1988 Volvo award in biomechanics. The triaxial coupling of torque generation of trunk muscles during isometric exertions and the effect of fatiguing isoinertial movements on the motor output and movement patterns

MEFFNet: Forecasting Myoelectric Indices of Muscle Fatigue in Healthy and Post-Stroke During Voluntary and FES-Induced Dynamic Contractions

Myoelectric indices forecasting is important for muscle fatigue monitoring in wearable technologies, adaptive control of assistive devices like exoskeletons and prostheses, functional electrical stimulation (FES)-based Neuroprostheses, and more. Non-stationary temporal development of these indices in dynamic contractions makes forecasting difficult. This study aims at incorporating transfer learning into a deep learning model, Myoelectric Fatigue Forecasting Network (MEFFNet), to forecast myoelectric indices of fatigue (both time and frequency domain) obtained during voluntary and FES-induced dynamic contractions in healthy and post-stroke subjects respectively. Different state-of-the-art deep learning models along with the novel MEFFNet architecture were tested on myoelectric indices of fatigue obtained during [Formula: see text] voluntary elbow flexion and extension with four different weights (1 kg, 2 kg, 3 kg, and 4 kg) in sixteen healthy subjects, and [Formula: see text] FES-induced elbow flexion in sixteen healthy and seventeen post-stroke subjects under three different stimulation patterns (customized rectangular, trapezoidal, and muscle synergy-based). A version of MEFFNet, named as pretrained MEFFNet, was trained on a dataset of sixty thousand synthetic time series to transfer its learning on real time series of myoelectric indices of fatigue. The pretrained MEFFNet could forecast up to 22.62 seconds, 60 timesteps, in future with a mean absolute percentage error of 15.99 ± 6.48% in voluntary and 11.93 ± 4.77% in FES-induced contractions, outperforming the MEFFNet and other models under consideration. The results suggest combining the proposed model with wearable technology, prosthetics, robotics, stimulation devices, etc. to improve performance. Transfer learning in time series forecasting has potential to improve wearable sensor predictions.

Trunk stability in fatiguing frequency-dependent lifting activities

BACKGROUND

Work-related low-back disorders (WLBDs) are one of the most frequent and costly musculoskeletal conditions. It has been showed that WLBDs may occur when intervertebral or torso equilibrium is altered by a biomechanical perturbations or neuromuscular control error. The capacity to react to such disturbances is heavily determined by the spinal stability, provided by active and passive tissues and controlled by the central nervous system.

RESEARCH QUESTION

This study aims to investigate trunk stability through the Lyapunov's maximum exponent during repetitive liftings in relation to risk level, as well as to evaluate its ability to discriminate these risk levels.

METHODS

Fifteen healthy volunteers performed fatiguing lifting tasks at three different frequencies corresponding to low, medium, and high risk levels according to the National Institute for Occupational Safety and Health (NIOSH) equation. We investigated changes in spinal stability during fatiguing lifting tasks at different risk levels using the maximum Lyapunov's index (λ_Max) computed from trunk accelerations recorded by placing three IMUs at pelvis, lower and upper spine levels. A two-way repeated-measures ANOVA was performed to determine if there was any significant effect on λ_Max among the three risk levels and the time (start, mid, and end of the task). Additionally, we examined the Pearson's correlation of λ_Max with the trunk muscle co-activation, computed from trunk sEMG.

RESULTS

Our findings show an increase in trunk stability with increasing risk level and as the lifting task progressed over time. A negative correlation between λ_Max and trunk co-activation was observed which illustrates that the increase in spinal stability could be partially attributed to increased trunk muscle co-activation.

SIGNIFICANCE

This study highlights the possibility of generating stability measures from kinematic data as risk assessment features in fatiguing tasks which may prove useful to detect the risk of developing work-related low back pain disorders and allow the implementation of early ergonomic interventions.

Assessment of Fatigue and Recovery in Sport: Narrative Review

Fatigue is a phenomenon associated with decreases in both physical and cognitive performances and increases in injury occurrence. Competitive athletes are required to complete demanding training programs with high workloads to elicit the physiological and musculoskeletal adaptations plus skill acquisition necessary for performance. High workloads, especially sudden rapid increases in training loads, are associated with the occurrence of fatigue. At present, there is limited evidence elucidating the underlying mechanisms associating the fatigue generated by higher workloads and with an increase in injury risk. The multidimensional nature and manifestation of fatigue have led to differing definitions and dichotomies of the term. Consequently, a plethora of physiological, biochemical, psychological and performance markers have been proposed to measure fatigue and recovery. Those include self-reported scales, countermovement jump performance, heart rate variability, and saliva and serum biomarker analyses. The purpose of this review is to provide an overview of fatigue and recovery plus methods of assessments.

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.

The Influence of Fatigue on Throwing and YBT-UQ Performance in Male Adolescent Handball Players

Purpose: The goal of the present study was to assess the effects of fatigue on throwing and Upper Quarter Y Balance Test (YBT-UQ) performance in male adolescent handball players. We hypothesized that throwing and YBT-UQ performance will be decreased in response to an upper-body fatigue-protocol.

Method: All male participants (N = 24, age: 14.8 ± 0.7 yrs) were handball players of a regional youth selection team. A radar gun was used for the assessment of throwing velocity. The YBT-UQ was executed assessing medial, inferolateral and superolateral reach directions normalized to the upper limb length together with a composite score. Immediately following a fatigue protocol of different sets of push-ups until failure (i.e., not being able to perform 60% of the initial maximal amount of push-ups), throwing and YBT-UQ performance were assessed again.

Results: Fatigue resulted in a significant decrease in throwing velocity (−3%, p = 0.022, d = 0.32). Concerning YBT-UQ, the fatigue protocol produced significant decreases for the superolateral reach direction (throwing arm reach: −5%, p = 0.017, d = 0.39; non-throwing arm reach: −10%, p < 0.001, d = 0.87) and the composite score (throwing arm reach: −2%, p = 0.026, d = 0.31; non-throwing arm reach: −4%, p = 0.001, d = 0.52) but not for the medial and the inferolateral reach directions.

Conclusions: Fatigue was found to be an impairing factor for throwing performance and shoulder mobility and stability. Therefore, a lower level of fatigue and/or a higher tolerance of fatigue is desirable. Strength-endurance and mobility exercises especially for the shoulder girdle may be a valuable addition for the training routine of youth handball players.

Influencing lumbar posture through real-time biofeedback and its effects on the kinematics and kinetics of a repetitive lifting task

BACKGROUND

Repetitive, flexed lumbar postures are a risk factor associated with low back injuries. Young, novice workers involved in manual handling also appear at increased risk of injury. The evidence for the effectiveness of postural biofeedback as an intervention approach is lacking, particularly for repetitive, fatiguing tasks.

RESEARCH QUESTION

How does real-time lumbosacral (LS) postural biofeedback modify the kinematics and kinetics of repetitive lifting and the risk of low back injury?

METHODS

Thirty-four participants were randomly allocated to two groups: biofeedback (BF) and non-biofeedback (NBF). Participants repetitively lifted a 13 kg box at 10 lifts per minute for up to 20 min. Real-time biofeedback of LS posture occurred when flexion exceeded 80% maximum. Three-dimensional motion analysis and ground reaction forces enabled estimates of joint kinematics and kinetics. Rating of perceived exertion (RPE) was measured throughout.

RESULTS

The BF group adopted significantly less peak lumbosacral flexion (LSF) over the 20 min when compared to the NBF group, which resulted in a significant reduction in LS passive resistance forces. This was accompanied by increased peak hip and knee joint angular velocities in the BF group. Lower limb moments did not significantly differ between groups. Feedback provided to participants diminished beyond 10 min and subjective perceptions of physical exertion were lower in the BF group.

SIGNIFICANCE

Biofeedback of lumbosacral posture enabled participants to make changes in LSF that appear beneficial in reducing the risk of low back injury during repetitive lifting. Accompanying behavioural adaptations did not negatively impact on physical exertion or lower limb joint moments. Biofeedback of LS posture offers a potential preventative and treatment adjunct to educate handlers about their lifting posture. This could be particularly important for young, inexperienced workers employed in repetitive manual handling who appear at increased risk of back injury.

Influences of continuous sitting and psychosocial stress on low back kinematics, kinetics, discomfort, and localized muscle fatigue during unsupported sitting activities

Continuous seated postures may increase the risk of adverse health outcomes such as low-back pain, and this risk may be influenced by several modifying factors. In the present study, we aimed to quantify the effects of continuous sitting and psychosocial stress under an unsupported sitting condition. Fourteen participants completed continuous, 40 min. periods of computer-based tasks, involving both low and higher levels of psychosocial stress, while using a laptop computer without a desk. Continuous sitting significantly increased perceived discomfort (particularly in the upper and lower back), trunk flexion and metrics of localized muscle fatigue. A higher level of psychosocial stress increased estimated lumbosacral compression forces (by ∼12%). Only weak correlations were found between subjective and objective measures, while various fatigue metrics showed a good level of correspondence with each other. These results could support the future evaluation or design of diverse seated work configurations. Practitioner Summary: Continuous, 40 min. periods of unsupported sitting had broad impacts on subjective and objective outcomes, including discomfort, postures, spine loads and localized muscle fatigue, while psychosocial stress only had a substantial influence on lumbosacral compression. These results extend our understanding of sitting behaviors and provide information for designing future sitting environments.

The Effect of Training in the Preparatory and Competitive Periods on Trunk Rotational Power in Canoeists, Ice-Hockey Players, and Tennis Players

This study evaluates changes in trunk rotational power at different weights and velocities after the preparatory and competitive periods in ice-hockey players, tennis players, and canoeists. The subjects performed trunk rotations to each side with a barbell of different weights placed on the shoulders (6, 10, 12, 16, 20, 22, and 26 kg) prior to and after 6 weeks of the preparatory period and 6 weeks of the competitive period. The results showed that mean power produced in the acceleration phase of trunk rotations increased significantly at weights from 10 to 26 kg or 6 to 26 kg after the preparatory and competitive periods in tennis players. The values obtained during trunk rotations with weights ≥12 kg also increased significantly after the preparatory period in ice-hockey players, whereas there were no significant changes after the competitive period. Similarly, the mean power during trunk rotations with weights ≥10 kg increased significantly only after the preparatory period in canoeists. Similar changes were observed for the peak power. These findings demonstrate that changes in trunk rotational power reflect the specificity of their training programs. This information may provide a basis for designing exercises focused on improvements of power produced during trunk rotations under loading conditions.

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

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

Combined effect of low back muscle fatigue and passive tissue elongation on the flexion-relaxation response

Previous literature has documented the alterations in the flexion-relaxation response of the lumbar extensor musculature to passive tissue elongation (PTE) and muscle fatigue (MF). There is no study, however, that has explored this response as a function of the combined effect of both PTE and MF, which is often seen in occupational settings. Twelve participants performed three experimental protocols on three different days to achieve (1) PTE, (2) MF and (3) PTE&MF (combined). Trunk kinematics and muscle activities were monitored to assess the effects of these protocols on the peak lumbar flexion angle and the lumbar angle of the flexion-relaxation of the trunk extensor muscles. Results showed responses to the uni-dimensional stresses (PTE and MF) consistent with those seen in the previous literature, while the combined protocol elicited responses that more closely matched the PTE protocol.

Low back cutaneous vibration and its effect on trunk postural control

The current study investigated the effects of a low back pain (LBP) vibration modality on trunk motor control. Trunk repositioning error and responses to a sudden loading trunk perturbation were evaluated pre- and post-vibration (15min vibration exposure while sitting on a standard chair) as well as when concurrent cutaneous low back vibration was applied. Only minor effects were observed post-vibration when compared to pre-vibration. However, when vibration was applied at the same time as the sudden trunk perturbations, lumbar erector spinae and external oblique muscles were significantly more delayed in activating following the perturbation. In addition, the resting muscle activation prior to the trunk perturbation was higher in both the back extensor and abdominal muscles when concurrent vibration was applied. These findings suggest that cutaneous low back vibration significantly alters motor control responses and this should be considered before implementing cutaneous vibration as a low back pain management strategy.

Relationship between flexion-rotation test and ultrasound thickness measurement of the abdominal muscles

OBJECTIVE

The purpose of this study was to investigate the relationship between flexion-rotation test and ultrasound (US) thickness measurement of the antero-lateral abdominal muscles.

DESIGN

Following ethical approval, a convenience sample of 55 subjects between the ages of 20 and 30 years participated in this study. Endurance of the abdominal muscles was measured using the flexion-rotation test in all subjects. US thickness measurement for the transversus abdominis (TrA), internal oblique (IO) and external oblique (EO) muscles was performed on the right side at rest in a supine position.

RESULTS

Pearson correlation coefficient between the variables of the study showed no significant relationship between the flexion-rotation test and US thickness measurements of the TrA (r = -0.03, P = 0.80), IO (r = -0.13, P = 0.32), and EO (r = -0.14, P = 0.31) muscles. The significance level of 0.05 was chosen.

CONCLUSION

It seems that there is no significant relationship between the flexion-rotation test and US measurement of abdominal muscles thickness.

Assessment of isokinetic muscle function in Korea male volleyball athletes

Volleyball players performed numerous repetitions of spike actions, which uses and requires strong and explosive force, and control of the muscles of the shoulder, lower back, and legs. Muscle imbalance is one of the main causes of sport injuries. The purpose of this study was to assess isokinetic muscle functions in male volleyball players. We thus aim to accurately evaluate their muscle functions, and identify the best training strategy to achieve optimal muscle strength balance in future training programs. The participants in this study consisted of 14 male volleyball players. Muscle strength was measured using the isokinetic dynamometer. Muscle strength was evaluated in terms of peak torque and average power, calculated from five repeated measurements at an angular speed of 60°/sec. Three players who were left attackers showed shoulder imbalance, four players showed trunk joint imbalance, nine players had knee joint of extension/flexion imbalance and four players showed left/right imbalance. The results showed that the number of volleyball players with differences between the strength of the bilateral knee muscles, and between the strength of the hamstrings and quadriceps muscles was higher than the number of players with differences between the strength of the shoulder internal and external rotation muscles, and higher than the number of players with differences between the strength of the lower back extension and flexion muscles.

Variations in trunk muscle activities and spinal loads following posterior lumbar surgery: A combined in vivo and modeling investigation

BACKGROUND

Iatrogenic injuries to paraspinal muscles during posterior lumbar surgery cause a reduction in their contractile cross-sectional area and thus presumably their postoperative activation. This study investigates the effect of such intraoperative injuries on postoperative patterns of muscle activations and spinal loads during various activities using a combined modeling and in vivo MR imaging approach.

METHODS

A three-dimensional, multi-joint, musculoskeletal model was used to estimate pre- and postoperative muscle forces and spinal loads under various activities in upright and flexed postures. According to our in vivo pre- and postoperative (~6 months) measurements in six patients using a 3-Tesla-MR scanner, physiological cross-sectional areas of multifidus and erector spinae were reduced in the postoperative model by 26 and 11%, respectively.

FINDINGS

Postoperative trunk extension strength was predicted to decrease by ~23% from 215 Nm in the intact model to 165 Nm in the postoperative model. Postoperative force in multifidus fascicles decreased by ~21-40% in flexion tasks and by ~14-35% in upright tasks. In contrast, the sum of the forces in all other intact and less injured extensor muscles slightly increased (by <6%) in the postoperative model. Postoperative L5-S1 compressive and shear loads varied slightly (by ~3%).

INTERPRETATION

Intraoperative injuries induced a shift in load-sharing from the most injured muscle (multifidus) toward other less injured and intact muscles during all simulated activities. Postoperative rehabilitation programs should therefore strengthen and facilitate (while avoiding muscle imbalance) not only the injured multifidus but also other intact and less injured trunk muscles that play a compensatory role after the operation.

The Effects of Vibration and Muscle Fatigue on Trunk Sensorimotor Control in Low Back Pain Patients

INTRODUCTION

Changes in sensorimotor function and increased trunk muscle fatigability have been identified in patients with chronic low back pain (cLBP). This study assessed the control of trunk force production in conditions with and without local erector spinae muscle vibration and evaluated the influence of muscle fatigue on trunk sensorimotor control.

METHODS

Twenty non-specific cLBP patients and 20 healthy participants were asked to perform submaximal isometric trunk extension torque with and without local vibration stimulation, before and after a trunk extensor muscle fatigue protocol. Constant error (CE), variable error (VE) as well as absolute error (AE) in peak torque were computed and compared across conditions. Trunk extensor muscle activation during isometric contractions and during the fatigue protocol was measured using surface electromyography (sEMG).

RESULTS

Force reproduction accuracy of the trunk was significantly lower in the patient group (CE = 9.81 ± 2.23 Nm; AE = 18.16 ± 3.97 Nm) than in healthy participants (CE = 4.44 ± 1.68 Nm; AE = 12.23 ± 2.44 Nm). Local erector spinae vibration induced a significant reduction in CE (4.33 ± 2.14 Nm) and AE (13.71 ± 3.45 Nm) mean scores in the patient group. Healthy participants conversely showed a significant increase in CE (8.17 ± 2.10 Nm) and AE (16.29 ± 2.82 Nm) mean scores under vibration conditions. The fatigue protocol induced erector spinae muscle fatigue as illustrated by a significant decrease in sEMG median time-frequency slopes. Following the fatigue protocol, patients with cLBP showed significant decrease in sEMG root mean square activity at L4-5 level and responded in similar manner with and without vibration stimulation in regard to CE mean scores.

CONCLUSIONS

Patients with cLBP have a less accurate force reproduction sense than healthy participants. Local muscle vibration led to significant trunk neuromuscular control improvements in the cLBP patients before and after a muscle fatigue protocol. Muscle vibration stimulation during motor control exercises is likely to influence motor adaptation and could be considered in the treatment of cLBP. Further work is needed to clearly identify at what levels of the sensorimotor system these gains are achievable.

Effects of spinal manipulation on sensorimotor function in low back pain patients--A randomised controlled trial

BACKGROUND

Low back pain (LBP) is a major health problem in industrialized societies. Spinal manipulation (SM) is often used for treating LBP, though the therapeutic mechanisms remain elusive. Research suggests that sensorimotor changes may be involved in LBP. It is hypothesized that SM may generate its beneficial effects by affecting sensorimotor functions.

OBJECTIVES

To compare changes in sensorimotor function, as measured by postural sway and response to sudden load, in LBP patients following the delivery of high-velocity low amplitude (HVLA)-SM or low-velocity variable amplitude (LVVA)-SM versus a sham control intervention.

DESIGN

A three-arm (1:1:1 ratio) randomized controlled trial.

METHODS

A total of 221 participants who were between 21 and 65 years, having LBP intensity (numerical rating scale) ≥4 at either phone screen or the first baseline visit and ≥2 at phone screen and both baseline visits, and Quebec Task Force diagnostic classifications of 1, 2, 3 or 7 were enrolled to receive four SM treatments over two weeks. Study outcomes were measured at the first and fifth visits with the examiners blinded from participant group assignment.

RESULTS

The LVVA-SM group demonstrated a significant increase in medial-to-lateral postural excursion on the soft surface at the first visit when compared to the control group. No other significant between-group differences were found for the two sensorimotor tests, whether during the first visit or over two weeks.

CONCLUSIONS

It appears that short-term SM does not affect the sensorimotor functions as measured by postural sway and response to sudden load in this study.

The effect of contralateral submaximal contraction on the development of biceps brachii muscle fatigue

OBJECTIVE

The aim of this study was to determine if a submaximal contraction in the contralateral limb affected the fatigability of the dominant limb.

BACKGROUND

Muscle fatigue is a known risk factor for musculoskeletal injury; however, it is unknown whether a submaximal contraction in the nondominant limb, such as for stabilizing a tool or load, affects the rate of development of fatigue, potentially increasing risk of injury. Current ergonomic assessments of injury risk do not involve consideration of submaximal contralateral demands. It was hypothesized that increased neuromuscular drive and active muscle mass during bilateral contractions would increase fatigability.

METHOD

Twelve males isometrically maintained a 30% unilateral contraction and a 30% dominant + 15% nondominant bilateral contraction until failure on two different collection days, separated by 7 days.

RESULTS

No statistically significant differences were found for time to task failure (p = .6204), decrease in maximal force (p = .1698), or alterations in electromyography amplitude (p = .7223) or frequency (p = .3292) between unilateral and bilateral conditions.

CONCLUSION

The hypothesis that the addition of a lesser submaximal isometric contraction would increase fatigability was rejected.

APPLICATION

These findings indicate that in ergonomic settings, muscle fatigability can be estimated by the more demanding task and do not need to be complicated by lesser submaximal contractions in the opposing limb.

Exploring the effects of seated whole body vibration exposure on repetitive asymmetric lifting tasks

This study investigated changes in the physiological and behavioral responses to repetitive asymmetric lifting activity after exposure to whole body vibrations. Seventeen healthy volunteers repeatedly lifted a box (15% of lifter's capacity) positioned in front of them at ankle level to a location on their left side at waist level at the rate of 10 lifts/min for a period of 60 minutes. Prior to lifting, participants were seated on a vibrating platform for 60 minutes; in one of the two sessions the platform did not vibrate. Overall, the physiological responses assessed using near-infrared spectroscopy signals for the erector spinae muscles decreased significantly over time during the seating and the lifting tasks (p < 0.001). During repetitive asymmetric lifting, behavioral changes included increases in peak forward bending motion, twisting movement, and three-dimensional movement velocities of the spine. The lateral bending movement of the spine and the duration of each lift decreased significantly over the 60 minutes of repetitive lifting. With exposure to whole body vibration, participants twisted farther (p = 0.046) and twisted faster (p = 0.025). These behavioral changes would suggest an increase in back injury risk when repetitive lifting tasks are preceded by whole body vibration exposure.

Golf-related low back pain: a review of causative factors and prevention strategies

Golf is a popular sport with both perceived and real health benefits. However, certain injury risks are also prevalent, particularly to the lower back. Epidemiological studies have shown that lower back pain (LBP) from golf account for between 18% and 54% of all documented ailments, leading many researchers to regard the condition as the most common golf injury.

The purpose of this review was to examine the scientific literature to ascertain the risk factors associated with the development of LBP from playing golf and suggest methods to modify or limit these factors. Results of the review indicate that the high frequency of LBP appears multi-factorial although the asymmetrical and forceful nature of the swing along with excessive play and practice, particularly amongst elite players, appear to be common factors. Other factors include swing flaws leading to excessive side-bend and over-rotation of the spine, abnormal muscle recruitment, poor trunk endurance, restricted lead hip internal rotation and the use of unnecessarily stressful club transportation methods. Methods to help control or eliminate excessive stress on the lower back would include reducing the amount spent playing or practicing, seeking professional assistance to assess and adjust swing mechanics, improve trunk and hip flexibility, increase the strength and endurance of the trunk musculature, consider different footwear options and avoid carrying the golf bag. Adopting some or all of these recommendations should allow players to continue to enjoy the sport of golf well into their senior years.

Physiological and biomechanical responses to a prolonged repetitive asymmetric lifting activity

This study investigated the effects of a prolonged repetitive asymmetric lifting task on behavioural adaptations during repetitive lifting activity, measures of tissue oxygenation and spine kinematics. Seventeen volunteers repeatedly lifted a box, normalised to 15% of the participant's maximum lifting strength, at the rate of 10 lifts/min for a period of 60 min. The lifts originated in front of the participants at ankle level and terminated on their left side at waist level. Overall, perceived workload increased during the repetitive lifting task. Erector spinae oxygenation levels, assessed using near-infrared spectroscopy, decreased significantly over time. Behavioural changes observed during the repetitive lifting task included increases in the amount of forward bending, the extension velocity and the lateral bending velocity, and a reduced lateral bending moment on the spine. These changes, with the exception of the reduced lateral bending moment, are associated with increased risk of low back disorder.

Effects of repetitive lifting on kinematics: inadequate anticipatory control or adaptive changes?

In the present study, the effects of repetition on the kinematics in discrete lifting were studied in 10 subjects who lifted a barbell weighing 10% of body mass at a determined speed and along a determined trajectory 630 times during about 40 min. Three-dimensional (3-D) kinematics of the feet, lower and upper legs, pelvis, and trunk were recorded in the first 3 and the final 3 lifting movements of each set of 70 lifts. Over time, trunk extension velocity in the initial 250 ms of the lifting movement decreased, reaching negative (increasing flexion) values in most subjects. In contrast, hip extension velocity increased. Those changes resulted in an increased phase lag between hip and trunk extension. Also, over time, subjects started the lifting movement with their legs more extended and their trunks further flexed. Finally, the motion of the trunk around its longitudinal axis (twisting) increased. The increase in phase lag between hip and trunk extension is interpreted as a consequence of fatigue-more specifically, as the result of a decreased rate of force development of the back muscles. The change in initial posture more likely is an adaptation that functions to retard further fatigue development.

Predictors of low back pain in physically active conscripts with special emphasis on muscular fitness

BACKGROUND CONTEXT

Association between low physical fitness and low back pain (LBP) is contradictory in previous studies.

PURPOSE

The objective of the present prospective cohort study was to investigate the predictive associations of various intrinsic risk factors in young conscripts for LBP, with special attention to physical fitness.

STUDY DESIGN

A prospective cohort study.

PATIENT SAMPLE

A representative sample of Finnish male conscripts. In Finland, military service is compulsory for male citizens and 90% of young men enter into the service.

OUTCOME MEASURES

Incidence of LBP and recurrent LBP prompting a visit at the garrison health clinic during 6-month military training.

METHODS

Four successive cohorts of 18- to 28-year-old male conscripts (N=982) were followed for 6 months. Conscripts with incidence of LBP were identified and treated at the garrison clinic. Predictive associations between intrinsic risk factors and LBP were examined using multivariate Cox proportional hazard models.

RESULTS

The cumulative incidence of LBP was 16%, the incidence rate being 1.2 (95% confidence interval [CI], 1.0-1.4) per 1,000 person-days. Conscripts with low educational level had increased risk for incidence of LBP (hazard ratio [HR], 1.6; 95% CI, 1.1-2.3). Conscripts with low dynamic trunk muscle endurance and low aerobic endurance simultaneously (ie, having coimpairment) at baseline also had an increased risk for incidence of LBP. The strongest risk factor was coimpairment of trunk muscular endurance in tests of back lift and push-up (HR, 2.8; 95% CI, 1.4-5.9).

CONCLUSIONS

The increased risk for LBP was observed among young men who had a low educational level and poor fitness level in both muscular and aerobic performance.

Effect of spinal manipulation on sensorimotor functions in back pain patients: study protocol for a randomised controlled trial

Background

Low back pain (LBP) is a recognized public health problem, impacting up to 80% of US adults at some point in their lives. Patients with LBP are utilizing integrative health care such as spinal manipulation (SM). SM is the therapeutic application of a load to specific body tissues or structures and can be divided into two broad categories: SM with a high-velocity low-amplitude load, or an impulse "thrust", (HVLA-SM) and SM with a low-velocity variable-amplitude load (LVVA-SM). There is evidence that sensorimotor function in people with LBP is altered. This study evaluates the sensorimotor function in the lumbopelvic region, as measured by postural sway, response to sudden load and repositioning accuracy, following SM to the lumbar and pelvic region when compared to a sham treatment.

Methods/Design

A total of 219 participants with acute, subacute or chronic low back pain are being recruited from the Quad Cities area located in Iowa and Illinois. They are allocated through a minimization algorithm in a 1:1:1 ratio to receive either 13 HVLA-SM treatments over 6 weeks, 13 LVVA-SM treatments over 6 weeks or 2 weeks of a sham treatment followed by 4 weeks of full spine "doctor's choice" SM. Sensorimotor function tests are performed before and immediately after treatment at baseline, week 2 and week 6. Self-report outcome assessments are also collected. The primary aims of this study are to 1) determine immediate pre to post changes in sensorimotor function as measured by postural sway following delivery of a single HVLA-SM or LVVA-SM treatment when compared to a sham treatment and 2) to determine changes from baseline to 2 weeks (4 treatments) of HVLA-SM or LVVA-SM compared to a sham treatment. Secondary aims include changes in response to sudden loads and lumbar repositioning accuracy at these endpoints, estimating sensorimotor function in the SM groups after 6 weeks of treatment, and exploring if changes in sensorimotor function are associated with changes in self-report outcome assessments.

Discussion

This study may provide clues to the sensorimotor mechanisms that explain observed functional deficits associated with LBP, as well as the mechanism of action of SM.

Trial registration

This trial is registered in ClinicalTrials.gov, with the ID number of NCT00830596, registered on January 27, 2009. The first participant was allocated on 30 January 2009 and the final participant was allocated on 17 March 2011.

Computational model of the lumbar spine musculature: implications of spinal surgery

BACKGROUND

The development of a comprehensive and detailed model of the musculature of the lumbar region is required if biomechanical models are to accurately predict the forces and moments experienced by the lumbar spine.

METHODS

A new anatomical model representing the nine major muscles of the lumbar spine and the thoracolumbar fascia is presented. These nine muscles are modeled as numerous fascicles, each with its own force producing potential based on size and line of action. The simulated spine is fully deformable, allowing rotation in any direction, while respecting the physical constraints imposed by the skeletal structure. Maximal moments were predicted by implementing the model using a pseudo force distribution algorithm. Three types of surgery that affect the spinal musculature were simulated: posterior spinal surgery, anterior surgery, and total hip replacement.

FINDINGS

Predicted moments matched published data from maximum isometric exertions in male volunteers. The biomechanical changes for the three different types of surgery demonstrated several common features: decreased spinal compression and production of asymmetric moments during symmetric tasks.

INTERPRETATION

This type of analysis provides new opportunities to explore the effect of different patterns of muscle activity including muscle injury on the biomechanics of the spine.

The effect of fatigue on lower-limb biomechanics during single-limb landings: a systematic review

STUDY DESIGN

Systematic literature review.

OBJECTIVE

To evaluate the quality and outcomes of published research papers on the topic of fatigue-induced biomechanical changes in single-limb landings.

BACKGROUND

Lower extremity fatigue causes a number of biomechanical alterations that may increase the risk of knee injury. It has therefore been suggested that fatigue elements be incorporated into injury prevention programs. For this to be successful, protocols that reliably induce fatigue need to be identified and the effect fatigue has on the lower-limb joints needs to be documented.

METHODS

A systematic review was conducted to identify published studies that assessed the effect of fatigue on lower-limb biomechanics during single-limb landing tasks. Studies were identified by searching 6 databases, reference lists, and citation tracking. The methodological quality of each paper was assessed, and effect sizes were calculated to allow comparison of results across studies.

RESULTS

Eight studies met the inclusion criteria. Numerous methodological differences between the studies made synthesis of data challenging. There was some evidence to show that vertical ground reaction forces and hip and knee joint moments were reduced after fatigue. Kinematic changes were less consistent and require further study.

CONCLUSION

The current body of studies showed mixed findings, particularly in relation to landing kinematics after fatigue. Future studies should focus on developing standardized fatigue protocols that include both local and central fatigue effects and monitor progression of fatigue over time. This area of research should be extended to include individuals recovering from musculoskeletal injury or surgery.

Influence of back muscle fatigue on lumbar reflex adaptation during sudden external force perturbations

There is still conflicting evidence about the influence of fatigue on trunk reflex activity. The aim of this study was to measure response latency and amplitude changes of lumbar and abdominal muscles after heavy external force perturbation applied to the trunk in the sagittal plane before and after back muscle fatigue, in expected and unexpected conditions. Ten healthy subjects in a semi-seated position, torso upright in a specific apparatus performed an intermittent back muscle fatigue protocol. EMG reflex activity of erector spinae (ES) and external oblique muscles were recorded in unexpected and in expected (self pre-activation) conditions. After fatigue, the normalized reflex amplitude of ES increased in expected and unexpected conditions (P<0.05) while ES response latency was slightly decreased. Reflexes latencies for ES were systematically shorter (P<0.05) of 25% in expected compared to unexpected conditions. These findings suggest that a large external force perturbation would elicit higher paraspinal magnitude responses and possible earlier activation in order to compensate the loss of muscular force after fatigue. Because of the seated position the postural adjustments were probably not triggered and thus explain the lack of abdominal activation. The self-anticipated pre-activation in order to counteract perturbations was not affected by fatigue illustrating the natural muscular activation to maintain trunk stability.

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

STUDY DESIGN

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

OBJECTIVES

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

SUMMARY OF BACKGROUND DATA

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

METHODS

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

RESULTS

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

CONCLUSION

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

How many days of bed rest for acute low back pain? Objective assessment of trunk function

Bed rest is usually considered an efficient treatment for acute low back pain. However, the optimal duration of bed rest is still being discussed. The recommended periods vary from 2 days to 2 weeks. The duration of optimum length is an important topic given the economical and physiological drawbacks of prolonged inactivity. The purpose of this work is to measure objectively the efficacy of two different durations of bed rest through a dynamometric measure of trunk function. Some 51 male patients, students or self-employed, being treated for acute low back pain were randomized into two groups. Group I was prescribed a bed rest period of 3 days and group II, a period of 7 days. We used a multi-axis isoinertial trunk testing dynamometric device (Isostation B200, Isotechnologies, USA). Patients were all assessed on day 1 and also on day 5 for group I or on day 9 for group II. The variables measured in the sagittal plane were isometric torques in flexion and extension, unresisted range of motion, average dynamic torques and average velocities. Patients were also asked to fill in a visual analogue pain scale on both assessment days. The improvement of all performance measures were important and highly significant (P < 0.001) in both groups. The results of the functional testing and the visual analogue pain scale showed no significant differences between the groups. In these relatively young and motivated patients, a duration of bed rest of 3 days resulted in the same objective functional improvement of trunk function and pain rating as a period of 7 days. This shorter duration should be considered as preferable, given the same objective results but important physiological and economical advantages.

How does the central nervous system address the kinetic redundancy in the lumbar spine? Three-dimensional isometric exertions with 18 Hill-model-based muscle fascicles at the L4—L5 level

The human motor system is organized for execution of various motor tasks in a different and flexible manner. The kinetic redundancy in the human musculoskeletal system is a significant property by which the central nervous system achieves many complementary goals. An equilibrium-based biomechanical model of isometric three-dimensional exertions of trunk muscles has been developed. Following the definition and role of the uncontrolled manifold, the kinetic redundancy concept is explored in mathematical terms. The null space of the kinetically redundant system when a certain joint moment and/or stiffness are needed is derived and discussed. The aforementioned concepts have been illustrated, using a three-dimensional three-degrees-of-freedom biomechanical model of the spine with 18 anatomically oriented Hill-type-model muscle fascicles. The considerations of stability and its consequence on the internal loading of the spine and coactivation consequences are discussed in both general and specific cases. The results can shed light on the interaction mechanisms in muscle activation patterns seen in various tasks and exertions and can provide a significant understanding for future research studies and clinical practices related to low-back disorders. Alteration of recruitment patterns in low-back-pain patients has been explained on the basis of this biomechanical analysis. The higher coactivation results in higher internal loading while providing higher joint stiffness that enhances spinal stability, which guards against spinal deformation in the presence of any perturbations.

The association between isoinertial trunk muscle performance and low back pain in male adolescents

The literature reports inconsistent findings regarding the association between low back pain (LBP) and trunk muscle function, in both adults and children. The strength of the relationship appears to be influenced by how LBP is qualified and the means by which muscle function is measured. The aim of this study was to examine the association between isoinertial trunk muscle performance and consequential (non-trivial) low back pain (LBP) in male adolescents. Healthy male adolescents underwent anthropometric measurements, clinical evaluation, and tests of trunk range of motion (ROM), maximum isometric strength (STRENGTH) and peak movement velocity (VEL), using an isoinertial device. They provided information about their regular sporting activities, history and family history of LBP. Predictors of "relevant/consequential LBP" were examined using multivariable logistic regression. LBP status was reassessed after 2 years and the change from baseline was categorised. At baseline, 33/95 (35%) subjects reported having experienced consequential LBP. BMI, a family history of LBP, and regularly playing sport were each significantly associated with a history of consequential LBP (p < 0.05). 85/95 (89%) boys participated in the follow-up: 51 (60%) reported no LBP at either baseline or follow-up (never LBP); 5 (6%) no LBP at baseline, but LBP at follow-up (new LBP); 19 (22%) LBP at baseline, but none at follow-up; and 10 (12%) LBP at both time-points (recurrent/persistent LBP). The only distinguishing features of group membership in these small groups were: fewer sport-active in the "never LBP" group); worse trunk mobility, in the "persistent LBP" group, lower baseline sagittal ROM in the "never LBP" and "new LBP" (p < 0.05). Regular involvement in sport was a consistent predictor of LBP. Isoinertial trunk performance was not associated with LBP in adolescents.

Design and evaluation of a novel triaxial isometric trunk muscle strength measurement system

Maximal strength measurements of the trunk have been used to evaluate the maximum functional capacity of muscles and the potential mechanical overload or overuse of the lumbar spine tissues in order to estimate the risk of developing musculoskeletal injuries. A new triaxial isometric trunk strength measurement system was designed and developed in the present study, and its reliability and performance was investigated. The system consisted of three main revolute joints, equipped with torque sensors, which intersect at L5—S1 and adjustment facilities to fit the body anthropometry and to accommodate both symmetric and asymmetric postures in both seated and standing positions. The dynamics of the system was formulated to resolve validly the moment generated by trunk muscles in the three anatomic planes. The optimal gain and offset of the system were obtained using deadweights based on the least-squares linear regression analysis. The R2 results of calibration for all loading courses of all joints were higher than 0.99, which indicated an excellent linear correlation. The results of the validation analysis of the regression model suggested that the mean absolute error and the r.m.s. error were less than 2 per cent of the applied load. The maximum value of the minimum detectable change was found to be 1.63 N m for the sagittal plane torque measurement, 0.8 per cent of the full-scale load. The trial-to-trial variability analysis of the device using deadweights provided intra-class correlation coefficients of higher than 0.99, suggesting excellent reliability. The cross-talk analysis of the device indicated maximum cross-talks of 1.7 per cent and 3.4 per cent when the system was subjected to flexion—extension and lateral bending torques respectively. The trial-to-trial variability of the system during in-vivo strength measurement tests resulted in good to excellent reliability, with intra-class correlation coefficients ranging from 0.69 to 0.91. The results of the maximum voluntary isometric torques exertion measurements for 30 subjects indicated good agreement with the previously published data in the literature. The extensive capabilities and high reliability of the system are promising for more comprehensive investigations on the trunk biomechanics in future, e.g. isometric strength measurement at symmetric and asymmetric postures, muscle endurance, and recruitment pattern analysis.

Axial back pain in the athlete: pathophysiology and approach to rehabilitation

Back pain in athletes is common. Proper management of an athlete with back pain who is trying to return to competition must take into account the probable biomechanical contributors and incorporate these into a comprehensive rehabilitation program that moves steadily forward towards defined goals. This study will attempt to discuss pathological commonalities of low-back pain in athletes and how these can be applied to an evidence-based rehabilitation approach.

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

STUDY DESIGN

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

OBJECTIVE

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

SUMMARY OF BACKGROUND DATA

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

METHODS

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

RESULTS

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

CONCLUSION

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