Functional roles of abdominal and back muscles during isometric axial rotation of the trunk

Association between expiratory mouth pressure and abdominal muscle activity in healthy young males

PURPOSE

To clarify the association between forced expiration and the abdominal muscles by assessing the relationship between expiratory mouth pressure and abdominal muscle activity in healthy young males.

METHODS

Twenty-five males underwent forced expiration at 20, 30, 50, 75, and 100% of the maximal expiratory mouth pressure. Mouth pressure was measured using a bridge-type transducer connected to a mouth pressure meter. Abdominal crunch, twist crunch, and abdominal hollowing at maximal voluntary contraction were also performed. During forced expiration and abdominal exercises, the activity of the rectus abdominis (RA), oblique externus abdominis/oblique internus abdominis (OE/OI), and OI/transversus abdominis (OI/TrA) was measured using surface electromyography.

RESULTS

The determination coefficient (r2) for the linear relationship between mouth pressure and abdominal muscle activity was 0.86 ± 0.15 for the RA, 0.93 ± 0.06 for the OE/OI, and 0.90 ± 0.14 for the OE/OI. The slope of the linear relationship with r2 ≥ 0.50 showed no significant difference between the RA (0.22 ± 0.27) and the OE/OI (0.27 ± 0.21). However, it was significantly greater in the OI/TrA (1.78 ± 1.41) than in the RA and OE/OI. The OE/OI activity was significantly lower in the maximal forced expiration than in twist crunch, and the OI/TrA activity was not significantly greater in the maximal forced expiration than in twist crunch.

CONCLUSION

All abdominal muscles contribute to forced expiration with a greater contribution of the OI and TrA than the RA and OE. Furthermore, the contribution of the TrA would be greater than that of the OI.

Lumbar muscle adaptations to external perturbations are modulated by trunk posture

PURPOSE

To investigate if the recruitment of different regions within the lumbar extensor muscles in response to unexpected perturbations depends on trunk posture.

METHODS

In a semi-seated posture, healthy adult participants experienced unexpected posterior-anterior trunk perturbations in three different postures: neutral, trunk flexion and left trunk rotation. High-density surface electromyography was used to identify the regional distribution of activation within the lumbar erector spinae muscles. The effect of posture and side (left vs right) on muscle activity and centroid coordinates was investigated at baseline and in response to perturbations.

RESULTS

Higher muscle activity was observed in trunk flexion compared to neutral and rotation postures at baseline (multiple p < 0.001) and in response to the perturbation (multiple p < 0.01). At baseline, the centroid of the electromyographic amplitude distribution was localized more medially in trunk flexion compared to trunk neutral posture (p = 0.003), while activation was localized more laterally in response to the perturbation (multiple p < 0.05). When the trunk was rotated, the electromyographic amplitude distribution was localized more cranially on the left than the right side, both at baseline (p = 0.001) and in response to the perturbation (p = 0.001). Finally, a more lateral location of the centroid on the left side in rotation compared to neutral posture was observed in response to the perturbation (multiple p < 0.001).

CONCLUSIONS

Regional differences in the distribution of electromyographic amplitude indicate that different muscle regions were recruited in different trunk postures and in response to perturbations, possibly based on regional mechanical advantage of the erector spinae muscle fibers.

WALKING SLOPE AND HEAVY BACKPACK LOADS AFFECT TORSO MUSCLE ACTIVITY AND KINEMATICS

The independent effects of sloped walking or carrying a heavy backpack on posture and torso muscle activations have been reported. While the combined effects of sloped walking and backpack loads are known to be physically demanding, how back and abdominal muscles adapt to walking on slopes with heavy load is unclear. This study quantified three-dimensional pelvis and torso kinematics and muscle activity from longissimus, iliocostalis, rectus abdominis, and external oblique during walking on 0° and ± 10° degree slopes with and without backpack loads using two different backpack configurations (hip-belt assisted and shoulder-borne). Iliocostalis activity was greater during downhill and uphill compared to level walking, but longissimus was only greater during uphill. Rectus abdominis activity was greater during downhill and uphill compared to level, while external oblique activity decreased as slopes progressed from down to up. Longissimus, but not iliocostalis, activity was reduced during both backpack configurations compared to walking with no pack. Hip-belt assisted load carriage required less rectus abdominis activity compared to using shoulder-borne only backpacks; however, external oblique was not influenced by backpack condition. Our results revealed different responses between iliocostalis and longissimus, and between rectus abdominis and external obliques, suggesting different motor control strategies between anatomical planes.

Effects of "Taking the Waist as the Axis" Therapy on trunk postural control disorder after stroke: A randomized controlled trial

Background

Sufficient attention to trunk rehabilitation after stroke is still lacking. Loss of trunk selective activity is considered to be the leading cause of trunk postural control disorder after stroke. "Taking the Waist as the Axis" Therapy (WAT) was developed as a combination of the concept of "Taking the Waist as the Axis" from Tai Chi and the rehabilitation of trunk dysfunction after stroke. The present clinical trial examined and assessed the effects of WAT on stroke patients.

Methods

A total of 43 stroke hemiplegic patients with trunk postural control disorder, whose Trunk Impairment Scale (TIS) scoring between 8 and 18, participated in the present study and were allocated randomly to the experimental (n = 23) or control groups (n = 20). The experimental group received WAT plus conventional therapy, and the control group received "Trunk Selective Activity" Therapy (TSAT) plus conventional therapy. Both groups received treatment once daily and 5 times per week for 3 weeks. The Trunk Impairment Scale (TIS), Fugl-Meyer Assessment (FMA), Berg Balance Scale (BBS), change of Intra-abdominal Pressure (IAP), static balance ability assessment, rapid ventilation lung function test and the Modified Barthel Index (MBI) were evaluated before and after intervention for both groups.

Results

The experimental group was superior to the control group in TIS [4 (2, 5) vs. 3 (1.25, 4), p = 0.030], change of IAP [-3 (-8, -1.33) vs. -0.02 (-3.08, 6), p = 0.011], FMA-upper extremity [10 (6, 18) vs. 1 (0, 3), p = 0.002], FMA-lower extremity [2 (1, 4) vs. 1 (0, 2), p = 0.009] and FMA [14 (7, 21) vs. 2 (0.25, 3.75), p = 0.001]. Within experimental group, forced vital capacity (FVC) [81.35 (63.30, 94.88) vs. 91.75 (79.40, 97.90), p = 0.02] was significantly improved.

Conclusion

WAT was an effective trunk treatment after stroke, which significantly improved the patients' trunk posture control ability, motor function and forced vital capacity. However, the results still need to be interpreted with caution for the intervention only lasted for 3 weeks.

Verification of surface electromyographic activity of the oblique externus abdominis using ultrasound shear wave elastography

This study used ultrasound shear wave elastography (SWE) to revalidate whether surface electromyographic (EMG) electrodes placed on the oblique externus abdominis (OE) can detect only the OE activity without the confounding activity of the underlying oblique internus abdominis (OI). During left and right trunk rotations, the EMG activity was acquired using surface EMG electrodes placed on the right OE. Shear wave velocity (V_s ) values of the right OE and OI were acquired using SWE. The EMG activity during the left and right trunk rotations significantly increased as the level of exertion increased (25%, 50%, 75%, and 100% of the one-repetition maximum [1RM]). The V_s of the right OE was significantly different only between 25% and 75% 1RM in the right trunk rotation, but significantly increased from 25% to 75% 1RM during the left trunk rotation. The V_s of the right OI during the right trunk rotation significantly increased with increased levels of exertion, except between 50% and 75% 1RM. The results for the V_s of the OE and OI in the right trunk rotation suggest that surface EMG electrodes placed on the OE would detect not only the antagonistic OE activity but also the agonistic OI activity.

Electromyographic Comparison of an Abdominal Rise on a Ball with a Traditional Crunch

We propose a new exercise, the abdominal rise on the ball, to replace the traditional crunch in exercise programs. The aim of this study is to compare the activity of the abdominal muscles when performing an ARB with the same activity when performing a traditional crunch. Twenty healthy adults participated in the study. Surface electromyography (EMG) was recorded from the upper and lower rectus abdominis (URA, LRA), internal oblique (IO), external oblique (EO), transversus abdominis (TrA), and erector spinae (ES). EMG values were normalized to maximal voluntary isometric contraction. A paired t-test, nonparametric Wilcoxon test and correlation coefficient were used for statistical analysis. The normalized EMG values of EO, TrA and ES, were statistically significantly higher during the abdominal rise on the ball compared to the traditional crunch, while URA, LRA and IO were significantly lower during the abdominal rise on the ball compared to the traditional crunch. TrA, EO and IO are sufficiently activated during an abdominal rise on a ball, so the exercise could be deemed effective for strengthening these muscles.

Sex-Dependent Estimation of Spinal Loads During Static Manual Material Handling Activities-Combined in vivo and in silico Analyses

Manual material handling (MMH) is considered as one of the main contributors to low back pain. While males traditionally perform MMH tasks, recently the number of females who undertake these physically-demanding activities is also increasing. To evaluate the risk of mechanical injuries, the majority of previous studies have estimated spinal forces using different modeling approaches that mostly focus on male individuals. Notable sex-dependent differences have, however, been reported in torso muscle strength and anatomy, segmental mass distribution, as well as lifting strategy during MMH. Therefore, this study aimed to use sex-specific models to estimate lumbar spinal and muscle forces during static MHH tasks in 10 healthy males and 10 females. Motion-capture, surface electromyographic from select trunk muscles, and ground reaction force data were simultaneously collected while subjects performed twelve symmetric and asymmetric static lifting (10 kg) tasks. AnyBody Modeling System was used to develop base-models (subject-specific segmental length, muscle architecture, and kinematics data) for both sexes. For females, female-specific models were also developed by taking into account for the female’s muscle physiological cross-sectional areas, segmental mass distributions, and body fat percentage. Males showed higher absolute L5-S1 compressive and shear loads as compared to both female base-models (25.3% compressive and 14% shear) and female-specific models (41% compressive and 23.6% shear). When the predicted spine loads were normalized to subjects’ body weight, however, female base-models showed larger loads (9% compressive and 16.2% shear on average), and female-specific models showed 2.4% smaller and 9.4% larger loads than males. Females showed larger forces in oblique abdominal muscles during both symmetric and asymmetric lifting tasks, while males had larger back extensor muscle forces during symmetric lifting tasks. A stronger correlation between measured and predicted muscle activities was found in females than males. Results indicate that female-specific characteristics affect the predicted spinal loads and must be considered in musculoskeletal models. Neglecting sex-specific parameters in these models could lead to the overestimation of spinal loads in females.

Ultrasound Measurement of the Transverse Abdominis, Internal Oblique, and External Oblique Muscles Associated with Forward Head Posture and Reduced Cranio-Vertebral Angle

Background

Abnormal posture can affect the alignment of the cervical spine, which can lead to various physical problems. There are many ways to solve the problem by limiting the area around the neck to restore abnormal neck condition. However, there is a need to look at these problems from an enlarged perspective through the relationship between the cervical spine and trunk. This study aimed to investigate the significance of the thickness of the transverse abdominis, internal oblique, and external oblique muscles in patients with forward head posture and reduced cranio-vertebral angle.

Material/Methods

We included 24 healthy adult males in their 20s without lower back pain. The cranio-vertebral angle (CVA) in all the subjects was measured with the help of pictures taken in the sagittal plane using a digital camera. The thickness of muscles, including transverse abdominis (TrA), internal oblique (IO), and external oblique (EO), was measured using a diagnostic ultrasound device. Pearson’s correlation analysis was used to identify the correlation between the variables measured.

Results

CVA showed a statistically significant correlation with TrA thickness (r=0.506/p=0.012), and among the abdominal muscles, there was a significant correlation between IO and EO thickness (r=0.663/p=0.000).

Conclusions

A reduced CVA due to FHP was significantly associated with reduced TrA thickness. Therefore, increasing the bulk of the abdominal muscles with restoration of the abnormal CVA is a potential treatment approach and requires further study.

Segmental coordination and variability of change in direction in long-standing groin pain

BACKGROUND

Long-standing groin pain (LSGP) is a chronic painful condition resulting in both impaired performance and time loss from participation in multidirectional field sport.

RESEARCH QUESTION

What are the differences in intersegmental coordination strategy and variability of trunk-pelvic and thigh coupling during change of direction in subjects with athletic LSGP and asymptomatic control subjects?

METHODS

A motion analysis system was used to collect 3-D kinematic data of the continuous relative phase and the variability of the right and left leg hip. Thoracic-thigh segment data were also collected during multiple ipsilateral turns at a self-selected pace from 16 males with LSGP and 16 asymptomatic controls. It is worth mentioning that, for a more detailed analysis, we divided each cycle diagram into four phases. Independent T-tests were used to compare the two groups.

RESULTS

Subjects with LSGP demonstrate except in phase 2 of the left foot, more out-of-phase movement with both increased variabilities in right/ left thigh - pelvic coupling, right/ left thigh-thoracic, and pelvic- thoracic in every 4 phases and in the decoupling of segmental coordination.

SIGNIFICANCE

Decrease in coordination with higher variability is apparent in subjects with LSGP and this aberrant coordination may lead to unexpected compensatory strategies and control impairments.

Does athletic groin pain affect the muscular co-contraction during a change of direction

BACKGROUND

Groin pain is one of the common problems in multidirectional sports. It seems that abnormal muscular activity and improper movement strategy led to prolongation and high rate of this injury. Therefore, the aim of this study was to Comparing the Average amplitude of Electromyography (AEMG), co-contraction ratio (CCR) of selected thigh and thoracic muscle during turning in individuals with chronic groin pain and healthy individuals.

METHODS

Surface electromyography was collected from the internal oblique/transversus abdominis (IO/TrA), multifidus (MF), adductor Longus (AL) and gluteus Medius (GM) for AEMG and CCR analyzed in 16-males with LSGP and 16-controls in four motion phases during 11 cycles of gait coupled with turning.

RESULTS

Results revealed that in the AEMG apart from the third phase in the muscle of the IO/ Tr. A muscle and in the second phase in the MF muscle in the trunk and in the third phase in the muscle of the AL and the fourth phase in the GM foot Left There was a significant difference in other phases. There was a significant difference in the CCR, except in the second phase of the trunk and the fourth phase of the left foot in the rest of the phases.

CONCLUSIONS

It seems that in athletes with LSGP, have selective muscular activation and CCR have during turning, that may be resulting in compensatory strategies and movement control defects, which may be a useful tool to predict LSGP occurrence in players with a history of groin pain.

Comparison of Peak Ground Reaction Force, Joint Kinetics and Kinematics, and Muscle Activity Between a Flexible and Steel Barbell During the Back Squat Exercise

The flexible barbell is purported to improve training gains compared with an Olympic steel barbell (SB) during the back squat exercise with Division I collegiate American football programs. The two bars loaded at 30% 1-repetition maximum were compared with ten trained Division I American football players (n = 10; age = 19.5 years; body mass = 89.4 kg; body height = 182.0 cm) completing 10 repetitions of the back squat exercise. Analysis included integrated-peak values of electromyography of the rectus femoris, biceps femoris, rectus abdominis, erector spinae, external oblique, vastus lateralis, ground reaction forces, and joint kinematics and kinetics of the hip, knee, and ankle. The flexible bar elicited significant increases in peak joint kinetics (Hip Moment: 229 ± 54 Nm vs. 209 ± 52 Nm; Hip Power: 494 ± 151 W vs. 382 ± 134 W; Knee Power: 305 ± 108 W vs. 241 ± 63 W), peak vertical ground reaction forces (1195 ± 209 N vs. 1120 ± 203 N), and muscle activity (Vastus Lateralis: 75.7 vs. 66.5%, Rectus Abdominis: 190 vs. 115%, Rectus Femoris: 69.8 vs. 59.9%, External Oblique: 115 vs. 69.0%). Greater vertical ground reaction forces, hip moment, hip power, knee power, and muscle activity of the vastus lateralis, rectus abdominis, rectus femoris, and external oblique suggest the FB provides biomechanical and physiological mechanisms for training gains over the SB for 30% of 1-repetition maximum loads.

Trunk musculoskeletal response in maximum voluntary exertions: A combined measurement-modeling investigation

Maximum voluntary exertion (MVE) tasks quantify trunk strength and maximal muscle electromyography (EMG) activities with both clinical and biomechanical implications. The aims here are to evaluate the performance of an existing trunk musculoskeletal model, estimate maximum muscle stresses and spinal forces, and explore likely differences between males and females in maximum voluntary exertions. We, therefore, measured trunk strength and EMG activities of 19 healthy right-handed subjects (9 females and 10 males) in flexion, extension, lateral and axial directions. MVEs for all subjects were then simulated in a subject-specific trunk musculoskeletal model, and estimated muscle activities were compared with EMGs. Analysis of variance was used to compare measured moments and estimated spinal loads at the L5-S1 level between females and males. MVE moments in both sexes were greatest in extension (means of 236 Nm in males and 190 Nm in females) and least in left axial torque (97 Nm in males and 64 Nm in females). Being much greater in lateral and axial MVEs, coupled moments reached ∼50% of primary moments in average. Females exerted less moments in all directions reaching significance except in flexion. Muscle activity estimations were strongly correlated with measurements in flexion and extension (Pearson's r = 0.69 and 0.76), but the correlations were very weak in lateral and axial MVEs (Pearson's r = 0.27 and 0.13). Maximum muscle stress was in average 0.80 ± 0.42 MPa but varied among muscles from 0.40 ± 0.22  MPa in rectus abdominis to 0.99 ± 0.29 MPa in external oblique. To estimate maximum muscle stresses and evaluate validity of a musculoskeletal model, MVEs in all directions with all coupled moments should be considered.

Ankle restrictive firefighting boots alter the lumbar biomechanics during landing tasks

Firefighters incur high incidences of lower back and body injuries. Firefighting boots, with specific design requirements, have been shown to reduce ankle range of motion. This reduction has been associated with impaired force dissipation and lower body kinematic alterations. Thus, the aim of this study was to determine the relationship between firefighting boots, lumbar biomechanics and load carriage during landing. Our data indicates that when wearing firefighting boots, lumbar forces increased and kinematics changed in frontal and transverse planes. These changes may be occurring due to the restrictive shaft of the firefighting boot reducing ankle range of motion. Comparisons between unloaded and loaded conditions also showed increased changes in lumbar biomechanics, independent of footwear worn. Therefore, wearing firefighting boots, in addition to operational loading, may be placing firefighters at greater risk of lumbar injuries. Future research investigating firefighting boots and additional load carriage on lower body biomechanics during landing is recommended.

Equine Exercise in Younger and Older Adults: Simulated Versus Real Horseback Riding

Horseback riding is an effective exercise for improving postural control and balance. To reduce costs and improve accessibility, simulated horseback riding has been developed; but no differential effects of simulated and real horseback riding on muscle activation patterns in older adults have been studied. Thus, we compared muscle activation patterns for older and younger adults engaged in real and simulated horseback riding exercises, using surface electromyography recordings of the erector spinae, rectus abdominis, internal oblique abdominis, and rectus femoris muscles. We recorded muscle activity for three riding patterns: walk, slow trot, and fast trot. Muscle activation was uniformly higher for simulated (vs. real) horseback riding and increased from the walking pattern through slow and fast trot. There was no age effect, but among older participants, muscle activation was higher for simulated (vs. real) horseback riding across all gait types. Simulated and real riding produced a similar pattern of muscle activation of the thigh and trunk. These results demonstrate that simulated horseback riding can be an effective alternative to actual riding for increasing trunk and thigh muscle activation and improving postural control and balance, perhaps especially among older adults.

Relative mobility of the pelvis and spine during trunk axial rotation in chronic low back pain patients: A case-control study

Background

Trunk axial rotation is a risk factor for chronic low back pain (CLBP). The characteristics of rotational mobility in the pelvis and spine among CLBP patients are not fully understood.

Purpose

The purpose of this study was to examine three-dimensional kinematic changes, and to compare the differences of rotational mobility and coupled motion, in patients with and without CLBP.

Methods

Fifteen patients with CLBP and 15 age and sex matched healthy subjects participated in this study. Each subject performed trunk rotation to maximum range of motion (ROM) in a standing position. The kinematics data was collected using a three-dimensional motion analysis system. The outcomes measured were the rotational ROM and the spine/pelvis ratio (SPR) in transvers plane at both maximum and 50% rotation position. The coupled angles in sagittal and frontal planes were also measured.

Results

No significant differences in rotational ROM of the thorax, pelvis, and spine were observed between two groups at maximum rotation position. However, there was a significant interaction between groups and rotational ROM of pelvis and spine (F = 4.57, p = 0.04), and the SPR in CLBP patients was significantly greater than that of the healthy subjects (CLBP; 0.50 ± 0.10 Control; 0.41 ± 0.12, p = 0.04). The results at 50% rotation position were similar to that at maximum rotation. This indicates a relative increase in spinal rotation in the CLBP patients during trunk rotation. Moreover, the CLBP patients exhibited a significantly higher anterior tilt of the pelvis and extension of the spine in the sagittal plane coupled with rotation.

Conclusions

CLBP patients had relative hyper rotational mobility of the spine as well as excessive spinal extension coupled with trunk rotation. These results suggest that uncoordinated trunk rotation might be a functional failure associated with CLBP.

Trunk Muscle Function Deficit in Youth Baseball Pitchers With Excessive Contralateral Trunk Tilt During Pitching

OBJECTIVE

Pitching technique is one of many factors that affect injury risk. Exhibiting excessive contralateral trunk tilt (CLT) during pitching has been linked to higher ball speed but also to increased joint loading. Deficit in trunk muscle strength has been suggested as an underlying cause of this movement pattern. The purpose of the study was to compare trunk muscle strength between youth baseball pitchers with varying degree of CLT during pitching.

DESIGN

Cross-sectional study.

SETTING

Baseball practice fields.

PARTICIPANTS

Twenty-eight youth baseball pitchers.

INDEPENDENT VARIABLES

Pitching technique was captured using a video camera. Based on the 2-dimensional trunk contralateral flexion angle, pitchers were categorized into low (<15 degrees), moderate (15-30 degrees), or high (>30 degrees) CLT groups.

MAIN OUTCOME MEASURES

Maximum isometric strength tests for trunk flexion, extension, and bilateral rotation, measured using a dynamometer.

RESULTS

The pitchers with high CLT (n = 10) had longer pitching experience (P = 0.014), produced higher ball speed (P = 0.003) compared with the pitchers with moderate (n = 10) and low (n = 8) CLT, but demonstrated greater asymmetry in trunk rotation strength (relative weakness in rotation strength toward dominant side) compared with the pitchers with low CLT (P = 0.015).

CONCLUSIONS

Excessive CLT may be a strategy that young pitchers learn to achieve higher ball velocity but also may be associated with imbalance between the oblique muscles on dominant and nondominant side, which may be acquired from repetitive pitching. Strengthening and emphasizing the use of dominant side oblique muscles may keep pitchers from leaning excessively during pitching and thus decrease joint loading.

Development and clinical application of a computer-aided real-time feedback system for detecting in-bed physical activities

BACKGROUND AND OBJECTIVE

Being bedridden long-term can cause deterioration in patients' physiological function and performance, limiting daily activities and increasing the incidence of falls and other accidental injuries. Little research has been carried out in designing effective detecting systems to monitor the posture and status of bedridden patients and to provide accurate real-time feedback on posture. The purposes of this research were to develop a computer-aided system for real-time detection of physical activities in bed and to validate the system's validity and test-retest reliability in determining eight postures: motion leftward/rightward, turning over leftward/rightward, getting up leftward/rightward, and getting off the bed leftward/rightward.

METHODS

The in-bed physical activity detecting system consists mainly of a clinical sickbed, signal amplifier, a data acquisition (DAQ) system, and operating software for computing and determining postural changes associated with four load cell sensing components. Thirty healthy subjects (15 males and 15 females, mean age = 27.8 ± 5.3 years) participated in the study. All subjects were asked to execute eight in-bed activities in a random order and to participate in an evaluation of the test-retest reliability of the results 14 days later. Spearman's rank correlation coefficient was used to compare the system's determinations of postural states with researchers' recordings of postural changes. The test-retest reliability of the system's ability to determine postures was analyzed using the interclass correlation coefficient ICC(3,1).

RESULTS

The system was found to exhibit high validity and accuracy (r = 0.928, p < 0.001; accuracy rate: 87.9%) in determining in-bed displacement, turning over, sitting up, and getting off the bed. The system was particularly accurate in detecting motion rightward (90%), turning over leftward (83%), sitting up leftward or rightward (87-93%), and getting off the bed (100%). The test-retest reliability ICC(3,1) value was 0.968 (p < 0.001).

CONCLUSIONS

The system developed in this study exhibits satisfactory validity and reliability in detecting changes in-bed body postures and can be beneficial in assisting caregivers and clinical nursing staff in detecting the in-bed physical activities of bedridden patients and in developing fall prevention warning systems.

Holding a Handle for Balance during Continuous Postural Perturbations-Immediate and Transitionary Effects on Whole Body Posture

When balance is exposed to perturbations, hand contacts are often used to assist postural control. We investigated the immediate and the transitionary effects of supportive hand contacts during continuous anteroposterior perturbations of stance by automated waist-pulls. Ten young adults were perturbed for 5 min and required to maintain balance by holding to a stationary, shoulder-high handle and following its removal. Center of pressure (COP) displacement, hip, knee and ankle angles, leg and trunk muscle activity and handle contact forces were acquired. The analysis of results show that COP excursions are significantly smaller when the subjects utilize supportive hand contact and that the displacement of COP is strongly correlated to the perturbation force and significantly larger in the anterior than posterior direction. Regression analysis of hand forces revealed that subjects utilized the hand support significantly more during the posterior than anterior perturbations. Moreover, kinematical analysis showed that utilization of supportive hand contacts alter posture of the whole body and that postural readjustments after the release of the handle, occur at different time scales in the hip, knee and ankle joints. Overall, our findings show that supportive hand contacts are efficiently used for balance control during continuous postural perturbations and that utilization of a handle has significant immediate and transitionary effects on whole body posture.

Sportsman's hernia? An ambiguous term

Groin pain is common in athletes. Yet, there is disagreement on aetiology, pathomechanics and terminology. A plethora of terms have been employed to explain inguinal-related groin pain in athletes. Recently, at the British Hernia Society in Manchester 2012, a consensus was reached to use the term inguinal disruption based on the pathophysiology while lately the Doha agreement in 2014 defined it as inguinal-related groin pain, a clinically based taxonomy.

This review article emphasizes the anatomy, pathogenesis, standard clinical assessment and imaging, and highlights the treatment options for inguinal disruption.

Effects of flexi-bar and non-flexi-bar exercises on trunk muscles activity in different postures in healthy adults

[Purpose] The purpose of this study was to assess the effects of flexi-bar exercises and non-flexi-bar exercises on trunk muscle activity in different postures in healthy adults. [Subjects] Twenty healthy right-hand dominant adults (10 males and 10 females) were selected for this study. None of the participants had experienced any orthopedic problems in the spine or in the upper and lower extremities in the previous six months. [Methods] The subjects were instructed to adopt three exercise postures: posture 1, quadruped; posture 2, side-bridge; and posture 3, standing. Surface electromyography of selected trunk muscles was normalized to maximum voluntary isometric contraction. [Results] The external oblique, internal oblique, and erector spinae muscle activity showed significant differences between flexi-bar exercises and non-flexi-bar exercises. [Conclusion] The results of this study suggest that flexi-bar exercises are useful in the activation of trunk muscles.

The effect of chronic low back pain on trunk accuracy in a multidirectional isometric tracking task

STUDY DESIGN

A cross-sectional study to quantify trunk motor control during multidirectional isometric tracking tasks.

OBJECTIVE

To investigate the effect of chronic low back pain (LBP) on trunk neuromuscular performance while participants performed isometric exertions of trunk muscles to track targets in different angles with various magnitudes.

SUMMARY OF BACKGROUND DATA

Tracking tasks especially in multidirectional activities are among the common research methods to quantify human motor control in different conditions. However, little information is available on trunk motor control during these tasks. There is no study investigating trunk accuracy during multidirectional isometric tracking tasks in patients with LBP.

MATERIALS AND METHODS

Twelve patients with chronic LBP and 16 asymptomatic participants performed isometric target tracking tasks in 12 different directions with varying magnitude, from 0% to 80% of individual maximum voluntary exertion, in upright standing posture. The tracking system included a moving target object that moved on a straight line in a predefined angle with the rate of 6% maximum voluntary exertion/s. Trunk accuracy was quantified by computing constant error and variable error during each trial. A mixed model repeated measure analysis of variance was conducted to assess statistical analysis.

RESULTS

Patients with chronic LBP track the target object with higher error compared with healthy controls across almost all of the target angles (P < 0.01). Trunk accuracy decreased significantly in higher level of exertions (P < 0.01).

CONCLUSION

The results provided additional evidence of a change in trunk control strategies in patients with chronic LBP. Decreased accuracy of trunk during isometric tracking tasks especially in higher levels of asymmetric exertions may explain higher risk of low back injuries in these activities.

LEVEL OF EVIDENCE

4.

Axial rotation mechanics in a cadaveric lumbar spine model: a biomechanical analysis

BACKGROUND CONTEXT

Postoperative patient motions are difficult to directly control. Very slow quasistatic motions are intuitively believed to be safer for patients, compared with fast dynamic motions, because the torque on the spine is reduced. Therefore, the outcomes of varying axial rotation (AR) angular loading rate during in vitro testing could expand the understanding of the dynamic behavior and spine response.

PURPOSE

To observe the effects of the loading rate in AR mechanics of lumbar cadaveric spines via in vitro biomechanical testing.

STUDY DESIGN

An in vitro biomechanical study in lumbar cadaveric spines.

METHODS

Fifteen lumbar cadaveric segments (L1-S1) were tested with varying loading frequencies of AR. Five different frequencies were normalized with the base line frequency (0.125 Hz n=15) in this analysis: 0.05 Hz (n=6), 0.166 Hz (n=6), 0.2 Hz (n=10), 0.25 Hz (n=10), and 0.4 Hz (n=8).

RESULTS

The lowest frequency (0.05 Hz) revealed significant differences (p<.05) for all parameters (torque, passive angular velocity, axial velocity [AV], axial reaction force [RF], and energy loss [EL]) with respect to all other frequencies. Significant differences (p<.05) were observed in the following: torque (0.4 Hz with respect to 0.2 Hz and 0.25 Hz), passive sagittal angular velocity (SAV) (0.4 Hz with respect to all other frequencies; 0.166 Hz with respect to 0.25 Hz), axial linear velocity (0.4 Hz with respect to all other frequencies), and RF (0.4 Hz with respect to 0.2 Hz and 0.25 Hz). Strong correlations (R2>0.75, p<.05) were observed between RF with intradiscal pressure (IDP) and AR angular displacement with IDP. Intradiscal pressure (p<.05) was significantly larger in 0.2 Hz in comparison with 0.125 Hz.

CONCLUSIONS

Evidences suggest that measurements at very small frequencies (0.05 Hz) of torque, SAV, AV, RF, and EL are significantly reduced when compared with higher frequencies (0.166 Hz, 0.2 Hz, 0.25 Hz, and 0.4 Hz). Higher frequencies increase torque, RF, passive SAV, and AV. Higher frequencies induce a greater IDP in comparison with lower frequencies.

Angular velocity affects trunk muscle strength and EMG activation during isokinetic axial rotation

OBJECTIVE

To evaluate trunk muscle strength and EMG activation during isokinetic axial rotation at different angular velocities.

METHOD

Twenty-four healthy young men performed isokinetic axial rotation in right and left directions at 30, 60, and 120 degrees per second angular velocity. Simultaneously, surface EMG was recorded on external oblique (EO), internal oblique (IO), and latissimus dorsi (LD) bilaterally.

RESULTS

In each direction, with the increase of angular velocity, peak torque decreased, whereas peak power increased. During isokinetic axial rotation, contralateral EO as well as ipsilateral IO and LD acted as primary agonists, whereas, ipsilateral EO as well as contralateral IO and LD acted as primary antagonistic muscles. For each primary agonist, the root mean square values decreased with the increase of angular velocity. Antagonist coactiviation was observed at each velocity; however, it appears to be higher with the increase of angular velocity.

CONCLUSION

Our results suggest that velocity of rotation has great impact on the axial rotation torque and EMG activity. An inverse relationship of angular velocity was suggested with the axial rotation torque as well as root mean square value of individual trunk muscle. In addition, higher velocity is associated with higher coactivation of antagonist, leading to a decrease in torque with the increase of velocity.

Passive mechanical properties of rat abdominal wall muscles suggest an important role of the extracellular connective tissue matrix

Abdominal wall muscles have a unique morphology suggesting a complex role in generating and transferring force to the spinal column. Studying passive mechanical properties of these muscles may provide insights into their ability to transfer force among structures. Biopsies from rectus abdominis (RA), external oblique (EO), internal oblique (IO), and transverse abdominis (TrA) were harvested from male Sprague-Dawley rats, and single muscle fibers and fiber bundles (4-8 fibers ensheathed in their connective tissue matrix) were isolated and mechanically stretched in a passive state. Slack sarcomere lengths were measured and elastic moduli were calculated from stress-strain data. Titin molecular mass was also measured from single muscle fibers. No significant differences were found among the four abdominal wall muscles in terms of slack sarcomere length or elastic modulus. Interestingly, across all four muscles, slack sarcomere lengths were quite long in individual muscle fibers (>2.4 µm), and demonstrated a significantly longer slack length in comparison to fiber bundles (p < 0.0001). Also, the extracellular connective tissue matrix provided a stiffening effect and enhanced the resistance to lengthening at long muscle lengths. Titin molecular mass was significantly less in TrA compared to each of the other three muscles (p < 0.0009), but this difference did not correspond to hypothesized differences in stiffness.

The effects of safety handrails and the heights of scaffolds on the subjective and objective evaluation of postural stability and cardiovascular stress in novice and expert construction workers

Work performed on scaffolds carries the risk of falling that disproportionately threatens the safety and health of novice construction workers. Hence, objective measures of the postural stability, cardiovascular stress, and subjective difficulty in maintaining postural balance were evaluated for four expert and four novice construction workers performing a manual task in a standing posture on a scaffold with and without safety handrails at two different elevation heights. Based on a multivariate analysis of variance, the experience, scaffold height, and presence of a handrail were found to significantly affect measures of the postural stability and cardiovascular stress. At a lower level of worker experience, a higher scaffold height, and in the absence of a handrail (which may correspond to higher risk of a fall), postural stability was significantly reduced, while cardiovascular stress and subjective difficulties in maintaining postural balance increased. We emphasize the importance of training and handrails for fall prevention at construction sites.

Abdominal muscle strains in professional baseball: 1991-2010

BACKGROUND

The abdominal core muscles (internal and external oblique, rectus and transversus abdominis) play an important role in the baseball activities of pitching and hitting. Proper abdominal muscle activation during throwing and swinging is crucial for generating optimal ball velocity and bat speed. Abdominal muscle strains can result in substantial loss of playing time, and their incidence has never been reported in baseball.

HYPOTHESIS

The incidence of abdominal muscle strains in Major League Baseball has been rising over the past 20 years. Injuries contralateral to the dominant arm or batting side are more common and require more time to recover.

STUDY DESIGN

Descriptive epidemiology study.

METHODS

Abdominal muscle strains in baseball players were determined by retrospective review of the Major League Baseball disabled list from 1991 to 2010. Player age, position, dominant hand, batting side, and recovery time were recorded.

RESULTS

There were 393 abdominal muscle strains in Major League Baseball from 1991 to 2010, constituting 5% of all baseball injuries. At least 92% of these injuries were internal/external oblique or intercostal muscle strains, and 44% of injuries were sustained by pitchers. The reinjury rate was 12.1%. An upward trend was seen from 1991 to 2010, especially in early-season injuries, and the overall injury rate was 22% higher in the 2000s than in the 1990s. Pitchers averaged 35.4 days on the disabled list compared with 26.7 days for position players (P < .01); 78.1% of pitcher injuries were contralateral to their dominant arm, and 70.3% of position player injuries were contralateral to their dominant batting side (excluding switch hitters). Position players missed more time for contralateral than for ipsilateral injuries (28.9 vs 21.2 days, P = .03), whereas pitchers missed more time for ipsilateral injuries (44.5 vs 32.8 days, P = .04).

CONCLUSION

The incidence of abdominal muscle strains in baseball has been increasing over the past 20 years, especially early in the season, and there is a relatively high reinjury rate. This upward trend is in spite of new and more advanced diagnostic procedures, preventive core strengthening exercise programs, and rehabilitation techniques. Injuries contralateral to the dominant arm or batting side are more common.

Reliability of magnetic resonance imaging measurements of the cross-sectional area of the muscle contractile and non-contractile components

BACKGROUND/PURPOSE

Magnetic resonance imaging (MRI) is increasingly used to study skeletal muscles patients with muscular disorders. We report an MRI technique for evaluating the trunk muscles. This technique takes both the component surface area (CSA) and the density of the muscles on MRI axial slices into account . Using a computer-based image analysis system, we combined MRI data measuring the muscle CSA, which was separated into the contractile component (CCSA) and the non-contractile component (NCCSA). The purpose of this study was to analyze the reliability of this method of measuring the CSA, CCSA and NCCSA in trunk muscles on MRI axial slices through L4 and T12.

METHODS

Thirty volunteer subjects were enrolled in this study. Two acquisitions were performed. For the reliability analyses, each of the two slices (T12 and L4) from 30 subjects was measured by three raters trained in this technique, on two occasions 2 weeks apart. Each muscle was surrounded and its CSA, NCCSA and CCSA were recorded. For each muscle, the agreement between the two sets of 30 measurements performed by three observers was evaluated by calculating an intra-class correlation coefficient (ICC).

RESULTS

Regarding the slice through L4 and T12, the reliabilities of the measurement of CSA, CCSA were very good for all the muscles except the parietal muscles.

CONCLUSION

MRI measurements of the trunk muscle cross-sectional areas and of the CCSA and NCCSA are reliable.

The effect of exertion level on activation patterns and variability of trunk muscles during multidirectional isometric activities in upright posture

STUDY DESIGN

An experimental design to investigate activation patterns of trunk muscles during multidirectional exertions.

OBJECTIVES

To evaluate trunk muscle activation patterns in varying directions and moment magnitudes during an isometric task, and to investigate the effects of angle and level of isometric exertion on the electromyography (EMG) variability of trunk muscles in upright posture.

SUMMARY OF BACKGROUND DATA

Few studies have investigated trunk muscle activation patterns in multidirectional exertions with different moment magnitudes.

METHODS

A total of 12 asymptomatic male subjects were participated in the study. The EMG activity of 10 selected trunk muscles was collected in the 3 seconds end point matching tasks in 8 angles and 3 magnitudes of exertion. Trunk muscle activation patterns were examined using EMG tuning curves and measuring preferred direction (mean vector direction) and the index of spatial focus. The effect of exertion level on these measures was investigated by Rao test. The effects of angle and level of exertion on the EMG variability of trunk muscles were tested by analysis of variance with repeated measures design.

RESULTS

No significant difference in EMG tuning curves, preferred direction, and the index of spatial focus was found for each muscle studied across exertion levels (P > 0.05). The index of spatial focus of most muscles studied was not changed with increasing moment magnitude. EMG variability of trunk muscles was significantly affected by angle and level of exertion and their interaction effect (P < 0.001).

CONCLUSION

Consistent activation patterns of trunk muscles were found within and among subjects in different moment magnitudes. The index of spatial focus indicated that probably no shift to a higher co-contraction strategy has been adapted with increasing moment magnitude. The results suggested that increased EMG variability of trunk muscles in asymmetric exertions may be associated with lower trunk controllability during combined exertions.

Lower trunk kinematics and muscle activity during different types of tennis serves

BACKGROUND

To better understand the underlying mechanisms involved in trunk motion during a tennis serve, this study aimed to examine the (1) relative motion of the middle and lower trunk and (2) lower trunk muscle activity during three different types of tennis serves - flat, topspin, and slice.

METHODS

Tennis serves performed by 11 advanced (AV) and 8 advanced intermediate (AI) male tennis players were videorecorded with markers placed on the back of the subject used to estimate the anatomical joint (AJ) angles between the middle and lower trunk for four trunk motions (extension, left lateral flexion, and left and right twisting). Surface electromyographic (EMG) techniques were used to monitor the left and right rectus abdominis (LRA and RRA), external oblique (LEO and REO), internal oblique (LIO and RIO), and erector spinae (LES and RES). The maximal AJ angles for different trunk motions during a serve and the average EMG levels for different muscles during different phases (ascending and descending windup, acceleration, and follow-through) of a tennis serve were evaluated.

RESULTS

The repeated measures Skill x Serve Type x Trunk Motion ANOVA for maximal AJ angle indicated no significant main effects for serve type or skill level. However, the AV group had significantly smaller extension (p = 0.018) and greater left lateral flexion (p = 0.038) angles than the AI group. The repeated measures Skill x Serve Type x Phase MANOVA revealed significant phase main effects in all muscles (p < 0.001) and the average EMG of the AV group for LRA was significantly higher than that of the AI group (p = 0.008). All muscles showed their highest EMG values during the acceleration phase. LRA and LEO muscles also exhibited high activations during the descending windup phase, and RES muscle was very active during the follow-through phase.

CONCLUSION

Subjects in the AI group may be more susceptible to back injury than the AV group because of the significantly greater trunk hyperextension, and relatively large lumbar spinal loads are expected during the acceleration phase because of the hyperextension posture and profound front-back and bilateral co-activations in lower trunk muscles.

The effect of angle and level of exertion on trunk neuromuscular performance during multidirectional isometric activities

STUDY DESIGN

To quantify trunk muscle capability and controllability in different angles and levels of isometric exertion using a torque tracking system.

OBJECTIVE

To investigate the effect of biaxial isometric exertions on the maximum capability of trunk and to examine the effect of angle and level of isometric exertion on trunk controllability during the tracking task in upright posture.

SUMMARY OF BACKGROUND DATA

Combined motions of trunk at varying exertion levels occur in most daily and occupational activities and are important risk factors of low back pain. Few studies have investigated trunk capability and controllability during multidirectional activities with different exertion levels.

METHODS

Eighteen asymptomatic young male subjects performed isometric contractions of trunk muscles in 8 angles and 3 levels of exertion. The tracking system included a target, which was a thick line with a round endpoint. Subjects were asked to track the target line (path) and match the endpoint while maintaining torque for 3 seconds by exerting isometric contraction against B200 Isostation. The initial part of the tracking task was named path tracking phase and the final part, endpoint matching phase. Trunk capability was determined by measuring peak torque values obtained during maximal voluntary exertions. Trunk controllability was determined by measuring constant error and variable error during tracking tasks. Analysis of variance with repeated measures design was used to test the effects of angle and level of exertion on trunk capability and controllability.

RESULTS

Trunk capability was significantly decreased during biaxial exertions (P < 0.001). Constant error and variable error were significantly affected by angle (P < 0.001) and level (P < 0.001) of exertion during both phases of the tracking task.

CONCLUSION

Trunk capability and controllability were significantly decreased during biaxial exertions. Higher exertion levels had a major negative impact on trunk controllability in both uniaxial and biaxial exertions. The results suggested that combined exertions and more strenuous efforts may impair trunk neuromuscular control, increasing the risk of low back pain.

Analysis of phasic and tonic electromyographic signal characteristics: Electromyographic synthesis and comparison of novel morphological and linear-envelope approaches

The pattern of tonic and phasic components in an EMG signal reflects the underlying behaviour of the central nervous system (CNS) in controlling the musculature. One avenue for gaining a better understanding of this behaviour is to seek a quantitative characterisation of these phasic and tonic components. We propose that these signal characteristics can range between unvarying, tonic and intermittent, phasic activation through a continuum of EMG amplitude modulation. In this paper, we present two new algorithms for quantifying amplitude modulation: a linear-envelope approach, and a mathematical morphology approach. In addition we present an algorithm for synthesising EMG signals with known amplitude modulation. The efficacy of the synthesis algorithm is demonstrated using real EMG data. We present an evaluation and comparison of the two algorithms for quantifying amplitude modulation based on synthetic data generated by the proposed synthesis algorithm. The results demonstrate that the EMG synthesis parameters represent 91.9% and 96.2% of the variance of linear-envelopes extracted from lumbo-pelvic muscle EMG signals collected from subjects performing a repetitive-movement task. This depended, however, on the muscle and movement-speed considered (F=4.02, p<0.001). Coefficients of determination between input and output amplitude modulation variables were used to quantify the accuracy of the linear-envelope and morphological signal processing algorithms. The linear-envelope algorithm exhibited higher coefficients of determination than the most accurate morphological approach (and hence greater accuracy, T=8.16, p<0.001). Similarly, the standard deviation of the coefficients of determination was 1.691 times smaller (p<0.001). This signal processing algorithm represents a novel tool for the quantification of amplitude modulation in continuous EMG signals and can be used in the study of CNS motor control of the musculature in repetitive-movement tasks.

Trunk biomechanics during maximum isometric axial torque exertions in upright standing

BACKGROUND

Activities involving axial trunk rotations/moments are common and are considered as risk factors for low back disorders. Previous biomechanical models have failed to accurately estimate the trunk maximal axial torque exertion. Moreover, the trunk stability under maximal torque exertions has not been investigated.

METHODS

A nonlinear thoracolumbar finite element model along with the Kinematics-driven approach is used to study biomechanics of maximal axial torque generation during upright standing posture. Detailed anatomy of trunk muscles with six distinct fascicles for each abdominal oblique muscle on each side is considered. While simulating an in vivo study of maximal axial torque exertion, effects of antagonistic coactivities, coupled moments and maximum muscle stress on results are investigated.

FINDINGS

Predictions for trunk axial torque strength and relative muscle activities compared well with reported measurements. Trunk strength in axial torque was only slightly influenced by variations in coupled moments. Presence of abdominal antagonistic coactivities and alterations in maximum strength of muscles had, however, greater effect on maximal torque exertion. Abdominal oblique muscles play crucial role in generating moments in all three planes while back muscles are mainly effective in balancing moments in sagittal/coronal planes. Trunk stability is not of a concern in maximum axial torque exertions nor is it improved by antagonistic abdominal coactivities.

INTERPRETATION

In contrast to previous biomechanical model studies, the Kinematics-driven approach accurately predicts the trunk response in maximal isometric axial torque exertions by taking into account detailed anatomy of abdominal oblique muscles while satisfying equilibrium requirements in all planes/directions. In maximal torque exertions, the spine is at much higher risk of tissue injury due to large segmental loads than of instability.

The effect of increasing resistance on trunk muscle activity during extension and flexion exercises on training devices

Although progressive resistance training of trunk muscles on devices is very common, today, the effects of increasing resistance on trunk muscle activity during dynamic extension and flexion movements on training devices have not been reported yet. Thirty healthy subjects participated in maximal isometric and submaximal dynamic (at 30%, 50% and 70% of maximum mean torque (MMT)) extension and flexion exercises on Tergumed lumbar training devices. The normalized (as a percentage of maximal voluntary isometric contractions (MVIC)) electromyographic activity of 16 abdominal and back muscles was investigated. The results of the present study indicated that in general, with increasing resistance from 30% MMT to 50% MMT and 70% MMT, the activity of all back muscles during the extension exercises and the activity of all abdominal muscles during the flexion exercises increased significantly. To train strength (>60% of MVIC), low intensities (30% and 50% MMT) appeared sufficient to affect the back muscles, but for the abdominals higher resistance (70% MMT) was required. In contrast to the other back muscles, the lumbar multifidus demonstrated high activity levels during both the extension and the flexion exercises. As the lumbar multifidus is demonstrated to be an important muscle in segmental stabilization of the lumbar spine, this finding may help in understanding the efficacy of rehabilitation programs using specific training devices.

The influence of pain-related fear on peak muscle activity and force generation during maximal isometric trunk exertions

STUDY DESIGN

A cross-sectional study of peak activation of trunk muscles in 20 participants with chronic low back pain.

OBJECTIVE

To determine how pain-related fear influences peak activation of abdominal and trunk extensor muscles during maximal isometric trunk exertions.

SUMMARY OF BACKGROUND DATA

The pain adaptation model and the pain-spasm-pain model have been proposed to explain differences in trunk muscle activation between healthy participants and those with chronic low back pain. However, there is no clear consensus in the literature in support of either model, and there are no studies that have examined the role of pain-related fear on muscle activity in the context of these 2 models.

METHODS

Participants with chronic low back pain performed a series of maximal isometric exertions into extension, flexion, rotation right and left, and side-bend right and left from a tall kneeling position with the spine in a neutral posture. A doubly multivariate MANCOVA was conducted with a between subject factor of group (high pain-related fear, low pain-related fear), a within subject factor of direction (extension, flexion, rotation left and right, side bend left and right), McGill Pain Questionnaire ratings entered as covariates, and peak EMG for all 10 trunk muscles entered as dependent variables.

RESULTS

Averaged across all pull directions and all 10 trunk muscles assessed, participants with high pain-related fear had peak EMG that was only 49.5% of participants with low fear. Additionally, we found significantly smaller peak force for isometric exertions in flexion, side-bend right, and side-bend left directions.

CONCLUSION

Pain-related fear is associated with increased disability, in theory, because of avoidance behavior and disuse. Our data suggest that participants high in pain-related fear specifically avoid activation of the abdominal muscles during maximal isometric trunk exertions.

The effect of chronic low back pain on trunk muscle activations in target reaching movements with various loads

STUDY DESIGN

A cross-sectional study of the timing of trunk muscle activations between 19 participants with chronic low back pain (LBP) compared with 19 matched controls.

OBJECTIVE

To determine the effects of target height and load on trunk muscle coordination in whole body reaching tasks, and whether participants with chronic LBP display a shift in trunk muscle coordination performing these tasks.

SUMMARY OF BACKGROUND DATA

Changes in the precise timing of trunk muscle activation may cause an initial episode of back pain, or contribute to the development of recurrent or chronic symptoms. However, most paradigms used to examine timing of trunk muscle activation did not necessitate large displacements of the trunk.

METHODS

Participants with and without chronic LBP performed a series of bilateral reaching tasks to 3 target heights with 3 different loads held in the reaching hands. During reaching, joint motions were recorded with an optoelectric system and surface electromyographic signals were collected bilaterally from 5 trunk muscles: rectus abdominis, external oblique, internal oblique, iliocostalis lumborum, and the multifidis, and bilaterally from the deltoid muscle. The onset latencies of the antagonist trunk muscles relative to the deltoid muscle were analyzed to determine the effects of group, target height and load.

RESULTS

Onset of trunk extensor muscles was significantly delayed in participants with chronic LBP compared with control subjects. Further, the onset latency of the antagonist trunk muscles increased with target distance, but decreased with target load.

CONCLUSION

These findings suggest that a well documented control strategy generalizes beyond single joint movements and that individuals with chronic LBP display a shift in this strategy.

Neuromuscular response to cyclic lumbar twisting

OBJECTIVE

To study the influence of 10 min of cyclic twisting motion on abdominal and back muscle activities.

BACKGROUND

Repetitive (cyclic) occupational activity was identified by many epidemiological reports to be a risk factor for the development of work-related musculoskeletal disorders. Biomechanical and physiological confirmation, however, is lacking.

METHODS

Trunk muscle electromyography (EMG) was recorded while participants performed a continuous 10-min maximum lumbar cyclic twisting to the left, and maximum isometric twist to the left and right sides was measured before and after the exercise.

RESULTS

Abdominal muscles contracted symmetrically, independent of twisting direction. The left posterior muscles' integrated EMG (IEMG) decreased during the exercise, whereas the IEMG of the right posterior muscle increased. Simultaneously with increased antagonist coactivity level of the right posterior muscles after the exercise, decrease in maximal isometric left twisting torque was observed. The abdominal muscles did not exhibit any significant changes during the exercise. After the exercise, the right abdominals demonstrated a significant increase in effort, which was independent of the direction of the maximal effort isometric test.

CONCLUSIONS

The change in muscle activity is attributed to neuromuscular compensation for the development of laxity and microdamage in the soft tissue (ligaments, discs, facet capsules, etc.) of the lumbar spine.

APPLICATION

The results of this study increase understanding of the risk factors associated with low back disorder induced by labor-intensive occupations that involve cyclic lateral twisting.