Trunk Muscle Activation Levels Research Articles

Selecting the appropriate input variables in a regression approach to estimate actively generated muscle moments around L5/S1 for exoskeleton control

Back support exoskeletons are designed to prevent work-related low-back pain by reducing mechanical loading. For actuated exoskeletons, support based on moments actively produced by the trunk muscles appears a viable approach. The moment can be estimated by a biomechanical model. However, one of the main challenges here is the feasibility of recording the required input variables (kinematics, EMG data, ground reaction forces) to run the model. The aim of this study was to evaluate how accurate different selections of input variables can estimate actively generated moments around L5/S1. Different multivariate regression analyses were performed using a dataset consisting of spinal load, body kinematics and trunk muscle activation levels during different lifting conditions with and without an exoskeleton. The accuracy of the resulting models depended on the number and type of input variables and the regression model order. The current study suggests that third-order polynomial regression of EMG signals of one or two bilateral back muscle pairs together with exoskeleton trunk and hip angle suffices to accurately estimate the actively generated muscle moment around L5/S1, and thereby design a proper control system for back support exoskeletons.

Trunk muscle recruitment patterns in simulated precrash events

ABSTRACTObjectives: To quantify trunk muscle activation levels during whole body accelerations that simulate precrash events in multiple directions and to identify recruitment patterns for the development of active human body models.Methods: Four subjects (1 female, 3 males) were accelerated at 0.55 g (net Δv = 4.0 m/s) in 8 directions while seated on a sled-mounted car seat to simulate a precrash pulse. Electromyographic (EMG) activity in 4 trunk muscles was measured using wire electrodes inserted into the left rectus abdominis, internal oblique, iliocostalis, and multifidus muscles at the L2–L3 level. Muscle activity evoked by the perturbations was normalized by each muscle's isometric maximum voluntary contraction (MVC) activity. Spatial tuning curves were plotted at 150, 300, and 600 ms after acceleration onset.Results: EMG activity remained below 40% MVC for the three time points for most directions. At the 150- and 300 ms time points, the highest EMG amplitudes were observed during perturbations to the left (–90°) and left rearward (–135°). EMG activity diminished by 600 ms for the anterior muscles, but not for the posterior muscles.Conclusions: These preliminary results suggest that trunk muscle activity may be directionally tuned at the acceleration level tested here. Although data from more subjects are needed, these preliminary data support the development of modeled trunk muscle recruitment strategies in active human body models that predict occupant responses in precrash scenarios.

Trunk muscle activation levels during eight stabilization exercises used in the functional kinetics concept: A controlled laboratory study.

To ensure accurate implementation of stabilization exercises in rehabilitation, physical therapists need to understand the muscle activation patterns of prescribed exercise. Compare muscle activity during eight trunk and lumbar spine stabilization exercises of the Functional Kinetics concept by Klein-Vogelbach. A controlled laboratory study with a single-group repeated-measures design was utilized to analyze surface electromyographic intensities of 14 female and 6 male young healthy participants performing eight exercises. Data were captured from the rectus abdominis, external/internal oblique and lumbar paraspinalis. The normalized muscle activation levels (maximum voluntary isometric contraction, MVIC) for three repetitions during each exercise and muscle were analyzed. Side bridging (28 ± 20%MVIC) and advanced planking (29 ± 20%MVIC) reached the highest activity in the rectus abdominis. For external and internal oblique muscles, side bridging also showed the greatest activity of 99 ± 36%MVIC and 52 ± 25%MVIC, respectively. Apart from side bridging (52 ± 14%MVIC), the supine roll-out (31 ± 12%MVIC) and prone roll-out (31 ± 9%MVIC) showed the greatest activity for the paraspinalis. The advanced quadruped, seated back extension and flexion on chair/Swiss Ball, prone roll-out and advanced one-leg back bridging only yielded negligible muscle activities for the rectus abdominis (< 5%MVIC). Based on the data obtained, recommendations for selective trunk muscle activation during eight stabilization exercises were established, which will guide physical therapists in the development of exercises tailored to the needs of their patients.

Comparison of the Activity and Proprioception of Trunk Muscles According to Different Types of Bridge Exercises in Subjects with and without Chronic Low Back Pain

Purpose: The purpose of the present study was to examine joint position senses and muscle activity in subjects with and without chronic low back pain and to determine the effects of different types of bridge exercises on their trunk muscle activity. Methods: Thrity -eight subjects with chronic low back pain and thrity healthy controls participated in the experiment. Joint position senses and trunk muscle activity levels were measured during the different bridge exercise methods. Results: The joint position senses of the healthy group and chronic low back pain group showed significant differences during lumbar flexion, lumbar extension, lumbar lateral flexion, and lumbar rotation. The muscle activity levels of the transversus abdominis (TrA), internal oblique (IO), and external oblique (EO) were highest in the prone bridge exercise (PBE) group, followed by the supine bridge swiss ball exercise (SBSE) group and supine bridge exercise (SBE) group in order of precedence. The muscle activity level of the erector spinae (ES) was highest in the SBSE group, followed by the SBE and PBE groups in order of precedence. Conclusion: Overall, the results suggest that chronic low back pain is associated with declines in joint position senses and that PBEs increase trunk muscle activity more than conventional bridge exercises.

Should we be more on the ball? The efficacy of accommodation training on lumbar spine posture, muscle activity, and perceived discomfort during stability ball sitting.

The aim of this study was to evaluate the efficacy of a 9-day accommodation protocol on reducing perceived discomfort while sitting on a stability ball (SB); trunk muscle activity levels and lumbar spinal postures were also considered. Previous studies have compared SB sitting with office chair sitting with few observed differences in muscle activity or posture; however, greater discomfort during SB sitting has been reported. These findings may indicate an accommodation period is necessary to acclimate to SB sitting. For this study, 6 males and 6 females completed two separate, 2-hr sitting sessions on an SB. Half the participants completed a 9-day accommodation period between the visits, whereas the other half did not use an SB during the time. On both occasions, self-reported perceived discomfort ratings were collected along with erector spinae and abdominal muscle activity and lumbar spinal postures. Discomfort ratings were reduced in female participants following the accommodation; no effects on muscle activation or lumbar spine postures were observed. Accommodation training may reduce perceived low-back discomfort in females.Trunk muscle activity and lumbar spine postures during seated office work on an SB did not differ between groups; however, greater sample power was required to conclusively address these variables. Regarding whether to use an SB in place of a standard office chair, this study indicates that females electing to use an SB can decrease discomfort by following an accommodation protocol; no evidence was found to indicate that SB chair use will improve trunk strength or posture, even following an accommodation period.

Trunk Muscle Activity during Exercises Performed on Land and in Water

The study's purpose was to determine whether trunk muscle activity levels are different during spine stability exercises performed in water compared with on land. Eleven male participants performed four abdominal trunk exercises on land and in water at the depth of the xiphoid. The exercises were abdominal hollowing, abdominal bracing, and anteroposterior and mediolateral pelvic tilts. During the exercises, surface EMG activity of muscles rectus abdominis (RA), external oblique, lower abdominals, multifidus, and erector spinae (ES) were recorded. EMG data were normalized to a maximal voluntary contraction (MVC), and the subsequent percentage of activity was compared between environments (water and land) with paired t-tests. Normalized EMG values for muscles RA, external oblique, lower abdominals, multifidus, and ES were significantly greater for all exercises performed on land than in water (P = 0.026-0.001, effect sizes = 0.52-1.61). The only exception was for mediolateral pelvic tilts where muscle ES values were not different between environments (P = 0.098). When healthy adults perform abdominal hollowing, abdominal bracing, and pelvic tilt exercises in water, most trunk muscles display substantially lower EMG activity when compared with performing the same exercises on land (e.g., abdominal bracing for RA = 20% MVC for land and 10% MVC for water). It is possible that with hydrostatic pressure and buoyancy, trunk muscles play less of a stabilizing role in the aquatic environment, which minimizes their EMG activity levels. Regardless of the mechanism, patients with back pain may find it easier to perform trunk muscle exercises in an aquatic environment first then progress to the land environment because EMG activity may be gradually increased.

Trunk muscle activity during spine stabilization exercises performed in a pool

ObjectivesTo compare trunk muscle activity levels among a variety of therapeutic aquatic exercises designed for patients with low back pain. Study designQuantitative observational laboratory study. SettingSports medicine clinic housed in a University. ParticipantsEleven physically active males aged 25.7 ± 5.53 years. Main outcome measuresSurface electromyographic (EMG) data from muscles rectus abdominis (RA), external oblique (EO), lower abdominals (LA), multifidus (MT), and erector spinae (ES) were recorded and then normalized to a maximal voluntary contraction. ResultsEMG values during abdominal bracing and Swiss ball exercises for muscles RA, EO, LA, and ES were significantly greater than most other exercises tested that included pelvic tilt, marching, hip abduction, and alternating arm exercises (P = .04–.001). EMG values of muscle LA were also greater for the abdominal hollowing exercise, whereas muscle MT displayed the greatest EMG values during the hip abduction exercise when compared to most other exercises tested (P = .02–.001). ConclusionsThe aquatic exercises that maximize trunk muscle activity in the healthy males studied are abdominal bracing and Swiss ball exercises. Some muscles were selectively activated during abdominal hollowing (LA) and hip abduction (MT) exercises when compared to most other exercises.

Are kinetic chain rowing exercises relevant in shoulder and trunk injury prevention training?

BackgroundRecent guidelines emphasise the importance of functional kinetic chain exercises during injury prevention training. Knowledge of muscle activation levels during various unilateral rowing exercises is lacking.ObjectiveTo describe and compare the...

Acute effect of labile surfaces during core stability exercises in people with and without low back pain

Objective The purpose of this study was to measure trunk muscle activity, whole body balance, and lumbar range of motion during core stability exercises in individuals with and without low back pain (LBP) on and off a labile surface. Design Descriptive cross-sectional study. Setting University laboratory. Participants Ten individuals with chronic non-specific LBP and 10 matched control subjects. Main outcome measures Bilateral trunk muscle activity was measured using surface electromyography (EMG); whole body balance was measured by quantifying the dispersion of the centre of pressure (CoP); lumbar range of motion (LROM) was measured with single-axis inclinometers. Results Individuals with LBP had adaptive recruitment patterns during the side-bridge and modified push-up exercises. CoP dispersion and LROM were not different between groups for any exercise. The labile surface did not change the difference between groups, and only increased muscle activity during the side-bridge ( p < 0.05). The labile surface increased LROM ( p = 0.35) and CoP dispersion ( p < 0.001) during the quadruped, decreased LROM during squats ( p = 0.05), and increased CoP dispersion during push-ups ( p = 0.04). Conclusion Individuals with LBP exhibited adaptive trunk muscle activity levels while maintaining similar levels of balance and lumbar movement to healthy controls. Since research suggests no one mode of exercise is more beneficial in LBP rehabilitation, the practicality and safety of labile surfaces for LBP exercise rehabilitation must be questioned from this study.

The effects of horizontal load speed and lifting frequency on lifting technique and biomechanics

Lifting loads that have a horizontal velocity (e.g. lifting from a conveyor) is often seen in industry and it was hypothesised that the inertial characteristics of these loads may influence lifting technique and low back stress. Seventeen male participants were asked to perform lifting tasks under conditions of four horizontal load speeds (0 m/s, 0.7 m/s, 1.3 m/s and 2.4 m/s) and two lifting frequencies (10 and 20 lifts/min) while trunk motions and trunk muscle activation levels were monitored. Results revealed that increasing horizontal load speed from 0 m/s to 2.4 m/s resulted in an increase in peak sagittal angle (73° vs. 81°) but lower levels of peak sagittal plane angular acceleration (480°/s2 vs. 4°/s2) and peak transverse plane angular acceleration (200°/s per s vs. 140°/s per s) and a consistent increase in trunk muscle co-activation. Participants used the inertia of the load to reduce the peak dynamics of the lifting motion at a cost of increased trunk flexion and higher muscle activity. Statement of Relevance: Conveyors are ubiquitous in industry and understanding the effects of horizontal load speed on the lifting motions performed by workers lifting items from these conveyors may provide some insight into low back injury risk posed by these tasks.

Effect of instruction, surface stability, and load intensity on trunk muscle activity

The aim of this study was to assess the effect of verbal instruction, surface stability, and load intensity on trunk muscle activity levels during the free weight squat exercise. Twelve trained males performed a free weight squat under four conditions: (1) standing on stable ground lifting 50% of their 1-repetition maximum (RM), (2) standing on a BOSU balance trainer lifting 50% of their 1-RM, (3) standing on stable ground lifting 75% of their 1-RM, and (4) receiving verbal instructions to activate the trunk muscles followed by lifting 50% of their 1-RM. Surface EMG activity from muscles rectus abdominis (RA), external oblique (EO), transversus abdominis/internal oblique (TA/IO), and erector spinae (ES) were recorded for each condition and normalized for comparisons. Muscles RA, EO, and TA/IO displayed greater peak activity (39–167%) during squats with instructions compared to the other squat conditions ( P = 0.04–0.007). Peak EMG activity of muscle ES was greater for the 75% 1-RM condition than squats with instructions or lifting 50% of 1-RM ( P = 0.04–0.02). The results indicate that if the goal is to enhance EMG activity of the abdominal muscles during a multi-joint squat exercise then verbal instructions may be more effective than increasing load intensity or lifting on an unstable surface. However, in light of other research, conscious co-activation of the trunk muscles during the squat exercise may lead to spinal instability and hazardous compression forces in the lumbar spine.

Muscular contribution to low-back loading and stiffness during standard and suspended push-ups

Push-up exercises are normally performed to challenge muscles that span upper extremity joints. However, it is also recognized that push-ups provide an effective abdominal muscle challenge, especially when the hands are in contact with a labile support surface. The purpose of this study was to compare trunk muscle activation levels and resultant intervertebral joint (IVJ) loading when standard and suspended push-ups were performed, and to quantify and compare the contribution of trunk muscles to IVJ rotational stiffness in both exercises. Eleven recreationally trained male volunteers performed sets of standard and suspended push-ups. Upper body kinematic, kinetic, and EMG data were collected and input into a 3D biomechanical model of the lumbar torso to quantify lumbar IVJ loading and the contributions of trunk muscles to IVJ rotational stiffness. When performing suspended push-ups, muscles of the abdominal wall and the latissimus dorsi were activated to levels that were significantly greater than those elicited when performing standard push-ups (p<.05). As a direct result of these increased activation levels, model-predicted muscle forces increased and consequently led to significantly greater mean (p=.0008) and peak (p=.0012) lumbar IVJ compressive forces when performing suspended push-ups. Also directly resulting from the increased activation levels of the abdominal muscles and the latissimus dorsi during suspended push-ups was increased muscular contribution to lumbar IVJ rotational stiffness (p<.05). In comparison to the standard version of the exercise, suspended push-ups appear to provide a superior abdominal muscle challenge. However, for individuals unable to tolerate high lumbar IVJ compressive loads, potential benefits gained by incorporating suspended push-ups into their resistance training regimen may be outweighed by the risk of overloading low-back tissues.

A biomechanical analysis of anterior load carriage

Front load carriage is a common occupational task in some industries (e.g. agriculture, construction), but, as compared to lifting tasks, relatively little research has been conducted on the biomechanical loading during these activities. The focus of this study was to explore the low back biomechanics during these activities and, specifically, to examine the effects of load height and walking speed on trunk muscle activity and trunk posture. Eleven male participants participated in two separate front load-carriage experiments. The first experiment called for carrying a barbell (with weight corresponding to 20% of elbow flexion strength) at three heights (knuckle height, elbow height and shoulder height) at a constant horizontal distance from the spine. The second experiment called for participants to carry a bucket of potatoes weighing 14 kg at the same three heights, but with no further restrictions in technique. In both experiments, the participants performed this task while either standing still or walking at a self-selected speed. As they performed these tasks, the activity levels of the right-side muscle of the rectus abdominis, external oblique, biceps brachii, anterior deltoid and three levels (T9, T12 and L3) of the erector spinae were sampled. Mid-sagittal plane trunk posture was also quantified using three magnetic field-based motion sensors at T9, T12 and L3. The results showed a significant effect of both walking speed and load height on trunk posture and trunk muscle activity levels in both the barbell and bucket experiments. In the barbell experiment, the walking trials generated 43% more trunk muscle activity than the standing trials. Trials at shoulder height produced 11% more muscle activity than trials at elbow height in the T9 erector spinae muscles and 71% more muscle activity in the anterior deltoid. In the bucket experiment, trunk muscle activity responded in a similar fashion, but the key result here was the quantification of the natural hyperextension posture of the spine used to balance the bucket of potatoes. These results provide insight into muscle activation patterns in dynamic settings, especially (load) carrying biomechanics, and have implications in industrial settings that require workers to carry loads in front of their bodies.

Upper body kinematic and low-back kinetic responses to precision placement challenges and cognitive distractions during repetitive lifting

Exposure to cognitive distractions and precision placement challenges during manual lifting exertions may alter lumbar spine loading by influencing movement and/or motor patterns. In this study, the impact of such demands on upper body kinematics, trunk muscle activation, and lumbar spine loading during a repetitive lifting task was examined. Nine male volunteers performed four different sagittal plane lifting tasks in which a 15.9 kg mass was lifted repetitively at a fixed rate of 7.5 lifts/min for a total duration of 30 min (216 lifts/task). The physical dimensions of the experimental setup remained constant between tasks. Tasks differed based on the presence or absence of simultaneous cognitive distractions and/or precision placement challenges. Upper body kinematics and trunk muscle activation levels were monitored, and a two-dimensional dynamic biomechanical model was used to estimate L4/L5 joint loads. Reductions in elbow flexion (14.3%), elbow extension (16.6%), shoulder flexion (11.7%), and shoulder extension (10.2%) velocities were observed when precision placement challenges were imposed during lifting, and mean lift times increased by 27% as a result. This led to greater cumulative L4/L5 moments (23%), joint compression (15%), reaction shear (17%), and joint shear (10%) forces when precision placement constraints were imposed. Performing a cognitive distraction challenge while lifting had no impact on cumulative L4/L5 joint loads. The magnitude of cumulative L4/L5 loads was highly dependent on the preferred time taken to perform single-lift exertions, as there were no differences in peak L4/L5 loads between the tasks examined. This was further supported in that very few biomechanically significant changes were observed in trunk muscle activation levels or three-dimensional trunk kinematics as a function of the tasks performed. The results suggest that upper limb kinematic adaptations to precision placement constraints in repetitive lifting may alter the risk of reporting low back pain. Relevance to Industry The results of this study indicate that often overlooked task demands, particularly precision placement constraints, may modify the level of risk associated with the performance of repetitive manual lifting tasks. There was no evidence to suggest that exposure to simultaneous cognitive distractions while lifting would modify the level of risk under the conditions examined. Accordingly, these findings may be relevant in the design and biomechanical risk assessment of industrial lifting tasks.

Low back three-dimensional joint forces, kinematics, and kinetics during walking

Objective. The purpose of this study was to examine the three-dimensional low back loads, spinal motions, and trunk muscular activity during gait. Specific objectives involved assessment of the effects of walking speed, and arm swing on spinal loads, lumbar spine motion, and muscular activation. Design. An in vivo modeling experiment using five male participants. Thirty walking trials were performed by each participant yielding five repeats of each condition (3 walking cadences × 2 arm swing conditions). Background. Walking is often prescribed as a rehabilitation task for individuals with low back injuries. However, there are few studies which have examined the joint loading, spinal motions, and muscular activity present when walking. Additionally, the majority of studies examining spine loading during gait have used an inverse dynamics model, commencing at the cranial aspect of the body, approach which does not include the impulsive phases of gait (i.e. heel strikes and toe offs). Methods. Low back joint forces (bone on bone) and moments were determined using an anatomically complex three-dimensional model (detailing 54 muscles and the passive structures acting at the low back) during three walking cadences and with free arm swing or restricted arm swing. In order to assess the influence of the transient factors such as heel contact on the joint forces a bottom up (from the feet to the lumbar spine) rigid link segment analyses approach was used as one input to the three-dimensional anatomic model. Lumbar spine motion and trunk muscle activation levels were also recorded to assist in partitioning forces amongst the active and passive tissues of the low back. Results. Net joint anterior-posterior shear loading was the only variable significantly affected by walking cadence (fast versus slow P < 0.0003). No variable was significantly affected by the arm swing condition. Trends demonstrated an increase in all variables with increased walking cadence. Similarly, most variables, with the exception of axial twist and lateral bend lumbar spine motion and lateral joint shear, demonstrated increasing trends caused by the restriction of normal arm swing. Conclusions. Tissue loading during walking appears to be below levels caused by many specific rehabilitation tasks, suggesting that walking is a wise choice for general back exercise and rehabilitation programs. Slow walking with restricted arm swing produced more ‘static’ lumbar spine loading and motion patterns, which could be detrimental for certain injuries and tissues. Fast walking produced a more cyclic loading pattern.

The relationship between lumbar spine load and muscle activity during extensor exercises.

There have been no previous studies that quantitatively assessed the load on the spine during extensor exercises. The purpose of our study was to investigate the loading of the lumbar spine and trunk muscle activity levels while subjects performed typical trunk extensor exercises. Thirteen male volunteers (mean age = 21.0 years, SD = 1.0, range = 19-23; mean height = 176.0 cm, SD = 6.2, range = 165-188; mean mass = 77.0 kg, SD = 7.0, range = 63-89) participated. The subjects performed four different back exercises. Electromyographic (EMG) activity was recorded from 14 trunk muscles. The postures that corresponded to the maximum external moment were identified and quantified using rigid body modeling combined with an EMG-driven model to determine joint loading at the L4-5 joint. The exercises were then evaluated based on the lumbar spine loading and peak muscle activity levels. A reference task of lifting 10 kg from midthigh was included for comparison. The exercises involving active trunk extension produced the highest joint forces and muscle activity levels. Exercises involving leg extension with the spine held isometrically demonstrated asymmetrical activity of the trunk muscles, thereby reducing loads on the spine. The back extensor exercises examined provided a wide range of joint loading and muscle activity levels. Single-leg extension tasks appear to constitute a low-risk exercise for initial extensor strengthening, given the low spine load and mild extensor muscle challenge. When combined with contralateral arm extensions, the challenge and demand of the exercise were increased. The compressive loading and extensor muscle activity levels were highest for the trunk extension exercises.