Axial rotation strength in seated neutral and prerotated postures of young adults

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.

Reliability and criterion validity of handheld dynamometry for measuring trunk muscle strength in people with and without chronic non-specific low back pain

BACKGROUND

Evaluating trunk strength is an important aspect of the physical examination of people with low back pain (LBP). Thus, reliable, valid, and easily applied measurement tools are needed to quantify trunk muscle strength and monitor changes in response to interventions.

OBJECTIVES

To determine within-day and between-day test re-test reliability and criterion validity of a handheld dynamometer (HHD) to evaluate maximum isometric trunk strength in people with chronic LBP and asymptomatic individuals.

DESIGN

Reliability and criterion validity study.

METHODS

Twenty adult participants with chronic, non-specific LBP and 35 asymptomatic individuals participated. Isometric trunk flexion, extension, and rotation strength were evaluated with the HHD (Active force 2) and the within-day and between-day reliability were determined with intraclass correlation coefficients (ICC2,1) and the standard error of the measurements (SEM), minimal detectable change (MDC), and the limits of agreement (LOA) using Bland-Altman plots. Criterion validity was evaluated using Pearson correlation coefficients to compare HHD measurements to isokinetic dynamometry for both isometric trunk flexion and extension strength.

RESULTS

Good to excellent within-day and between-day reliability was observed for people with LBP and asymptomatic individuals with (ICC2,1) of 0.73-0.93 and 0.62-0.92 respectively. A moderate to strong correlation was found between measurements with the HHD and the isokinetic dynamometer with a correlation of r = 0.68-0.78 and r = 0.56-0.59 for people with LBP and asymptomatic participants respectively.

CONCLUSION

A HHD is a reliable, valid, and clinically applicable tool for the measurement of trunk strength in adults with and without chronic LBP.

Strength and Power-Related Measures in Assessing Core Muscle Performance in Sport and Rehabilitation

While force-velocity-power characteristics of resistance exercises, such as bench presses and squats, have been well documented, little attention has been paid to load, force, and power-velocity relationships in exercises engaging core muscles. Given that power produced during lifting tasks or trunk rotations plays an important role in most sport-specific and daily life activities, its measurement should represent an important part of the test battery in both athletes and the general population. The aim of this scoping review was 1) to map the literature related to testing methods assessing core muscle strength and stability in sport and rehabilitation, chiefly studies with particular focus on force-velocity-power characteristics of exercises involving the use of core muscles, 2) and to identify gaps in existing studies and suggest further research in this field. The literature search was conducted on Cochrane Library databases, Scopus, Web of Science, PubMed and MEDLINE, which was completed by SpringerLink, Google Scholar and Elsevier. The inclusion criteria were met in 37 articles. Results revealed that among a variety of studies investigating the core stability and core strength in sport and rehabilitation, only few of them analyzed force-velocity-power characteristics of exercises involving the use of core muscles. Most of them evaluated maximal isometric strength of the core and its endurance. However, there are some studies that assessed muscle power during lifting tasks at different loads performed either with free weights or using the Smith machine. Similarly, power and velocity were assessed during trunk rotations performed with different weights when standing or sitting. Nevertheless, there is still scant research investigating the power-velocity and force-velocity relationship during exercises engaging core muscles in able-bodied and para athletes with different demands on stability and strength of the core. Therefore, more research is needed to address this gap in the literature and aim research at assessing strength and power-related measures within cross-sectional and intervention studies. A better understanding of the power-force-velocity profiles during exercises with high demands on the core musculature has implications for designing sport training and rehabilitation programs for enhancement of athletes' performance and/or decrease their risk of back pain.

Trunk rotational strength asymmetry in adolescents with idiopathic scoliosis: an observational study

Background

Recent reports have suggested a rotational strength weakness in rotations to the concave side in patients with idiopathic scoliosis. There have been no studies presenting normative values of female adolescent trunk rotational strength to which a comparison of female adolescents with idiopathic scoliosis could be made. The purpose of this study was to determine trunk rotational strength asymmetry in a group of female adolescents with AIS and a comparison group of healthy female adolescents without scoliosis.

Methods

Twenty-six healthy adolescent females served as the healthy group (HG) (average age 14 years) and fourteen otherwise healthy adolescent females with idiopathic scoliosis served as the idiopathic scoliosis group (ISG) (average age 13.5 years, average Cobb 28°). Participant's isometric trunk rotational strength was measured in five randomly ordered trunk positions: neutral, 18° and 36° of right and left pre-rotation. Rotational strength asymmetry was compared within each group and between the two groups using several different measures.

Results

The HG showed strength asymmetry in the 36° pre-rotated trunk positions when rotating towards the midline (p < 0.05). The ISG showed strength asymmetry when rotating towards the concavity of their primary curve from the neutral position (p < 0.05) and when rotating towards the concavity from the 18° (p < 0.05) and 36° (p < 0.05) concave pre-rotated positions. The ISG is significantly weaker than the HG when rotating away from the midline toward the concave (ISG)-left (HG) side from the concave/left pre-rotated 18° (p < 0.05) and 36° (p < 0.05) positions.

Conclusion

The AIS females were found to be significantly weaker when contracting toward their main curve concavity in the neutral and concave pre-rotated positions compared to contractions toward the convexity. These weaknesses were also demonstrated when compared to the group of healthy female adolescent controls. Possible mechanisms for the strength asymmetry in ISG are discussed.

High loading rate during spinal manipulation produces unique facet joint capsule strain patterns compared with axial rotations

PURPOSE

Lumbar spinal manipulation (SM) is a popular, effective treatment for low back pain but the physiological mechanisms remain elusive. During SM, mechanoreceptors innervating the facet joint capsule (FJC) may receive a novel stimulus, contributing to the neurophysiological benefits of SM. The biomechanics of SM and physiological axial rotations were compared to determine whether speed or loading site affected FJC strain magnitudes or patterns.

METHODS

Human lumbar spine specimens were tested during physiological rotations and simulated SM while measuring applied torque, vertebral motion, and FJC strain. During physiological rotations, specimens were actuated at T12 to 20 degrees left and right axial rotation at 2 degrees to 125 degrees per second. During SM simulations, a 7-mm impulse displacement was applied to L3, L4, or L5 at 5 to 50 mm per second.

RESULTS

Physiological rotations. Increasing displacement rate resulted in significantly larger torque magnitudes (P < .001), whereas vertebral kinematics and FJC strain magnitudes were unchanged (P > .05). Physiological rotations vs SM. Applied torque and vertebral rotation magnitudes were similar across speed and vertebral level. Total vertebral translations were slightly larger during physiological rotations vs SM at a given loading rate (P < .05). Patterns of vertebral motions and FJC strain during SM and physiological rotations varied significantly with loading rate (P < .05) but not with actuation site (P > .15).

CONCLUSIONS

The similar patterns observed in vertebral motion and FJC strain across actuation sites during SM and physiological rotations suggest that site specificity of SM may have minimal clinical relevance. High loading rates during lumbar SM resulted in unique patterns in FJC strain, which may result in unique patterns of FJC mechanoreceptor response.

Ergonomics and biology of spinal rotation

Spinal rotation, though being a very common motion of the body, is poorly understood. Furthermore, this motion and the extent of its development is unique to the human. Beyond the extent of its need in common activities, spinal rotation is a destabilizating motion for an inherently unstable structure. Spinal rotation has been argued to be an essential feature for an efficient bipedal gait. Also, it provides leverage to the upper extremities in delivering a forceful impact. An artificial restriction/elimination of spinal rotation resulted in significantly shorter stride length, slower walking velocity, and higher energy consumption in walking (p < 0.05). Spinal rotation also decreases the amount of force the spinal muscles can generate (to 25% of spinal extension). However, its extensive employment in industrial activities has been associated with 60.4% of back injuries. It is further stated that the amount of scientific information currently available is inadequate to biomechanically model the spinal response in a working environment. For example, when the spine is pre-rotated, a further rotation in the direction of pre-rotation decreases the force production significantly (p < 0.01) and increases the EMG activity significantly (p < 0.01) but the pattern changes with effort in the opposite direction. This and other properties (described in the paper) render biomechanical models inadequate. Muscle activation pattern and neuromotor behaviour of spinal muscles in flexion/extension and rotation of the spine are significantly different from each other (p < 0.01). The localized fatigue in different spinal muscles in the same contraction is significantly different and has been called differential fatigue. Finally, the trunk rotation, being pivotal for bipedal locomotion has brought many back problems to the human race.

Axial neck rotation strength in neutral and prerotated postures

OBJECTIVE

To characterize isometric rotation strength in the neutral and in different prerotated positions of the neck.

DESIGN

This was a descriptive study involving maximal isometric strength measurements of the cervical musculature.

BACKGROUND

The literature contains only a few studies pertaining to strength levels of the neck rotator muscles in the neutral position. None of these studies have dealt in detail with maximal neck strength in selected prerotation positions.

METHOD

Twenty healthy men volunteered as subjects. Maximal axial rotation strength of the neck muscles was measured in a neutral position and bilaterally at 30 degrees and 60 degrees rotation using the isometric neck strength measurement system. Isometric maximum voluntary contractions of the neck muscles in flexion and extension were also tested.

RESULTS

The highest strength values were not reached in the neutral position, but at the largest joint angles, while turning the head in the opposite direction from the prerotated position. Maximal strength increased with increasing angle, and at the 60 degrees prerotation angle it was 44% higher towards the right and 27% higher towards the left compared to the values obtained in the neutral position. The smallest strength values were also produced at the largest prerotation angles, but in the same direction.

CONCLUSIONS

The present results show a clear relationship between the prerotated position of the neck and maximal voluntary strength in rotation.

RELEVANCE

The data suggest that neck strength is highly prerotation angle dependent. Neck strength should be measured at several prerotation positions in addition to the neutral position in order to obtain the true strength values throughout the entire range of motion. Maximal neck rotation strength between subjects is differentiated best at the greatest prerotation angles.

Trunk muscle strength in flexion, extension, and axial rotation in patients managed with lumbar disc herniation surgery and in healthy control subjects

STUDY DESIGN

A cross-sectional study was conducted.

OBJECTIVE

To compare maximal flexion, extension, and rotation strength as well as force-time characteristics of trunk muscles in patients who undergo lumbar disc herniation with those in healthy control subjects 2 months after surgery.

SUMMARY OF BACKGROUND DATA

Insufficient attention has been paid to muscle strength characteristics after lumbar disc herniation surgery.

METHODS

For this study, 30 postoperative patients with lumbar disc herniation and 30 healthy control subjects volunteered to participate. Isometric trunk flexion, extension in the standing position, and seated rotation strength were tested bilaterally in a neutral posture and at 30 degrees axial prerotation. The area under the curve was calculated to analyze explosive force capacity. Dynamic endurance strength was measured by calculating the repetition maximum. Pain during the strength measurements was assessed by a visual analog scale.

RESULTS

The healthy control subjects showed 44% and 36% higher isometric trunk flexion (P < 0.001) and extension (P < 0.001) forces, respectively, than the patients. The respective values for the area under the curve were 41% and 37% higher for the trunk flexors (P < 0.001) and extensors (P < 0.001) in the healthy control subjects than in the patients. The differences in trunk rotation force between the groups were statistically significant when the lower body was rotated 30 degrees to the right (P = 0.023) or to the left (P = 0.043) and the upper body was rotated in the opposite direction. Furthermore, in the dynamic endurance strength test, the healthy control subjects performed 70% more repetitions both for trunk flexors and extensors than did the patients. Some of the patients reported mild pain during the strength measurements, but the level of pain did not correlate with the strength values.

CONCLUSIONS

The recovery of maximal endurance and explosive type strength characteristics is incomplete in patients with lumbar disc herniation 2 months after surgery. Active strength training is recommended to restore muscle function in these patients.

An electromyographic study of isokinetic axial rotation in young adults

BACKGROUND CONTEXT

Trunk rotation is associated with over 60% of all low back injuries. However, there are gaps in the knowledge about trunk rotation.

PURPOSE

To study the axial rotation torque and electromyographs (EMGs) of seven trunk muscles bilaterally in static and isokinetic modes with increasing angular velocity to determine qualitative and quantitative muscle response.

STUDY DESIGN

An electromyographic study of seven trunk muscles bilaterally was carried out in 50 normal subjects during static and isokinetic axial rotation at varying angular velocity. The qualitative and quantitative force and EMG measures were made and analyzed phenomenologically and statistically.

METHODS

Fifty normal young adults (27 men, 23 women) performed an isometric maximal voluntary contraction (MVC) from the neutral upright-seated posture to their right and left. Also, these subjects performed isokinetic axial rotation from neutral seated position to right and left, and from prerotated right and left "end of range posture" toward the neutral at 10, 20 and 40 degrees per second angular velocity. All experimental trials were made on axial rotation tester designed for the study. EMG was recorded from the erector spinae at L3 and T10 vertebral levels, latissimus dorsi, pectoralis major, rectus abdominis and external and internal obliques bilaterally. The torque and EMG in isokinetic condition were normalized against those of isometric condition. Descriptive statistics were calculated. Data were subjected to analysis of variance, and torque was regressed on EMG.

RESULTS

The peak isokinetic torques were significantly lower than the isometric torques (p<.01), but the EMGs of the isokinetic conditions were significantly higher than those of isometric trials (p<.01). The isokinetic axial rotation torque decreased by 1 Nm to 1.5 Nm with per degree increase in velocity of rotation, with the values for 10, 20 and 40 degrees per second angular velocities being significantly different (p<.01). There was a significant increase (p<.01) in percent EMG (up to 28%) per unit torque with increasing angular velocity of rotation. The rotation torque from prerotated position to neutral was significantly higher than that of rotation away from the neutral (p<.001). The EMG magnitude increased significantly with increasing velocity (2% to 17% at 10 degrees per second), 21% to 28% at 20 degrees per second, 30% to 36% at 40 degrees per second). Regression analysis revealed poor predictability of torque based on EMG. The latter was suggested because of the role and behavior of the ligaments and joint capsules of the spine.

CONCLUSION

The axial rotation is initiated and maintained by the contralateral external obliques, ipsilateral latissimus dorsi and internal oblique. The ipsilateral erector spinae likely play a stabilizer role. The isometric torque is greater than the isokinetic, which decreases with increasing velocity. Even with decreasing torque, EMG progressively increases, indicating a disproportionally higher stress in the spinal connective tissues potentiating injury. The data presented here suggest that, for safety, load and velocity of rotation should be kept low.