Investigation on the effectiveness of abdominal hollowing home-exercises using a portable ultrasound: Randomized controlled trial

We used a 3-arm randomized control trial to investigate whether abdominal hollowing (AH) home exercise using pocket-sized ultrasonography (US)—miruco (AH with miruco group)—was more effective than conventional AH home exercise using abdominal palpation and or also a wait-and-see approach (control group) to improve isolated control of the transversus abdominis (TrA) muscle during AH. We randomized 60 participants with low back pain into the three groups equally. Primary outcome measures for the US group were percentage of change in TrA thickness and excursion of the edge of the TrA fascia during AH when the thickness of the internal or external oblique muscles increased. Score on the Oswestry Disability Index (ODI) was a secondary outcome measure. The intervention period was 1 week, followed by 1 week without intervention. As a result, we found no statistically significant interaction effect (P > .05) in changes of the primary outcome measures from baseline for each follow-up period. The AH with miruco group had a statistically lower ODI (P = .036) than did the control group after the intervention. Results indicate a limited benefit for use of the miruco in AH home exercise to improve isolated control of the TrA muscle during AH.     

Location and sequence of muscle onset in deep abdominal muscles measured by different modes of ultrasound imaging

Various modes of ultrasound (US) imaging have been introduced as an alternative to electromyography for determining muscle onset. The purpose of this study was to compare the agreement between US motion-mode (US_m-mode) and US strain rate (US_SR) derived from tissue velocity imaging in determining latency time, location and sequence of muscle onset in abdominal muscles using the same data set (contractions). Twenty-four subjects performed four rapid arm flexions in response to a light signal while US recordings were made from the abdominal muscles on the contralateral side. The examined muscles were transversus abdominis (TrA), superficial and deep obliquus internus abdominis (OI_deep and OI_sup), and obliquus externus abdominis (OE). The results showed that the two methods detected the first muscle onset on average within 0.1 ms (95% CI; ±1.4 ms) of each other. US_SR detected the second muscle onset on average 27 ms after US_m-mode. While US_SR and US_m-mode can be used interchangeably to detect the first muscle onset, the location of both first onset and subsequent muscle onsets can be reliably detected by US_SR only. Furthermore, this study indicates that OI may be functionally subdivided into a superficial and deep region, with onset in OI_deep occurring on average 53 ms before OI_sup. First onset was detected more frequently in OI than in TrA (65% versus 25% of detected onsets, 10% were equal).     

In a dynamic lifting task,the relationship between cross-sectional abdominal muscle thickness and the corresponding muscle activity is affected by the combined use of a weightlifting belt and the Valsalva maneuver

It has been shown that under isometric conditions, as the activity of the abdominal muscles increases, the thicknesses of the muscles also increase. The purpose of this experiment was to determine whether change in muscle thickness could be used as a measure of muscle activity during a deadlift as well as determining the effect of a weightlifting belt and/or the Valsalva maneuver on the muscle thicknesses. The Transversus Abdominis (TrA) and Internal Obliques (IO) muscles were analyzed at rest and during a deadlift. Muscle thickness was measured using ultrasound imaging and muscle activity was simultaneously recorded using electromyography. Each subject performed deadlift under normal conditions, while performing the Valsalva maneuver, while wearing a weightlifting belt and while both utilizing the belt and the Valsalva maneuver. There was no relationship between change in muscle thickness and muscle activity for both the TrA and IO (R² < 0.13 for all conditions). However it was found that the Valsalva maneuver increased abdominal muscle thickness whereas the belt limited muscle expansion; each with an increase in activity. These results indicate that ultrasound cannot be used to measure muscle activity for a deadlift and that the belt affects how the IO and TrA function together.     

Comparison between muscle activation measured by electromyography and muscle thickness measured using ultrasonography for effective muscle assessment

In this study, we aimed to compare the intrarater reliability and validity of muscle thickness measured using ultrasonography (US) and muscle activity via electromyography (EMG) during manual muscle testing (MMT) of the external oblique (EO) and lumbar multifidus (MF) muscles. The study subjects were 30 healthy individuals who underwent MMT at different grades. EMG was used to measure the muscle activity in terms of ratio to maximum voluntary contraction (MVC) and root mean square (RMS) metrics. US was used to measure the raw muscle thickness, the ratio of muscle thickness at MVC, and the ratio of muscle thickness at rest. One examiner performed measurements on each subject in 3 trials. The intrarater reliabilities of the % MVC RMS and raw RMS metrics for EMG and the % MVC thickness metrics for US were excellent (ICC = 0.81–0.98). There was a significant difference between all the grades measured using the % MVC thickness metric (p < 0.01). Further, this % MVC thickness metric of US showed a significantly higher correlation with the EMG measurement methods than with the others (r = 0.51–0.61). Our findings suggest that the % MVC thickness determined by US was the most sensitive of all methods for assessing the MMT grade.     

Validity of architectural properties of the hamstring muscles: Correlation of ultrasound findings with cadaveric dissection

The purpose of this study was to compare the architectural parameters of the long head of biceps femoris (BFlh) and semitendinosus (ST) muscles by comparing measurements from ultrasound (US) with those obtained from direct dissection. The BFlh and ST architectures were examined bilaterally in 6 legs from 3 male cadavers. The fascicle length, pennation angle, muscle thickness and muscle and tendon length were obtained from direct measurement and US scans along each muscle. Intraclass correlation coefficients between the two methods ranged from 0.905 to 0.913 for the BFlh variables and from 0.774 to 0.974 for the ST parameters. Compared with the direct measurements, the US method showed a mean typical error of 0.09–0.14 cm for muscle thickness, 1.01–1.31° for the pennation angle, 0.92–1.71 cm for fascicle length and muscle–tendon length measurements. The US method is a valid alternative tool for assessing basic architectural parameters of ST and BFlh components of the hamstring muscles.     

Differential activation of psoas major and rectus femoris during active straight leg raise to end range

The purpose of this study was to investigate the activation of the hip flexor and abdominal muscles during an active straight leg raise (ASLR) to end range of hip flexion. Data were recorded from nine healthy men. Fine-wire electromyography (EMG) electrodes were inserted into psoas major (PM), and surface electrodes were placed over rectus femoris (RF), rectus abdominis, obliquus externus abdominis (OE), and obliquus internus abdominis/transversus abdominis (OI/TrA). EMG and kinematic data were obtained during concentric, hold (at end range) and eccentric phases of an ASLR. Concentric and eccentric movements were divided into three phases (early, mid, and late). Onsets of EMG relative to the onset of the ALSR movement and EMG amplitudes in each phase were compared between muscles. Onsets of the PM (–33 ± 245 ms) and RF (-3 ± 119 ms) EMG prior to leg elevation were significantly earlier than those of the OE and OI/TrA. PM EMG showed highest activation in the late concentric, hold, early eccentric phase, and was significantly higher than RF EMG. OI/TrA EMG was significantly greater in mid and late concentric, hold, and early eccentric phase than other phases. During the ASLR, unlike RF, PM EMG continues to increase towards the end range of hip flexion. Activation of OI/TrA muscle may be involved in control trunk and pelvic movement.     

Measurement of cervical multifidus contraction pattern with ultrasound imaging

Deep muscle training has become the focus of research and exercise for patients with chronic neck pain. The objective of this in vivo study was to establish a non-invasive assessment tool for the activation of deep cervical muscles. The pattern of the change in the thickness of the cervical multifidus is described with a mathematical equation and used to compare the changes among different levels of resistance (0%, 25%, 50%, 75%, and 100%) and at different cervical levels (fourth, fifth, and sixth cervical (C4, C5, and C6) vertebrae). Twenty asymptomatic subjects (five women and 15 men; 24.3 ± 4.7 years old) were recruited for this experiment. Ultrasonography (US) with synchronized force recording was used to measure the thickness of the cervical multifidus during progressive isometric extension against resistance. Linear and quadratic models were used to estimate the patterns of change in the thickness of cervical multifidus in relation to force. Two-way analysis of variance with repeated measurement and post hoc analysis were used to investigate the differences in thickness. The change in thickness and force was better fitted by quadratic model (y = ax² + bx + c) than by the linear model. The thickness at 50% of maximum contraction was significantly increased compared with that at 25% of maximum contraction. This quantitative non-invasive measurement may provide an assessment tool for further investigation for the physiological function of the deep muscles. Further research is required to investigate whether the change of thickness was predominately determined by the recruitment of muscle fibers or the extensibility of non-contractile tissues.     

The effect of inspiratory and expiratory loads on abdominal muscle activity during breathing in subjects “at risk” for the development of chronic obstructive pulmonary disease and healthy

The abdominal muscle activity has been shown to be variable in subjects with chronic obstructive pulmonary disease (COPD) when respiratory demand increases and their recruitment pattern may change the mechanics, as well as the work and cost of breathing. The scientific evidence in subjects “at risk” for the development of COPD may be important to understand the natural history of this disease. This study aims to evaluate the effect of inspiratory and expiratory loads on the abdominal muscle activity during breathing in subjects “at risk” for the development of COPD and healthy. Thirty-one volunteers, divided in “At Risk” for COPD (n = 17; 47.71 ± 5.11 years) and Healthy (n = 14; 48.21 ± 6.87 years) groups, breathed at the same rhythm without load and with 10% of the maximal inspiratory or expiratory pressures, in standing. Surface electromyography was performed to assess the activation intensity of rectus abdominis (RA), external oblique and transversus abdominis/internal oblique (TrA/IO) muscles, during inspiration and expiration. During inspiration, in “At Risk” for COPD group, RA muscle activation was higher with loaded expiration (p = 0.016); however, in Healthy group it was observed a higher activation of external oblique and TrA/IO muscles (p < 0.050). During expiration, while in “At Risk” for COPD group, RA muscle activation was higher with loaded inspiration (p = 0.009), in Healthy group TrA/IO muscle showed a higher activation (p = 0.025). Subjects “at risk” for the development of COPD seemed to have a specific recruitment of the superficial layer of ventrolateral abdominal wall for the mechanics of breathing.     

Slow expiration reduces sternocleidomastoid activity and increases transversus abdominis and internal oblique muscle activity during abdominal curl-up

The aim of this study was to investigate the effects of quiet inspiration versus slow expiration on sternocleidomastoid (SCM) and abdominal muscle activity during abdominal curl-up in healthy subjects. Twelve healthy subjects participated in this study. Surface electromyography (EMG) was used to collect activity of bilateral SCM, rectus abdominis (RA), external oblique (EO), and transversus abdominis/internal oblique (TrA/IO) muscles. A paired t-test was used to determine significant differences in the bilateral SCM, RF, EO, and TrA/IO muscles between abdominal curl-up with quiet inspiration and slow expiration. There were significantly lower EMG activity of both SCMs and greater EMG activity of both IOs during abdominal curl-up with slow expiration, compared with the EMG activity of both SCMs and IOs during abdominal curl-up with quiet inspiration (p < .05). The results of this study suggest that slow expiration would be recommended during abdominal curl-up for reduced SCM activation and selective activation of TrA/IO in healthy subjects compared with those in abdominal curl up with quiet inspiration.     

Site specificity of mechanical and structural properties of human fascia lata and their gender differences: A cadaveric study

The whole thigh muscles are covered with the fascia lata, which could have morphological and mechanical features that match the underlying muscles’ functions. In this study, we investigated the morphological and elastic properties of the human fascia lata taken from four (anterior, medial, lateral, and posterior) sites on the thigh of 17 legs of 12 cadavers (6 males and 6 females, 75–92 years). The thickness of the fascia lata was determined with a caliper. The interwoven collagen fiber’s directions were measured and classified into longitudinal, transverse, and diagonal in two opposing directions, relative to the thigh. Tensile strength test along the longitudinal and transverse directions was performed, and the stiffness, Young’s modulus, and hysteresis were determined. Fascia lata at the lateral site (0.8 ± 0.2 mm) was significantly thicker compared to other sites (0.2–0.3 mm). Fiber’s directions showed substantial variability among sites, and longitudinally directed fibers were higher in proportion (28–32%) than those in other directions (20–27%) at all sites except for the posterior site. The stiffness and Young’s modulus in the longitudinal direction (20–283 N/mm; 71.6–275.9 MPa, highest at the lateral site) were significantly higher than in the transverse direction (3–16 N/mm; 3.2–41.9 MPa, lowest at the lateral site). At the medial site, the proportion of the transversely directed fibers was higher in females than males, with higher stiffness and Young’s modulus thereof. The present study shows that the fascia lata possesses site- and gender-dependence of the morphological characteristics and elastic properties.     

Lower extremity muscle activation during horizontal and uphill running

Sloniger, Mark A., Kirk J. Cureton, Barry M. Prior, andEllen M. Evans. Lower extremity muscle activationduring horizontal and uphill running. J. Appl.Physiol. 83(6): 2073-2079, 1997.To provide more comprehensive information on theextent and pattern of muscle activation during running, we determinedlower extremity muscle activation by using exercise-induced contrastshifts in magnetic resonance (MR) images during horizontal and uphillhigh-intensity (115% of peak oxygen uptake) running to exhaustion(2.0-3.9 min) in 12 young women. The mean percentage of musclevolume activated in the right lower extremity was significantly(P <0.05) greater during uphill (73 ± 7%) than during horizontal (67 ± 8%) running. Thepercentage of 13 individual muscles or groups activated varied from 41 to 90% during horizontal running and from 44 to 83% during uphillrunning. During horizontal running, the muscles or groups mostactivated were the adductors (90 ± 5%), semitendinosus (86 ± 13%), gracilis (76 ± 20%), biceps femoris (76 ± 12%), andsemimembranosus (75 ± 12%). During uphill running, the musclesmost activated were the adductors (83 ± 8%), biceps femoris (79 ± 7%), gluteal group (79 ± 11%), gastrocnemius (76 ± 15%), and vastus group (75 ± 13%). Compared with horizontalrunning, uphill running required considerably greater activation of thevastus group (23%) and soleus (14%) and less activation of the rectusfemoris (29%), gracilis (18%), and semitendinosus (17%). We concludethat during high-intensity horizontal and uphill running to exhaustion,lasting 2-3 min, muscles of the lower extremity are not maximallyactivated, suggesting there is a limit to the extent to whichadditional muscle mass recruitment can be utilized to meet the demandfor force and energy. Greater total muscle activation during exhaustive uphill than during horizontal running is achieved through an altered pattern of muscle activation that involves increased use of some muscles and less use of others.

     

Onset in abdominal muscles recorded simultaneously by ultrasound imaging and intramuscular electromyography

Delayed onset of muscle activity in abdominal muscles has been related to low back pain. To investigate this in larger clinical trials it would be beneficial if non-invasive and less cumbersome alternatives to intramuscular electromyography (EMG) were available. This study was designed to compare onset of muscle activity recorded by intramuscular EMG to onset of muscle deformations by ultrasound imaging. Muscle deformations were recorded by two ultrasound imaging modes at high time resolution (m-mode and tissue velocity) in separate sessions and compared to simultaneously recorded intramuscular EMG in three abdominal muscles. Tissue velocity imaging was converted to strain rate which measures deformation velocity gradients within small regions, giving information about the rate of local tissue shortening or lengthening along the beam axis. Onsets in transversus abdominis (TrA), obliquus internus abdominis (OI) and obliquus externus abdominis (OE) were recorded during rapid arm flexions in ten healthy subjects. During ultrasound m-mode recordings, the results showed that mean onsets by EMG were detected 7 ms (95% CI of mean difference; ±4 ms) and 2 ms (95% CI of mean difference; ±6 ms) before concurrent ultrasound m-mode detected onsets in TrA and OI, respectively. In contrast, OE onset was recorded 54 ms (95% CI of bias; ±16 ms) later by EMG compared to ultrasound m-mode. The discrepancy of ultrasound m-mode to accurately record onset in OE was practically corrected in the ultrasound-based strain rate recordings. However, this could only be applied on half of the subjects due to the angle dependency between the ultrasound beam and the direction of the contraction in strain rate recordings. The angle dependency needs to be further explored.     

Feedforward activation of the quadratus lumborum during rapid shoulder joint abduction

This study aimed to clarify the difference in the onset of EMG activity between eight trunk muscles, including the anterior (QL-a) and posterior (QL-p) layers of the quadratus lumborum during rapid shoulder joint abduction. Thirteen healthy men participated in this study. Electromyography of the QL-a, QL-p, transversus abdominis (TrA), internal oblique (IO), external oblique (EO), rectus abdominis (RA), lumbar multifidus (LMF), lumbar erector spinae (LES) on non-movement side, and middle deltoid (MD) on the movement side were measured. Subjects who were standing in a relaxed position performed rapid shoulder abduction with the dominant hand after light stimulus with or without a 3 kg wrist weight. Two-way ANOVA (muscles × weight conditions) was used to compare the onset of trunk muscles relative to that of MD. There was a significant main effect of the muscles. The onset of the QL-a, QL-p, and TrA was significantly earlier than that of the IO, EO, LMF, and LES (P < 0.01). This result suggests that the activities of the QL-a, QL-p, and TrA have a crucial role in controlling the center of mass within the base of support and stabilizing the lumbar spine in the coronal plane during shoulder abduction.     

Trunk Muscle Activation at the Initiation and Braking of Bilateral Shoulder Flexion Movements of Different Amplitudes

The aim of this study was to investigate if trunk muscle activation patterns during rapid bilateral shoulder flexions are affected by movement amplitude. Eleven healthy males performed shoulder flexion movements starting from a position with arms along sides (0°) to either 45°, 90° or 180°. EMG was measured bilaterally from transversus abdominis (TrA), obliquus internus (OI) with intra-muscular electrodes, and from rectus abdominis (RA), erector spinae (ES) and deltoideus with surface electrodes. 3D kinematics was recorded and inverse dynamics was used to calculate the reactive linear forces and torque about the shoulders and the linear and angular impulses. The sequencing of trunk muscle onsets at the initiation of arm movements was the same across movement amplitudes with ES as the first muscle activated, followed by TrA, RA and OI. All arm movements induced a flexion angular impulse about the shoulders during acceleration that was reversed during deceleration. Increased movement amplitude led to shortened onset latencies of the abdominal muscles and increased level of activation in TrA and ES. The activation magnitude of TrA was similar in acceleration and deceleration where the other muscles were specific to acceleration or deceleration. The findings show that arm movements need to be standardized when used as a method to evaluate trunk muscle activation patterns and that inclusion of the deceleration of the arms in the analysis allow the study of the relationship between trunk muscle activation and direction of perturbing torque during one and the same arm movement.     

Reliability of real-time ultrasound for the assessment of transversus abdominis function

Transversus abdominis (TrA) has now been established as a key muscle for the stabilization of the lumbar spine and sacroiliac joints. Significantly, dysfunction of this muscle has also been implicated in low back pain. Real-time ultrasound (US) is a non-invasive procedure that has the potential to evaluate objectively the function of TrA. Objective: To investigate M-mode US as a reliable method of assessing TrA function. Method: M-mode US was used to measure the width of TrA as subjects drew in their lower abdominal wall at a controlled speed to a target depth. Eleven subjects were imaged. Results: the measures of TrA width were reliable and ranged between 3.14mm relaxed and 6.35mm contracted. The standard error of measurement ranged between 0.18mm and 0.57mm. Conclusion: M-mode US provides a reliable non-invasive measure of a controlled contraction of TrA.     

Comparison of ultrasonographic characteristics of deep abdominal muscles in women with and without chronic neck pain: a case-control study

Objectives:To compare ultrasonography (USG) parameters of deep abdominal muscles (transversus abdominis-TrA, internal obliques-IO) between women with and without chronic neck pain (CNP).Methods:Women with CNP (n=18; mean-age=37.7 years; mean-BMI=22.7 kg/m²) and asymptomatic individuals (n=18; mean-age=36.1 years; mean-BMI=21.8 kg/m²) participated in the study. The activation of the deep neck flexors (ADNF) was measured using cranio-cervical flexion test. Muscle thickness, changes in thickness (ΔT), and contraction ratio (CR) of deep abdominal muscles were evaluated by ultrasonography device in two conditions: standard-protocol and during ADNF. For each condition, ultrasound image of abdominal muscles was captured at rest and during abdominal draw-in manoeuvre (ADIM).Results:Comparative statistics revealed no significant difference between groups regarding ultrasonography parameters in the standard-protocol (p>0.05). Besides, there was no difference in the CR of TrA and IO between groups in the two conditions. However, women with CNP showed less muscle thickness of TrAADIM during ADNF than the asymptomatic participants (p<0.05). The CNP group also had decreased ΔT of TrA(ADIM-rest) during ADNF compared to the asymptomatic group (p<0.05).Conclusions:The ultrasonography parameters of TrA suggest that motor control in the lumbar region is altered in women with CNP. The combination of cervical stabilization exercises with ADIM can be a novel strategy in the treatment of CNP.     

Effect of knee joint angle on individual hamstrings morphology quantified using free-hand 3D ultrasonography

Exercise responses and injury rates differ between individual hamstrings and this may be linked with their morphology. The aim of this study was to compare muscle length and tendon dimensions between the individual hamstrings at two knee joint angles using free hand three-dimensional ultrasound (3D US). Muscle-tendon length and distal tendon cross-sectional area (CSA), volume, length and echogenicity of biceps femoris long (BFlh) and short (BFsh) head, semimembranosus (SM) and semitendinosus (ST) of 16 individuals were measured using free-hand 3D US at 0° (full extension) and 45° of knee flexion. ST showed the greatest length than all muscles and BFsh the lowest (p < 0.05). No difference was observed between SM and BFlh length (p > 0.05). Of the four muscles, ST tendon was longer, with less volume and CSA but greater echogenicity than the other tendons. In contrast, SM and BFlh showed shorter tendons and lower echogenicity but a greater volume and CSA than ST (p < 0.05). Muscle and tendon lengthened from 45° to 0° knee flexion angle (p < 0.05) but this change was not statistically different between individual hamstrings (p > 0.05). Freehand 3D US indicated that hamstring muscle length and distal tendon dimensions differ between individual hamstrings. All muscles and tendons lengthened as the knee was extended but this change was similar for all individual hamstrings.     

3D Topography of the Young Adult Anal Sphincter Complex Reconstructed from Undeformed Serial Anatomical Sections

Background

Pelvic-floor anatomy is usually studied by artifact-prone dissection or imaging, which requires prior anatomical knowledge. We used the serial-section approach to settle contentious issues and an interactive 3D-pdf to make the results widely accessible.

Method

3D reconstructions of undeformed thin serial anatomical sections of 4 females and 2 males (21–35y) of the Chinese Visible Human database.

Findings

Based on tendinous septa and muscle-fiber orientation as segmentation guides, the anal-sphincter complex (ASC) comprised the subcutaneous external anal sphincter (EAS) and the U-shaped puborectal muscle, a part of the levator ani muscle (LAM). The anococcygeal ligament fixed the EAS to the coccygeal bone. The puborectal-muscle loops, which define the levator hiatus, passed around the anorectal junction and inserted anteriorly on the perineal body and pubic bone. The LAM had a common anterior attachment to the pubic bone, but separated posteriorly into puborectal and “pubovisceral” muscles. This pubovisceral muscle was bilayered: its internal layer attached to the conjoint longitudinal muscle of the rectum and the rectococcygeal fascia, while its outer, patchy layer reinforced the inner layer. ASC contraction makes the ano-rectal bend more acute and lifts the pelvic floor. Extensions of the rectal longitudinal smooth muscle to the coccygeal bone (rectococcygeal muscle), perineal body (rectoperineal muscle), and endopelvic fascia (conjoint longitudinal and pubovisceral muscles) formed a “diaphragm” at the inferior boundary of the mesorectum that suspended the anorectal junction. Its contraction should straighten the anorectal bend.

Conclusion

The serial-section approach settled contentious topographic issues of the pelvic floor. We propose that the ASC is involved in continence and the rectal diaphragm in defecation.     

Deep abdominal muscle activity following supratentorial stroke

This study assessed the level and symmetry of deep abdominal muscle activation following a supratentorial stroke during a modified hip flexion task. Movement-related activation levels in the transversus abdominus (TrA) and internal oblique (IO) were investigated in people with a subacute (<3.25 months) supratentorial stroke (n = 11) and a matched control group (n = 11). Electromyographic activity in TrA and IO were recorded using fine wires inserted under ultrasound guidance while participants performed a standardised head lift or unilateral hip flexion. During head lift there was no significant difference in the amplitude of activation ipsi- and contra-lateral to the stroke or between groups. During unilateral hip flexion the TrA and IO were activated more on both sides when moving the paretic leg. In the control group muscle activity was modulated by task with activity being higher ipsilateral to the moving leg; in contrast in the stroke group IO muscle activity tended to be higher on the non-paretic side irrespective of moving limb. Greater TrA and IO muscle activity during hip flexion of the paretic leg may represent compensatory activity that acts to facilitate activation of the paretic hip flexors and/or the presence of overflow.     

Activity of deep abdominal muscles increases during submaximal flexion and extension efforts but antagonist co-contraction remains unchanged

Lumbo-pelvic stability relies, amongst other factors, on co-contraction of the lumbo-pelvic muscles. However, during submaximal trunk flexion and extension efforts, co-contraction of antagonist muscles is limited. It was predicted that activity of the deeper lumbo-pelvic muscles that are often excluded from analysis (transversus abdominis (TrA) and the deep fascicles of multifidus (DM)), would increase with load in each direction. In eleven healthy subjects, electromyographic activity (EMG) was recorded from eight trunk muscles using surface and fine-wire electrodes. Subjects performed isometric flexion and extension efforts to submaximal loads of 50, 100, 150 and 200 N and a maximal voluntary contraction (MVC). Loading tasks were then repeated in trials in which subjects knew that the load would release at an unpredictable time. Compared to the starting position, EMG of all muscles, except DM, increased during MVC efforts in both directions. During the flexion and extension submaximal tasks, there was no increased co-contraction of antagonist muscles. However, TrA EMG increased in both directions. In the unpredictable trials, EMG of all lumbo-pelvic muscles except TrA was decreased. These findings provide further support for a contribution of TrA to lumbo-pelvic stability. In submaximal tasks, TrA activation may enhance stability as a strategy to improve trunk stiffness without requiring a concurrent increase in activity of the larger torque producing trunk muscles.