10RM). Electromyography (EMG) sampled at 1 kHz was recorded from the pectoralis major (PM), anterior deltoid (DA), and triceps brachii (TB). Kinematic data (60 Hz) were synchronized to define upward and downward phases of exercise. No significant (p > 0.05) changes were seen in tonic control of PM and DA muscles between P1 and P2. However, TB tonic aspect of neurophysiologic behavior of motor units was significantly higher (p < 0.05) during P1. Moreover, phasic control of PM, DA, and TB muscles were not affected (p > 0.05). The kinematic pattern of movement changed as a result of muscular weakness in P1. Angular velocity of the right shoulder performed during the upward phase of the bench press exercise was significantly slower (p < 0.05) during P1. Our results suggest that the strategies set by the central nervous system to provide the performance required by the exercise are held constant throughout the exercise, but the tonic aspects of the central drive are increased so as to adapt to the progressive occurrence of the neuromuscular fatigue. Changes in tonic control as a result of the muscular weakness and fatigue can cause changes in movement techniques. These changes may be related to limited ability to control mechanical loads and mechanical energy transmission to joints and passive structures.

Contraction of the human diaphragm during rapid postural adjustments

1. The response of the diaphragm to the postural perturbation produced by rapid flexion of the shoulder to a visual stimulus was evaluated in standing subjects. Gastric, oesophageal and transdiaphragmatic pressures were measured together with intramuscular and oesophageal recordings of electromyographic activity (EMG) in the diaphragm. To assess the mechanics of contraction of the diaphragm, dynamic changes in the length of the diaphragm were measured with ultrasonography. 2. With rapid flexion of the shoulder in response to a visual stimulus, EMG-activity in the costal and crural diaphragm occurred about 20 ms prior to the onset of deltoid EMG. This anticipatory contraction occurred irrespective of the phase of respiration in which arm movement began. The onset of diaphragm EMG-coincided with that of transversus abdominis. 3. Gastric and transdiaphragmatic pressures increased in association with the rapid arm flexion by 13.8 +/- 1.9 (mean +/- S.E.M.) and 13.5 +/- 1.8 cmH(2)O, respectively. The increases occurred 49 +/- 4 ms after the onset of diaphragm EMG, but preceded the onset of movement of the limb by 63 +/- 7 ms. 4. Ultrasonographic measurements revealed that the costal diaphragm shortened and then lengthened progressively during the increase in transdiaphragmatic pressure. 5. This study provides definitive evidence that the human diaphragm is involved in the control of postural stability during sudden voluntary movement of the limbs.

Activation of the human diaphragm during a repetitive postural task

1. The co-ordination between respiratory and postural functions of the diaphragm was investigated during repetitive upper Limb movement. It was hypothesised that diaphragm activity would occur either tonically or phasically in association with the forces from each movement and that this activity would combine with phasic respiratory activity. 2. Movements of the upper limb and ribcage were measured while standing subjects performed repetitive upper limb movements 'as fast as possible'. Electromyographic (EMG) recordings of the costal diaphragm were made using intramuscular electrodes in four subjects. Surface electrodes were placed over the deltoid and erector spinae muscles. 3. In contrast to standing at rest, diaphragm activity was present throughout expiration at 78 +/- 17% (mean +/- S.D.) of its peak inspiratory magnitude during repeated upper limb movement. 4. Bursts of deltoid and erector spinae EMG activity occurred at the Limb movement frequency (similar to 2.9 Hz). Although the majority of diaphragm EMG power was at the respiratory frequency (similar to 0.4 Hz), a peak was also present at the movement frequency. This finding was corroborated by averaged EMG activity triggered from upper limb movement. In addition, diaphragm EMG activity was coherent with ribcage motion at the respiratory frequency and with upper limb movement at the movement frequency. 5. The diaphragm response was similar when movement was performed while sitting. In addition, when subjects moved with increasing frequency the peak upper limb acceleration correlated with diaphragm EMG amplitude. These findings support the argument that diaphragm contraction is related to trunk control. 6. The results indicate that activity of human phrenic motoneurones is organised such that it contributes to both posture and respiration during a task which repetitively challenges trunk posture.

Feedforward contraction of transversus abdominis is not influenced by the direction of arm movement

Because the structure of the spine is inherently unstable, muscle activation is essential for the maintenance of trunk posture and intervertebral control when the limbs are moved. To investigate how the central nervous system deals with this situation the temporal components of the response of the muscles of the trunk were evaluated during rapid limb movement performed in response to a visual stimulus. Fine-wire electromyography (EMG) electrodes were inserted into transversus abdominis (TrA), obliquus internus abdominis (OI) and obliquus externus abdominis (OE) of 15 subjects under the guidance of real-time ultrasound imaging. Surface electrodes were placed over rectus abdominis (RA), lumbar multifidus (MF) and the three parts of deltoid. In a standing position, ten repetitions of shoulder flexion, abduction and extension were performed by the subjects as fast as possible in response to a visual stimulus. The onset of TrA EMG occurred in advance of deltoid irrespective of the movement direction. The time to onset of EMC activity of OI, OE, RA and MF varied with the movement direction, being activated earliest when the prime action of the muscle opposed the reactive forces associated with the specific limb movement. It is postulated that the non-direction-specific contraction of TrA may be related to the control of trunk. stability independent of the requirement for direction-specific control of the centre of gravity in relation to the base of support.

Contractions of specific abdominal muscles in postural tasks are affected by respiratory maneuvers

The influence of respiratory activity of the abdominal muscles on their reaction time in a postural task was evaluated. The electromyographic (EMG) onsets of the abdominal muscles and deltoid were evaluated in response to shoulder flexion initiated by a visual stimulus occurring at random throughout the respiratory cycle. Increased activity of the abdominal muscles was produced by inspiratory loading, forced expiration below functional residual capacity, and a static glottis-closed expulsive maneuver. During quiet breathing, the latency between activation of the abdominal muscles and deltoid was not influenced by the respiratory cycle. When respiratory activity of the abdominal muscles increased, the EMG onset of transversus abdominis and internal oblique, relative to deltoid, was significantly earlier for movements beginning in expiration, compared with inspiration [by 97-107 ms (P < 0.01) and 64-90 ms (P < 0.01), respectively]. However, the onset of transversus abdominis EMG was delayed by 31-54 ms (P < 0.01) when movement was performed during a static expulsive effort, compared with quiet respiration. Thus changes occur in early anticipatory contraction of transversus abdominis during respiratory tasks but they cannot be explained simply by existing activation of the motoneuron pool.