Back and hip extensor muscle function during therapeutic exercises

Sex differences in in vivo soft tissue compressive properties of the human hip in young adults: a comparison between passive vs active state

Hip injuries are a frequent outcome of falls. Studying the biomechanics of hip injuries requires a comprehensive understanding of soft tissue properties and their responses to external loads. Particularly, muscle activity is crucial in arresting a fall and is likely to affect soft tissue properties. Failing to consider muscle activation might result in incorrect conclusions regarding the processes underlying injuries and the efficacy of preventive strategies. Soft tissue response is also affected by loading rate, sex, and mechanical testing protocols, highlighting the need for precise experimental design and interpretation. Forty individuals (age = 25.53 ± 3.41 years) were recruited (20 males and 20 females) to investigate the hip soft tissue response during a high-speed cyclic indentation testing. Muscle activity was recorded using electromyography (EMG) and soft tissue thickness was measured using ultrasound imaging. Peak force, energy, and tissue stiffness were measured using tissue indentation. The hip soft tissue exhibited hysteresis and was nonlinear during loading. Sex differences in trochanteric soft tissue stiffness resulted in males having 38% higher peak force than females and absorbed energy was 32% higher in the active state than the passive state (in combined participants). Characterizing the range of tissue responses for in vivo hip soft tissues emphasizes the natural variability in healthy human tissues and the need to consider the range of tissue behaviors in models, not just the average response. Both sex and muscle activation increased tissue mechanical variability and need to be considered in future physical and computational models of hip impact.

The Application of Surface Electromyography Technology in Evaluating Paraspinal Muscle Function

Surface electromyography (sEMG) has emerged as a valuable tool for assessing muscle activity in various clinical and research settings. This review focuses on the application of sEMG specifically in the context of paraspinal muscles. The paraspinal muscles play a critical role in providing stability and facilitating movement of the spine. Dysfunctions or alterations in paraspinal muscle activity can lead to various musculoskeletal disorders and spinal pathologies. Therefore, understanding and quantifying paraspinal muscle activity is crucial for accurate diagnosis, treatment planning, and monitoring therapeutic interventions. This review discusses the clinical applications of sEMG in paraspinal muscles, including the assessment of low back pain, spinal disorders, and rehabilitation interventions. It explores how sEMG can aid in diagnosing the potential causes of low back pain and monitoring the effectiveness of physical therapy, spinal manipulative therapy, and exercise protocols. It also discusses emerging technologies and advancements in sEMG techniques that aim to enhance the accuracy and reliability of paraspinal muscle assessment. In summary, the application of sEMG in paraspinal muscles provides valuable insights into muscle function, dysfunction, and therapeutic interventions. By examining the literature on sEMG in paraspinal muscles, this review offers a comprehensive understanding of the current state of research, identifies knowledge gaps, and suggests future directions for optimizing the use of sEMG in assessing paraspinal muscle activity.

Effect of different isometric trunk extension intensities on the muscle stiffness of the lumbar and lower limbs

Purpose: To investigate the effect of isometric prone trunk extension (IPTE) contraction intensity on the stiffness of erector spinae (ES), semitendinosus (ST), biceps femoris (BF), and gastrocnemius muscles to understand the overall muscle mechanical behavior during IPTE and to explore the mechanisms of oordinated contraction of the body kinetic chain. Methods: Twenty healthy females were recruited, and participants underwent IPTE at three contraction intensities, i.e., 0% maximum voluntary isometric contraction (MVIC), 30% MVIC, and 60% MVIC, and muscle stiffness was measured using MyotonPRO. Results: Muscle stiffness was moderately to strongly positively correlated with contraction intensity (r = 0.408-0.655, p < 0.001). The percentage increase in stiffness at low intensity was much greater in ES than in lower limb muscles and greater in ST and BF than in gastrocnemius, whereas at moderate intensity, the percentage increase in stiffness decreased in all muscles, and the percentage increase in stiffness in ES was lower than that in ST. There was a moderate to strong positive correlation between ES stiffness variation and ST (r = 0.758-0.902, p < 0.001), BF (r = 0.454-0.515, p < 0.05), MG (r = 0.643-0.652, p < 0.01), LG (r = 0.659-0.897, p < 0.01). Conclusion: IPTE significantly affected the stiffness of lumbar and lower limb muscles, and low-intensity IPTE activated the ES more efficiently. There were significant coordinated muscle contractions between ES, ST, and LG. This provides preliminary evidence for exploring the overall modulation pattern of the lumbar and lower limb muscles' kinetic chains. In future studies, we will combine other stiffness assessment methods (such as Magnetic Resonance Elastography, Shear Wave Elastography, or electromyography) to corroborate our findings.

Trunk muscle activation of core stabilization exercises in subjects with and without chronic low back pain

BACKGROUND

Weakness and atrophy in trunk muscles have been associated with chronic low back pain (CLBP).

OBJECTIVE

This study aimed to identify isometric exercises resulting the highest trunk muscle activity for individuals with and without CLBP.

METHODS

Fourteen males with CLBP and 15 healthy age-matched healthy subjects were recruited for this study. Muscle activity during maximal voluntary isometric contraction (MVIC) was measured for a comparative reference with surface electromyography (sEMG) from six trunk muscles. Thereafter maximum EMG amplitude values were measured during eleven trunk stability exercises. The maximal EMG activity in each exercise relative to the MVICs was analyzed using generalizing estimating equations (GEE) models with the unstructured correlation structure.

RESULTS

The GEE models showed statistically significant differences in muscle activity between exercises within both groups (p< 0.001), with no significant differences between groups (p> 0.05). The highest muscle activity was achieved with the hip flexion machine for multifidus, side pull with a resistance band for lumbar extensors, side and single-arm cable pull exercises for thoracic extensors, rotary plank and the hip flexion machine for abdominal.

CONCLUSION

This study found five isometric trunk exercises that exhibited highest muscle activity depending on muscle tested, with no significant difference between individuals with and without CLBP.

Variation of muscle recruitment during exercises performed below horizontal arm elevation that target the lower trapezius: A repeated measures cross-sectional study on asymptomatic individuals

The gold standard exercise for recruitment of the lower trapezius is the Y prone exercise which is performed above 90° of shoulder elevation. However, clinicians often prescribe exercises that avoid high elevation postures during early stages of rehabilitation. Comparatively little data exists on relative muscle recruitment during lower arm elevation exercises. This study examined the EMG activity of four shoulder girdle muscles during four exercises accomplished below 90° of shoulder elevation and compared them to the Y prone while considering sex effects. Variance across exercises of the ratio between upper trapezius and lower trapezius was also explored. 32 healthy participants completed standardized muscle-specific MVCs and two repetitions of each exercise. The side lying external rotation and the wall slide exercises produced the highest peak EMG for the lower trapezius, both 33 and 29% lower than the Y Prone. For the upper trapezius to lower trapezius ratio, the side lying external rotation elicited the lowest value, followed by the Y prone and wall slide (53 and 59% respectively higher). Sex influenced some EMG values, typically interacting with exercise type. Thus, side lying external rotation and the wall slide are recommended for targeting the lower trapezius muscle during early rehabilitation.

The Effects of Abdominal Hollowing and Bracing Maneuvers on Trunk Muscle Activity and Pelvic Rotation Angle during Leg Pull Front Pilates Exercise

Pilates methods use mats for trunk muscles stabilization exercises, and leg pull front (LPF) is one of the traditional Pilates mat exercises. Abdominal hollowing (AH) and Abdominal bracing (AB) maneuvers are recommended to stabilize the trunk muscles and prevent unwanted pelvic movement during motion. This study aimed to explore the effects of AH and AB on electromyography (EMG) activity of the trunk muscles and angle of pelvic rotation during LPF. A total of 20 healthy volunteers participated in the study. AH, AB, and without any condition (WC) were randomly performed during LPF exercise. Each was repeated three times for 5 s. The trunk muscle activities were measured using EMG and rotation of pelvis was measured using a Smart KEMA device. The activities of the transversus abdominis/obliquus internus abdominis (TrA/IO) and right obliquus externus abdominis (EO) muscles were highest in LPF-AH compared to the other conditions. Multifidus (MF) activity was significantly greater in LPF-AH and LPF-AB compared to that of without any condition. The pelvic rotation angle was significantly smaller in LPF-AB. Therefore, AH maneuver during LPF for trunk muscle stabilization exercises is suitable for selective activation of the TrA/IO, and AB maneuver during LPF is recommended for the prevention of unwanted pelvic rotation.

Effects of arm and leg positions on lumbar multifidus muscle activity while on hands and knees or while standing

BACKGROUND

The lumbar multifidus (LMF) muscle, which is involved in the mechanical stability of the lumbar spine, reportedly undergoes atrophy in patients with low back pain. Preventing or mitigating low back pain requires strengthening the LMF muscle; however, methods for triggering selective and significant contraction of this muscle have not been fully studied. This study aims to clarify how, in the hands-and-knees or standing position, the position of the arm and leg on one side affects the activity of the lumbar erector spinae (LES) and LMF muscles.

METHODS

We recruited nine adult men with no prior history of low back pain. Measurements were taken in four different postures under varying conditions (that is, one arm and one leg were lifted in either the hands-and-knees or standing position,) as follows: (1) shoulder joint flexion and hip joint extension in the hands-and-knees position; (2) 90° shoulder joint abduction and hip joint abduction in the hands-and-knees position; (3) shoulder joint flexion and hip joint extension in the standing position; and (4) 90° shoulder joint abduction and hip joint abduction in the standing position. The 90° shoulder joint abduction involved simultaneous horizontal abduction, while the hip joint abduction involved simultaneous extension. Muscle activity of the LES and LMF in each posture was measured using a surface electromyograph.

RESULTS

Muscle activity of the LMF was significantly higher in 90° shoulder joint abduction and hip joint abduction than in shoulder joint flexion and hip joint extension in both the hands-and-knees and standing positions. The LES muscle showed no significant differences in activity between each posture.

CONCLUSIONS

The results suggest that unilateral 90° shoulder joint abduction and contralateral hip joint abduction in the hands-and-knees and standing positions may produce selective and significant contraction of the LMF muscle.

Acute Responses of Core Muscle Activity during Bridge Exercises on the Floor vs. the Suspension System

This study aimed to compare the neuromuscular activation of selected core musculature in supine and prone bridge exercises under stable versus suspended conditions. Forty-three healthy male participants were recruited to measure the electromyographic activities of the rectus abdominis (RA), lumbar multifidus (LM), thoracic erector spinae (TES), rectus femoris (RF), gluteus maximus (GM), and biceps femoris (BF) during supine and prone bridge exercises under six conditions: control, both arms and feet on the floor (Prone_con and Supine_con); arms on the floor and feet on the suspension system (Prone-Feet_suspension and Supine-Feet_suspension); and arms on the suspension system and feet on the floor (Prone-Arm_suspension and Supine-Arm_suspension). Prone-Arm_suspension yielded significantly higher activities in the RA, RF, TES, and LM than Prone-Feet_suspension (p < 0.01) and Prone_con (p < 0.001). Moreover, Supine-Feet_suspension elicited significantly higher activities in the RA, RF, TES, LM, and BF than Supine-Arm_suspension (p < 0.01) and Supine_con (p < 0.001). Furthermore, Supine-Feet_suspension elicited significantly higher activities in the RF, TES, and BF than Supine_con (p < 0.01). Therefore, if the RA and/or RF were the target training muscles, then Prone-Arm_suspension was recommended. However, if the TES, LM, and/or BF were the target training muscles, then Supine-Feet_suspension was recommended.

Effect of Increased Lumbar Lordosis on Lumbar Multifidus and Longissimus Thoracis Activation During Quadruped Exercise in Patients With Chronic Low Back Pain: An EMG Study

The objective was to investigate the electromyographic activity of the lumbar multifidus (MF) muscle and longissimus thoracis muscle, along with their activity ratio (MF longissimus thoracis ratio), during quadruped stabilization exercise performed with neutral posture and with increased lumbar lordosis in patients with chronic low back pain (CLBP). A total of 23 patients with CLBP (12 females and 11 males) were recruited based on inclusion and exclusion criterion. Each patient performed 4 exercises in random order, with surface electromyography electrodes and an electrogoniometer attached. A cross-sectional study design was used to measure the amplitude of muscle activation (as a percentage of maximum voluntary contraction) in each patient across the 2 muscles (MF and longissimus thoracis) during quadruped stabilization exercise with neutral posture and with increased lumbar lordosis. A 2-way analysis of variance was conducted, which demonstrated a statistically significant increase in the recruitment of MF with increased lumbar lordosis in patients with CLBP during quadruped exercise. An increase of 9.7% and 16.9% maximum voluntary contraction in MF electromyographic activity was observed in lumbar lordosis posture during the quadruped leg raise and quadruped leg-arm raise exercise, respectively (P < .01), when compared to the neutral posture. The increased recruitment of MF with lumbar lordosis in the quadruped position has strong implications in the assessment and management of patients with CLBP.

Change in the circulation and activity of the lower erector spinae muscles after repeated trunk extension movement

BACKGROUND

The optimum repetition number of standing back-extension exercise (SBEE) effective for the prevention and improvement of low back pain (LBP) is unknown.

OBJECTIVE

To determine the effect of physiotherapy on LBP by investigating the optimum repetition number of SBEE via optical analysis and electromyographic (EMG) examination of the multifidus muscles.

METHODS

Hemodynamics and multifidus muscle activity were examined in 16 healthy adult men using near-infrared spectroscopy and surface EMG after performing repetitive SBEE.

RESULTS

Oxidized hemoglobin (Oxy-Hb) levels significantly increased in the second extension phase but decreased in the third and subsequent extension phases; deoxidized hemoglobin (deOxy-Hb) levels increased in the third and subsequent extension phases. In the standing phase, no significant difference was observed; in the third and subsequent phases, Oxy-Hb levels decreased and deOxy-Hb levels increased. Muscular activity significantly decreased in the second standing phase but increased in the third and subsequent phases. No significant difference was observed in the extension phase with respect to the number of SBEE repetitions performed. In healthy individuals, hemodynamics improved up to second repetition of SBEE; subsequent repetitions may decrease hemodynamics because of increased activity of the multifidus muscles.

CONCLUSIONS

In healthy individuals, hemodynamics improved up to second repetition of SBEE.

Hip and Trunk Muscle Activity During the Star Excursion Balance Test in Healthy Adults

CONTEXT

Dynamic balance is a measure of core stability. Deficits in the dynamic balance have been related to injuries in the athletic populations. The Star Excursion Balance Test (SEBT) is suggested to measure and improve dynamic balance when used as a rehabilitative tool.

OBJECTIVE

To determine the electromyographic activity of the hip and the trunk muscles during the SEBT.

DESIGN

Descriptive.

SETTING

University campus.

PARTICIPANTS

Twenty-two healthy adults (11 males and 11 females; 23.3 [3.8] y, 170.3 [7.6] cm, 67.8 [10.3] kg, and 15.1% [5.0%] body fat).

INTERVENTION

Surface electromyographic data were collected on 22 healthy adults of the erector spinae, external oblique, and rectus abdominis bilaterally, and gluteus medius and gluteus maximus muscle of the stance leg. A 2-way repeated measures analysis of variance was used to determine the interaction between the percentage maximal voluntary isometric contraction (%MVIC) and the reach directions. The %MVIC for each muscle was compared across the 8 reach directions using the Sidak post hoc test with α at .05.

MAIN OUTCOME MEASURES

%MVIC.

RESULTS

Significant differences were observed for all the 8 muscles. Highest electromyographic activity was found for the tested muscles in the following reach directions-ipsilateral external oblique (44.5% [38.4%]): anterolateral; contralateral external oblique (52.3% [40.8%]): medial; ipsilateral rectus abdominis (8% [6.6%]): anterior; contralateral rectus abdominis (8% [5.3%]): anteromedial; ipsilateral erector spinae (46.4% [20.2%]): posterolateral; contralateral erector spinae (33.5% [11.3%]): posteromedial; gluteus maximus (27.4% [11.7%]): posterior; and gluteus medius (54.6% [26.1%]): medial direction.

CONCLUSIONS

Trunk and hip muscle activation was direction dependent during the SEBT. This information can be used during rehabilitation of the hip and the trunk muscles.

Individuals With and Without Low Back Pain Use Different Motor Control Strategies to Achieve Spinal Stiffness During the Prone Instability Test

BACKGROUND

The prone instability test is used to identify individuals with low back pain (LBP) who would benefit from trunk stabilization exercises. Although activity from muscles during the leg-raising portion of the prone instability test theoretically enhances spinal stiffness and reduces pain, evidence for this is lacking.

OBJECTIVES

To compare and contrast (1) pain and stiffness changes between prone instability testing positions, and (2) muscle activation patterns during the prone instability test leg raise in individuals with and without LBP.

METHODS

Participants with (n = 10) and without (n = 10) LBP participated in this laboratory case-control study. Spinal stiffness was measured using a beam-bending model and 3-D kinematic data. Stiffness changes were compared across the test positions and between groups. Surface electromyographic data were collected on trunk and limb musculature. Principal-component analysis was used to extract muscle synergies.

RESULTS

Spinal stiffness increased across testing positions in all participants (P<.05). Participants with LBP experienced reduced pain during the test (P<.001). No between-group difference was found in spinal stiffness during leg raising during the test (P>.05). Participants without LBP used 3 muscle synergies during the leg raise and participants with LBP used 2 muscle synergies.

CONCLUSION

Spinal stiffness increased in all participants; however, participants without LBP demonstrated a muscle synergy pattern where each synergy was associated with a distinct function of the prone instability test. Participants with LBP used a more global stabilization pattern, which may reflect a maladaptive method of enhancing spinal stability. J Orthop Sports Phys Ther 2019;49(12):899-907. Epub 3 Aug 2019. doi:10.2519/jospt.2019.8577.

Reproducibility of elastic modulus measurement of the multifidus using the shear wave elastography function of an ultrasound diagnostic device

[Purpose] This study aimed to obtain evidence of the musculo-physiological involvement in the effect of physiotherapy on low back pain by examining the reproducibility of elasticity measurements of the multifidus muscle at different trunk angles via the shear wave elastography function of an ultrasound diagnostic device. [Participants and Methods] This study included 11 healthy adults. Measurements were conducted with participants in the prone position, and the elasticity of the superficial and deeper layers of the multifidus muscle was measured under the following 3 conditions: trunk at neutral position, trunk flexed at 40°, and trunk extended at 20°. Next, intraclass correlation coefficients (1, 1) were calculated to examine the intrarater reliability. [Results] All intraclass correlation coefficients for the superficial and deeper layers of the multifidus muscle were ≥0.85 for all 3 conditions. [Conclusion] Regardless of the trunk position, the elastic modulus measurement of inner muscles via shear wave elastography serves as an assessment of biological changes in individuals with lower back pain in response to interventions.

Exploring Neuromuscular Electrical Stimulation Intensity Effects on Multifidus Muscle Activity in Adults With Chronic Low Back Pain: An Ultrasound Imaging-Informed Investigation

Study design:

Cross-sectional study.

Background:

Neuromuscular electrical stimulation (NMES) is an effective tool for stimulating multifidus muscle contractions. Ultrasound imaging (USI) is valid and reliable for quantifying multifidus activity represented by percent thickness change from a resting to contracted state. Thus, USI may be used to help determine optimal NMES intensity.

Objectives:

To explore NMES intensity effects on multifidus thickening in adults with chronic low back pain (CLBP).

Methods:

Sixty patients with CLBP participated. L4/5 multifidus ultrasound images were obtained and percent thickness change from a resting to a contracted state was determined at baseline with a limb lift and during NMES application. During NMES, the examiner recorded the intensity, in milliampere, when the multifidus first started to thicken as observed with USI. The examiner also recorded the NMES intensity that resulted in no further multifidus thickening (ie, high-tolerance group) or, in cases where maximal thickening was not observed, the NMES intensity of the submaximal contraction (ie, low-tolerance group). Differences between participants with high versus low NMES tolerance were evaluated.

Results:

During NMES, the multifidus began thickening at a higher intensity for the high-tolerance group (n = 39), that is, 34 mA, compared with the low-tolerance group (n = 21), that is, 32 mA (P = .001). A greater mean intensity in the high-tolerance group, that is, 62 mA, as compared to 45 mA in the low-tolerance group, resulted in a larger percent thickness change, that is, 30.89% compared to 20.60%, respectively (P < .001).

Conclusions:

Results provide clinicians with NMES intensity targets to facilitate multifidus muscle thickening, which provides insight into muscle activity.

Reliability and Validity of a Novel Trunk-Strength Assessment for High-Performance Sprint Flat-Water Kayakers

PURPOSE

To determine the reliability and validity of a novel trunk maximal isometric force assessment involving 7 different tasks with 200-m times for elite sprint flat-water kayakers.

METHODS

Ten elite sprint flat-water kayakers performed a series of maximal isometric voluntary contractions (MVCs) on 2 separate days to assess reliability. MVC force was assessed as the participants sat on a modified kayak ergometer and applied their maximal isometric force to a uniaxial load cell during 7 different tasks. The 7 tasks of interest were a seated trunk-forward flexion, bilateral (left and right) rotational pulls, bilateral rotational pushes, and a sport-specific bilateral kayak-stroke simulation. Twenty elite flat-water kayak athletes (10 male and 10 female) participated in the validity portion by completing the series of tasks in conjunction with a 200-m race.

RESULTS

MVC force values ranged from 84 to 800 N across all participants and all tasks. The average coefficient of variation of the 7 tasks ranged from 2.4% to 7.7%. Regression analysis showed Pearson correlations ranging from -.84 to -.22 for both absolute and relative values with 200-m performance times.

CONCLUSIONS

MVC force measured in each task was considered reliable as a small degree of variance between trials was found. The summation of the 7 trunk scores showed very strong correlations with on-water performance, indicating that this assessment is valid for elite sprint kayakers.

Revisiting the effect of manipulating lumbar stability with load magnitudes and positions: The effect of sex on trunk muscle activation

BACKGROUND

Lumbar spine stability is regularly studied by positioning different loads at different heights and distance and measuring trunk muscle activation changes. Some of these studies have reported sex differences, but this needs to be revisited while controlling for confounding factors.

METHOD

20 males and 20 females sustained three static standing postures, with various loads (0, 5 and 10% of body weight), to evaluate the effect of height and distance. Activation of 12 trunk muscles was recorded with surface electromyography (EMG).

RESULTS

Females activated their external obliques a little more than males, with increases ranging between 1.5 and 2.3% of maximal voluntary activation (MVA), which corresponds to strong effect sizes (Cohen's d ranging between 0.86 and 1.13). However, the significant Sex × Height, Sex × Distance and Sex × Load interactions observed for different trunk muscles led to small differential effects (≤1% MVA). Increasing load height slightly increased and decreased back and abdominal muscle activation, respectively, generally by less than 1% MVA.

CONCLUSION

The higher activation of the external obliques observed in females might be of clinical value, relative to the required overall trunk muscle activation (5%), to preserve lumbar stability. Other effects were negligible.

Does a core stabilization exercise program have a role on shoulder rehabilitation? A comparative study in young females

OBJECTIVES

This study aims to evaluate the effect of core stabilization exercises and to explore the immediate effect of core muscles-activated posture on shoulder maximal voluntary isometric contraction (MVIC) strength.

PATIENTS AND METHODS

Between November 2016 and January 2015, a total of 75 healthy female volunteers (mean age 25.36 years; range, 18 to 30 years) were included. Of these, 42 consecutive volunteers were assigned as the study group, while the remaining 33 volunteers were assigned as the control group. The study group completed a six-week core stabilization home-based exercise program. Two measurements were performed with six-week interval. A set of three repetitions for each shoulder side was performed by an electronic dynamometer under two conditions: core muscles relaxed and activated. Measurements were monitored real-time with a connected computer and recorded in Newton.

RESULTS

The activation of core muscles during the measurement significantly decreased the MVIC values in both groups (p<0.05). The MVIC values significantly increased after home-based exercise program in both conditions (p<0.05).

CONCLUSION

Our study showed that six-week core stabilization exercise program had a significant positive effect on the shoulder MVIC strength. This result may support the use of core stabilization exercises in the early periods of shoulder rehabilitation when the shoulder muscle strengthening exercises are painful.

Effects of Volume Training on Strength and Endurance of Back Muscles: A Randomized Controlled Trial

CONTEXT

Strength/resistance training volume has historically been supported in the American College of Sports Medicine recommendations. However, for the back muscles, exercise prescription related to the number of sets, such as single versus multiple, is not well established in the literature.

OBJECTIVE

The purpose of this study was to compare the effects of 2 training volumes on strength and endurance of back-extensor muscles in untrained young participants with regard to a repeated-measures design.

DESIGN

Randomized controlled trial.

SETTING

Laboratory of functional evaluation and human motor performance.

PARTICIPANTS

Forty-four untrained young participants (mean age = 21 y) were randomized into single-set (n = 14), multiple-set (MSG, n = 15), and untrained control (n = 15) groups.

INTERVENTION

The single-set group and MSG underwent a 10-week progressive resistance training program (2 d/wk) using a 45° Roman chair.

MAIN OUTCOME MEASURES

Back maximal strength (dynamometer) and isometric and dynamic endurance (time limit, trunk extension-flexion cycles, and electromyography muscle fatigue estimates).

RESULTS

The results showed differences between the MSG and control group for isometric endurance time (mean = 19.8 s; 95% confidence interval, -44.1 to 4.8), but without time intervention significance. Significant improvement after training (P < .05) was found predominantly during dynamic endurance (number of repetitions) for both the MSG (+61%) and single-set group (+26%) compared with preintervention, whereas the control group reported no benefit. There was no significant (P > .05) difference in either strength or electromyography estimates after training.

CONCLUSIONS

Both multiple and single volume training were efficient in promoting better back endurance during dynamic performance based on mechanical variables (time and number of repetitions).

Activity of Lower Limb Muscles During Squat With and Without Abdominal Drawing-in and Pilates Breathing

Barbosa, AC, Martins, FM, Silva, AF, Coelho, AC, Intelangelo, L, and Vieira, ER. Activity of lower limb muscles during squat with and without abdominal drawing-in and Pilates breathing. J Strength Cond Res 31(11): 3018-3023, 2017-The purpose of this study was to assess the effects of abdominal drawing-in and Pilates breathing on the activity of lower limb muscles during squats. Adults (n = 13, 22 ± 3 years old) with some Pilates experience performed three 60° squats under each of the following conditions in a random order: (I) normal breathing, (II) drawing-in maneuver with normal breathing, and (III) drawing-in maneuver with Pilates breathing. Peak-normalized surface electromyography of the rectus femoris, biceps femoris, gastrocnemius medialis, and tibialis anterior during the knee flexion and extension phases of squat exercises was analyzed. There were significant differences among the conditions during the knee flexion phase for the rectus femoris (p = 0.001), biceps femoris (p = 0.038), and tibialis anterior (p = 0.001), with increasing activation from conditions I to III. For the gastrocnemius medialis, there were significant differences among the conditions during the knee extension phase (p = 0.023), with increased activity under condition I. The rectus and biceps femoris activity was higher during the extension vs. flexion phase under conditions I and II. The tibialis anterior activity was higher during the flexion compared with the extension phase under all conditions, and the medial gastrocnemius activity was higher during the extension phase under condition I. Doing squats with abdominal drawing-in and Pilates breathing resulted in increased rectus, biceps femoris, and tibialis anterior activity during the flexion phase, increasing movement stability during squat exercises.

Comparison of electromyographic activities of lumbar iliocostalis and lumbar multifidus muscles during stabilization exercises in prone, quadruped, and sitting positions

[Purpose] The purposes of this study were: 1) describe a hierarchy of electromyographic activity production, using percentage maximum voluntary contraction of lumbar iliocostalis and lumbar multifidus muscles during prone, quadruped and sitting exercises; and 2) identify optimal recruitment exercises for both lumbar iliocostalis as a global multi-segmental stabilizer and lumbar multifidus as a segmental stabilizer. [Subjects] Twelve healthy volunteers (six male and six female) aged 24 to 45 participated. [Methods] Surface electromyographic activity data were collected bilaterally from lumbar iliocostalis and lumbar multifidus muscles during exercises. [Results] Two-way ANOVA showed that prone extension, and prone alternate arm and leg lifting exercises produce a statistically significant difference in percent maximum voluntary contraction of lumbar iliocostalis and lumbar multifidus bilaterally compared to other exercises. Quadruped alternate arm and leg lifting exercises produce greater activity in lumbar multifidus muscle than sitting exercises [Conclusion] Prone exercises generate the greatest electromyographic activity and may be the most effective exercises for strengthening both lumbar iliocostalis and lumbar multifidus muscles. Quadruped alternate arm and leg lifting produces electromyographic activity at the recommended percent maximum voluntary contraction for training the lumbar multifidus in its role as a segmental stabilizer and is an effective training exercise for this goal.

A comparison of multidisciplinary team residential rehabilitation with conventional outpatient care for the treatment of non-arthritic intra-articular hip pain in UK Military personnel - a protocol for a randomised controlled trial

BACKGROUND

Non-arthritic hip disorders are defined as abnormalities of the articulating surfaces of the acetabulum and femur before the onset of osteoarthritis, including intra-articular structures such as the acetabular labrum and chondral surfaces. Abnormal femoroacetabular morphology is commonly seen in young men who constitute much of the UK military population. Residential multidisciplinary team (MDT) rehabilitation for patients with musculoskeletal injuries has a long tradition in the UK military, however, there are no studies presenting empirical data on the efficacy of a residential MDT approach compared with individualised conventional outpatient treatment. With no available data, the sustainability of this care pathway has been questioned. The purpose of this randomised controlled trial is to compare the effects of a residential multidisciplinary intervention, to usual outpatient care, on the clinical outcomes of young active adults undergoing treatment for non-arthritic intra-articular hip pain.

METHODS/DESIGN

The trial will be conducted at the Defence Medical Rehabilitation Centre, Headley Court, UK. One hundred military male participants with clinical indicators of non-arthritic intra-articular hip pain will be randomly allocated to either: (1) 7-day residential multidisciplinary team intervention, n = 50; (2) 6-week physiotherapist-led outpatient intervention (conventional care), n = 50. Measurements will be taken at baseline, post-treatment (1-week MDT group; 6-weeks physiotherapy group), and 12-weeks. The primary outcome measures are the function in daily living sub-scale of the Copenhagen Hip and Groin Outcome Score (HAGOS), the physical function subscale of the Non-arthritic Hip Score (NAHS), and VAS pain scale. Secondary outcomes include objective measures of physical capacity and general health. An intention-to-treat analysis will be performed using linear and mixed models.

DISCUSSION

This study will be the first to assess the efficacy of intensive MDT rehabilitation, versus conventional outpatient care, for the management of non-arthritic hip pain. The results from this study will add to the evidence-base and inform clinical practice for the management of intra-articular non-arthritic hip pain and femoroacetabular impingement in young active adults.

TRIAL REGISTRATION

ISRCTN Reference: ISRCTN 59255714 dated 11-Nov-2015.

Associations between Trunk Extension Endurance and Isolated Lumbar Extension Strength in Both Asymptomatic Participants and Those with Chronic Low Back Pain

BACKGROUND

Strength and endurance tests are important for both clinical practice and research due to the key role they play in musculoskeletal function. In particular, deconditioning of the lumbar extensor musculature has been associated with low back pain (LBP). Due to the relationship between strength and absolute endurance, it is possible that trunk extension (TEX) endurance tests could provide a proxy measure of isolated lumbar extension (ILEX) strength and thus represent a simple, practical alternative to ILEX measurements. Though, the comparability of TEX endurance and ILEX strength is presently unclear and so the aim of the present study was to examine this relationship.

METHODS

Thirty eight healthy participants and nineteen participants with non-specific chronic LBP and no previous lumbar surgery participated in this cross-sectional study design. TEX endurance was measured using the Biering-Sorensen test. A maximal ILEX strength test was performed on the MedX lumbar-extension machine.

RESULTS

A Pearson's correlation revealed no relationship between TEX endurance and ILEX strength in the combined group (r = 0.035, p = 0.793), the chronic LBP group (r = 0.120, p = 0.623) or the asymptomatic group (r = -0.060, p = 0.720).

CONCLUSIONS

The results suggest that TEX is not a good indicator of ILEX and cannot be used to infer results regarding ILEX strength. However, a combination of TEX and ILEX interpreted together likely offers the greatest and most comprehensive information regarding lumbo-pelvic function during extension.

Changes in gait kinematics and lower back muscle activity post-radiofrequency denervation of the zygapophysial joint: a case study

BACKGROUND CONTEXT

Using diagnostic anesthetic blocks, the lumbar zygapophysial (facet) joint has been shown to be the primary cause of pain in approximately 15% of patients with chronic low back pain. Radiofrequency neurotomy (RFN) of the lumbar medial branch innervating the zygapophysial joint has been shown to provide a significant decrease in pain in patients selected by dual comparative anesthetic blocks, but quantitative improvements in mobility have not been fully elucidated. A theoretical concern with RFN is that the multifidus muscle, a stabilizing paraspinal muscle, is also denervated during this procedure, which may have adverse effects on mobility and spine stability.

PURPOSE

The purpose of this study was to examine gait kinematics and muscle activity of the low back during treadmill walking both before and after RFN.

STUDY DESIGN

Case study.

PATIENT SAMPLE

One 33-year-old female, with 15 years of chronic left low back pain and a diagnosis of L4/L5 lumbar zygapophysial joint pain by dual comparative anesthetic blocks was studied.

OUTCOME MEASURES

Self-reported measures of perceived pain and effort; in addition to physiologic measures of heart rate, gait kinematics and surface electromyography (EMG) activity of the multifidus and erector spinae muscles were collected before and after the procedure.

METHODS

The participant walked for 15 consecutive minutes on a treadmill. The first and last 5-minute intervals were at a self-selected pace, and the middle 5-minute interval was at a 50% increase of the self-selected pace. Gait kinematics and lumbar paraspinal surface EMG activity were recorded during the last minute of each walking interval. Heart rate, perceived effort, and perceived pain were also collected at the end of each walking interval. Data were collected both 7 and 1 days before RFN, and on the following days post-RFN: 0, 8, 14, 28, and 58.

RESULTS

Perceived effort did not change despite an increase in treadmill speed and heart rate. Pain decreased by 60% in the first two weeks and by 92% by 4 weeks post-RFN. There were also gradual positive changes in gait kinematics across all post-sessions and an immediate and sustained decrease in surface EMG activity over the left multifidus and erector spinae muscles following RFN.

CONCLUSIONS

The results of this pilot study are the first to show quantitative positive changes in gait and muscle activity post-RFN, suggesting that the relationship between this procedure and mobility warrant further investigation.

An Analysis of Muscle Activities of Healthy Women during Pilates Exercises in a Prone Position

[Purpose] This study analyzed the activities of the back and hip muscles during Pilates exercises conducted in a prone position. [Subjects] The subjects were 18 healthy women volunteers who had practiced at a Pilates center for more than three months. [Methods] The subjects performed three Pilates exercises. To examine muscle activity during the exercises, 8-channel surface electromyography (Noraxon USA, Inc., Scottsdale, AZ) was used. The surface electrodes were attached to the bilateral latissimus dorsi muscle, multifidus muscle, gluteus maximus, and semitendinous muscle. Three Pilates back exercises were compared: (1) double leg kick (DLK), (2) swimming (SW), and (3) leg beat (LB). Electrical muscle activation was normalized to maximal voluntary isometric contraction. Repeated measures analysis of variance was performed to assess the differences in activation levels among the exercises. [Results] The activity of the multifidus muscle was significantly high for the SW (52.3±11.0, 50.9±9.8) and LB exercises(51.8±12.8, 48.3±13.9) and the activity of the semitendinosus muscle was higher for the LB exercise (49.2±8.7, 52.9±9.3) than for the DLK and SW exercises. [Conclusion] These results may provide basic material for when Pilates exercises are performed in a prone position and may be useful information on clinical Pilates for rehabilitation programs.

The effects of sling exercise using vibration on trunk muscle activities of healthy adults

[Purpose] This study compared the effects of sling exercises with and without vibration on the muscular activity of the internal oblique (IO), rectus abdominis (RA), multifidus (MF), and erector spinae (ES) muscles of healthy adults. [Methods] Eleven healthy university students (11 men) with a mean age of 22.8 years were enrolled in this study. Subjects performed supine and prone bridge exercises with the knees flexed using a sling suspension system with and without vibration. The amplitudes of the EMG activities of selected trunk muscles (internal oblique, rectus abdominis, erector spinae, multifidus) were recorded. Two types of exercise conditions were executed in a random sequence for 5 seconds each. The signals detected from the middle 3 seconds (after discarding the signals of the first and the last one seconds) were used in the analysis. A 3-minute break was given after each exercise to minimize muscle fatigue. [Results] During the supine bridge exercise with vibration, the activities of the IO, RA, MF, and ES muscles were significantly higher than those of the supine bridge exercise without vibration. Additionally, during the prone bridge exercise with vibration, the activities of the IO, RA, MF, and ES were significantly higher than those of the prone bridge exercise without vibration. [Conclusion] Sling exercises with vibration improved the trunk muscle activities of healthy adults compared to the sling exercises without vibration. The information presented here is important for clinicians who use lumbar stabilization exercises as an evaluation tool or a rehabilitation exercise.

Co-contractive activation of the superficial multifidus during volitional preemptive abdominal contraction

OBJECTIVE

To investigate whether the superficial multifidus (MF) muscle at the lower lumbar spine displayed co-contraction during volitional preemptive abdominal contraction (VPAC) through the abdominal drawing-in maneuver (ADIM) or the abdominal bracing maneuver (ABM) in 3 different postural positions.

DESIGN

A within-subject cohort design.

SETTING

A clinical laboratory.

PARTICIPANTS

A healthy convenience sample of 21 women and 13 men; mean age (SD), 25.5 ± 6.5 years.

METHODS

We collected surface electromyographic measurements for the superficial MF at the L5 vertebral level and abdominal wall muscles. Ultrasound imaging was used during screening and testing sessions for confirming transverse abdominis muscle activation while subjects maintained a relaxed state without volitional abdominal contraction (no-VPAC) and performed ADIM and ABM in 3 postural positions: supine, 4-point kneeling, and upright standing.

MAIN OUTCOME MEASUREMENT

The frequency of superficial MF co-contraction occurrences (percentage of the total number of conditions) was measured during ADIM and ABM in 3 different postural positions.

DATA ANALYSES

A Cochran Q test for k-related samples (α = 0.05) was used for data analysis.

RESULTS

Activation of the abdominal wall by using either VPAC strategy resulted in a significantly greater MF co-contraction occurrence when compared with no-VPAC in each position. The ABM produced a significantly higher MF co-contractive occurrence versus the ADIM in the supine position.

CONCLUSION

Both VPAC strategies produced a co-contractive MF response, which appears to be important for lumbar segmental stabilization and control. Analysis of the results suggests that VPAC strategies are appropriate for coactivating the MF, which can enhance spinal protection and rehabilitation responses.

Posterior muscle chain activity during various extension exercises: an observational study

Background

Back extension exercises are often used in the rehabilitation of low back pain. However, at present it is not clear how the posterior muscles are recruited during different types of extension exercises. Therefore, the present study will evaluate the myoelectric activity of thoracic, lumbar and hip extensor muscles during different extension exercises in healthy persons. Based on these physiological observations we will make recommendations regarding the use of extensions exercises in clinical practice.

Methods

Fourteen healthy subjects performed four standardized extension exercises (dynamic trunk extension, dynamic-static trunk extension, dynamic leg extension, dynamic-static leg extension) in randomized order at an intensity of 60% of 1-RM (one repetition maximum). Surface EMG signals of Latissimus dorsi (LD), Longissimus thoracis pars thoracic (LTT) and lumborum (LTL), Iliocostalis lumborum pars thoracic (ILT) and lumborum (ILL), lumbar Multifidus (LM) and Gluteus Maximus (GM) were measured during the various exercises. Subsequently, EMG root mean square values were calculated and compared between trunk and leg extension exercises, as well as between a dynamic and dynamic-static performance using mixed model analysis. During the dynamic exercises a 2 second concentric contraction was followed by a 2 second eccentric contraction, whereas in the dynamic-static performance, a 5 second isometric interval was added in between the concentric and eccentric contraction phase.

Results

In general, the muscles of the posterior chain were recruited on a higher level during trunk extension (mean ± SD, 56.6 ± 30.8%MVC) compared to leg extension (47.4 ± 30.3%MVC) (p ≤ 0.001). No significant differences were found in mean muscle activity between dynamic and dynamic-static performances (p = 0.053). The thoracic muscles (LTT and ILT) were recruited more during trunk extension (64.9 ± 27.1%MVC) than during leg extension (54.2 ± 22.1%MVC) (p = 0.045) without significant differences in activity between both muscles (p = 0.138). There was no significant differences in thoracic muscle usage between the dynamic or dynamic-static performance of the extension exercises (p = 0.574).

Lumbar muscle activity (LTT, ILL, LM) was higher during trunk extension (70.6 ± 22.2%MVC) compared to leg extension (61.7 ± 27.0%MVC) (p = 0.047). No differences in myoelectric activity between the lumbar muscles could be demonstrated during the extension exercises (p = 0.574). During each exercise the LD (19.2 ± 13.9%MVC) and GM (28.2 ± 14.6%MVC) were recruited significantly less than the thoracic and lumbar muscles.

Conclusion

The recruitment of the posterior muscle chain during different types of extension exercises was influenced by the moving body part, but not by the type of contraction. All muscle groups were activated at a higher degree during trunk extension compared to leg extension. Based on the recruitment level of the different muscles, all exercises can be used to improve the endurance capacity of thoracic muscles, however for improvement of lumbar muscle endurance leg extension exercises seem to be more appropriate. To train the endurance capacity of the LD and GM extension exercises are not appropriate.

Which exercises target the gluteal muscles while minimizing activation of the tensor fascia lata? Electromyographic assessment using fine-wire electrodes

STUDY DESIGN

Controlled laboratory study, repeated-measures design.

OBJECTIVES

To compare hip abductor muscle activity during selected exercises using fine-wire electromyography, and to determine which exercises are best for activating the gluteus medius and the superior portion of the gluteus maximus, while minimizing activity of the tensor fascia lata (TFL).

BACKGROUND

Abnormal hip kinematics (ie, excessive hip adduction and internal rotation) has been linked to certain musculoskeletal disorders. The TFL is a hip abductor, but it also internally rotates the hip. As such, it may be important to select exercises that activate the gluteal hip abductors while minimizing activation of the TFL.

METHODS

Twenty healthy persons participated. Electromyographic signals were obtained from the gluteus medius, superior gluteus maximus, and TFL muscles using fine-wire electrodes as subjects performed 11 different exercises. Normalized electromyographic signal amplitude was compared among muscles for each exercise, using multiple 1-way repeated-measures analyses of variance. A descriptive gluteal-to-TFL muscle activation index was used to identify preferred exercises for recruiting the gluteal muscles while minimizing TFL activity.

RESULTS

Both gluteal muscles were significantly (P<.05) more active than the TFL in unilateral and bilateral bridging, quadruped hip extension (knee flexed and extending), the clam, sidestepping, and squatting. The gluteal-to-TFL muscle activation index ranged from 18 to 115 and was highest for the clam (115), sidestep (64), unilateral bridge (59), and both quadruped exercises (50).

CONCLUSION

If the goal of rehabilitation is to preferentially activate the gluteal muscles while minimizing TFL activation, then the clam, sidestep, unilateral bridge, and both quadruped hip extension exercises would appear to be the most appropriate.

COMPARISON OF THE ACTIVITIES OF THE DEEP TRUNK MUSCLES MEASURED USING INTRAMUSCULAR AND SURFACE ELECTROMYOGRAPHY

Surface electromyography (EMG) has been used to estimate deep trunk muscle activity. However, it remains unknown whether surface EMG provides an accurate estimation of this activity. The purposes of this study were to compare surface and intramuscular EMG activity measurements and investigate the efficacy of surface EMG measurement for the transversus abdominis (TrA) and the multifidus (MF) muscles. Eight healthy men participated in the study. TrA and MF activities were simultaneously measured by both intramuscular and surface EMG during isometric trunk exercises. Spearman correlation coefficients for the relationship between the two activity measurements for the right TrA, left TrA, right MF, and left MF were 0.55, 0.36, 0.67, and 0.79, respectively. For the TrA, Bland–Altman plots revealed that mean differences between measurements obtained by intramuscular EMG and surface EMG were not close to zero, with a systematic bias toward higher surface EMG values. In conclusion, surface and intramuscular EMG activity measurements were strongly correlated for MF muscles, but poorly correlated for TrA muscles.

Efficacy of movement control exercises versus general exercises on recurrent sub-acute nonspecific low back pain in a sub-group of patients with movement control dysfunction. Protocol of a randomized controlled trial

Background

Practice guidelines recommend various types of exercise for chronic back pain but there have been few head-to-head comparisons of these interventions. General exercise seems to be an effective option for management of chronic low back pain (LBP) but very little is known about the management of a sub-acute LBP within sub-groups.

Recent research has developed clinical tests to identify a subgroup of patients with chronic non-specific LBP who have movement control dysfunction (MD).

Method/Design

We are conducting a randomized controlled trial (RCT) to compare the effects of general exercise and specific movement control exercise (SMCE) on disability and function in patients with MD within recurrent sub-acute LBP. The main outcome measure is the Roland Morris Disability Questionnaire.

Discussion

European clinical guideline for management of chronic LBP recommends that more research is required to develop tools to improve the classification and identification of specific clinical sub-groups of chronic LBP patients. Good quality RCTs are then needed to determine the effectiveness of specific interventions aimed at these specific target groups. This RCT aims to test the hypothesis whether patients within a sub-group of MD benefit more through a specific individually tailored movement control exercise program than through general exercises.

A comparison of trunk muscle activation amplitudes during gait in older adults with and without chronic low back pain

OBJECTIVE

To investigate abdominal and low back muscle activation amplitudes of older adults (at least 50 years of age) experiencing nonspecific chronic low back pain (LBP) and of adults without LBP while they walked on a level surface at a self-selected speed.

DESIGN

Cross-sectional.

SETTING

Dynamics of human motion laboratory.

PARTICIPANTS

Nine asymptomatic control participants (mean ± standard deviation: 64.9 ± 8.8 years) and 9 participants experiencing LBP (61.4 ± 9.8 years) were selected for this study.

METHODS

Surface electromyography (EMG) was recorded over the bilateral lower rectus abdomini, internal obliques, lateral erector spinae longissimus, and lumbar multifidus muscle sites while participants walked across a pressure-sensor mat at a self-selected speed. To normalize EMG amplitudes during gait, the participants performed a series of maximal voluntary isometric contractions. EMG signals were full-wave rectified and low-pass filtered to yield a linear envelop waveform. For the gait trials, a window was identified from right heel strike to the second left heel strike and 4 subphases, including right and left loading response and mid stance, were identified. EMG amplitudes were calculated for each subphase.

MAIN OUTCOME MEASUREMENTS

Two sample t-tests compared demographic information and spatiotemporal gait parameters between groups. EMG activation amplitude differences between groups and among subphases of gait were analyzed for each muscle with use of general linear models, followed by Tukey honestly significant difference post hoc comparisons.

RESULTS

No differences were found between the groups for demographic or gait parameters. The control group participants activated their lower rectus abdomini muscles (P < .05) and right internal oblique muscles significantly more than did the LBP group (P < .05), whereas the LBP group activated their left lateral erector spinae and both lumbar multifidi sites significantly more than did the control group (P < .05).

CONCLUSIONS

The activation amplitudes of the anterior muscle sites were lower for participants with LBP, whereas the posterior sites were activated to higher amplitudes than in the control group. Although most muscles responded to the subphases indicating muscle synergies, the group by muscle interactions for the right internal oblique and lateral erector spinae show that the differences between groups were not systematic. These results describe neuromuscular alterations in persons between 50-80 years with LBP that can be used for developing subject-specific management related to maintaining spinal stability.

Effect of a specific exercise program on the strength and resistance levels of lumbar muscles in warehouse workers

OBJECTIVE

The aim of this study was to verify the influence of a specific exercise program on the strength and resistance levels of lumbar flexors and extensors in warehouse workers.

MATERIALS AND METHODS

The population used in this randomized controlled trial included 557 warehouse male workers from a food distribution company in Oporto/Portugal. Upon the application of the selection criteria, 98 workers deemed eligible were randomized in two groups: 57 were assigned to the intervention group and 41 to the control group. The intervention included 9 easily-executed exercises to promote stretching and strengthening of the lumbar region, to be executed daily, at the beginning of the working time, at the company facilities and lasting 8'. Trunk muscles' voluntary strength and resistance were measured using an isometric electronic dynamometer (Globus Ergometer, Globus, Codigné, Italy) at baseline and eleven months after implementing the exercise program. The data was analyzed using SPSS®, version 17.0.

RESULTS

After implementation of the exercise program, in the intervention group, all variables increased, significant differences were observed as for the muscle strength and resistance values (p = 0.014 and p = 0.006, respectively), as well as in the ratio extensors/flexors (p = 0.037). In the control group, all variables decreased, with a statistically significant decrease of the trunk flexors strength level (p = 0.009).

CONCLUSION

The results of this study suggest that a specific exercise intervention program can increase trunk extensors strength and resistance.

Does increased muscular tension along the torso impair postural equilibrium in a standing posture?

This paper focused on the relationship between active muscular tension along the torso and postural equilibrium while standing. Eleven healthy male subjects underwent a posturographic examination associated with a bimanual compression of a dynamometric bar, which was used to set the torso muscular activity at three different levels (0MVC, 20MVC, 40MVC). Electromyographic pre-tests identified the main superficial muscles of the compressive load as: pectoralis major, latissimus dorsi, thoracic and lumbar erector spinae. Kinematics of the chest wall was recorded by means of two sensing belts, in order to assess the respiratory component of the center of pressure (CP) signal. The analysis of time-domain stabilometric parameters showed that CP displacements were larger and faster in 40MVC that in 20MVC, with no variation between 0MVC and 20MVC. The respiratory component of the CP signal was not sensitive to the compressive load. It was concluded that increased muscular tension along the torso is likely to disturb postural equilibrium, but only when it exceeds a given level.