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Effect of a Stiff Lifting Belt on Spine Compression During Lifting
Abstract
An in vivo study on weightlifters.
To determine if and how a stiff back belt affects spinal compression forces in weightlifting.
In weightlifting, a back belt has been reported to enhance intraabdominal pressure (IAP) and to reduce back muscle EMG and spinal compression forces.
Nine experienced weightlifters lifted barbells up to 75% body weight while inhaling and wearing a belt, inhaling and not wearing a belt, and exhaling and wearing a belt. IAP, trunk muscle EMG, ground reaction forces, and kinematics were measured. An EMG-assisted trunk model, including IAP effects, was used to calculate spinal compression and shear forces and to reveal the contribution of back muscles, abdominal muscles, and IAP to moment generation.
The belt reduced compression forces by about 10%, but only when inhaling before lifting. The moment generated by IAP increased when wearing a belt and inhaling, but this moment was small and the increase was largely negated by the flexing moment generated by abdominal muscles.
Wearing a tight and stiff back belt while inhaling before lifting reduces spine loading. This is caused by a moment generated by the belt rather than by the IAP.
... Twenty-one studies assessed EMG of muscles while using LSO [7,8,12,[25][26][27][28][29][30][31][32][33][34][35][36][38][39][40]47,48,51]. The most frequently evaluated muscles included erector spinae (ES), external oblique (EO), and rectus abdominis (RA). ...
... Seven studies reported reduced EMG activity among the trunk extensor muscles [7,12,28,33,34,36,51]. In the study by Granata et al. [26], whereas ES muscle activity was reduced by 4% when wearing an elastic belt, no change in EMG was observed in the ES or latissimus dorsi muscles when leather or fabric belts were worn. ...
... The effect of back support on IAP was investigated in seven studies [28,30,33,39,40,50,53]. Two studies reported no change in IAP [40,50], and five found increased IAP with the use of LSO [28,30,33,39,53]. ...
Background:
Wearing lumbosacral orthosis (LSO) is one of the most common treatments prescribed for conservative management of low back pain. Although the results of randomized controlled trials suggest effectiveness of LSO in reducing pain and disability in these patients, there is a concern that prolonged use of LSO may lead to trunk muscle weakness and atrophy.
Purpose:
The present review aimed to evaluate available evidence in literature to determine whether LSO results in trunk muscle weakness or atrophy.
Study design:
This is a systematic review.
Methods:
A systematic search of electronic databases including PubMed, Scopus, ScienceDirect, and Medline (via Ovid) followed by hand search of journals was performed. Prospective studies published in peer-reviewed journals, with full text available in English, investigating the effect of lumbar orthosis on trunk muscle activity, muscle thickness, strength or endurance, spinal force, and intra-abdominal pressure in healthy subjects or in patients with low back pain, were included. Methodological quality of selected studies was assessed by using the modified version of Downs and Black checklist. This research had no funding source, and the authors declare no conflicts of interest-associated biases.
Results:
Thirty-five studies fulfilled the eligibility criteria. The mean and standard deviation of the quality score was 64±9.7%. Most studies investigating the effect of lumbar orthosis on electromyographic activity (EMG) of trunk muscles demonstrated a decrease or no change in the EMG parameters. A few studies reported increased muscle activity. Lumbosacral orthosis was found to have no effect on muscle strength in some studies, whereas other studies demonstrated increased muscle strength. Only one study, which included ultrasound assessment of trunk muscle stabilizers, suggested reduced thickness of the abdominal muscles and reduced cross-sectional area of the multifidus muscles. Out of eight studies that investigated spinal compression load, the load was reduced in four studies and unchanged in three studies. One study showed that only elastic belts reduced compression force compared to leather and fabric belts and ascribed this reduction to the elastic property of the lumbar support.
Conclusion:
The present review showed that the changes in outcome measures associated with muscle work demands were inconsistent in their relation to the use of lumbar supports. This review did not find conclusive scientific evidence to suggest that orthosis results in trunk muscle weakness.
... Moreover, it is observed that wearing a lifting belt gives a false sense of stability leading people to lift weights that are not appropriate for their level of strength and ignore other factors that are known to prevent back injuries. [26,30] Controlling inhalation and exhalation during RT is a technique that also can be used to decrease the intra-abdominal pressure, which could decrease the amount of force sustained by the lumbar spine during weight lifting. [30] Physiotherapists should emphasize this and introduce it to their rehabilitation and prevention programs. ...
... [26,30] Controlling inhalation and exhalation during RT is a technique that also can be used to decrease the intra-abdominal pressure, which could decrease the amount of force sustained by the lumbar spine during weight lifting. [30] Physiotherapists should emphasize this and introduce it to their rehabilitation and prevention programs. ...
... Given that previous research has indicated various anatomical differences may exist between the sexes and across some racial groups, the results of this study may have been different if the sample size was larger, more diverse, and inclusive of female participants (2,6,9). In fact, previous research has found differences in peak and average velocities between males and females performing the CDL (17). ...
The purpose of this preliminary analysis was to determine if there are relationships between anthropometric characteristics (arm length, torso length, thigh length, and shank length) and conventional deadlift (CDL) kinematics and kinetics during a 5 sets of 5 repetitions (5 × 5) CDL routine in resistance-trained males. Eleven males who had experience with the deadlift exercise were included in this analysis (age: 21.5 ± 1.4 y; height: 180.7 ± 5.7 cm; body mass: 89.9 ± 16.0 kg). Anthropometrics were measured by a 3-dimensional optical scanner. The participants underwent a 5 × 5 CDL workout using a self-selected load corresponding to a rating of perceived exertion (RPE) of 8 out of 10. Performance outcomes were measured synchronously using a 3-dimensional 12-camera motion capture system and two force platforms. Outcomes were averaged across all sets and analyzed using multiple linear regression. The selected anthropometric variables were not significantly related to the CDL performance outcomes, except for concentric ankle work. However, in the overall model, anthropometric predictors did not significantly predict ankle concentric work (p = 0.11; R 2 = 0.67; R_2adj = 0.45). Independently, thigh length significantly correlated with ankle concentric work (p = 0.03). In this model, thigh length accounted for 55% of the normalized variance in ankle concentric work. The results from this preliminary study suggest that arm length, torso length, and shank length may not play a clear role in the examined CDL outcomes, but thigh length may be positively correlated with ankle concentric work during a 5 × 5 CDL routine in resistance-trained males.
... En adición, Anders menciona que el uso de cinturón en sujetos sanos disminuye la actividad de los músculos estabilizadores del tronco a corto plazo, pero, al no poseer datos de la planificación de entrenamiento de los levantadores se vuelve difícil definir si el uso es inadecuado (4). Por consiguiente, gran parte de los deportistas evaluados, al querer aumentar la carga y reducir las fuerzas de compresión tiene un alto uso mensual del cinturón lo que compromete la musculatura disminuyendo su función, lo cual concuerda Kingma, en donde relata que acompañar el uso de cinturón con una buena respiración disminuye las cargas de compresión sobre la columna (14). ...
Objetivos: Determinar la capacidad estabilizadora del Transverso abdominal a través del Test de estabilidad central de Sahrmann en deportistas de halterofilia de la Federación Deportiva del Azuay. Métodos: Estudio descriptivo, transversal, realizado en deportistas de la FDA. Para la recolección de datos se utilizó un formulario de registro y para la evaluación el Test de Estabilidad Central de Sahrmann junto con el dispositivo Chattanooga Stabilizer Pressure Biofeedback. La tabulación y análisis de los datos requirió de los programas GNU PSPP v1.6.2 y Microsoft Excel 2016. La información se almacenó en una base de datos y los resultados fueron expresados en tablas. Resultados: Más de la mitad de la población estudiada (66.6%) presenta una menor capacidad estabilizadora alcanzando los niveles 1 y 2 en su mayoría mediante la ejecución del test de estabilidad central de Sahrmann. Conclusiones: Nuestros resultados permitieron identificar que la capacidad de activación del TrA es insuficiente, con una estabilidad reducida en un 66,7% de los atletas de la Federación Deportiva del Azuay, al no alcanzar un nivel superior a 2 en el test de estabilidad de Sahrmann, lo que sugiere un alto riesgo de lesión.
... As the experimental task, the participants were asked to lift an object five times with a 1-min interval after each lifting (Trials 1-5). The object consisted of a 520×365×305-mm box placed on the ground and weighing 37.5% of participant's body weight, as it an earlier study [32]. That study indicated that the positional relationship between the subject's feet and the box affected the low back load during lifting [33]. ...
Purpose
To identify impaired trunk movement during work-related activity in individuals with low back pain (LBP) and investigate whether abnormalities were caused by generalized fear of movement-related pain.
Methods
This cross-sectional study was conducted at a hospital in Japan. We recruited 35 participants with LBP (LBP group; 26 males, 9 females) and 20 healthy controls (HC group) via posters at our hospital. The task required lifting an object. We used a 3D motion capture system to calculate the peak angular velocity of trunk flexion and extension during a lifting task. Pain-related factors for the LBP group were assessed using the visual analogue scale (VAS) for pain intensity over the past 4 weeks and during the task, the Tampa Scale for Kinesiophobia (TSK), the Pain Catastrophizing Scale (PCS), and the Pain Anxiety Symptoms Scale-20 (PASS-20). We compared kinematic variables between groups with a generalized linear mixed model and investigated the relationship between kinematic variables, VAS scores, and psychological factors by performing a mediation analysis.
Results
The peak angular velocity of trunk extension showed significant main effects on the group factors (LBP group vs. HC group) and their interactions; the value of the kinematic variable was lower at Trial 1 in the LBP group. No LBP participant reported pain during the experiment. The mediation analysis revealed that the relationship between the VAS score for pain intensity over the past 4 weeks and the peak angular velocity of trunk extension in the first trial was completely mediated by the TSK (complete mediation model, 95% bootstrapped CI: 0.07–0.56).
Conclusion
Individuals with LBP had reduced trunk extension during a lifting task. Generalized fear of movement-related pain may contribute to such impaired trunk movement. Our findings suggest that intervention to ameliorate fear of movement may be needed to improve LBP-associated disability.
... These findings are against some previous studies which suggested that back belts may reduce trunk muscle activities via an intra-abdominal pressure mechanism [5], intra-abdominal pressure could indirectly generate an extensor moment on the lumbar spine which consequently reduces or delays muscle fatigue. Some studies found no differences between lifting with a back belt and without a back belt [6,[27][28][29]. This might because the study protocol used in the present study was different from previous studies such as task stimulation; lifting excursion and lifting technique, in the present study, were mainly designed to focus on trunk movement. ...
To study the effects of back belt application on trunk muscle fatigue during repetitive lifting. Eighteen healthy subjects (12 females and 6 males), Age 27.78 ±3.54 years, Body Mass Index (BMI) 20.48 ±1.53 kg./m.2, had no experiences wearing a back belt. The lifting task was to lift and lower a wooden box on an adjustable shelf. Lifting weight was equal to 10 % of the subjects’ body weight and the test lasted for 12 min. Electromyography of four trunk muscles on the left side, multifidus (MF), erector spinae (ES), transversus abdominis/internal abdominal oblique (TrA/IO) and external abdominal oblique (EO), were recorded at the beginning and every 3-minute of each test. At min 3, the percent median frequency of MF in with back belt condition was significantly decreased with a larger reduction than without a back belt (p<0.05). At min 9 and 12, percent median frequency of EO in with back belt condition was significantly decreased with a larger reduction than without a back belt (p<0.05). For the main effect of time on percent median frequency reduction was significant in MF (p<0.001), ES (p<.001) and EO (p<0.001). The interaction between back belt and time on percent median frequency reduction was found significant only in MF. (p<0.001). Back belt application condition showed a larger reduction of percent median frequency over time than without back belt condition especially in MF and EO. In conclusion, a back belt application during lifting increases muscle fatigue in some trunk muscles, the uses of the back belt based upon ergonomic criteria should call into question the recommended prescription of the devices under the presumption of hazard control.
... Increased abdominal pressure helps to extend the trunk, which in turn reduces the activation of the back muscles and lumbar compression (Stokes et al., 2010). However, if the increased intra-abdominal pressure is achieved by cocontraction of the abdominal and back muscles, this negates the decrease in lumbar compression (Arjmand and Shirazi-Adl, 2006;Kingma et al., 2006). Increasing abdominal pressure without co-contracting the trunk muscles, or with reduced co-contraction, would allow for an increase in lumbar stability without increasing lumbar compression. ...
Background:
Lumbar belts have been shown to increase lumbar stiffness, but it is unclear if this is associated with trunk muscle co-contraction, which would increase the compression on the spine. It has been hypothesized that lumbar belts increase lumbar stiffness by increasing intra-abdominal pressure, which would increase spinal stability without increasing the compressive load on the spine.
Methods:
Trunk muscle activity and lumbar stiffness and damping were measured in healthy and low-back pain subjects during three conditions: no lumbar belt; wearing an extensible lumbar belt; wearing a non-extensible lumbar belt. Muscle activity was measured while subjects performed controlled forward and backward 20° trunk sways. Lumbar stiffness and damping were measured by applying random continuous perturbation to the chest.
Findings:
External oblique activity was decreased when wearing either lumbar belt during all phases of movement, while rectus abdominis and iliocostalis activity were decreased during the phase of movement where the muscles were maximally active while wearing either belt. Trunk stiffness was greatly increased by wearing either belt. There were no consistent differences in either lumbar stiffness or muscle activity between the two belts. Wearing a lumbar belt had little to no effect on damping. There were no group differences in any of the measures between healthy and low-back pain populations.
Interpretation:
The findings are consistent with the hypothesis that lumbar belts can increase spinal stability by increasing intra-abdominal pressure, without any increase in the compressive load on the spine. The findings can also be generalized, for the first time, to subjects with low-back pain.
... The use of a powerlifting belt up to 13 mm in diameter and 40 mm in width is permitted in classic powerlifting. In combination with the Valsalva manoeuvre, the use of a lifting belt has been purported to increase intra-abdominal pressure, reduce spinal loading, reduce the extension moment created by the back extensors and generate an extension moment within the belt itself (Kingma et al., 2006). ...
... Most powerlifters use a stiff weightlifting belt in order to perform a breathing technique called the valsava maneuver which allows them to increase intra-abdominal pressure by pushing against the belt with their abdominal muscles. Using a stiff belt for squats and deadlifts has been shown to increase strength as well as increasing activation in different muscle groups (lumbar erectors, quadriceps etc) (16). It is important to note that powerlifters perform the squat with two different techniques, "high bar" and "low bar". ...
Low back strength has been shown to significantly impact performance in a plethora of sports. Aside from its effect on sport performance, low back strength is strongly associated with low back pain. A sport that heavily involves the lower back musculature is powerlifting. The present study looked to compare isolated lumbar extension (ILEX) strength in competitive and non-competitive powerlifters and recreationally trained males. Thirteen competitive powerlifters (CPL group; 31.9 ± 7.6 years; 173.4 ± 5.5 cm; 91.75 ± 18.7 kg), 10 non-competitive powerlifters (NCPL group; 24 ± 3.5 years; 179 ± 4.8 cm; 92.39 ± 15.73 kg, and 36 recreationally trained males (RECT group; 24.9 ± 6.5 years; 178.5 ± 5.2 cm; 81.6 ± 10.0kg) were tested for isolated lumbar extension strength (ILEX). ILEX strength was measured at every 12° throughout participant’s full range of motion and expressed as the following: ’strength index’ calculated as the area under a torque curve from multiple angle testing (SI), average torque produced across each joint angle (AVG) and maximum torque produced at a single angle (MAX). Deadlift and squat strength was measured using 1 repetition maximum (1RM) for the competitive and non-competitive powerlifters. The following powerlifting characteristics were recorded for the competitive and non-competitive powerlifters: primary deadlift stance, primary squat bar position, use of belt, use of performance enhancing drugs (PEDs) and use of exercises to target the lower back musculature. Significant between group effects were found for participant characteristics (age, stature, body mass, and range of motion). However, analysis of covariance with participant characteristics as covariates found no significant between group effects for SI (p=0.824), AVG (p=0.757), or MAX (p=0.572). In conclusion this study suggests that powerlifting training likely has little impact upon conditioning of the lumbar extensors.
... При миографическом исследовании чаще всего при решении данной задачи оцениваются параметры активности мышцы, выпрямляющей позвоночник, прямой мышцы живота и наружной косой мышцы живота. В основном оценивалась амплитуды паттерна произвольной активности [37][38][39][40][41]. В некоторых исследованиях сообщается о развитии мышечной слабости при использовании ортезов -на 4 % в мышце, выпрямляющей позвоночник [38], и уменьшении её активности справа при симметричной нагрузке [42]. ...
Our literature review analyzes the available studies on the effect of long- and short-term lumbo-sacral orthotic (LSO) treatment on the muscles of the back. We reviewed the existing diagnostic approaches to evaluation of muscle changes, including surface EMG, measurements of muscle strength and tolerance, and findings on muscle ultrasound study. It has been revealed that none of the available works confirmed a significant negative effect of LSO, both by short- and long-term application, or atrophic changes in the muscles. Thus, we may conclude that there are no significant data on the effect of the LSO treatment on the main parameters that are measured and reflect spinal muscles weakness and/or atrophy.
... Or, comme mentionné cidessus, une hausse significative de la PIA ne se fait pas sans la cocontraction des muscles abdominaux et dorsaux , pouvant mener à un effet net nul. En effet, l'augmentation de la compression lombaire par l'action des muscles abdominaux et dorsaux peut contrecarrer la diminution de la compression produite par la PIA (Arjmand et Shirazi-Adl, 2006;Kingma et al., 2006). La deuxième hypothèse résulte des modèles biomécaniques plus récents, qui prennent en compte non seulement l'équilibre du système, mais aussi sa stabilité (modèle biomécanique de stabilité lombaire). ...
Bien que les ceintures lombaires (CL) soient inefficaces pour prévenir un premier épisode de lombalgie, l’avancement des connaissances soutient leur utilisation chez les travailleurs souffrant déjà de ce mal. Dans la perspective où un retour au travail tardif risque de nuire à la condition de santé des travailleurs, l’option du port de la CL peut potentiellement être avantageuse, car elle pourrait permettre, lors du retour progressif au travail, d’apporter un soutien psychologique afin de rassurer le patient. Cela pourrait donc représenter un outil additionnel, parmi les moyens entrepris pour intervenir sur les facteurs psychosociaux reliés à l’individu et son environnement de travail, pour faciliter ce retour au travail et également pour aider le travailleur à se maintenir au travail. Cependant, il importe aussi que la CL apporte un support biomécanique en matière de stabilité mécanique de la colonne vertébrale lombaire afin de rehausser la sécurité du travailleur. Deux catégories de ceintures souples permettent un niveau suffisant de confort pour être utilisées en milieu de travail, soit les ceintures (1) extensibles (élastiques) ou CL-E; (2) non extensibles ou CL-NE. La présente étude a pour but de comparer ces deux catégories de CL en ce qui a trait aux soutiens psychologique et biomécanique qu’elles prodiguent, cela autant chez des sujets en santé que chez des sujets avec maux de dos (lombalgies). À titre exploratoire, il devenait aussi pertinent de vérifier si différents sous-groupes de sujets lombalgiques, déterminés en fonction d’hypothèses biomécanique (instabilité lombaire) ou psychologique (peurs du mouvement ou de la douleur), présenteraient des effets biomécaniques différents. Dans la perspective de l’évaluation de l’effet du port d’une CL dans un éventuel essai clinique, il était nécessaire d’évaluer, aussi à titre exploratoire, certaines variables associées à l’adoption à ce type d’intervention.
Deux groupes de sujets, répartis également selon le sexe, ont été comparés, soient 20 sujets sains et 40 sujets lombalgiques; ces derniers démontrant de grandes variations au regard des signes d’instabilité lombaire (dimension biomécanique) et de peur du mouvement (dimension psychologique). Deux séances en laboratoire ont permis d’évaluer différents paramètres psychologiques et biomécaniques lors de trois conditions expérimentales (sans CL, CL-E, CL-NE). Séance 1 : (1) douleur (sujets lombalgiques); (2) proprioception lombaire à l’aide d’une chaise motorisée permettant des mouvements (10º) en rotation axiale (torsion) de la région lombaire; (3) contrôle postural du tronc sur une chaise instable; (4) rigidité de la colonne lombaire à l’aide d’un appareil permettant de générer de légères secousses (avant et arrière) du tronc. Séance 2: (avec mesures d’activation musculaire et de mouvements): (5) ajustements posturaux anticipatoires (préactivation des muscles du tronc précédant une perturbation anticipée) à une flexion rapide du bras droit; (6) coordination musculaire et étendue de mouvement lombaires lors de trois tâches standardisées. Ces trois tâches étaient des levées/dépôts de caisses, des flexions maximales du tronc vers l’avant et retour en position verticale et de légères (± 20º) flexions et extensions du tronc près de la position neutre (verticale). Lors des deux séances, des questions portant sur les peurs liées à la douleur ont été posées aux sujets lombalgiques après exécution de certaines de ces tâches, soit celles qui étaient les plus menaçantes pour la colonne lombaire. De façon exploratoire, les sujets lombalgiques ont aussi été interrogés, à la fin de la séance 2, sur des éléments présumés associés à l’adoption du port d’une CL, soit leurs attitudes favorables au port d’une CL, leur sentiment d’efficacité fonctionnelle et la stigmatisation anticipée de la part de leur entourage. Les résultats recueillis en laboratoire ont été analysés de manière à non seulement comparer les trois conditions expérimentales (sans CL, CL-E, CL-NE), mais aussi pour comparer les groupes (sujets sains et lombalgiques), et plus encore pour comparer des sous-groupes de sujets lombalgiques constitués en fonction de mesures qui sont présumées associées à l’instabilité lombaire ou à la peur du mouvement/douleur, cela en fonction des hypothèses biomécaniques et psychologiques qui soutiennent le port d’une CL.
Plusieurs effets immédiats des CL ont été étudiés, mais ils étaient équivalents entre les deux CL souples (CL-E et CL-NE). En effet, ni les mesures associées à la douleur, ni les mesures biomécaniques, ni les mesures potentiellement associées à l’adoption d’une ceinture, ni même la préférence pour l’une ou l’autre des CL n’a permis de déterminer quelle CL pouvait générer des effets positifs. Les deux CL semblent donc offrir les mêmes avantages, du moins en ce qui a trait aux effets immédiats. Sur le plan mécanique, ces résultats suggèrent aussi que la CL-NE ne produirait pas plus de pression intra-abdominale que la CL-E, par son manque d’extensibilité lors de perturbations ou changements de posture du tronc.
Les deux CL ont engendré une diminution de la douleur en position debout et une diminution de la peur et de la dramatisation de la douleur lors de différentes tâches jugées menaçantes pour la région lombaire, notamment celles qui imposent un chargement plus important sur les structures. En ce qui a trait aux variables biomécaniques, plusieurs effets semblables ont été observés et démontrés entre les sujets sains et les sujets lombalgiques. Tout d’abord, les effets sur les variables liées aux mécanismes du contrôle moteur étaient mixtes, c’est-à-dire sans effet sur la proprioception lombaire et avec des effets de faible amplitude qui étaient tantôt favorables, tantôt défavorables, en ce qui a trait aux ajustements posturaux anticipatoires et à l’équilibre postural. Ensuite, les variables biomécaniques associées aux effets mécaniques ont produit des conséquences plus claires et positives au regard de la hausse de la rigidité lombaire, de la diminution de la flexion lombaire maximale et de la réduction de l’activation des muscles du tronc. Finalement, les effets sur le plan fonctionnel, c’est-à-dire lors d’une tâche de levées/dépôts de caisses, ont aussi été positifs en étant associés à une réduction de la flexion lombaire sans, en contrepartie, affecter négativement le mouvement des segments adjacents tel que la flexion thoracique, du bassin ou des genoux.
Dans l’ensemble, l’exploration de la présence possible de sous-groupes cliniques, formés sur la base d’hypothèses biomécanique (stabilité lombaire) et psychologique (peur de la douleur/mouvement), n’a pas été concluante, mais demeure une idée à considérer dans un éventuel essai clinique permettant d’étudier les effets à long terme. Par contre, l’étude exploratoire des variables qui sont présumées associées à l’adoption du port d’une CL, soient les attitudes favorables au port d’une CL, le sentiment d’efficacité fonctionnelle et la stigmatisation anticipée mesurés chez les sujets lombalgiques a produit des résultats encourageants, peu importe l‘âge et le sexe des participants. Ces résultats laissent même croire en une association entre les attitudes favorables au port d’une CL et la diminution des peurs et de la dramatisation de la douleur lors des tâches jugées menaçantes pour le dos.
En somme, les variables psychologiques associées à la douleur et celles qui sont présumées associées à l’adoption du port d’une CL soutiennent l’hypothèse que ce port aurait pour effet de rassurer les patients souffrant d’une lombalgie, ce qui en retour pourrait favoriser le maintien au travail en périodes de récidives ou accélérer le retour au travail des travailleurs en période d’absence. Les variables biomécaniques, de leur côté, indiquent que les effets mécaniques ont le potentiel de rendre cette pratique sécuritaire. Un essai clinique randomisé visant la prévention secondaire (prévention de l’arrêt de travail) et tertiaire (prévention de l’arrêt prolongé) serait nécessaire pour vérifier ces hypothèses auprès d’une population de travailleurs dans la phase subaiguë de leur lombalgie ou souffrant d’une lombalgie récurrente.
... 7-15° Außenrotation[Escamilla et al., 2000[Escamilla et al., , 2002). DieCholewicki & McGill, 1992Cholewicki, Juluru & McGill, 1999, Cholewicki et al., 1999, Kingma et al. 2006, McGill, Norman & Sharratt, 1990 ...
... In powerlifting and Olympic weightlifting, it is common for athletes to employ a variety of external material aids such as weightlifting/squat shoes/boots (International Weightlifting Federation, 2015;Sato, Fortenbaugh, & Hydock, 2012;Sato, Fortenbaugh, Hydock, & Heise, 2013), thick belts (Aurslanian, 1993;Bourne & Reilly, 1991;Faigenbaum & Liatsos, 1994;Harman, Rosenstein, Frykman, & Nigro, 1989;Kingma et al., 1976;Lander, Hundley, & Simonton, 1992;Lander, Simonton, & Giacobbe, 1990;McGill, Norman, & Sharratt, 1990;Miyamoto, Iinuma, Maeda, Wada, & Shimizu, 1999;Renfro & Ebben, 2006;Zink, Whiting, Vincent, & McLaine, 2001), and elastic knee wraps (Harman & Frykman, 1990;Totten, 1990) that may influence muscular activity throughout a BBS. When performing a BBS in standard running shoes, Sinclair, McCarthy, Bentley, Hurst, and Atkins (2014) reported a significantly greater activation in the rectus femoris compared to a barefoot condition, and no significant difference in activity was reported when weightlifting shoes were worn. ...
The barbell back-squat is one of the most common exercises in strength and conditioning practice; especially in Olympic weightlifting and powerlifting. There are two main bar placements within the back-squat; the high-bar and low-bar positions. The high-bar position, favoured by Olympic weightlifters, closely resembles the upright body position of the two competition lifts of the sport; the snatch and clean and jerk. The low-bar position, favoured by powerlifters, typically allows greater loads to be lifted by utilising the posterior-chain musculature during the back-squat (one of the three competition lifts in the sport). Unfortunately, little research exists comparing the high-bar back-squat with the low-bar back-squat, and no research has examined either lift above 90% of one repetition maximum. Furthermore, no authors have biomechanically compared the high-bar back-squat to the Olympic lifts (e.g. snatch and clean and jerk). The aims of this thesis were to (1) review the current literature and quantitatively assess the kinetic and kinematic findings among the limited research; (2) compare and contrast the high-bar back-squat and low-bar back-squat up to maximal effort; and (3) assess the differences and/or similarities between the high-bar back-squat and the Olympic lifts. Through an extensive literature review, the high-bar back-squat was found to commonly present a larger hip angle, smaller knee angle and equivalent ankle angle compared to the low-bar back-squat; inferring the high-bar placement creates a more upright truck position for the lifter and requires more quadriceps muscle activation. Experimentally, these findings were confirmed with the high-bar back-squat producing larger hip angles and smaller knee angles compared to the powerlifters (16–21% larger and 10–12% smaller, respectively) and low-bar controls (16–21% larger and 10–12% smaller, respectively). While the Olympic weightlifters and powerlifters lifted similar relative loads, the low-bar controls were able to lift 2.5–5.2% larger relative loads compared to the high-bar controls. As expected, the high-bar back-squat also showed similar kinematics to the snatch and the clean but substantially different kinetics across all loads lifted. Performing a back-squat with a low-bar placement, situates the lifter (advanced and recreational) in a stronger position to lift larger loads compared to the high-bar placement. The establishment of a more advantageous kinematic posture during the low-bar back-squat could potentially maximise the utilisation of the stronger posterior hip musculature thus increasing the stability and moment arm at the hip. The low-bar back-squat therefore appears to provide the best chance of lifting the largest relative load. The kinematic similarities in posture between the high-bar back-squat and the Olympic lifts suggests the potential of similar trunk, hip and thigh muscular activity of key stabilising muscles and repetitive positional alignment in the “catch” position. The differing kinetics however, are more likely due to technical differences between the high-bar back-squat, snatch and clean; wherein the Olympic lifts require additional elements of upper-body strength and stability. The high-bar back-squat does appear to yield an efficient carryover to the Olympic lifts as a suitable supplementary exercise; provided the technical components of the lifts are maintained.
... However, there is a study of the effect of weightlifting's belt on lumbar spine to decrease risk of developing low back pain, which is showed 10% reducing of load on lumbar spine. [32] Elbow injuries Injuries of the elbow are most likely overuse injury at medial, and lateral epicondyle and a suitable term for these conditions are epicondylosis. [33] The proportion of elbows injury in weightlifting is (11%). ...
Weightlifting is considered as a dynamic strengthen exercise and power sport in which the athletes lifts a maximum weight with one repetition. The weightlifting as other sports has common musculoskeletal injuries in different body location corresponding to the sports beneficial. However, identifying the injuries incidence and the etiology is a first two-step in the model of the injury prevention in order to introduce preventive measures for sports. Therefore, this literature review is aimed to focus on the incidence and the etiology related to injuries of the weightlifting. However, the incidence injuries studies revealed that the children have more injuries related to accident than the adults. Whereas, the adults have more injuries related to strain and sprain. The most common injured locations are shoulder, lumbar spine, knee, elbow, hand, and wrist in the weightlifters. The percentage of the injuries according to location is the shoulder (36%), lumbar spine (24%), elbow (11%), and the knee (9%). In the other hand, the rule and regulation in the weightlifting had been changed since 1972 in which the clean and press lift eliminated from the competition due to the risk of this lift. Finally, weightlifting considered as safe sport if it is compared with other sports.
... The waist belts of weight lifters contribute to the success of the athlete in the face of competition by reducing the load on the spine by 20 % under increased intra-abdominal pressure by means of inhalation (Kingma et al. 2006). ...
As a result of competition among athletes, a number of auxiliary tools and treatments have been used
to increase the physical power, agility, durability, and performance of the athletes on the field. Some
substances and treatments containing factors that disrupt the balance in the competition are called
doping and are banned by the rules of the World Anti-Doping Agency (WADA). Beyond these,
healing accelerator biological applications are utilized in the treatment of disabilities in orthopedic
practice. Several locally effective hormones, genetic treatments, scaffolds, and cellular tissue
engineering products will be the center of interest in the near future. In this paper, we summarize
the current literature regarding applications that increase athletic performance and allow injured
athletes to return to active sports.
... As noted above, ample research has been conducted on back belts, suggesting their use is warranted as a performance booster in competitive sports (Kingma et al., 2006;Miyamoto et al., 1999;Clark et al., 2012). However, the findings are mixed, as it relates to their use as a functional brace aimed at reducing injuries, with results varying in respect to variables such as age group, resisted activities included in the design/research question, work or exercise setting, and other factors (Giorcelli et al., 2001;Minor, 1996;Hodgson, 1996). ...
Shot put throwing distances of 18 male Division I track and field athletes in the United States were compared among three wrist wrap conditions: 1) a large heavy wrist wrap, typically worn by athletes competing in the shot put event, 2) a small light wrist wrap and 3) no wrist wrap. The average and maximum throwing distances when the athletes were wearing the heavy wrist wrap (12.31 ± 1.699maximum; 11.92 ± 1.627average) were greater than when the athletes were not wearing a wrist wrap (12.05 ± 1.550maximum; 11.70 ± 1.457average). Performance increases exceeded criteria for the smallest worthwhile improvements in the shot put event, suggesting that heavy wrist wraps provide a competitive advantage. These results revealed previously undocumented, beneficial effects of taping and bracing on sports performance in the shot put throw.
... The results of this study further illustrate the potential benefits associated with use of the PLAD as a means of reducing low back loads incurred during static flexed postures and lifting tasks. They are consistent with the theoretical proof developed by and other research that has documented the potential benefits associated with lifting belts Kingma et al., 2006) and lumbosacral orthoses . However, the results are suspect to several limitations that should be acknowledged. ...
... 6 In particular, the positive and negative effects of physical activity are mainly centered on the lumbar region of the spine. 7 Previous studies have demonstrated that among athletes, weightlifters have a higher lifetime risk of specifi c spinal pathologies, obviously correlated with loading. Indeed, radiological changes are more common in weightlifters (84%) than in other athletes such as runners, jumpers, and throwers (72%). ...
Study design:
Case-control study.
Objective:
To evaluate early intervertebral disc degeneration quantified by T1ρ- and T2-weighted magnetic resonance imaging (MRI) in asymptomatic weightlifters compared with a healthy control group matched for sex and age.
Summary of background data:
Athletes consistently recruit or transfer high levels of repetitive forces through the spine, and MRI has documented a higher rate of intervertebral disc degeneration in athletes compared with matched controls. This study aims to analyze the potential role of T1ρ-MRI in the assessment of early degenerative changes occurring in intervertebral discs of young asymptomatic weightlifters compared with healthy controls.
Methods:
Twenty-six asymptomatic young male weightlifters versus a sedentary control group matched for age and sex, both having no lower back pain nor any spinal symptoms, underwent MRI (1.5 T). Degenerative grade was assessed using T2-weighted images, according to the Pfirrmann scale. T1ρ mapping and values in the nucleus pulposus (n=130) were obtained. Differences in T1ρ value between among the groups and linear regression analyses with degenerative grade were determined.
Results:
Pfirrmann degenerative grade did not show significant differences among groups. Instead, T1ρ values were significantly lower in the lumbar spine of weightlifters compared with controls (P<0.05). T1ρ values decreased linearly with degenerative grade.
Conclusion:
T1ρ values were significantly lower in athletes compared with a sedentary matched control group showing differences in intervertebral disc degeneration onset among individuals with lifestyle and environmental factors leading to back pain. T1ρ can be potentially used as a valid clinical tool to identify early changes in intervertebral disc on the verge of new emerging intervertebral discs regenerative strategies and treatments.
Level of evidence:
4.
... La scoperta dell'incremento elettromiografico della parete addominale associato con l'uso della cintura viene supportata anche da altri studi (Granata et al 1997, Lander et al 1992, Lantz e Schultz 1986, Marley e Duggasani 1996). In effetti sembra comunque fondamentale la respirazione per garantire la massima resa della cintura e quindi inspirare prima dello sforzo (Kingma et al 2006) garantendo una riduzione del 10% del carico sulla zona lombare. Questa riduzione non sembra essere causata dalla IAP ma dal momento generato dalla cintura (quando vi sia contestuale inspirazione) ...
Abstract: La protezione del rachide durante l’esecuzione di esercizi con sovraccarichi nella pratica del Fitness, al di là di ovvie e banali raccomandazioni, sull’entità del carico e sul mantenimento delle curve fisiologiche, spesso non viene adeguatamente sottolineata. Ancor meno vengono evidenziate le implicazioni della respirazione e del meccanismo della cosìdetta IAP (Intra Abdominal Pressure) sulla protezione del rachide sotto carico e durante esercizio. In questa review vengono analizzati gli studi, compresi quelli basilari e pioneristici di Nachemson, sui meccanismi fisiologici di protezione del rachide da sollecitazioni compressive durante l’esecuzione di esercizi; viene inoltre analizzata l’azione della cintura da sollevamento, “device” spesso usato in maniera non adeguata quando non abusato nei centri Fitness.
... The weightlifters are a very specific type of athlete and most literature concerns spine and muscle problems in this population [6][7][8]. It is well known that repeated heavy workouts increase the volume of many soft tissue structures such as muscles, tendons and extra-articular ligaments. ...
In a group of high performance weightlifters increased values of the cruciate ligaments (CLs) cross-sectional areas were observed. The purpose of this research was to investigate if repeated heavy workouts increase the volume of those structures.
The knee examinations were performed with an 1,5T MRI system. The area of the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL) midsubstance cross-section were evaluated in T1-weighted images with administration of contrast medium in a group of nine athletes. A control group of 19 participants was also examined using the same protocol.
Significant differences of the ACL and the PCL midsubstance cross-sectional areas were observed between groups. The area of the CLs' midsubstance and the onset of training were strongly negatively correlated and the PCL cross-sectional area was strongly positively correlated with the duration of training.
This research is the first description of the CLs hypertrophy, which is probably caused by heavy training that was started about the age of puberty. The age of training onset seems to have a greater impact on the hypertrophy process than the training duration. Knowledge of the phenomenon of cruciate ligament overgrowth is vital for orthopaedics because, possible changes of the CLs mechanical properties and three-dimensional orientation, may affect the incidence of trauma and reconstruction procedures technique.
... In majority of pervious works, the focus was on studying and modeling of movement in order to recognize and calculate kinematic parameters of weightlifter but there was less consideration given to power enhancement of weightlifter. It seems that the work on power enhancement can be divided in two branches: the first one focused on optimizing the effect of body parameters and sport facilities like weightlifters belt [10][11][12][13][14] and the second focused on the technique modification of weightlifter through mathematical modeling and various optimization methods [8,9,[15][16][17][18][19] . ...
In this research, an athlete's body on sagittal plane in tension phase of snatch weightlifting has been modeled in two dimensions for calculating the generated torques in joints. The error back propagation multi-layer perceptrons has been used for modeling the torque through changing the angular velocity, angular acceleration and absolute angle of each segment. Finally, the torque in joints has been minimized by particle swarm optimization technique and the power of athlete has been maximized. The method of weightlifting has been captured by high speed camera and the films have been analyzed through motion analysis software. Consequently, the required kinematic data for mathematical model of weightlifter has been produced. Unlike previous research reports, the technique of weightlifting has been modified with the aid of artificial neural network modeling to enhance athlete's power, instead of optimizing the effect of body parameters and sport facilities. In addition, this study focuses on computational intelligent techniques for optimization instead of classical methods.
» Chronic lower back pain (LBP) is common in both nonathletes and weight lifters, but the diagnosis and treatment should be approached differently in these 2 populations based on the unique movement patterns causing the pain.
» Injury rates of weight lifters are far less than those of contact sports, ranging from 1.0 to 4.4 injuries per 1,000 workout hours. However, the lower back was consistently one of the top 2 injury sites for weight lifters, accounting for anywhere from 23% to 59% of all injuries. LBP was most often associated with the squat or deadlift.
» Guidelines for evaluating general LBP are applicable to weight lifters, including a thorough history and physical examination. However, the differential diagnosis will change based on the patient's lifting history. Of the many etiologies of back pain, weight lifters are most likely to be diagnosed with muscle strain or ligamentous sprain, degenerative disk disease, disk herniation, spondylolysis, spondylolisthesis, or lumbar facet syndrome.
» Traditional recommended therapies include nonsteroidal anti-inflammatory drugs, physical therapy, and activity modification, which are often insufficient to resolve pain and prevent injury recurrence. Because most athletes will want to continue to lift weights, lifting-specific behavior modifications focused on improved technique and correcting mobility and muscular imbalances are important aspects of management in this patient population.
[Purpose] To clarify the effect of wearing an abdominal belt on dynamic standing balance. [Participants and Methods] The forward reach test (distance), 5-m tandem gait test (time), and repeated stepping test (time) were conducted for 14 healthy university students when wearing and not wearing an abdominal belt for comparison. [Results] Neither the forward reach distance nor time needed for 10-m tandem gait varied between when wearing and when not wearing an abdominal belt, whereas the time needed for repeated stepping was significantly shorter when wearing it. [Conclusion] In the case of healthy participants, the effect of wearing an abdominal belt was most marked on repeated stepping of all the 3 motor tasks requiring dynamic standing balance, possibly due to the level of difficulty of this task and its movement characteristics.
Although, widely used the mechanisms of action and the effectiveness of back belts in the prevention of occupational low back disorders remains uncertain, generating controversy about its use. Therefore, the purpose of this study was to do a critical literature review about back belts use in the prevention of occupational low back pain in the occupational setting. In order to do that, a bibliographic research in the following data basis: Medline, SciELO and LILACS was conducted. There is evidence that back belts use reduces spine range of motion, however the studies about intra-abdominal pressure and muscle activity presented contradictory results, as the epidemiologic studies, not allowing the recommendation of its use in the prevention of occupational low back pain. Based on this literature review it is suggested therefore, the implementation of new studies, to confirm or not the effectiveness of back belts as personal protective equipment, in the prevention of occupational low back disorders.
Ergonomics addresses both improving performance and reducing incidence and severity of injuries. The bulk of injuries confronting industry are attributed to overexertion that produces a mosaic of biomechanical, metabolic, and thermal strain. Mechanistically, such injuries are caused by failure to recognize some hazards, poor work design, and equipment use strategies, presenting excessively demanding motor tasks from an information processing, biomechanical and work physiological perspective, or when performing work in excessively stressful thermal environments. The human concomitantly considers and adapts to perceptual, cognitive, motor, biomechanical, metabolic and thermal stresses in a complex and time-variant manner. These stressors can be identified if one comprehensively examines the interfaces among task demands, human capabilities, the working environment, and machine design. Injury epidemiological efforts that fail to evaluate what the human is evaluating are likely to prove myopic in design and produce weak outcomes. The systematic approach advocated for the evaluation of overexertion injuries, and cited studies and models, may be mapped onto other injury outcomes linked to poor ergonomic design. © Springer Science+Business Media, LLC 2012. All rights reserved.
Introduction: The use of back support is one of the common methods aimed to prevent low back pain. The purpose of the present study was to investigate the effect of wearing a lumbosacral support on lumbar spine velocity and torque in six directions during combined trunk motion. Materials and Methods: In this interventional study, 30 young healthy men were selected simply from convenient samples. They were asked to stand in Isostation B200 system and perform three-dimensional trunk motion against a resistance of 50% of maximal voluntary contraction torque while wearing or not wearing a lumbosacral support. Under each condition of test, five successive motions of trunk were performed in downward direction (as flexion, right lateral flexion, and right rotation) and upward direction (as extension, left lateral flexion, and left rotation), and the variables of average velocity and average torque were recorded during motion. Results: With the use of a lumbosacral support, average velocity was significantly increased in flexion (P=0.015) and extension (P=0.005), but no significant changes were found in other directions (P>0/05). Back support decreased average torque of right rotation significantly (P=0.006), but did not significantly changed this variable in other directions (P>0/05). Conclusion: Wearing a lumbosacral support can increase velocity in sagittal plane. Decreased rotation torque of trunk, as a result of using a back support, may reduce the twisting forces on lumbar spine joints.
When participating in sport and exercise activities, various – often agedependent – injuries to any part of the spine are possible. The neck is most commonly injured in sports that involve contact, which place the cervical spine at risk of injury, in some cases with catastrophic consequences. The thoracic spine is less likely to be injured because it is relatively immobile and has extra support, but M. Scheuermann can lead to symptoms. The lower back is subject to a great deal of repetitive strain in many sports, which can result in nonspecific lumbago or more specific lumbar spine conditions, like spondylolysis and spondylolisthesis, disk disease, and lumbar stenosis which need further clinical and radiological investigation. This chapter describes the most common acute and chronic sportsrelated injuries of the spine.
Ergonomics is the practice and research of the interaction between the human and the physical environment with the goal of optimizing human well-being and overall system performance. For public health ergonomics programs, the major goal is the prevention of work-related musculoskeletal disorders (MSDs) associated with lifting and repetitive tasks. These prevention efforts encompass many different areas of ergonomics and public health disciplines ranging from engineering to epidemiology. Systematic and process approaches to physical ergonomic interventions work best to reduce the incidence of work-related MSDs.
As a result of competition among athletes, a number of auxiliary tools and treatments have been used to increase the physical power, agility, durability, and performance of the athletes on the field. Some substances and treatments containing factors that disrupt the balance in the competition are called doping and are banned by the rules of the World Anti-Doping Agency (WADA). Beyond these, healing accelerator biological applications are utilized in the treatment of disabilities in orthopedic practice. Several locally effective hormones, genetic treatments, scaffolds, and cellular tissue engineering products will be the center of interest in the near future. In this paper, we summarize the current literature regarding applications that increase athletic performance and allow injured athletes to return to active sports.
Low back injury due to manual lifting is historically prevalent in labor intensive industries. Improving risk management options is necessary to reduce the risk of low back injury. Workers lifting unstable loads are at greater risk of back injury compared to workers lifting stable loads. This study focused on the effect of engineering controls on trunk muscle activity. Engineering controls were designed to control the instability of a liquid load. Thirty-nine healthy subjects manually lifted asymmetrically in the transverse direction stable loads, unstable loads, and unstable loads with engineering controls. Trunk and load kinematic and trunk muscle electromyography data were collected during lifting. Unstable loads with engineering controls significantly (p < 0.001) reduced trunk muscle activity compared to unstable loads. Engineering controls should be implemented to reduce the risk of injury to workers handling unstable liquid loads.Relevance to industryManually handling containers filled with liquids is necessary in many industrial workplaces. Risk management solutions for low back injury due to manual lifting of such loads should focus on reducing muscular demand. This study demonstrates that engineering controls designed to increase the stability of a liquid load reduced muscular demand.
Powerlifting is a discipline of competitive weightlifting. To date, no investigations have focused on pain encountered during routine training. The aim of the study was to identify such pain, assign it to particular exercises and assess the data regarding injuries as well as the influence of intrinsic and extrinsic factors. Data of 245 competitive and elite powerlifters was collected by questionnaire. Information regarding current workout routines and retrospective injury data was collected. Study subjects were selected from 97 incorporated powerlifting clubs. A percentage of 43.3% of powerlifters complained of problems during routine workouts. Injury rate was calculated as 0.3 injuries per lifter per year (1 000 h of training=1 injury). There was no evidence that intrinsic or extrinsic factors affected this rate. Most commonly injured body regions were the shoulder, lower back and the knee. The use of weight belts increased the injury rate of the lumbar spine. Rate of injury to the upper extremities was significantly increased based on age >40 years (shoulder/p=0.003, elbow/p=0.003, hand+wrist/p=0.024) and female gender (hand+wrist/p=0.045). The daily workout of a large proportion of powerlifters is affected by disorders which do not require an interruption of training. The injury rate is low compared to other sports.
Unexpected ventral and dorsal perturbations and expected, self-induced ventral perturbations were delivered to the trunk by suddenly loading a vest strapped to the torso. Six male subjects were measured for intra-abdominal pressure (IAP) and intra-muscular electromyography of the transversus abdominis (TrA), obliquus internus abdominis (OI), obliquus externus abdominis (OE) and rectus abdominis (RA) muscles. Erector spinae (ES) activity was recorded using surface electromyography. Displacements of the trunk and head were registered using a video-based system. Unexpected ventral loading produced activity in TrA, OI, OE and RA, and an IAP increase well in advance of activity from ES. Expected ventral loading produced pre-activation of all muscles and an increased IAP prior to the perturbation. The TrA was always the first muscle active in both the unexpected and self-loading conditions. Of the two ventral loading conditions, forward displacement of the trunk was significantly reduced during the self-loading. Unexpected dorsal loading produced coincident activation of TrA, OI, OE, RA and ES. These results indicate a response of the trunk muscles to sudden expected and unexpected ventral loadings other than the anticipated immediate extensor torque production through ES activation. It is suggested that the increase in IAP is a mechanism designed to improve the stability of the trunk through a stiffening of the whole segment.
The increased intra-abdominal pressure (IAP) commonly observed when the spine is loaded during physical activities is hypothesized to increase lumbar spine stability. The mechanical stability of the lumbar spine is an important consideration in low back injury prevention and rehabilitation strategies. This study examined the effects of raised IAP and an abdominal belt on lumbar spine stability. Two hypotheses were tested: (1) An increase in IAP leads to increased lumbar spine stability, (2) Wearing an abdominal belt increases spine stability. Ten volunteers were placed in a semi-seated position in a jig that restricted hip motion leaving the upper torso free to move in any direction. The determination of lumbar spine stability was accomplished by measuring the instantaneous trunk stiffness in response to a sudden load release. The quick release method was applied in isometric trunk flexion, extension, and lateral bending. Activity of 12 major trunk muscles was monitored with electromyography and the IAP was measured with an intra-gastric pressure transducer. A two-factor repeated measures design was used (P < 0.05), in which the spine stability was evaluated under combinations of the following two factors: belt or no belt and three levels of IAP (0, 40, and 80% of maximum). The belt and raised IAP increased trunk stiffness in all directions, but the results in extension lacked statistical significance. In flexion, trunk stiffness increased by 21% and 42% due to 40% and 80% IAP levels respectively; in lateral bending, trunk stiffness increased by 16% and 30%. The belt added between 9% and 57% to the trunk stiffness depending on the IAP level and the direction of exertion. In all three directions, the EMG activity of all 12 trunk muscles increased significantly due to the elevated IAP. The belt had no effect on the activity of any of the muscles with the exception of the thoracic erector spinae in extension and the lumbar erector spinae in flexion, whose activities decreased. The results indicate that both wearing an abdominal belt and raised IAP can each independently, or in combination, increase lumbar spine stability. However, the benefits of the belt must be interpreted with caution in the context of the decreased activation of a few trunk extensor muscles.
OBJECTIVE: To demonstrate the influence of different types of lifting belts on trunk motion, muscle activity and spine loading during symmetric and asymmetric lifting exertions. DESIGN. IN VIVO: measurements were achieved representing lifting dynamics, applied trunk moments and myoelectric activity. Dynamic spinal loads were determined from a validated biomechanical model of lifting. BACKGROUND: There is a great deal of controversy as to whether lifting belts are a benefit or a liability to manual materials-handling activities. A review of the literature demonstrates that there is a large amount of conflicting evidence and few definitive, well-executed studies upon which to base an opinion regarding these devices. METHODS: Fifteen subjects lifted boxes of 14 kg and 23 kg from sagitally symmetric and asymmetric origins to an upright posture. Dynamic trunk motions, lifting moments, myoelectric activity and modelled spinal loads were examined as a function of three belt styles (elastic, leather, and orthotic) and compared with results from a no-belt condition. RESULTS: Lifting belts reduced peak trunk angles, velocities and accelerations in the sagittal, lateral and transverse planes. However, only the elastic belt successfully reduced trunk motions in all three dimensions. The orthotic belt significantly increased the lifting moment associated with a given weight. A minor redistribution in muscle activity was observed when wearing an elastic belt. A statistically significant reduction in spinal load was associated with the elastic belt. However, a great deal of variability between subjects was noted. Some subjects experienced increased spinal load while wearing the elastic lifting belt. CONCLUSIONS: These results demonstrate that the biomechanical operation of lifting can be influenced by the type of lifting belts used.
A two-dimensional dynamic linked segment model was constructed and applied to a lifting activity. Reactive forces and moments were calculated by an instantaneous approach involving the application of Newtonian mechanics to individual adjacent rigid segments in succession. The analysis started once at the feet and once at a hands/load segment. The model was validated by comparing predicted external forces and moments at the feet or at a hands/load segment to actual values, which were simultaneously measured (ground reaction force at the feet) or assumed to be zero (external moments at feet and hands/load and external forces, beside gravitation, at hands/load). In addition, results of both procedures, in terms of joint moments, including the moment at the intervertebral disc between the fifth lumbar and first sacral vertebra (L5-S1), were compared. A correlation of r = 0.88 between calculated and measured vertical ground reaction forces was found. The calculated external forces and moments at the hands showed only minor deviations from the expected zero level. The moments at L5-S1, calculated starting from feet compared to starting from hands/load, yielded a coefficient of correlation of r = 0.99. However, moments calculated from hands/load were 3.6% (averaged values) and 10.9% (peak values) higher. This difference is assumed to be due mainly to erroneous estimations of the positions of centres of gravity and joint rotation centres. The estimation of the location of L5-S1 rotation axis can affect the results significantly. Despite the numerous studies estimating the load on the low back during lifting on the basis of linked segment models, only a few attempts to validate these models have been made. This study is concerned with the validity of the presented linked segment model. The results support the model's validity. Effects of several sources of error threatening the validity are discussed.
Intra-abdominal pressure (IAP) has been proposed as an important mechanism in manual lifting and breathing mechanics. Direct (invasive) measures of IAP have required the swallowing of a radio transducer or insertion of a pressure sensor into the rectum or down the oesophagus to the stomach. The purpose of this study was to investigate the relationship between a non-invasive method (EMG) and IAP. Several tasks involving abdominal muscle activation were performed to assess whether or not IAP played a common role in these tasks. IAP and EMG from rectus abdominis, the abdominal obliques, intercostals and erector spinae were measured. Peak IAP reached 340 mmHg (valsalva) for one subject but most values were less than 100 mmHg for tasks other than valsalva. The IAP and EMG data provide some insight into the role of IAP during the performance of specific tasks. Peak IAP within 60 ms of the onset of vigorous abdominal activation indicated the importance of a very rapid pressure response to abdominal muscle activation. The correlations between various muscle EMG time histories and IAP exceeded 0·80 for only two activities (i.e. r(2) = 0·82 between the intercostals and IAP during valsalva manoeuvres). These data suggest that no unifying hypothesis exists to explain the role of IAP for a wide variety of movement tasks; rather, the role of IAP is task specific.
Removal of electrocardiographic (ECG) contamination of electromyographic (EMG) signals from torso muscles is often attempted by high-pass filtering. This study investigated the effects of the cut-off frequency used in this high-pass filtering technique on the resulting EMG signal. Surface EMGs were recorded on five subjects from the rectus abdominis, external oblique, and erector spinae muscles. These signals were then digitally high-pass filtered at cut-off frequencies of 10, 30, and 60 Hz. Integration and power analyses of the filtered EMGs were subsequently performed. It was found that an increase in the cut-off frequency affects the integrated EMG signal by (1) reducing the ECG contamination, (2) decreasing the amplitude, and (3) smoothing the signal. It was concluded that the use of a high-pass filter is effective in reducing ECG interference in integrated EMG recordings, and a cut-off frequency of approximately 30 Hz was optimal.
Electromyographic recordings of torso muscles are often used in the development of low-back biomechanical models. Unfortunately, these recordings are usually contaminated by electrocardiographic interference. High-pass filtering methods are sometimes used to diminish the influence of ECG from surface EMGs; however, the effects of these filters on the recorded and processed EMG have not been reported. The findings show that high-pass filtering is effective in reducing ECG contamination and motion artefact from integrated EMGs when the appropriate cut-off frequency is used. Inappropriate cut-off frequencies lead to either incomplete ECG removal or excess filtering of the EMG signal.
The increases in pressure in the thoracic and abdominal cavities when pushing, pulling and stooping to lift hove been measured in 16 male and 15 female young adults. The greatest pressure increases in the largest number of subjects occurred when pushing, and least pressure changes occurred when pulling. It is suggested that changes in intratruncal pressures may be used as an index of the magnitudes of forces acting on the trunk during working manoeuvres.
In studies related to human movement, linked segment models (LSM's) are often used to quantify forces and torques, generated in body joints. Some LSM's represent only a few body segments. Others, for instance used in studies on the control of whole body movements, include all body segments. As a consequence of the complexity of 3-dimensional (3-D) analyses, most LSM's are restricted to one plane of motion. However, in asymmetric movements this may result in a loss of relevant information. The aim of the current study was to develop and validate a 3-D LSM including all body segments. Braces with markers, attached to all body segments, were used to record the body movements. The validation of the model was accomplished by comparing the measured with the estimated ground reaction force and by comparing the torques at the lumbo-sacral joint that resulted from a bottom-up and a top-down mechanical analysis. For both comparisons, reasonable to good agreement was found. Sources of error that could not be analysed this way, were subjected to an additional sensitivity analysis. It was concluded that the internal validity of the current model is quite satisfactory.
This study investigated the effects of initial load height and foot placement instruction in four lifting techniques: free, stoop (bending the back), squat (bending the knees) and a modified squat technique (bending the knees and rotating them outward). A 2D dynamic linked segment model was combined with an EMG assisted trunk muscle model to quantify kinematics and low back loading in 10 subjects performing 19 different lifting movements, using 10.5 kg boxes without handles. When lifting from a 0.05 m height with the feet behind the box, squat lifting resulted in 19.9% (SD 8.7%) higher net moments (p < 0.001) and 17.0% (SD 13.2%) higher compression forces (p < 0.01) than stoop lifting. This effect was reduced to 12.8% (SD 10.7%) for moments and a non-significant 7.4% (SD 16.0%) for compression forces when lifting with the feet beside the box and it disappeared when lifting from 0.5 m height. Differences between squat and stoop lifts, as well as the interaction with lifting height, could to a large extent be explained by changes in the horizontal L5/S1 intervertebral joint position relative to the load, the upper body acceleration, and lumbar flexion. Rotating the knees outward during squat lifts resulted in moments and compression forces that were smaller than in squat lifting but larger than in stoop lifting. Shear forces were small ( < 300 N) at the L4/L5 joint and substantial (1100 - 1400 N) but unaffected by lifting technique at the L5/S1 joint. The present results show that the effects of lifting technique on low back loading depend on the task context.
The purpose of this study was to examine the effectiveness of weight-belts during multiple repetitions of the parallel back squat exercise. Five subjects were filmed (50 fps) as they performed eight consecutive trials at each of two weight-belt conditions [with belt = WB, without belt = WOB] in random order at their eight-repetition maximum effort. Other parameters examined were ground reaction forces, intra-abdominal pressure (IAP), and mean electromyography (mEMG) for the external oblique (EO), erector spinae (ES), vastus lateralis (VL), and bicep femoris (BF) muscles. All parameters were collected and interfaced to a computer via an A/D converter. WB repetitions were generally performed faster than WOB repetitions, especially by the later repetitions (3.34 vs 3.56 s). WB IAP values were consistently greater (P less than 0.05) than WOB values by 25-40%. IAP increased by approximately 11.5% from the first to the last repetitions. No differences were observed for ES and EO mEMG for belt usage, but values increased by up to 20% across repetitions. Several differences were observed between WB and WOB for the VL and BF mEMG, with WB values being significantly greater. These data suggest that a weight-belt aids in supporting the trunk by increasing IAP, and that any differential effect due to wearing a weight-belt did not occur over eight repetitions.
The purpose of this study was to examine the effectiveness of weight-belts during the performance of the parallel squat exercise. Six subjects were filmed (40 fps) as they performed three trials at each of three belt conditions (NB, none; LB, light; HB, heavy) in random order and three load conditions (70, 80, 90% 1RM (one repetition maximum] in increasing order. The parameters examined were collected and interfaced to a computer via an analog-to-digital (A/D) converter: ground reaction forces, intra-abdominal pressure (IAP), and EMG for the rectus abdominus (RA), external oblique (EO), and erector spinae (ES) muscles. Most differences were observed during the 90% 1RM condition, and only they are presented in this paper. Maximum IAP values were always greater (P less than 0.05) for the weight-belt conditions (LB, 29.2; HB, 29.1 greater th an NB, 26,8 kPa). Similar results were observed for the mean IAP. The integrated EMG (iEMG) activity of the muscles and adjusted mean values for back compressive force and back muscle force followed a similar but opposite pattern, with NB being the greatest. ES mEMG/(L5/S1) values for HB (18.1%) were the least, followed by LB (20.01%) and NB (22.3%). Few differences were observed between belt types. These data suggest that a weight-belt can aid in supporting the trunk by increasing IAP.
The aim of this study was to compare trunk muscle strength and intra-abdominal pressure during lifting in low-back patients and in healthy controls. Twenty male workers with 2-18 year history (median 5.5 years) of low-back pain went through strength tests of trunk flexion and extension and a series of standardized lifts. The intra-abdominal pressure (IAP) and the EMG activity of the oblique abdominal muscles and of the erector spinae muscles were recorded. The results were compared with those in 20 healthy men exposed to similar loads at work and at leisure. The low-back patients had reduced abdominal muscle strength (-25%) compared with the healthy controls. The IAP during lifting was the same in the two groups despite the difference in abdominal muscle strength. The trunk extension strength was the same in the two groups. The oblique abdominal muscles were only moderately activated during lifting (5-15% of maximum activity with 25 kg) both in low-back patients and in healthy controls. The erector spinae muscle was strongly activated during lifting (40-60% of maximum activity with 25 kg) both in low-back patients and in healthy controls. During backlifting the duration of erector spinae activity varied. Back patients had extended activity compared with the healthy controls. Stiffness seemed to affect the duration of activity in both groups. The oblique abdominal muscles seem to be of no decisive importance to the IAP.
Biomechanical models used to estimate loads on the lumbar spine often predict internal low back forces for heavy lifts that exceed known tissue tolerances, yet the particular lift caused no apparent damage to the lifter. To deal with this paradox, many researchers have incorporated some form of spinal compression alleviation from intra-abdominal pressure (IAP). The purpose of this work was to re-examine some of the issues involved in the feasibility of IAP to reduce spinal loads during stressful lifts. Questions remain over the trade-off between the beneficial tensile force on the spine, exerted via the diaphragm and pelvic floor when IAP is produced, and the undesirable compressive effects of abdominal muscular force required to maintain the pressure within the abdomen. Various strategies of modelling IAP and its effects on low back loading were employed, Three major differences between this and most previous models of IAP effects were the attempt to quantify the size of abdominal muscle forces and the utilization of a considerably smaller diaphragm cross-sectional area and corresponding IAP moment arm. Abdominal EMG recorded from rectus abdominis, external oblique and internal oblique generally indicated low levels of activity throughout the high loading phase of the lifts. However, model output predicted that the compressive forces generated by the abdominal wall musculature were larger than the beneficial action of those forces thought to alleviate spinal compression via IAP. These results suggest that modelling IAP as a force vector which produces a trunk extensor moment and lumbar disc compression alleviation, without accounting for the compressive effects of abdominal muscle forces required to produce the IAP, is incorrect. This does not exclude a possible role of IAP in assisting the trunk during loading, only that the role of IAP is not modelled properly at present. IAP may indeed play a role in spinal stabilization as yet not well understood.
The ability of a partial or full Valsalva maneuver (voluntary pressurization of the intraabdominal cavity) to unload the spine was investigated in four subjects. During the performance of five isometric tasks, intraabdominal and intradiscal pressures and surface myoelectric activities in three lumbar trunk muscle groups were measured. The tasks were carried out without voluntary pressurization of the intraabdominal cavity and then when the subjects performed partial and full Valsalva maneuvers. A biomechanical model analysis of each task was made to help interpret the experimental measurements. Intraabdominal pressure was found not to be an indicator of spine load in these experiments. The Valsalva maneuvers did raise intraabdominal pressure, but in four of the five tasks increased rather than decreased lumbar spine compressions occurred.
The study is an investigation into the form of the abdominal pressure reflex in normal individuals under isometric loading of the torso. Various directions of load are imposed, and both flexed and upright postures are adopted. The sensitivity of the pressurization to the applied moment is calculated, the form of the response being linear in each case. The results show that the response sensitivity varies with subject posture and mass and with the direction and site of loading. The highest sensitivities are in response to extensor moments and the lowest, when the torso is flexed. It would appear that the supportive influence of the trunk cannot be considered constant under all loading conditions, nor can a single explanation of its function be adequate under both extensor and flexor applied moments.
A three-dimensional muscle model with complex geometry is described and tested against experimental data. Using this model, several muscles were constructed. These muscles have equal optimum length but differ in architecture. The force exerted by the constructed muscles, in relation to their actual length and velocity of shortening, is discussed. Generally speaking, the constructed muscles with considerable pennation have great fiber angles, a great physiological cross section, a narrow active and steep passive length-force relation, and a low maximal velocity of shortening. The maximal power (force times velocity) delivered by the constructed muscles is shown to be almost independent of the architecture of the muscles. The steepness of the passive length-force relation is determined mainly by the shortest fibers within the group of constructed muscles, whereas maximal velocity of shortening and the width of the active length-force relation are determined mainly by the longest fibers. The validity of the three-dimensional muscle model with respect to some morphological and functional characteristics is tested. Length-force relations of constructed muscles are compared with the actual length-force relations of mm. gastrocnemii mediales and mm. semimembranosi of male Wistar rats. Moreover, actual fiber angle, fiber length, and muscle thickness of three mm. gastrocnemii mediales are compared with values found for constructed muscles. It is concluded that the three-dimensional muscle model closely approximates the actual muscle form and function.
To study spinal movements during work, an instrument that measured angles and angle changes in relation to a vertical plane was adapted to continuously measure forward flexion of the trunk. The instrument, which is battery-powered and worn on the back, registers the amount of flexion and its distribution over time during a work cycle by recording the time spent in each of five 18 degrees intervals between 0 degrees and 90 degrees. Also the number of times that the angle of flexion changed from one interval to another is recorded. A total of 43 subjects from three occupations--dentistry, nurses' aide work, and warehouse work--were each tested during a 60 minute work cycle. On the average, the dentists spent most of the time (52.2 minutes) in a semi-flexed position not exceeding 36 degrees and performed eight deep forward flexions (greater than 73 degrees). The nurses' aides spent one-half of the work cycle (34.4 minutes) in an upright position (0-18 degrees) and performed 70 deep forward flexions. The warehouse workers spent less than one-half of the work cycle in an upright position (27.5 minutes) and performed 153 deep forward flexions that nearly always were associated with lifting.
The difference in physiological stress between static posture loading and dynamic lift is poorly understood. Therefore, the quantitative pattern of gradual increase and decrease of stress as measured by EMG of erectores spinae at T12 and L3 and intraabdominal pressure (IAP) due to steady progressive loading and unloading in static stooping posture was studied and compared with that of stoop lifting of the same weight. For dynamic loading and unloading a steady flow of 25 kg of water into or out of a plastic tub held in the hand while maintaining a stooping posture was used. The subjects also performed stoop lifting weights of 15 and 25 kg. In static posture loading the mean EMG at T12 was approximately 50% of the L3 level. During unloading in that posture it was reduced to 33%. The level of electromyographic activity at T12 for loading was not significantly different from unloading. At L3 however, the magnitude increased significantly for unloading. The EMG and intraabdominal pressure responses of static posture were between 33 and 50% of the corresponding phases during stoop lifting of the same weight. An insignificant difference in IAP and heart rate between static posture loading and stoop lifting indicates a less critical role of IAP and no difference in cardiac stress in less stressful tasks.
A weight of 10 kg was lifted by 11 normal male volunteers (mean age 34·2 years) from ground to knee, hip, and shoulder levels in the sagittal, lateral and oblique planes. During these lifting manoeuvres intra-abdominal pressure was measured by telemetry and the activity of erector spinae and external oblique were recorded by electromyography. The values obtained for peak and sustained intra-abdominal pressure and the averaged electromyographic activities of erectores spinae and external obliques were subjected to analysis of variance and correlation analysis. A significant difference between the responses in these three planes was found: the sagittal plane activities evoke least response. Intra-abdominal pressures, erector spinae activity and external oblique activity were highly significantly correlated in each of the three planes.
The transmission of load through the lumbar spine was analyzed in a model of the five lumbar vertebrae, the sacrum/pelvis and the thorax, and 66 symmetric pairs of multijoint muscles. The model was used to test the hypotheses that (1) the need to maintain equilibrium simultaneously at all vertebral levels precludes simultaneous maximum activation of synergistic muscles and (2) that the maximum loads which could be carried by the spine and the degree of muscle activation increases with increasing motion segment stiffness. Maximum moments applied to T12 were calculated for moments in three principal directions, subject to equilibrium at all six joints and to constraints on the maximum muscle stress and intervertebral displacements. A model with realistic motion segment stiffness predicted maximum efforts between 1.4 and 3.3 times greater than a model with 'ball-and-socket' joints, and in better agreement with published results from maximum effort experiments. The differences in maximal effort were greater than the moments transmitted through the joints. While muscle activation levels were greater, many synergistic muscles were still submaximally activated. Antagonistic muscles were recruited to maintain multijoint equilibrium. We concluded that (1) muscle activations permitted in single anatomic level analyses are generally not compatible with equilibrium at other levels; (2) the effect of moment transmission in the joints gives a more realistic representation of the lumbar spine.
Intra-abdominal pressure (IAP), force and electromyographic (EMG) activity from the abdominal (intra-muscular) and trunk extensor (surface) muscles were measured in seven male subjects during maximal and sub-maximal sagittal lifting and lowering with straight arms and legs. An isokinetic dynamometer was used to provide five constant velocities (0.12-0.96 m.s-1) of lifting (pulling against the resistance of the motor) and lowering (resisting the downward pull of the motor). For the maximal efforts, position-specific lowering force was greater than lifting force at each respective velocity. In contrast, corresponding IAPs during lowering were less than those during lifting. Highest mean force occurred during slow lowering (1547 N at 0.24 m.s-1) while highest IAP occurred during the fastest lifts (17.8 kPa at 0.48-0.96 m.s-1). Among the abdominal muscles, the highest level of activity and the best correlation to variations in IAP (r = 0.970 over velocities) was demonstrated by the transversus abdominis muscle. At each velocity the EMG activity of the primary trunk and hip extensors was less during lowering (eccentric muscle action) than lifting (concentric muscle action) despite higher levels of force (r between -0.896 and -0.851). Sub-maximal efforts resulted in IAP increasing linearly with increasing lifting or lowering force (r = 0.918 and 0.882, respectively). However, at any given force IAP was less during lowering than lifting. This difference was negated if force and IAP were expressed relative to their respective lifting and lowering maxima.(ABSTRACT TRUNCATED AT 250 WORDS)
Models of the abdominal musculature, which used single slice MRI or CT scans to reconstruct the anatomy, were unable to explain magnitudes of abdominal flexion moment which exceed 100 Nm in living subjects. For example, the muscle areas and corresponding flexor moment arms measured from a transverse scan at L4-L5 predict maximum moments less than 50 Nm. The architecture of rectus abdominis, external and internal obliques, and transverse abdominis was examined from cadaveric specimens, from which the geometric details were incorporated into a revised model. Scaling of the muscles to obtain physiological cross-sectional areas were obtained using two methods: serial MRI slices; and from several locations of ultrasound measurement. The two major anatomically justified improvements that had dramatic effects on flexor moment production were: the increase in flexor moment arms of muscles (approximately 30%) measured in a standing posture when compared to the supine posture for MRI examination; reinterpretation of the line of action of the obliques which transmit their flexor forces through the linea semilunaris (increasing their effective flexor moment arm) to eventual skeletal attachment at the pelvis.
Few studies have been carried out on the changes in biomechanical loading on low-back tissues during prolonged lifting. The purpose of this paper was to develop a model for continuously estimating erector spinae muscle loads during repetitive lifting and lowering tasks. The model was based on spine kinematics and bilateral lumbar and thoracic erector spinae electromyogram (EMG) signals and was developed with the data from eight male subjects. Each subject performed a series of isometric contractions to develop extensor moments about the low back. Maximum voluntary contractions (MVCs) were used to normalize all recorded EMG and moment time-histories. Ramp contractions were used to determine the non-linear relationship between extensor moments and EMG amplitudes. In addition, the most appropriate low-pass filter cut-off frequencies were calculated for matching the rectified EMG signals with the moment patterns. The mean low-pass cut-off frequency was 2.7 (0.4) Hz. The accuracy of the non-linear EMG-based estimates of isometric extensor moment were tested with data from a series of six rapid contractions by each subject. The mean error over the duration of these contractions was 9.2 (2.6)% MVC. During prolonged lifting sessions of 20 min and of 2 h, a model was used to calculate changes in muscle length based on monitored spine kinematics. EMG signals were first processed according to the parameters determined from the isometric contractions and then further processed to account for the effects of instantaneous muscle length and velocity. Simple EMG estimates were found to underestimate peak loading by 9.1 (4.0) and 25.7 (11.6)% MVC for eccentric and concentric phases of lifting respectively, when compared to load estimates based on the mechanically corrected EMG. To date, the model has been used to analyze over 5300 lifts.
Fourteen young male students (mean age 21 years, mean weight 69.4 kg, and mean height 175.4 cm) and 12 young female students (mean age 22.2 years, mean weight 60.6 kg, and mean height 169.3 cm) held 9.07 kg and 6.8 kg, respectively, at their three-quarters horizontal reach distance in upright and stooping postures for a period of 5 min. During these periods the external torque on the lumbosacral disc, intra-abdominal pressure, and electromyographic signals from erectores spinae at T12 and L3 levels, latissimus dorsi and external obliques were recorded at 1 kHz for 2.1 s every 15 s for a period of 5 min. The EMGs were processed in magnitude and time domains to determine muscle fatigue. Through the data obtained it was seen that the intra-abdominal pressure did not follow or reflect either the spinal load or the muscle activity. Based on the arguments presented, it was concluded that the intra-abdominal pressure does not appear to have a role of relieving the spine of some of its load. Instead, it is suggested that it is a dependent variable manifesting itself when mechanisms for spinal stability are evoked to overcome large voluntary and inertial loads.
Previous studies on how an increase in intra-abdominal pressure (IAP) effects the loading of the lumbar spine during back extension show diverging results. From a critical review of the literature we deduce a simplified, but consistent, model of the mechanisms involved in IAP-induced unloading of the lumbar spine. The model is then expanded by explicitly incorporating equilibrium equations for the pressurised abdomen and the abdominal wall. It is shown that the unloading effect of IAP can be viewed as that of a pressurised column of fixed cross-sectional area, between the rib cage and pelvis. Different abdominal forms are examined and a form with zero longitudinal curvature is found to have some important mechanical benefits for the generation of IAP-induced alleviation of compressive loading of the lumbar spine.
To verify that maximization of endurance is important among the functional criteria determining trunk muscle activation patterns, symmetric and asymmetric exertions were simulated using a detailed model consisting of 114 muscle slips crossing the lumbosacral junction and employing a cost function which maximizes endurance. First, the question whether meaningful comparisons can be made between activity predictions for individual muscle slips and surface EMG data recorded from larger anatomical entities was addressed. This was answered affirmatively, since activation patterns predicted by a coarse and a middle version of the model, in which activation was constrained to be equal within 14 or 32 groups of muscle slips, were similar to those predicted with each muscle slip controlled independently. Median correlation coefficients between activity vectors predicted by the simplified models and the detailed model were 0.88 and 0.97, respectively. The coarse model underestimated the endurance capacity by a median of 21%, the middle model by only 0.7%. Second, predicted activities within anatomical entities defined at this level of detail were compared to reference data derived from the literature (Lavender et al. 1992, Human Factors 34, 239-247; 1992, Journal of Orthopaedic Research 10, 691-700; Vink et al., 1988, Electromyography and Clinical Neurophysiology 28, 517-525). The predicted activity patterns of the erector spinae, external oblique and rectus abdominis muscles closely resembled the EMG patterns (r2 = 0.48-0.99). Furthermore, the observed distribution of activity between parts of the erector spinae muscle was adequately predicted.
Currently, intra-abdominal pressure (IAP) is thought to provide stability to the lumbar spine but the exact principles have yet to be specified. A simplified physical model was constructed and theoretical calculations performed to illustrate a possible intra-abdominal pressure mechanism for stabilizing the spine. The model consisted of an inverted pendulum with linear springs representing abdominal and erector spinae muscle groups. The IAP force was simulated with a pneumatic piston activated with compressed air. The critical load of the model was calculated theoretically based on the minimum potential energy principle and obtained experimentally by increasing weight on the model until the point of buckling. Two distinct mechanisms were simulated separately and in combination. One was antagonistic flexor extensor muscle coactivation and the second was abdominal muscle activation along with generation of IAP. Both mechanisms were effective in stabilizing the model of a lumbar spine. The critical load and therefore the stability of the spine model increased with either increased antagonistic muscle coactivation forces or increased IAP along with increased abdominal spring force. Both mechanisms were also effective in providing mechanical stability to the spine model when activated simultaneously. Theoretical calculation of the critical load agreed very well with experimental results (95.5% average error). The IAP mechanism for stabilizing the lumbar spine appears preferable in tasks that demand trunk extensor moment such as lifting or jumping. This mechanism can increase spine stability without the additional coactivation of erector spinae muscles.
Relative phase angle was used to study segmental motion patterns during a lifting and lowering task.
To investigate the effect of back belts, breathing technique, and their interaction on lumbar and pelvic motion patterns.
Trunk and pelvic coordination has been investigated in healthy and low back pain populations. Back belts have been shown to alter range of motion and intra-abdominal pressure. Little has been reported about belts and coordination during lifting and lowering. Phase angle has been used for quantifying segmental coordination.
Six individuals performed lifting/lowering tasks with a 23-kg load under elastic, rigid, and no belt conditions. During a second session, individuals were trained in Valsalva's maneuver and repeated the protocol. Cinematography was used to track trunk and pelvis displacements.
Segmental coordination during lowering generally was found to be the inverse of lifting. Significant differences in the relation between lumbar and pelvis phase angles were found during the initial stage of lifting because of the interaction of belt use and breathing. Lumbar range of motion decreased significantly with belt use during lifting and lowering. No significant change in pelvis range of motion was observed.
Back belt use and breathing technique interacted during the initial stage of lifting to significantly alter the lumbar and pelvis phase angles. The change in segmental kinematics was similar to that previously reported for patients with a history of low back pain. Lumbar range of motion significantly decreased with belt use during both lifting and lowering.
In lifting, the abdominal muscles are thought to be activated to stabilize the spine. As a detrimental effect, they contribute to spinal compression. The existing literature is not conclusive about the biological relevance of this effect. From biological, mechanical and anatomical considerations it was hypothesised that the relative abdominal contribution to compression would be minor in the beginning of the lift, that the relative and absolute abdominal contribution to compression would rise throughout the lift, and that the obliques would contribute to a larger extent than the rectus abdominis. To investigate these hypotheses, 10 subjects lifted 0.5, 10.5 and 22.5 kg. EMG levels obtained from the rectus abdominis and the obliques were converted into force using normalized EMG, muscle potential and area values, and modulating factors for muscle length and contraction velocity. An anatomical model was applied to compute the abdominal effects on spinal compression in three consecutive phases within a lift. If expressed relative to the total spinal compression, the abdominal contribution for the three weight conditions was 7.1% (SD, 1.7), 10.4% (4.7) and 12.5% (4.4) in the begin and 21.0% (5.8), 19.0% (5.3) and 22.2% (6.6) in the end phase. Thus, the relative abdominal contribution to compression was minor in the beginning and increased towards the end. The absolute abdominal contribution was constant throughout the lift. The contributions could be retraced to the obliques rather than the rectus, while during the lift a shift in activation from the obliquus externus to internus was observed.
It is hypothesized that, in a large number of cases of aspecific low back pain, the primary cause of the pain is a fracture of the vertebral endplate caused by compression forces. Clinical studies have shown that, in many low back pain patients, damage of the vertebral bodies and or the intervertebral disc is present. In vitro studies reveal that the most likely type of failure of this anterior part of the spine is a fracture of the endplate as a result of compression. The high incidence of aspecific low back pain concurs with the likeliness of compression fractures of the endplate to occur in everyday life. Furthermore, epidemiological findings and the natural history of low back pain appear to be in line with the proposed hypothesis.
OBJECTIVE: To determine the relative importance of modelled peak spine loads, hand loads, trunk kinematics and cumulative spine loads as predictors of reported low back pain (LBP). BACKGROUND: The authors have recently shown that both biomechemical and psychosocial variables are important in the reporting of LBP. In previous studies, peak spinal load risk factors have been identified and while there is in vitro evidence for adverse effects of excessive cumulative load on tissue, there is little epidemiological evidence. METHODS: Physical exposures to peak and cumulative lumbar spine moment, compression and shear forces, trunk kinematics, and forces on hands were analyzed on 130 randomly selected controls and 104 cases. Univariable and multivariable odds ratios of the risk of reporting were calculated from a backwards logistic regression analysis. Interrelationships among variables were examined by factor analysis. RESULTS: Cases showed significantly higher loading on all biomechanical variables. Four independent risk factors were identified: integrated lumbar moment (over a shift), 'usual' hand force, peak shear force at the level of L(4)/L(5) and peak trunk velocity. Substituting lumbar compression or moment for shear did not appreciably alter odds ratios because of high correlations among these variables. CONCLUSIONS: Cumulative biomechanical variables are important risk factors in the reporting of LBP. Spinal tissue loading estimates from a biomechanical model provide information not included in the trunk kinematics and hand force inputs to the model alone. Workers in the top 25% of loading exposure on all risk factors are at about six times the risk of reporting LBP when compared with those in the bottom 25%. RELEVANCE: Primary prevention, treatment, and return to work efforts for individuals reporting LBP all require understanding of risk factors. The results suggest that cumulative loading of the low back is important etiologically and highlight the need for better information on the response of spinal tissues to cumulative loading.
Objective. This study was designed to help interpret the biomechanical role of intraabdominal pressure during lifting type motions of the trunk. Design. An in vivo study was performed in which intra-abdominal pressure was observed as subject trunks were subjected to different dynamic trunk loading conditions common during industrial lifting. Background. There is a little consensus as to the biomechanical role of intra-abdominal pressure during lifting. Previous studies have suggested that: it may assist in load relief when lifting, may be involved in trunk stability, and/or may be used as a measure fo spine loading. Thus, in general, our understanding of intra-abdominal pressure is rather poor. Methods. In this study intra-abdominal pressure was monitored using a radio pill in 114 subjects over a series of four experiments. Subject's trunks were subjected to different dynamic trunk symmetric and asymmetric trunk loading conditions that are common during industrial lifting tasks. Results. The results indicated that (1) intra-abdominal pressure increased to significant levels (above 10 mmHg) only when more than 54 Nm of trunk torque were supported; (2) intra-abdominal pressure increases monotonically (up to 150 mmHg) as a function of trunk velocity; and (3) under concentric conditions intra-abdominal pressure increases as a function of greater asymmetry, whereas, under eccentric conditions the response changes to a much lesser extent as asymmetry changes. Conclusions. These findings suggest that intra-abdominal pressure appears to be more a by-product of trunk muscle coactivation. Any mechanical advantage gained from intraabdominal pressure might be in the form of a preparatory action resulting from muscle coactivation that stiffens the trunk just prior to a rapid trunk extension exertion. This function may reinforce previous hypotheses regarding the stability role of intra-abdominal pressure.
This study examined the effect of a belt on ventilation and trunk muscle activities during repetitive lifting tasks with a control of breathing type and belt pressure.
To evaluate the effect of the lifting belt on the trunk muscle electromyography (EMG) and to parse out potential interaction between ventilatory changes and lifting belts.
Although both tensed thorax and compressed abdomen are considered to assist transferring the force from torso to pelvis in lifting, there has not been any consideration of the interaction between the two chambers in most published analyses.
Eleven male study participants participated in the study. They performed five minutes of paced repetitive squat lifts at frequencies of one or three lifts per minute, with loads of 10 or 25 kg. Belt pressure was set at 0 (no belt), 10, and 20 mm Hg. Study participants lifted with inspire-hold and expire-hold for a period of 5 minutes. Lift ventilation data and trunk muscle normalized electromyography (NEMG) (including rectus abdominis, external oblique, latissimus dorsi, and erector spinae) for the final lift were collected for analysis.
The results indicate that the ventilation demand for lifting was not different with or without use of a belt. The prelifting erector spinae NEMG was 8-11% maximum voluntary contraction (MVC) lower and the latissimus dorsi NEMG was 15-21% MVC lower than that without belt. This is also the case in the lifting phase. The rectus abdominis NEMG was increased by 4% MVC and the external oblique NEMG was increased by 3-5% MVC while lifting with a belt.
These data do not lead to a statistical effect of lifting belt pressure on ventilatory behavior. It appears that the use of a belt in lifting significantly decreased the back muscular activation yet increased the abdominal muscular activation. Thus, claims of benefits derived from the use of a belt in lifting remain controversial. The simultaneous controls of the air volume held and pressure of the belt during the moment-controlled lifting tasks allowed this presentation of belt effects on trunk muscle NEMG unique from that in most of the literature.
The six-degrees-of-freedom elastic behavior of spinal motion segments can be approximated by a stiffness matrix. A method is described to measure this stiffness matrix directly with the motion segment held under physiological conditions of axial preload and in an isotonic fluid bath by measuring the forces and moments associated with each of the six orthogonal translations and rotations. The stiffness matrix was obtained from the load-displacement measurements by linear least squares assuming a symmetric matrix. Results from a pig lumbar spinal motion segment in an isotonic bath, with and without a 500 N axial preload, showed a large stiffening effect with axial preload.
The purpose of the present study was to investigate whether increased intra-abdominal pressure (IAP) can be achieved without elevating the overall trunk muscle co-contraction that causes increased spine compression force. Ten subjects performed isometric trunk flexion, extension, and lateral bending exertions while generating 0%, 40% and 80% of their maximal IAP or while co-contracting trunk muscles without consciously raising IAP. An additional three subjects performed a variety of ramp IAP, co-contraction and isometric exertion tasks while holding their breaths and while exhaling. An 18 degree-of-freedom, electromyogram (EMG)-assisted biomechanical model was used to quantify trunk muscle co-contraction with calculations of spine compression force and stability. Spine stability and compression force increased proportionally with increased IAP regardless of whether the subjects intentionally generated IAP or consciously avoided it. This increase was accomplished with significantly greater co-contraction of 12 major trunk muscles. The EMG activation of all muscles was highly correlated with IAP and intra-thoracic pressure (ITP) ( r from 0.59 to 0.95). Activity of the thoracic erector spinae correlated the best with ITP ( r=0.81), which in turn was correlated with IAP ( r=0.91). It was not possible to co-contract trunk muscles without generating IAP and ITP, or conversely to generate IAP without trunk muscle co-contraction and increased ITP.
In this study, sudden load was applied to the trunk and situations with alternating low levels of intra-abdominal pressure (IAP) realistic to work situations were compared. The aim was to see if IAP and the small increases in co-contraction of back muscles that follow are capable of increasing the stiffness of the lumbar spine. Nine subjects participated in ten sudden load situations during which they were asked to hold a box and conduct a percentage of maximal IAP. The hip was fixed and the load was applied horizontally on the trunk. EMG, IAP, and movement of the trunk were measured. It was found that IAP of a size likely to appear in work situations, and the concomitant increase in muscle co-activation increased the spine stiffness. This increase in stiffness decreased the movement caused by the sudden load. These results show that both abdominal- and back muscles may have an important role in stabilising the spine, and in decreasing movements caused by sudden loads likely to appear in numerous work
The purpose of this study was to develop and evaluate a biomechanical model of lumbar back extension over a wide range of positions for the lumbar spine, incorporating the latest information on muscle geometry and intra-abdominal pressure (IAP). Analysis of the Visible Human data was utilised in order to obtain anatomical information unavailable from the literature and magnetic resonance imaging was used to generate subject-specific anatomical descriptions. The model was evaluated by comparisons with measured maximal voluntary static back-extension torques. Predicted maximal specific muscle tensions agreed well with in vitro measurements from the literature. When modelling the maximal static back-extension torque production, it was possible to come fairly close to simultaneous equilibrium about all the lumbar discs simply by a uniform muscle activation of all back-extensor muscles (the caudal part showed, however, less agreement). This indicates that equilibrium in the lumbar spine is mainly regulated by passive mechanical properties, e.g. muscle length changes due to postural changes, rather than due to complex muscle coordination, as earlier proposed. The model showed that IAP (measured during torque exertions) contributes about 10% of the total maximal voluntary back-extensor torque and that it can unload the spine from compression. The spinal unloading effect from the IAP was greatest with the spine held in a flexed position. This is in opposition to the effects of changed muscle lever arm lengths, which for a given load would give the largest spinal unloading in the extended position. These findings have implications for the evaluation of optimal lifting techniques.
1. Since the publication by Bradford and Spurling in 1945 of The Intervertebral Disc, there has been argument about the figure of 1,600 pounds that they calculated as the load on each lower lumbar intervertebral disc when a person lifts a heavy load with the trunk flexed, especially since experiments have shown that intervertebral discs subjected to increasing pressures yield at values well below this figure. In the author's experiments the discs were destroyed by pressures ranging from 350 to 1,400 pounds, with a mean of 710 pounds.
2. It occurred to the writer that the spine is not necessarily the only structure in the body that can transmit pressure forces from the shoulder to the pelvis. A raised intra-abdominal pressure impacts a thrust under the diaphragm, which will be transmitted to the thoracic spine and the shoulders by means of the ribs. This thrust can take care of part of the lifted weight and thus decrease the load on the spine.
3. In experiments in which the intra-abdominal pressure was measured by means of a small balloon in the stomach it was found that the pressure rose proportionally with the amount of weight lifted.
4. It is suggested that the abdominal fluid ball can exert a longitudinal force only if there is no contraction of the longitudinal muscles (at least anteriorly). Electromyographic studies of the abdominal muscles during weight lifting showed that the transverse and possibly the oblique abdominal muscles contract, but not the recti.
5. It thus seems that the load on the intervertebral discs is not necessarily so great as Bradford and Spurling calculated, but can remain within safe limits. It is hard to give accurate figures for the amount of load that is taken off the spine in this way, but an estimate would put it at several hundred pounds. The importance of a reflex contraction of the abdominal wall during effort as a protective mechanism for the spine must therefore be appreciated. Voluntary contraction may also be called upon to increase the intra-abdominal pressure and so reduce the load on the discs. This is done by many weight lifters.
This study focused on intra-abdominal pressure (IAP) during sudden trunk loads. Ten participants were exposed to heavy, sudden trunk loads as they might occur during patient handling.
The aim was to study the development of intra-abdominal pressure when well-trained participants cope with heavy, sudden trunk loads. It is hypothesized that high IAP develops sufficiently fast to be present when the large torques act on the low-back structures.
Well-trained sportsmen expose themselves to heavy sudden loads of the trunk without getting injured, but it is unknown how they cope with these loads. Do they use IAP? IAP is believed to play a significant role in spine stability, but this has only been documented in experimental studies with light trunk loads.
Ten well-trained judo and jujitsu fighters were exposed to heavy sudden trunk loads through imitated patient handling situations in which the patient fell, and the fighters were to hold the patient and prevent the fall. IAP was measured with a catheter in the stomach. Along with the IAP measurement, the load on the low back during the patient falls was quantified by a three-dimensional dynamic biomechanical calculation of the torques and the compression at the L4/L5 joint.
High IAP developed quickly and timed in relation to the external torque when the fighters were exposed to a sudden patient fall. When the trunk load was heavy and sudden, IAP was developed to be present at the time when low-back structures had to cope with the large load.
High IAP was developed sufficiently fast to be present when the low-back structures had to cope with the large torques released from the sudden trunk loading.
Mechanical loading of the low back during lifting is a common cause of low back pain. In this study two-handed lifting is compared to one-handed lifting (with and without supporting the upper body with the free hand) while lifting over an obstacle. A 3-D linked segment model was combined with an EMG-assisted trunk muscle model to quantify kinematics and joint loads at the L5S1 joint. Peak total net moments (i.e., the net moment effect of all muscles and soft tissue spanning the joint) were found to be 10+/-3% lower in unsupported one-handed lifting compared to two-handed lifting, and 30+/-8% lower in supported compared to unsupported one-handed lifting. L5S1 joint forces also showed reductions, but not of the same magnitude (18+/-8% and 15+/-10%, respectively, for compression forces, and 15+/-17% and 11+/-14% respectively, for shear forces). Those reductions of low back load were mainly caused by a reduction of trunk and load moment arms relative to the L5S1 joint during peak loading, and, in the case of hand support, by a support force of about 250 N. Stretching one leg backward did not further reduce low back load estimates. Furthermore, one-handed lifting caused an 6+/-8 degrees increase in lateral flexion, a 9+/-5 degrees increase in twist and a 6+/-6 degrees decrease in flexion. Support with the free hand caused a small further increase in lumbar twisting. It is concluded that one-handed lifting, especially with hand support, reduces L5S1 loading but increases asymmetry in movements and moments about the lumbar spine.
The objectives of this study were to obtain linearized stiffness matrices, and assess the linearity and hysteresis of the motion segments of the human lumbar spine under physiological conditions of axial preload and fluid environment. Also, the stiffness matrices were expressed in the form of an 'equivalent' structure that would give insights into the structural behavior of the spine. Mechanical properties of human cadaveric lumbar L2-3 and L4-5 spinal motion segments were measured in six degrees of freedom by recording forces when each of six principal displacements was applied. Each specimen was tested with axial compressive preloads of 0, 250 and 500 N. The displacements were four slow cycles of +/-0.5mm in anterior-posterior and lateral displacements, +/-0.35 mm axial displacement, +/-1.5 degrees lateral rotation and +/-1 degrees flexion-extension and torsional rotations. There were significant increases with magnitude of preload in the stiffness, hysteresis area (but not loss coefficient) and the linearity of the load-displacement relationship. The mean values of the diagonal and primary off-diagonal stiffness terms for intact motion segments increased significantly relative to values with no preload by an average factor of 1.71 and 2.11 with 250 and 500 N preload, respectively (all eight tests p<0.01). Half of the stiffness terms were greater at L4-5 than L2-3 at higher preloads. The linearized stiffness matrices at each preload magnitude were expressed as an equivalent structure consisting of a truss and a beam with a rigid posterior offset, whose geometrical properties varied with preload. These stiffness properties can be used in structural analyses of the lumbar spine.
This was a repeated measures study examining 11 asymptomatic subjects while performing dynamic lifting using various postures, loads, and breath control methods.
To examine the effects of breath control on magnitude and timing of intra-abdominal pressure during dynamic lifting.
Intra-abdominal pressure has been shown to increase consistently during static and dynamic lifting tasks. The relationship between breath control and intra-abdominal pressure during lifting is not clear.
Eleven healthy subjects were tested using lifting trials consisting of two levels of posture and load and four levels of breath control (natural breathing, inhalation-hold, exhalation-hold, inhalation-exhalation). Intra-abdominal pressure was measured using a microtip pressure transducer placed within the stomach through the nose. Timing of intra-abdominal pressure was determined relative to lift-off of the weights. Repeated measures analysis of variance was used to determine the effect of breath control, posture, and load on intra-abdominal pressure magnitude and timing.
There was a significant effect of breath control (P < 0.018) and load (P < 0.002), but not of posture (P < 0.434), on intra-abdominal pressure magnitude. The inhalation-hold form of breath control produced significantly greater peak intra-abdominal pressure than all other forms of breath control (P < 0.000 for all comparisons). No other comparisons among levels of breath were significantly different. No significant main effects of breath control were found relative to intra-abdominal pressure timing.
Breath control is a significant factor in the generation of intra-abdominal pressure magnitude during lifting tasks. The effects of respiration should be controlled in studies analyzing intra-abdominal pressure during lifting.
Ten participants were exposed to heavy sudden trunk loads as they might occur during patient handling.
The aim was to observe if well-trained men and women use their full rate of intra-abdominal pressure (IAP) development when exposed to heavy sudden trunk loads. Further, to elucidate to what degree the rectus abdominus muscle is activated when the IAP is developed.
Well-trained judo fighters are used to heavy sudden trunk loads and can produce a high IAP. It is unknown whether they use their full potential. IAP can increase the spinal stability and has been suggested to unload the spine. The unloading effect will, however, disappear if the development of the IAP demands substantial activity in the vertical fibers of the abdominal muscles.
Five male and five female well-trained judo and jujitsu fighters were exposed to heavy sudden trunk loadings through imitated patient handling situations where the patient fell and the fighters should hold the patient and prevent the fall. IAP was measured with a catheter in the stomach. Along with the IAP measurement, EMG was measured on the abdominal muscles, and the load on the low back was quantified by a three-dimensional dynamic biomechanical calculation of the torques at the L4-L5 joint.
The well-trained judo fighters did not use their full potential of the IAP development when exposed to the heavy sudden trunk loads, but the women had to use a higher level of their IAP and extension torque capacity to comply with the heavy loads. The rectus abdominus muscle does not contribute to the IAP development when the trunk is exposed to a sudden heavy load.
Estimates of spinal forces are quite sensitive to model assumptions, especially regarding antagonistic co-contraction. Optimization based models predict co-contraction to be absent, while electromyography (EMG) based models take co-contraction into account, but usually assume equal activation of deep and superficial parts of a muscle. The aim of the present study was to compare EMG based and optimization based estimates of spinal forces in a wide range of work tasks. Data obtained from ten subjects performing a total of 28 tasks were analysed with an EMG driven model and three optimization models, which were specifically designed to test the effects of the above assumptions. Estimates of peak spinal forces obtained using the different modelling approaches were similar for total muscle force and its compression component (on average EMG based predictions were 5% higher) and were closely related (R > 0.92), while differences in predictions of the peak shear component of muscle force were more substantial (with up to 39% lower estimates in optimization based models, R > 0.79). The results show that neither neglecting antagonistic co-contraction, nor assuming equal activation of deep and superficial muscles, has a major effect on estimates of spinal forces. The disparity between shear force predictions was due to an overestimation of activity of the lateral part of the internal oblique muscle by the optimization models, which is explained by the cost function preferentially recruiting larger muscles. This suggests that a penalty for active muscle mass should be included in the cost function used for predicting trunk muscle recruitment.
Activity of the abdominal muscles during symmetric lifting has been a consistent finding in many studies. It has been hypothesized that this antagonistic coactivation increases trunk stiffness to provide stability to the spine. To test this, we investigated whether abdominal activity in lifting is increased in response to destabilizing conditions. Ten healthy male subjects lifted 35 l containers containing 15 l of water (unstable condition), or ice (stable condition). 3D-kinematics, ground reaction forces, and EMG of selected trunk muscles were recorded. Euler angles of the thorax relative to the pelvis were determined. Inverse dynamics was used to calculate moments about L5S1. Averaged normalized abdominal EMG activity was calculated to express coactivation and an EMG-driven trunk muscle model was used to estimate the flexor moment produced by these muscles and to estimate the L5S1 compression force. Abdominal coactivation was significantly higher when lifting the unstable load. This coincided with significant increases in estimated moments produced by the antagonist muscles and in estimated compression forces on the L5S1 disc, except at the instant of the peak moment about L5S1. The lifting style was not affected by load instability as evidenced by the absence of effects on moments about L5S1 and angles of the thorax relative to the pelvis. The data support the interpretation of abdominal cocontraction during lifting as subserving spinal stability. An alternative function of the increased trunk stiffness due to cocontraction might be to achieve more precise control over the trajectory of lifted weight in order to avoid sloshing of the water mass in the box and the consequent perturbations.
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High-pass filtering to remove electrocardiographic interference from torso EMG recordings E838 Spine @BULLET Volume 31 @BULLET Number 22 @BULLET 2006 36 Mechanically corrected EMG for the continuous estimation of erector spinae muscle loading during repetitive lifting
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