Abdominal muscle activation changes if the purpose is to control pelvis motion or thorax motion

The aim of this study was to compare trunk muscular recruitment and lumbar spine kinematics when motion was constrained to either the thorax or the pelvis. Nine healthy women performed four upright standing planar movements (rotations, anterior–posterior translations, medial–lateral translations, and horizontal circles) while constraining pelvis motion and moving the thorax or moving the pelvis while minimizing thorax motion, and four isometric trunk exercises (conventional curl-up, reverse curl-up, cross curl-up, and reverse cross curl-up). Surface EMG (upper and lower rectus abdominis, lateral and medial aspects of external oblique, internal oblique, and latissimus dorsi) and 3D lumbar displacements were recorded. Pelvis movements produced higher EMG amplitudes of the oblique abdominals than thorax motions in most trials, and larger lumbar displacements in the medial–lateral translations and horizontal circles. Conversely, thorax movements produced larger rotational lumbar displacement than pelvis motions during rotations and higher EMG amplitudes for latissimus dorsi during rotations and anterior–posterior translations and for lower rectus abdominis during the crossed curl-ups. Thus, different neuromuscular compartments appear when the objective changes from pelvis to thorax motion. This would suggest that both movement patterns should be considered when planning spine stabilization programs, to optimize exercises for the movement and muscle activations desired.     

Are recruitment patterns of the trunk musculature compatible with a synergy based on the maximization of endurance?

To verify that maximization of endurance is important among the functional criteria determining trunk muscle activation patterns, symmetric and asymmetric exertions were simulated using a detailed model consisting of 114 muscle slips crossing the lumbosacral junction and employing a cost function which maximizes endurance. First, the question whether meaningful comparisons can be made between activity predictions for individual muscle slips and surface EMG data recorded from larger anatomical entities was addressed. This was answered affirmatively, since activation patterns predicted by a coarse and a middle version of the model, in which activation was constrained to be equal within 14 or 32 groups of muscle slips, were similar to those predicted with each muscle slip controlled independently. Median correlation coefficients between activity vectors predicted by the simplified models and the detailed model were 0.88 and 0.97, respectively. The coarse model underestimated the endurance capacity by a median of 21%, the middle model by only 0.7%. Second, predicted activities within anatomical entities defined at this level of detail were compared to reference data derived from the literature (Lavender et al. 1992, Human Factors 34, 239–247; 1992, Journal of Orthopaedic Research 10, 691–700; Vink et al., 1988, Electromyography and Clinical Neurophysiology 28, 517–525). The predicted activity patterns of the crector spinae, external oblique and rectus abdominis muscles closely resembled the EMG patterns (r² = 0.48–0.99). Furthermore, the observed distribution of activity between parts of the crector spinae muscle was adequately predicted.     

Co-activation of vastus lateralis and biceps femoris muscles in pubertal children and adults

Determining the mechanisms of co-activation around the knee joint with respect to age and sex is important in terms of our greater understanding of strength development. The purpose of this study was to examine the effects of age, sex and muscle action on moment of force and electromyographic (EMG) activity of the agonist and antagonist muscle groups during isokinetic eccentric and concentric knee extension and flexion. The study comprised nine pubertal boys [mean age 12.6 (SD 0.5) years], nine girls [12.7 (SD 0.5) years] nine adult men [23.1 (SD 2.1) years] and nine adult women [23.7 (SD 3.1) years] who performed maximal isometric eccentric and concentric efforts of knee extensors and flexors on a dynamometer at 30 degrees x s(-1). The moment of force and surface EMG activity of vastus lateralis and biceps femoris muscles were recorded. The moment of force:agonist averaged EMG (aEMG) ratios were calculated. The antagonist aEMG values were expressed as a percentage of the aEMG activity of the same muscle, at the same angle, angular velocity and muscle action when the muscle was acting as agonist. Three-way analysis of variance (ANOVA) designs indicated no significant effects of age or sex on moment:aEMG ratios. Eccentric ratios were significantly higher than the corresponding concentric ones (P < 0.05). The results also indicated no significant effect of age and sex on the aEMG of the vastus lateralis and biceps femoris muscles when acting as antagonists. The antagonist aEMG was significantly greater during concentric agonist efforts compared with the corresponding eccentric ones (P < 0.05). These findings would suggest that the moment exerted per unit of agonist EMG and the antagonist activity are similar in children compared with adults and are not sex dependent. Future comparisons between eccentric and concentric moments of force and agonist ENG should take into consideration the antagonist effects, irrespective of age or sex.     

Comparison of humeral rotation co-activation of breast cancer population and healthy shoulders

Upper limb morbidities are common amongst the breast cancer population (BCP) and have a direct impact on independence. Comparing muscle co-activation strategies between BCP and healthy populations may assist in identifying muscle dysfunction and promote clinical interpretation of dysfunction, which could direct preventative and therapeutic interventions. The purposes of this study were to define humeral rotation muscle co-activation of a BCP and to compare it with a previously defined co-activation relationship of a healthy population. Fifty BCP survivors performed 18 isometric internal and external rotation exertions at various postures and intensities. Surface and intramuscular electrodes recorded shoulder muscle activity. BCP co-activation was predicted at r² = 0.77 during both exertion types. Humeral abduction angle and task intensity were important factors in the prediction of co-activation in both populations. Comparisons made between populations identified differing muscle strategies used by BCP to maintain postural control. Compared to healthy co-activation, the BCP demonstrated greater activation of internal (IR) and external rotator (ER) type muscles during their respective rotation type. The BCP demonstrated increased (⩾8.7%) activation of pectoralis major. This study has provided insight into how BCP muscles compensate during dysfunction. Continued advancement of this knowledge can provide more understanding of dysfunction, promote generation of evidence-based therapies, and can be useful in biomechanical modeling.     

Electromyographic basis of inaccurate movement; its dependence upon the mode of muscle contraction

The electromyographic basis of inaccurate performance was investigated in two rapid precision-grip skills controlled by concentric and eccentric muscle contractions respectively. Surface electromyograms, recorded from the first dorsal interosseous (DI), adductor pollicis (AP) and abductor pollicis brevis, were utilised to identify changes in the timing and intensity of muscle activation which may be responsible for inaccurate performance. The results showed that when fast precision-grip skills were controlled by concentric DI and AP muscle contraction, variations in the intensity of muscle contraction were responsible for inaccurate performance. However, when these skills were controlled by eccentric DI and AP muscle contractions, inaccurate performance resulted from variations in the timing of muscle activation. It was concluded that the nature of the deficiency in the patterns of muscle activation resulting in inaccurate performance was dependent upon the type of muscle contraction used in the skill.     

Motor control and cardiovascular responses during isoelectric contractions of the upper trapezius muscle: evidence for individual adaptation strategies

Ten females (25–50 years of age) performed isometric shoulder flexions, holding the right arm straight and in a horizontal position. The subjects were able to see the rectified surface electromyogram (EMG) from either one of two electrode pairs above the upper trapezius muscle and were instructed to keep its amplitude constant for 15 min while gradually unloading the arm against a support. The EMG electrodes were placed at positions representing a “cranial” and a “caudal” region of the muscle suggested previously to possess different functional properties. During the two contractions, recordings were made of: (1) EMG root mean square-amplitude and zero crossing (ZC) frequency from both electrode pairs on the trapezius as well as from the anterior part of the deltoideus, (2) supportive force, (3) heart rate (HR) and mean arterial blood pressure (MAP), and (4) perceived fatigue. The median responses during the cranial isoelectric contraction were small as compared to those reported previously in the literature: changes in exerted glenohumeral torque and ZC rate of the isoelectric EMG signal of −2.81% · min⁻¹ (P = 0.003) and 0.03% · min⁻¹ (P= 0.54), respectively, and increases in HR and MAP of 0.14 beats · min⁻² (P= 0.10) and 0.06 mmHg · min⁻¹ (P= 0.33), respectively. During the contraction with constant caudal EMG amplitude, the corresponding median responses were −2.51% · min⁻¹ (torque), 0.01% · min⁻¹ (ZC rate), 0.31 beats · min⁻² (HR), and 0.93 mmHg · min⁻¹ (MAP); P=0.001, 0.69, 0.005, and 0.003, respectively. Considerable deviations from the “isoelectric” target amplitude were common for both contractions. Individuals differed markedly in response, and three distinct subgroups of subjects were identified using cluster analysis. These groups are suggested to represent different motor control scenarios, including differential engagement of subdivisions of the upper trapezius, alternating motor unit recruitment and, in one group, a gradual transition towards a greater involvement of type II motor units. The results indicate that prolonged low-level contractions of the shoulder muscles may in general be accomplished with a moderate metabolic stress, but also that neuromuscular adaptation strategies differ significantly between individuals. These results may help to explain why occupational shoulder-neck loads of long duration cause musculoskeletal disorders in some subjects but not in others. Accepted: 1 March 1997     

Kinematic and electromyographic analyses of a karate punch

The aims of this study were: (i) to present the kinematic and electromyographic patterns of the choku-zuki punch performed by 18 experienced karatekas from the Portuguese team, and (ii) to compare it with the execution of 19 participants without any karate experience. The kinematic and electromyographic data were collected from the arm and forearm during the execution of the specific punch. A two-way analysis of variance (ANOVA) was used with significant level set at p ? 0.05. We found that the kinematic and neuromuscular activity in this punch occurs within 400 ms. Muscle activities and kinematic analysis presented a sequence of activation bracing a near-distal end, with the arm muscles showing greater intensity of activation than muscles in the forearm. In the skill performance, the arm, flexion and internal rotation, and the forearm extension and pronation movements were executed with smaller amplitude in the karate group. Based on the results of this study, the two groups’ presented distinct kinematic and electromyographic patterns during the performance of the choku-zuki punch.     

Corrective sitting strategies: An examination of muscle activity and spine loading

The purpose of this study was to quantify the load on the lumbar spine of subjects when they are asked to adjust from a slouched sitting posture into an upright posture with one of three different strategies: “free” (no instruction) and two coached patterns: “lumbopelvic” dominant and “thoracic” dominant. The activity of selected muscles and kinematic data was recorded from 20 volunteers while performing the three movement patterns to adjust sitting posture. Moments and forces at the lumbar spine were computed from an anatomically detailed model that uses kinematics and muscle activation as input variables.The lumbopelvic pattern produces less joint moment on the lumbar spine (on average 31.2 ± 3.9 N m) when compared to the thoracic pattern (43.8 ± 5.8 N m). However, the joint compression force was similar for these two patterns, but it was smaller in the free pattern, when no coaching was given (lumbopelvic: 1279 ± 112 N, thoracic: 1367 ± (125 N, free: 1181 ± 118 N). Lower thoracic erector muscle activity and higher lumbar erector activity were measured in the lumbopelvic pattern in comparison with the other two. In summary the lumbopelvic pattern strategy using predominantly the movement of anterior pelvic tilt results in smaller joint moments on the lumbar spine and also positions the lumbar spine closest to the neutral posture minimizing passive tissue stress. This may be the strategy of choice for people with low back flexion intolerance.     

无阿片类药物全麻复合双侧TAPB应用于妇科腹腔镜手术中的随机对照研究

摘要 目的：观察无阿片类药物全麻复合双侧腹横肌平面阻滞（TAPB）应用于妇科腹腔镜手术中的效果。方法：采用随机数字表法将126例需行妇科腹腔镜手术治疗的患者分为单一组（接受全凭静脉全身麻醉,n=63）和联合组（接受无阿片类药物全麻复合双侧TAPB,n=63）。观察两组术后疼痛、镇静情况、麻醉术后恢复时间、抑郁、睡眠改善情况和术后恶心呕吐发生情况、止吐药物应用情况。结果：术后12 h、24 h,两组视觉模拟评分法（VAS）评分升高,Ramsay镇静评分下降（P＜0.05）,且联合组VAS评分低于单一组同期,Ramsay镇静评分高于单一组同期（P＜0.05）。联合组自主呼吸恢复时间、苏醒时间、气管插管拔除时间短于单一组（P＜0.05）。术后7 d、14 d,两组汉密尔顿抑郁量表-17（HAMD-17）、匹兹堡睡眠质量指数（PSQI）评分下降（P＜0.05）,且联合组HAMD-17、PSQI评分低于单一组同期（P＜0.05）。联合组术后恶心呕吐发生情况、止吐药物应用情况低于单一组（P＜0.05）。结论：无阿片类药物全麻复合双侧TAPB在妇科腹腔镜手术中效果较好,可显著镇静、镇痛,促进术后恢复,改善患者术后抑郁情况和睡眠质量,且安全性较好。     

Muscles within muscles: the neuromotor control of intra-muscular segments

The aim of this investigation was to anatomically identify, and then determine the function of, individual segments within the human deltoid muscle. The anatomical structure of the deltoid was determined through dissection and/or observation of the shoulder girdles of 11 male cadavers (aged 65–84 years). These results indicate that the deltoid consists of seven anatomical segments (D1–D7) based upon the distinctive arrangement of each segment's origin and insertion. Radiographic analysis of a cadaveric shoulder joint suggested that only the postero-medial segment D7 has a line of action directed below the shoulder joint's axis of rotation. The functional role of each individual segment was then determined utilising an electromyographic (EMG) technique. Seven miniature (1 mm active plate; 7 mm interelectrode distance) bipolar surface electrodes were positioned over the proximal portion of each segment's muscle belly in 18 male and female subjects (18–30 years). EMG waveforms were then recorded during the production of rapid isometric shoulder abduction and adduction force impulses with the shoulder joint in 40 degrees of abduction in the plane of the scapula. Each subject randomly performed 15 abduction and 15 adduction isometric force impulses following a short familiarisation period. All subjects received visual feed back on the duration and amplitude of each isometric force impulse produced via a visual force-time display which compared subject performance to a criterion force-time curve. Movement time was 400 ms (time-to-peak isometric force) at an intensity level of 50% maximal voluntary contraction. Temporal and intensity analyses of the EMG waveforms, as well as temporal analysis of the isometric force impulses, revealed the neuromotor control strategies utilised by the CNS to control the activity of each muscle segment. The results showed that segmental neuromotor control strategies differ across the breadth of the muscle and that individual segments of the deltoid can be identified as having either “prime mover”, “synergist”, “stabiliser” or “antagonist” functions; functional classifications normally associated with whole muscle function. Therefore, it was concluded that the CNS can “fine tune” the activity of at least six discrete segments within the human deltoid muscle to efficiently meet the demands of the imposed motor task. Accepted: 15 December 1997     

Transient pain developers show increased abdominal muscle activity during prolonged sitting

BackgroundSitting is a commonly adopted posture during work and prolonged exposures may have detrimental effects. Little attention has been paid to the thoracic spine and/or multiple axes of motion during prolonged sitting. Accordingly, this study examined three-dimensional motion and muscle activity of the trunk during two hours of uninterrupted sitting.MethodsTen asymptomatic males sat during a simulated office task. Kinematics were analyzed from six segments (Neck, Upper-, Mid-, and Lower-thoracic, Lumbar, and Pelvis) and electromyography was recorded from eight muscles bilaterally.ResultsFour participants developed transient pain. These participants showed higher average muscle activations in the abdominal muscles. Additionally, the non-pain group showed less lateral bend positional change in the mid-thoracic region compared to the upper- and lower-thoracic regions. Weak-to-moderate positive correlations were also found between rated pain and low back muscle activation.DiscussionThe results provided further evidence of reduced movement in non-pain developers and altered muscle activation patterns in pain developers. Low-level, prolonged static contractions could lead to an increased risk of injury; and though the increased abdominal activity in the pain developers was not directly associated with increased rated pain scores, this could indicate a pre-disposition to, or enhancer of, transient pain development.     

超声引导下腹横肌平面阻滞与静脉镇痛在腹股沟疝气手术中的应用价值

摘要 目的：分析超声引导下腹横肌平面阻滞与静脉镇痛在腹股沟疝气手术中的应用价值。方法：选择2019年1月～2020年12月我院的120例腹股沟疝气手术患者为研究对象,按照麻醉镇痛方法的差异分为两组,对照组采用静脉镇痛,观察组采用腹横肌平面阻滞。记录两组患者术中丙泊酚、麻黄碱以及芬太尼的使用剂量以及手术后不同时间的VAS评分和芬太尼追加次数;比较两组术后恶心呕吐的发生率,并比较进食时间、肠道功能恢复时间以及下床活动时间。结果：观察组患者丙泊酚、麻黄碱以及芬太尼的使用剂量均显著少于对照组(P<0.05);观察组疝气手术后1 h(T0)、5 h(T1)、10 h(T2)、1d (T3)、2 d(T4)的VAS评分均明显低于对照组(P<0.05);观察组的芬太尼追加次数为4次/人,明显低于对照组的11次(P<0.05);观察组疝气手术后恶心呕吐的发生率（6.67%）、进食时间、肠道功能恢复时间以及下床活动时间均明显低于对照组(P<0.05)。结论：腹横肌平面阻滞对腹股沟疝气手术后患者的镇痛效果明显优于静脉镇痛,且更有助于促进术后恢复。     

The neural control of coactivation during fatiguing contractions revisited

In addition to the role of muscle coactivation, a major question in the field is how antagonist activation is controlled to minimize its opposing effect on agonist muscle performance. Muscle fatigue is an interesting condition to analyze the neural adjustments in antagonist muscle activity and to gain more insights into the control mechanisms of coactivation. In that context, previous studies have reported that although the EMG activity of agonists and antagonists increase in parallel, the ratio between EMG activities in the two sets of muscles during a fatiguing submaximal contraction decreased progressively and contributed to a reduction in the time to task failure. In contrast, more recent studies using a novel normalization procedure indicated that the agonist/antagonist ratio remained relatively constant, suggesting that the fatigue-related increase in coactivation does not impede performance. Current knowledge also indicates that peripheral mechanisms cannot by themselves mediate the intensity of antagonist coactivation during fatiguing contractions, implying that supraspinal mechanisms are involved. The unique modulation of the synaptic input from Ia afferents to the antagonist motor neurones during a fatiguing contraction of the agonist muscles further suggests a separate control of the two sets of muscles.