Unilateral Arm Flexion Research Articles

A coactivation strategy in anticipatory postural adjustments during voluntary unilateral arm movement while standing in individuals with bilateral spastic cerebral palsy

Individuals with bilateral spastic cerebral palsy (BSCP) reportedly has problems with anticipatory postural adjustments (APAs) while standing. However, the use of coactivation strategy in APAs in individuals with BSCP has conflicting evidence. Hence, this study aimed to investigate postural muscle activities in BSCP during unilateral arm flexion task in which postural perturbations occur in the sagittal, frontal, and horizontal planes. We included 10 individuals with BSCP with level II on the Gross Motor Function Classification System (BSCP group) and 10 individuals without disability (control group). The participants stood on a force platform and rapidly flexed a shoulder from 0° to 90° at their own timing. Surface electromyograms were recorded from the rectus femoris, medial hamstring, tibialis anterior, and medial gastrocnemius. The control group showed a mixture of anticipatory activation and inhibition of postural muscles, whereas the BSCP group predominantly exhibited anticipatory activation with slight anticipatory inhibition. Compared with the control group, the BSCP group tended to activate the ipsilateral and contralateral postural muscles and the agonist–antagonist muscle pairs. The BSCP group had a larger disturbance in postural equilibrium, quantified by the peak displacement of center of pressure during the unilateral arm flexion, than those without disability. Individuals with BSCP may use coactivation strategy, mainly the anticipatory activation of postural muscle activity, during a task that requires a selective postural muscle activity to maintain stable posture.

EMG Analysis of Trunk Muscle Recruitment Patterns of Anticipatory Postural Adjustments during Unilateral Arm Flexion in Chronic Neck Pain Patients

Introduction: EMG recruitment pattern of trunk muscles can change to compensate pain. One of these pattern alterations occurs in anticipatory postural adjustments (APAs) or feedforward activity of trunk muscles prior to arm movements. No study has determined the EMG pattern alterations of trunk muscle recruitments during the arm movement in patients with chronic neck pain (CNP). This study was examined the effect of CNP on EMG activities of trunk muscles for APAs during rapid arm flexion. Material and Methods: Sixteen patients with CNP for at least 3 months and sixteen healthy individuals matched in gender, age and weight were selected in this semi-experimental study. Surface EMG was utilized to evaluate 8 trunk muscles bilaterally and right anterior fibers of deltoid muscle during a unilateral rapid arm flexion. Anticipatory muscle activity was calculated by EMG onset latency of the trunk muscle from 100 ms before deltoid activity to 100 ms after it. Also, the values of root mean square (RMS) in 4 epochs around the onset of deltoid EMG were measured and compared. A two-tailed t-test and repeated-measure ANOVA were used for statistical analyses.Results: The onset latency of muscles in left and right side, except left erector spine muscle, in patients showed a significantly higher delay compared to healthy controls (P<0.05). The analysis of RMS in the 4 epochs revealed that in the control group, the values of RMS for rectus abdominus and erector spine in both sides, left external oblique and left transverse abdominus/internal oblique increased significantly during Epochs 3 and 4 , but in CNP subjects, the RMS of these muscles did not change significantly in 4 epochs.Conclusion: The patients with CNP had alterations in their recruitment patterns of particular trunk muscles in response to arm movement.Therefore, these patients have impaired motor control of trunk muscles during internal perturbation. These results indicated that not only the alterations in recruitment of trunk muscles occur, but also the intensity of their contractions decreases. In conclusion, CNP may alter in order to control the reactive forces resulting from limb movement.

Improved compensatory postural adjustments of the deep abdominals following exercise in people with chronic low back pain

The purpose of this study was to determine if 8 weeks of exercise affects motor control in people with chronic low back pain (CLBP), measured by anticipatory (APAs) and compensatory postural adjustments (CPAs). APAs and CPAs were measured prior to and following 8 weeks in two groups of people with CLBP: an exercise group (n=12) who attended three exercise sessions per week for 8 weeks; and a non-exercise control group (n=12) who were advised to continue their usual activities for the duration of the study. APAs and CPAs were recorded during unilateral arm flexion, bilaterally from rectus abdominis (RA), transverse abdominis/internal oblique (TA/IO), and erector spinae (ES) via surface electromyography. Analysis of muscle onsets and APA amplitudes suggests APAs did not change for either group. Ipsi-lateral TA/IO CPAs increased for the exercise group and ipsi-lateral TA/IO CPAs decreased for the control group. Only exercise promoted a pattern of TA/IO activity during CPAs similar to healthy individuals, suggesting improved control of rotational torques. These results show motor control improvement following exercise in people with CLBP, highlighted by improved side specific control of TA/IO.

Normal postural responses preceding shoulder flexion: co-activation or asymmetric activation of transverse abdominis?

It is suggested that activation of the transverse abdominis muscle has a stabilizing effect on the lumbar spine by raising intra-abdominal pressure without added disc compression. However, its feedforward activity has remained a controversial issue. In addition, research regarding bilateral activation of trunk muscles during a unilateral arm movement is limited. The aim of this study was to evaluate bilateral anticipatory activity of trunk muscles during unilateral arm flexion. Eighteen healthy subjects (aged 25 ± 3.96 years) participated in this study and performed 10 trials of rapid arm flexion in response to a visual stimulus. The electromyographic activity of the right anterior deltoid (AD) and bilateral trunk muscles including the transverse abdominis/internal oblique (TA/IO), superficial lumbar multifidus (SLM) and lumbar erector spine (LES) was recorded. The onset latency and anticipatory activity of the recorded trunk muscles were calculated. The first muscle activated in anticipation of the right arm flexion was the left TA/IO. The right TA/IO activated significantly later than all other trunk muscles (P < 0.0005). In addition, anticipatory activity of the right TA/IO was significantly lower than all other trunk muscles (P < 0.0005). There was no significant difference in either onset latency or anticipatory activity among other trunk muscles (P > 0.05). Healthy subjects showed no bilateral anticipatory co-activation of TA/IO in unilateral arm elevation. Further investigations are required to delineate normal muscle activation pattern in healthy subjects prior to prescribing bilateral activation training of transverse abdominis for subjects with chronic low back pain.

ANTICIPATORY POSTURAL ADJUSTMENTS OF TRUNK MUSCLES DURING UNILATERAL ARM FLEXION

ABSTRACT Background and Aim: Controversy regarding feedforward activation of transversus abdominis and limited studies regarding bilateral activation of trunk muscles during unilateral arm movement lead us to perform a study to evaluate bilateral anticipatory activity of trunk muscles during unilateral arm flexion. Materials and Methods: Eighteen healthy subjects participated in this study. The electromyographic activity of the right Anterior Deltoid (AD) and bilateral trunk muscles including the Transversus Abdominis/Obliquus Internus (TA/OI), Superficial Lumbar Multifidus (SLM) and Lumbar Erector Spinae (LES) during rapid flexion of the right upper limb in response to a visual stimulus was recorded and the onset latency and anticipatory activity of the recorded trunk muscles were calculated. Results: The cotralateral TA/OI was the first muscle activated in anticipation of the right arm flexion. The ipsilateral TA/OI activated significantly later than all other trunk muscles (P 0.05). Conclusion: Normal anticipatory activity during unilateral arm flexion was not bilateral anticipatory co-activation of TA/OI. Further surveys are required to detect normal muscle activation pattern in healthy subjects prior to prescribing bilateral activation training of Transversus Abdominis for subjects with chronic low back pain. Key words: Anticipatory Postural Adjustments, Motor Control, Low Back, Internal Perturbation

Spinal stability exercises: evidence of preferential activation of internal oblique muscles in 3 and 2 point kneeling exercises

Rehabilitation of spinal stability muscles for the sportsperson with low back pain is common place in physical rehabilitation programmes with the aim of reducing re-occurrence of low back pain and improving function (O’Sullivan et al., 1997, Hides, Jull, & Richardson, 2001). Many exercise regimes are purported to activate the local spinal stability muscles (Beith, Synnott, & Newman, 2001) but there is little evidence regarding the actual muscle activation of these exercises and their progressions. The aim of this study was to identify the difference between muscle activation of 3 point and 2 point kneeling exercises. The muscles of interest were internal oblique and rectus abdominus. Twenty healthy subjects (age 20.7 years SD 5.33)who all participated in sport, were recruited according to specific inclusion and exclusion criteria which included the ability to perform the abdominal hollowing manoeuvre (AHM) (Jull et al., 1993) SEMG was applied to internal obliques (IO) and rectus abdominus (RA). Maximum voluntary contractions were performed for normalisation of EMG data. Data was collected whilst performing the AHM followed by unilateral arm flexion (3 point kneeling) and then combined with contralateral leg/hip extension (2 point kneeling). Results indicated in both 3 point and 2 point kneeling there was preferential activation of internal obliques compared to rectus abdominus, (mean IO 48.90, 56.13, RA 17.67, 19.28, microvolts, respectively) with a significant difference in activation of internal oblique only between 3 and 2 point kneeling. ( p = 0.43 ). This is the first study to identify that progression of exercises from 3 point to 2 point kneeling preferentially activates internal obliques which are known to play a role in spinal stabilisation. This is key in rehabilitation of the sportsman who often has over riding global muscle activity.

Postural responses to unilateral arm perturbation in young, elderly, and hemiplegic subjects

Objective: To compare postural responses during standing associated with self-paced unilateral arm flexion exhibited by young and elderly healthy subjects and subjects with hemiplegia from stroke. Design and Setting: Descriptive cross-sectional study in a laboratory setting. Patients: Ten young, 10 elderly healthy subjects, and 12 volunteers with longstanding hemiparesis following stroke were tested. The hemiplegic group had good functional balance scores on the Berg Balance Scale (BBS). Main Outcome Measures: The peak arm acceleration, center of pressure (CP) excursion speed, and the electromyographic activity in the posterior leg muscles (bilateral hamstrings and triceps surae) were monitored during self-initiated rapid unilateral arm flexion and during quiet stance. Results: During unilateral arm flexion, the young group showed the highest arm accelerations and lowest CP excursion speeds. The variability of postural responses was largest in the elderly and hemiplegic groups with hemiplegic subjects showing the greatest CP excursion speeds for the lowest arm accelerations. The first burst of activity in ipsilateral hamstrings muscle was the same in all subjects. However, the hemiplegic group had less activation (latency and amplitude) of other posterior leg muscles. Conclusion: The elderly subjects had more variable responses to perturbation than the young subjects despite similar BBS scores. This may indicate that the BBS fails to detect differences in balance at the high end of the scale. Although the hemiplegic subjects demonstrated some anticipatory control of standing balance, they consistently performed poorer than elderly and young controls. The failure to coordinate postural leg muscle activity with focal movement may contribute to the instability of subjects with hemiplegia.

Standing balance during internally produced perturbations in subjects with hemiplegia: validation of the balance scale.

To examine the concurrent validity of the Berg Balance Scale (BBS) in subjects with hemiparesis after stroke by correlating functional balance performance on the BBS with laboratory measures of balance (center of pressure [CP] and electromyographic [EMG] activity of leg musculature during rapid arm flexion and during quiet stance). Concurrent validation study. Consistency of performance was determined through repeat measures obtained from 13 subjects. Laboratory. Twenty-four volunteers with longstanding hemiparesis from cerebrovascular accident (CVA) were tested. BBS scores were compared with CP excursion speed during (1) self-initiated rapid unilateral arm flexion with the nonhemiplegic arm and (2) quiet stance. The peak tangential arm acceleration and the sequence of EMG events in the posterior leg muscles were monitored during the arm flexion movement. In the arm flexion condition, BBS performance was significantly correlated with arm acceleration and CP excursion speed (multiple regression R = .81). BBS performance was also related to the presence of anticipatory activation of ipsilateral hamstrings during the rapid arm flexion movement. BBS performance and CP excursion speed during quiet stance were also significantly related (r = .76). The initial and repeat measures were not significantly different in magnitude (paired tests of difference, p < .01). The BBS appears to reflect differing abilities to tolerate the internally produced perturbation to standing balance associated with forward arm flexion in individuals with hemiparesis from CVA.

Effects of arm acceleration and behavioral conditions on the organization of postural adjustments during arm flexion.

Nine standing subjects performed unilateral arm flexion movements over an eight-fold range of speeds, under two behavioral conditions. In the visually-guided condition, a visual target informed subjects about the correct movement speed. Seven subjects also made movements of different speeds during a self-paced condition, without a visual target. Angular displacement and acceleration of the arm, and EMG activity from the hamstrings (HM), erector spinae (ES) and the anterior deltoid (AD) muscles were measured. The following results were observed. Mean rectified amplitudes of EMG activity in HM and ES were typically correlated with the average arm acceleration and presumably the disturbance to posture and/or balance. HM and ES amplitudes were correlated for only six subjects. Functions relating the ratios of HM/ES EMG amplitudes to acceleration varied between subjects. HM onset latencies were highly variable for slow movements and usually lagged movement. For movements above a threshold-like point in acceleration, HM latencies were correlated with arm acceleration and recruited before movement. ES latencies were constant for fast movements, and negatively correlated with acceleration for slower movements. The recruitment order of HM and AD was influenced by the behavioral condition but not by arm acceleration for fast movements. HM and AD were recruited coincidentally for visually-guided movements, while for self-paced movements, HM was recruited before AD. We conclude that for the arm flexion task: HM and ES are not tightly coupled; both behavioral and mechanical conditions affect the recruitment of postural muscles; and postural and focal components of the movement are probably organized by parallel processes.

Anticipatory control of postural and task muscles during rapid arm flexion.

A multicomponent pattern of premovement (anticipatory) activity in both task and postural muscles was examined for a unilateral rapid arm flexion movement (Belen'kii, Gurflnkel, & Pal'tsev, 1967) performed under simple visual reaction-time conditions. Subjects performed 30 right- and 30 left-side responses on each of four consecutive days. The anticipatory postural muscle activity may be considered a valid component of voluntary unilateral arm flexion. Invariances and variability in the spatial and temporal characteristics of the neuromuscular pattern are described in relationship to behavioral and motor control models of response organization. It is suggested that some temporal patterning among response components may not be preprogrammed centrally.