Transversus Abdominis Activation Research Articles

Are Fear Avoidance Beliefs Associated with Abdominal Muscle Activation Outcome for Patients with Low Back Pain?

Activation of transversus abdominis and fear avoidance beliefs have both been related to low back pain (LBP). This exploratory study aims to investigate associations between fear avoidance beliefs at baseline and deep abdominal muscle activation after an 8-week period of supervised exercises for chronic LBP. A cohort of patients with chronic non-specific LBP (N = 108) enrolled in a clinical trial was studied longitudinally. Fear avoidance beliefs for physical activity and work were measured before intervention. Activation in transversus abdominis and obliquus internus abdominis during abdominal drawing-in manoeuvre and rapid arm flexion was measured by ultrasound before and after intervention. Associations between baseline fear avoidance beliefs and deep abdominal muscle activation after exercises were analysed with multiple linear regression methods. High fear avoidance beliefs for physical activity (≥16 on the subscale) were negatively associated with transversus abdominis slide after the intervention period, β = -4.92 (-8.40 to -1.45). There were no associations between fear avoidance beliefs for physical activity and abdominal muscle onset, transversus abdominis or obliquus internus contraction ratio. Fear avoidance beliefs for work were not associated with any of the muscle activation parameters. This study suggests that there is some negative association between fear avoidance beliefs for physical activity before intervention and transversus abdominis recruitment measured by lateral slide after intervention. No other significant associations between fear avoidance beliefs and abdominal muscle activation were found. We cannot exclude random findings, meaning that the results should be considered hypothesis generating for further investigations.

Transversus Abdominis Activation During a Side-Bridge Exercise Progression Is Similar in People with Recurrent Low Back Pain and Healthy Controls

Low back pain (LBP) affects 70-80% of the population. The transversus abdominis (TrA) has been implicated as part of the cause of LBP. Prevention and rehabilitation of LBP often target the TrA using exercises such as the side bridge accompanied with the abdominal drawing-in maneuver (ADIM). However, it is unknown whether individuals with recurrent LBP, when they are in a period of no pain, are able to activate the TrA and healthy individuals during this exercise. The purpose of our study was to compare the activation ratio of the TrA during a 5-level side-bridge exercise progression. Twenty-three subjects with a history of recurrent, nonspecific LBP, but not experiencing an exacerbation of symptoms and 24 healthy controls volunteered. All the subjects performed the ADIM and side-bridge exercises with clinician feedback (verbal cueing). Each participant performed the side-bridge exercise progression while ultrasound images were taken. The subjects were only progressed if they successfully completed the previous level. The thickness of the TrA was measured in rested and contracted states at each exercise level to find the activation ratio (TrA contracted/TrA rest). Separate analyses of covariance did not reveal a difference in activation ratios between groups (p > 0.40) when the ratio at the lowest level was used as the covariate. The results from this study indicate that both groups were able to contract the TrA with verbal cueing during a side-bridge exercise progression. Because the TrA contracted similarly during exercise in both groups, the association of LBP with the TrA may be because of another mechanism, such as delayed activation in the feed-forward mechanism during activity or a lack of endurance of the TrA.

Concurrent validity of the pressure biofeedback unit and surface electromyography in measuring transversus abdominis muscle activity in patients with chronic nonspecific low back pain

The Pressure biofeedback unit (PBU) is an assessment tool used in clinical practice and research aimed to indirectly analyze the transversus abdominis (TrA) muscle activity. The concurrent validity of the PBU in a clinically relevant sample is still unclear. The purpose of this study was to evaluate the concurrent validity and diagnostic accuracy of the PBU in measuring TrA muscle activity in patients with chronic nonspecific low back pain. This study was performed using a validation, cross-sectional design. Fifty patients with chronic nonspecific low back pain were recruited for this study. To test the concurrent validity both PBU measures (index test) and superficial electromyographic measures (reference-standard test) were compared and collected by a physical therapist in a series of voluntary contraction maneuvers of TrA muscle. Participants were on average 22 years old, weighed 63.7 kilos, 1.70 meters height and mean low back pain duration was 1.9 years. It was observed a weak and non-significant Phi coefficient (r=0.2, p<0.20). With regards to diagnostic accuracy tests, our results suggest a low sensitivity (60%) and specificity (60%) of the PBU. The positive predictive value was high (0.8) and negative predictive value was low (0.2). Concurrent validity of the PBU in measuring TrA muscle activity in patients with chronic nonspecific low back pain is poor given the low correlation and diagnostic accuracy with superficial EMG.

Abdominal muscle feedforward activation in patients with chronic low back pain is largely unaffected by 8 weeks of core stability training

Does timing of abdominal muscle activation in response to rapid shoulder flexion change after 8 weeks with low-load core stability exercises (CSE), high-load sling exercises (SE), or general exercises (GE) in chronic nonspecific low back pain (LBP) patients? A randomised, controlled trial with concealed allocation. Patients were recruited from general practitioners, physiotherapists, or by advertising at a regional hospital in Norway. Men and women, aged 18-60 years, with chronic nonspecific LBP for 3 months or more, and pain score of 2 or more on a 0-10 numeric rating scale were included. Key exclusion criteria included radiating pain below the knee or neurological signs from nerve root compression, and former back surgery. Randomisation of 109 participants allocated 36 to CSE, 36 to SE, and 37 to GE. Patients in the three groups attended treatment once a week for 8 weeks, supervised by a physiotherapist. All were encouraged to stay active and received an information booklet with general information on LBP. The CSE were individualised according to protocols focusing on isolated activation of transversus abdominis during an abdominal drawing-in manoeuver in supine hook-lying position with ultrasound feedback. Written instructions to carry out the drawing-in exercise (10 × 10 seconds 2-3 times per day) at home were also provided. The SE maintained the lumbar spine stable in neutral position throughout a range of leg/arm positions and movements, using elastic bands attached to the pelvis to help the patient maintain a neutral spine position. The SE was performed for 40 minutes in a physiotherapy clinic. The GE group received generalised trunk strengthening and stretching exercises supervised by a physiotherapist at a fitness centre. Primary outcome was change in onset of the deep abdominal muscles in response to rapid shoulder flexion. 102 participants completed the study. No or small changes were found in onset after treatment. Baseline adjusted between-group differences showed a 15 milliseconds (95% CI 1 to 28) and a 19 millisecond (95% CI 5 to 33) improvement with SE relative to CSE and GE, respectively, but on one side only. There was no association between changes in pain and onset over the intervention period (R(2)≤0.02). Abdominal muscle onset was largely unaffected by 8 weeks of exercises in chronic LBP patients with changes in onset of less than 20 milliseconds between groups.

Low impact weight-bearing exercise in an upright posture increases the activation of two key local muscles of the lumbo-pelvic region

To date, a range of exercises have been used to improve the function of the lumbar multifidus (LM) and transversus abdominis (TrA) muscles in people with low back pain, but uncertainty remains as to what exactly constitutes meaningful LM and TrA training. We examined the effects of exercising with a new device which combines weight-bearing, an unstable base of support (BOS) (feet), an upright posture with a relatively stable lumbo-pelvic area, and functional lower limb movement, with the aim of exploring which of these elements may be effective, in increasing LM and TrA muscle activity. Twelve non-symptomatic participants had ultrasound images taken of their LM and TrA during a range of conditions, including rest, traditional exercise approaches to LM and TrA recruitment, and exercising on the new device. Our results indicate that an unstable BOS on its own is not enough to increase LM and TrA activity, and that a combination of weight-bearing, an unstable BOS (feet), an upright posture with a relatively stable lumbo-pelvic area, and functional lower limb movement is most effective at increasing LM and TrA activity. This way of exercising appears to recruit LM more effectively than the widely used “swelling” of LM, and to cause automatic TrA and LM recruitment. Importantly, our findings also indicate LM and TrA may have slightly different roles during trunk stabilisation.

Reliability of real-time ultrasound measurement of transversus abdominis thickness in healthy trained subjects

To investigate intra- and inter-rater reliability of the ultrasound measurement of transversus abdominis (TrA) thickness and thickness change (difference between thickness at rest and during contraction) in asymptomatic, trained subjects. To define the number of repeated measurements that provide acceptable level of reliability. To investigate variability of the measurements over time of 5 days and the reliability of duplicate analysis of images. A single-group repeated-measures design was used to assess reliability. Healthy volunteers (n = 10) were subjected to 1-week training in voluntary activation of TrA. Real-time ultrasound imaging and subsequent measurement of the TrA thickness at rest and during voluntary contraction were repeated on Monday, Wednesday and Friday of the next week. Using a single repeated measurement, intraclass correlation coefficients (ICCs) for TrA thickness were: 0.86-0.95 (intra-rater), 0.86-0.92 (inter-rater); and for TrA thickness change: 0.34-0.56 (intra-rater), 0.47-0.61 (inter-rater). Using the mean of three repeated measurements respective values were: 0.97, 0.96-0.98; and 0.81-0.84, 0.80-0.90. No significant differences were found between mean values of TrA thickness as well as thickness change obtained on three consecutive measurement days. Duplicate analysis of the images was highly reliable with ICCs of 0.89-0.99. Two repeated measurements for TrA thickness and at least three measurements for TrA thickness change are needed to achieve acceptable levels of intra- and inter-rater reliability. In healthy trained volunteers TrA thickness and thickness change are relatively stable parameters over a 5-day period. Duplicate analysis of the same images by two blinded observers is reliable.

Corset hypothesis rebutted — Transversus abdominis does not co-contract in unison prior to rapid arm movements

BackgroundThe aim of this paper is to test “corset” model of spinal stability, specifically the hypothesis that feed forward transversus abdominis activity is bilaterally symmetrical and independent of the direction of perturbation to posture due to arm. This study will assess transversus abdominis electromyographical activity bilaterally. MethodsFeed forward intramuscular transversus abdominis electromyographical data and reaction forces on the thorax due to the arm movement were collected and processed for 6 healthy subjects during 6 trials of 8 types of arm movements (randomised order). Reciprocal transversus abdominis indices were calculated as the difference between the normalised integrated feed forward transversus abdominis electromyographical data from each side of the trunk. FindingsThe main finding of the study was that the reciprocal transversus abdominis index was significantly related to the axial rotational forces on the thorax due to arm movement (F=109.991, p<0.001). Right arm movements produced clockwise axial rotation forces on the thorax and dominant left transversus abdominis muscle activity. InterpretationThe consequence of this finding is that feed forward transversus abdominis activity is not bilaterally symmetrical and is not independent of the direction of perturbation to posture due to arm movement. Transversus abdominis forms part of a synergy of muscles contributing to the generation of axial rotation forces in the core that oppose the forces due to arm movement. These findings indicate that training bilateral pre-activation of the transversus abdominis prior to rapid movement is not justified and may potentially be problematic for the production of normal movement patterns.

Recruitment order of the abdominal muscles varies with postural task

Abdominal muscle recruitment strategies in response to a postural perturbation contradict the theory that the deeper abdominal muscles are always recruited in advance of the more superficial muscles. The purpose of this study was to determine whether such contrasting muscle recruitment patterns are due to the postural task or the predictability of a postural task. Participants performed an arm raise task as well as an unpredictable and a predictable balance perturbation task (i.e. support-surface translation) while intramuscular electromyographic (EMG) recordings were obtained from the deep [transversus abdominis (TrA)] and superficial [obliquus externus (OE)] abdominal muscles. The abdominal muscle recruitment order was dependent on the postural task but not on the predictability of a postural perturbation. Whereas arm raises elicited similar EMG onset latencies in TrA and OE, the OE onset latency was 48 ms earlier than the TrA following an unpredictable translation (P = 0.003). The early OE activation persisted when the translation was made predictable to the participant (P = 0.024). These results provide evidence that the abdominal muscle recruitment order varies with the trunk stability requirements specific to each task. Rehabilitation strategies focusing on an early TrA activation to improve postural stability may not be appropriate for all everyday tasks.

Pelvic floor muscle and transversus abdominis activation in abdominal hypopressive technique through surface electromyography

The abdominal hypopressive technique (AHT) is performed mainly via transversus abdominis (TrA) activation and has been indicated for pelvic floor muscle (PFM) disorders. In some European countries, this technique has become widely used. This study aimed to investigate PFM and TrA activation during the AHT through surface electromyography. Thirty-four nulliparous physical therapists in good general health were asked to participate in the trial. To ascertain a correct PFM contraction, each of the participants was assessed by inspection and digital palpation. Ability to contract the TrA was assessed by surface electromyography and AHT training was given before analysis. TrA and PFM activity was recorded using surface electromyography. The mean age of the volunteers was 28.1 (±6.0) years and the mean body mass index was 23.7 (±3.3) kg/m(2) . More than half of the volunteers were physically active (61.3%) and regularly performed PFM training (52.9%) but not TrA exercises (58.8%). Although the AHT activates the PFM when compared to resting tone (P < 0.001), this method is significantly less effective than PFM alone (P < 0.001). Additionally, the combination of the two techniques (AHT + PFM) was similarly effective as isolated PFM contraction (P = 0.586). Although the AHT activated the TrA significantly more than did PFM alone (P = 0.002), the addition of PFM contraction to the AHT significantly increased the amount of TrA activation (P < 0.001). Based on our results, the AHT is less effective than PFM contraction alone, and adding PFM contraction to AHT also improves the TrA contraction.

Is activation of transversus abdominis and obliquus internus abdominis associated with long-term changes in chronic low back pain? A prospective study with 1-year follow-up

ObjectiveTo investigate associations between deep abdominal muscle activation and long-term pain outcome in chronic non-specific low back pain (LBP).MethodsRecruitment of transversus abdominis and obliquus internus abdominis during the abdominal drawing-in...

Ultrasound Measurement of Transversus Abdominis During Loaded, Functional Tasks in Asymptomatic Individuals: Rater Reliability

To examine the ability of 2 clinicians to consistently measure recorded contractions of the transversus abdominis (TrA) muscle via ultrasound imaging (USI) during lifting and reaching tasks typical of everyday or work-related activities. Methodologic survey that measured inter- and intrarater reliability. University laboratory. A subset of 54 cine-loop images that were randomly selected from 6 randomly selected asymptomatic adults from a larger study that consisted of a sample of convenience of 20 asymptomatic adults, with a mean (SD) age of 18.8 ± 2.5 years and mean (SD) body mass index of 25.5 ± 3.5 kg/m(2). Thickness changes in the TrA muscle at rest and during contraction while performing 5 functional, loaded tasks. Intraclass correlation coefficients (ICC) were used to estimate reliability. ICC model 2,1 was used for all reliability analyses on 3 TrA muscle measures: minimum thickness, maximum thickness, and percentage change in muscle thickness. Percentage thickness change of TrA muscle was calculated as ([thickness(max) - thickness(min)]/thickness(min)) × 100. Two clinicians both scored 9 trials of 6 randomly selected participants (54 cine loops). Rater 1 scored these images again 28 days later. All image information (participant, trial, task, and testing session) was masked. Interrater ICC (2,1) for TrA muscle measures were moderate (0.71 rested state, 0.83 contracted state, 0.81 percentage change of muscle thickness); and high for intrarater ICC (2,1) (0.97 rested state, 0.99 contracted state, and 0.95% change in muscle thickness). This study provides data for ensuring acceptable reliability of USI measures of TrA muscle thickness and thickness changes taken during loaded and functional activities. This study is the first to examine interrater and intrarater reliability of recorded cine loop images of asymptomatic adults in upright positions on 3 measures of TrA muscle activation (minimum, maximum, and percent change in muscle thickness). Reliable USI measures of TrA muscle thickness changes meet the ongoing need for clinicians' knowledge of proper and sufficiently adequate muscle activation in the clinical setting to assist progression of lumbar stabilization exercises.

Reproducibility of the pressure biofeedback unit in measuring transversus abdominis muscle activity in patients with chronic nonspecific low back pain

The Pressure Biofeedback Unit (PBU) is often used by clinicians and researchers to indirectly evaluate transversus abdominis (TrA) muscle activity. The purpose of this study was to evaluate the inter and intra-examiner reproducibility of the PBU in measuring TrA muscle activity in fifty patients with chronic nonspecific low back pain. This study was performed using a test-retest design with a seven day interval. An Intraclass Correlation Coefficient (ICC(2,1)) of 0.74 (95% CI 0.54 to 0.85) and 0.76 (95% CI 0.58 to 0.86) was observed for the intra and inter-examiner reproducibility, respectively. The intra-examiner agreement (Limits of Agreement - LOA = 2.1 to -1.8 mmHg) and the inter-examiner agreement (LOA = 2.0 to -1.9 mmHg) were within the limits of agreement on 95% of occasions. The reproducibility of PBU in measuring TrA muscle activity in patients with chronic nonspecific low back pain ranged from satisfactory to excellent.

Activation of transversus abdominis varies with postural demand in standing

Transversus abdominis (TrA) is a multifunctional muscle, being involved in pressure regulation within the abdominal cavity and thereby in direction independent stabilization of the spine and resistance to imposed trunk flexion moments. Indirect evidence suggests a role of TrA also in postural control of the erect human trunk. The main purpose here was to investigate if the magnitude of TrA activation is related to postural demand. Eleven healthy males performed seven different symmetrical static bilateral arm positions holding 3 kg in each hand. The arm positions were selected to systematically vary the height of the centre of mass (COM) keeping imposed moments constant and vice versa. EMG was recorded bilaterally with fine-wire intramuscular electrodes from TrA and obliquus internus (OI) and with surface electrodes from rectus abdominis (RA) and erector spinae (ES). Intra-abdominal pressure (IAP) was measured via a pressure transducer in the gastric ventricle. TrA was the only muscle that displayed activation co-varying with the vertical position of the COM. Further, TrA activation increased, together with IAP and ES activation, with imposed flexion moment, i.e. with arms extended horizontally forward. In contrast to OI, RA and ES, TrA activation was independent of the direction of the imposed moment (arms held inclined forward or backward). In conclusion, TrA activation level is uniquely associated with increased postural demand caused by elevated COM. Also, TrA appears to assist in counteracting trunk flexion via increased IAP, and contribute to general spine stabilization when the trunk is exposed to moderate flexion and extension moments.

Effect of pilates mat exercises and conventional exercise programmes on transversus abdominis and obliquus internus abdominis activity: Pilot randomised trial

Pilates training is said to increase Transversus abdominis (TrA) and Obliquus internus (OI) activation during exercise and functional activities. 34 Pain-free health club members with no Pilates experience, mean (SD) age 30(7) years, were randomised to Pilates mat exercises or strength training. Participants exercised unsupervised twice-weekly for eight weeks. TrA and OI thickness (a proxy for muscle activity at the low-medium efforts of our exercises) were measured with ultrasound pre- and post-training during Pilates exercises ‘Imprint’ (an abdominal drawing-in manoeuvre) and ‘Hundreds A’ (lying supine, arms slightly raised, hips and knees flexed to 90°) and ‘Hundreds B’ (as A, with neck flexion) and functional postures sitting and standing. Pilates participants had increased TrA thickness in Hundreds A [all values mean (SD) mm]: 3.7(1.3) pre-intervention, 4.7(1.1) post-intervention ( P = 0.007); and decreased OI muscle thickness during Imprint: 11.7(2.8) pre-intervention, 10.8(3.5) post-intervention ( P = 0.008). Strength training participants had greater OI thickness during Imprint ( P = 0.014), Hundreds A ( P = 0.018) and Hundreds B ( P = 0.004) than Pilates participants post-intervention. There were no changes in muscle thickness at rest or during functional postures. Pilates training appears to increase TrA activity but only when performing Pilates exercises. Further research is required into Pilates in clinical populations and how to increase deep abdominal activation during functional activities.

Deep and superficial abdominal muscle activation during trunk stabilization exercises with and without instruction to hollow

The deepest muscle of the human ventro-lateral abdominal wall, the Transversus Abdominis (TrA), has been ascribed a specific role in spine stabilization, which has motivated special core stability exercises and hollowing instruction to specifically involve this muscle. The purpose here was to evaluate the levels of activation of the TrA and the superficial Rectus Abdominis (RA) muscles during five common stabilization exercises performed in supine, bridging and four-point kneeling positions, with and without instruction to hollow, i.e. to continuously pull the lower part of the abdomen towards the spine. Nine habitually active women participated and muscle activity was recorded bilaterally from TrA and RA with intramuscular fine-wire electrodes introduced under the guidance of ultrasound. Results showed that subjects were able to selectively increase the activation of the TrA, isolated from the RA, with the specific instruction to hollow and that side differences in the amplitude of TrA activity, related to the asymmetry of the exercises, remained even after the instruction to hollow. The exercises investigated caused levels of TrA activation from 4 to 43% of that during maximal effort and can thus be used clinically to grade the load on the TrA when designing programs aiming at training that muscle.

Abdominal hollowing and lateral abdominal wall muscles' activity in both healthy men & women: An ultrasonic assessment in supine and standing positions

The objective of this study was to investigate the effects of Abdominal Hollowing (AH) maneuver on External Oblique (EO), Internal Oblique (IO) and Transversus Abdominis (TrA) muscles in both healthy men and women during the two postures of supine and upright standing. The study was conducted on 43 asymptomatic volunteers (22 males and 21 females) aged 19-44 (27.8±6.4) years. Rehabilitative Ultrasonic Imaging (RUSI) was simultaneously performed to measure muscle thickness in both rest and during AH maneuvers while activation of the TrA during AH was controlled by Pressure Biofeedback (PBF) device. Mixed-model ANOVA with repeated measures design, and Pearson correlation tests were used to analyze the data. Muscle thickness of all muscles was significantly higher for male subjects (F>6.2, p<0.017). The interaction effect of gender and muscle status was significant only for IO (F=7.458, p=0.009) indicating that AH maneuver increased the thickness of IO in men. Interaction effect of posture and muscle status on muscular thickness indicated that changing position only affects the resting thickness of TrA (F=5.617, p=0.023). Standing posture significantly affected the TrA contraction ratio (t=3.122, p=0.003) and TrA preferential activation ratio (t=2.76, p=0.008). There was no relationship between age and muscle thickness (r=0.262, p=0.09). The PBF has been introduced as a clinical and available device for monitoring TrA activity, while RUSI showed that both TrA and IO muscles had activated after AH maneuver. We recommend performing further investigations using electromyography and RUSI simultaneously at more functional postures such as upright standing.

Driving plasticity in the motor cortex in recurrent low back pain

The sensory and motor systems can reorganise following injury and learning of new motor skills. Recently we observed adaptive changes in motor cortical organisation in patients with recurrent low back pain (LBP), which are linked to altered motor coordination. Although changes in motor coordination can be trained and are associated with improved symptoms and function, it remains unclear whether these training-induced changes are related to reorganisation of the motor cortex. This was investigated using the model of a delay in postural activation of the deep abdominal muscle, transversus abdominis (TrA) in 20 individuals with recurrent LBP. Subjects were allocated to either motor skill training that involved isolated voluntary contractions of TrA, or a control intervention of self-paced walking exercise for 2 weeks. Electromyographic (EMG) activity was recorded from TrA bilaterally using intramuscular fine-wire electrodes. Motor cortical organisation using transcranial magnetic stimulation (TMS) and postural activation associated with single rapid arm movements were investigated before and after training. Motor skill training induced an anterior and medial shift in motor cortical representation of TrA, towards that observed in healthy individuals from our previous study. This shift was associated with earlier postural activation of TrA. Changes were not observed following unskilled walking exercise. This is the first observation that motor training can reverse reorganisation of neuronal networks of the motor cortex in people with recurrent pain. The observed relationship between cortical reorganisation and changes in motor coordination following motor training provides unique insight into potential mechanisms that underlie recovery.

The Relationship of Transversus Abdominis and Lumbar Multifidus Activation and Prognostic Factors for Clinical Success With a Stabilization Exercise Program: A Cross-Sectional Study

Hebert JJ, Koppenhaver SL, Magel JS, Fritz JM. The relationship of transversus abdominis and lumbar multifidus activation and prognostic factors for clinical success with a stabilization exercise program: a cross-sectional study. Objective To examine the relationship between prognostic factors for clinical success with a stabilization exercise program and lumbar multifidus (LM) and transversus abdominis (TrA) muscle activation assessed using rehabilitative ultrasound imaging (RUSI). Design Cross-sectional study. Setting Outpatient physical therapy clinic. Participants Volunteers with current low back pain (N=40). Intervention Not applicable. Main Outcome Measures We examined the relationship between prognostic factors associated with clinical success with a stabilization exercise program (positive prone instability test, age <40y, aberrant movements, straight leg raise >91°, presence of lumbar hypermobility) and degree of TrA and LM muscle activation assessed by RUSI. Results Significant univariate relationships were identified between LM muscle activation and the number of prognostic factors present (Pearson correlation coefficient [ r] =−.558, P=.001), as well as the individual factors of a positive prone instability test (point biserial correlation coefficient [ r pbis ]=.376, P=.018) and segmental hypermobility ( r pbis =.358, P=.025). The multivariate analyses indicated that after controlling for other variables, the addition of the variable “number of prognostic factors present” resulted in a significant increase in R 2 ( P=.006). No significant univariate or multivariate relationships were observed between the prognostic factors and TrA muscle activation. Conclusions Decreased LM muscle activation, but not TrA muscle activation, is associated with the presence of factors predictive of clinical success with a stabilization exercise program. Our findings provide researchers and clinicians with evidence regarding the construct validity of the prognostic factors examined in this study, as well as the potential clinical importance of the LM muscle as a target for stabilization exercises.

Abdominal muscle and epipubic bone function during locomotion in Australian possums: Insights to basal mammalian conditions and eutherian‐like tendencies in Trichosurus

Mammals have four hypaxial muscle layers that wrap around the abdomen between the pelvis, ribcage, and spine. However, the marsupials have epipubic bones extending anteriorly into the ventral hypaxial layers with two additional muscles extending to the ventral midline and femur. Comparisons of South American marsupials to basal eutherians have shown that all of the abdominal hypaxials are active bilaterally in resting ventilation. However, during locomotion marsupials employ an asymmetrical pattern of activity as the hypaxial muscles form a crosscouplet linkage that uses the epipubic bone as a lever to provide long-axis support of the body between diagonal limb couplets during each step. In basal eutherians, this system shifts off the femur and epipubic bones (which are lost) resulting in a shoulder to pelvis linkage associated with shifts in both the positions and activity patterns of the pectineus and rectus abdominis muscles during locomotion. In this study, we present data on hypaxial function in two species (Pseudocheirus peregrinus and Trichosurus vulpecula) representing the two major radiations of possums in Australia: the Pseudocheiridae (within the Petauroidea) and the Phalangeridae. Patterns of gait, motor activity, and morphology in these two Australian species were compared with previous work to examine the generality of 1) the crosscouplet lever system as the basal condition for the Marsupialia and 2) several traits hypothesized to be common to all mammals (hypaxial tonus during resting ventilation, ventilation to step synchrony during locomotion, and bilateral transversus abdominis activity during locomotor expiration). Our results validate the presence of the crosscouplet pattern and basic epipubic bone lever system in Australian possums and confirm the generality of basal mammalian patterns. However, several novelties discovered in Trichosurus, reveal that it exhibits an evolutionary transition to intermediate eutherian-like morphological and motor patterns paralleling many other unique features of this species.

Trunk muscle reactions to sudden unexpected and expected perturbations in the absence of upright postural demand

The aim was to increase the understanding of the multifunctional role of the trunk muscles in spine control, particularly transversus abdominis (TrA). In 11 healthy males, intramuscular fine-wire electromyography (EMG) was obtained bilaterally from TrA, obliquus externus (OE), rectus abdominis (RA) and erector spinae (ES). The subjects lay on their right side on a horizontal swivel-table with immobilized pelvis and lower limbs and the trunk strapped to a movable platform. Unexpected or expected release of loads attached to the table by steel cables produced a perturbation inducing either trunk flexion or extension. The timing and the amplitude of activation of TrA were independent of direction of induced trunk movement. Furthermore, timing of TrA activation was simultaneous to or later than that of the more superficial abdominal muscles. Expectation of the perturbation caused a general shortening of onset latencies. The results indicate a direction independent function of TrA in lumbar spine control. Balancing the trunk vertically appears to add specific demands, since the recruitment of TrA in relation to the other abdominal muscles differed from earlier experiments in standing.