Differences in lumbar spine intradiscal pressure between standing and sitting postures: a comprehensive literature review.

Background: Musculoskeletal disorders (MSDs), especially in the lumbar spine, are a leading concern in occupational health. Work activities associated with excessive exposure are a source of risk for MSDs. The optimal design of workplaces requires changes in both sitting and standing postures. In order to secure such a design scientifically proved quantitative data are needed that would allow for the assessment of differences in spine load due to body posture and/or exerted force. Intradiscal pressure (IP) measurement in the lumbar spine is the most direct method of estimating spinal loads. Hence, this study aims at the quantitative evaluation of differences in lumbar spine load due to body posture and exerted forces, based on IP reported in publications obtained from a comprehensive review of the available literature. Methodology: In order to collect data from studies measuring IP in the lumbar spine, three databases were searched. Studies with IP for living adults, measured in various sitting and standing postures, where one of these was standing upright, were included in the analysis. For data to be comparable between studies, the IP for each position was referenced to upright standing. Where different studies presented IP for the same postures, those relative IPs (rIP) were merged. Then, an analysis of the respective outcomes was conducted to find the possible relationship of IPs dependent on a specific posture. Results: A preliminary analysis of the reviewed papers returned nine items fulfilling the inclusion and exclusion criteria. After merging relative IPs from different studies, rIP for 27 sitting and 26 standing postures was yielded. Some of the data were useful for deriving mathematical equations expressing rIP as a function of back flexion angle and exerted force in the form of a second degree polynomial equation for the standing and sitting positions. The equations showed that for the standing posture, the increase in IP with increasing back flexion angle is steeper when applying an external force than when maintaining body position only. In a sitting position with the back flexed at 20°, adding 10 kg to each hand increases the IP by about 50%. According to the equations developed, for back flexion angles less than 20°, the IP is greater in sitting than in standing. When the angle is greater than 20°, the IP in the sitting position is less than in the standing position at the same angle of back flexion. Conclusions: Analysis of the data from the reviewed papers showed that: sitting without support increases IP by about 30% in relation to upright standing; a polynomial of the second degree defines changes in IP as a function of back flexion for for both postures. There are differences in the pattern of changes in IP with a back flexion angle between sitting and standing postures, as back flexion in standing increases IP more than in sitting.

Effectiveness of workplace intervention strategies in lower back pain prevention: a review.

The aim of this study was to identify effective work place intervention strategies for the prevention of low back pain (LBP). The study focused on interventions to two major groups: personal interventions and technical interventions. Data basis were searched for with inclusion criteria: study design based on randomised controlled trial; outcome measures including non-specific LBP occurrence expressed by prevalence or intensity; intervention met the definition of the technical and/or personal (physical exercises, behavioural training, educational) intervention programme. Eighteen papers were selected for full analysis. The diversification of quantitative indicators of differences between control and intervention groups were carried out using Cohen's d index. The results of analysis showed strong differences in effects among intervention strategies, as well as among different cases within similar intervention strategies. LBP severity before intervention and the length of intervention were discussed as potentially influencing factors. The results of the analysis suggest that the most effective strategies for LBP prevention include technical modifications of the workstand and education based on practical training. Behavioural and physical training seems to be of lesser importance. LBP severity before intervention and the time when the measurements of outcome measures take place play an important role in the effectiveness of intervention.

Effectiveness of bimanual coordination tasks performance in improving coordination skills and cognitive functions in elderly.

BACKGROUND: The purpose of the study was to determine the impact of the performance of bimanual coordination tasks with specific characteristics on the changes in quality of coordination, musculoskeletal load of the upper limbs and cognitive functions. METHODS AND FINDINGS: A group of 26 people aged 60-67 years performed 6 sessions of bimanual coordination training. Each session included set of tasks that varied depending on the shape in which the cursor moved, the coordination mode (in-phase, anti-phase, complex) and the tracking mode (imposed or freely chosen speed). Performance was assessed by: Error, Variability and Execution. The load of upper limb muscles was expressed with the value of the normalized EMG amplitude. Cognitive functions were evaluated using the Vienna Test System. The Variability and Error values obtained during the sixth training session decreased by more than 50% of the initial values. Tasks with freely chosen speed showed changes from 15% to 34% for Error and from 45% to 50% for Variability. For tasks with imposed speed and coordination mode anti-phase or complex it was between 51% and 58% for Error and between 58% and 68% for Variability. Statistically significant differences between load during the sixth training session compared to the first session occurred in three out of four muscles and were between 9% to 39%. There were statistically significant differences in motor time and no differences in variables describing attention and working memory. CONCLUSIONS: Coordination mode is meaningful for improving coordination skills; tasks in the anti-phase and complex are recommended. Tracking mode also plays a role, tasks with an imposed cursor movement speed have greater potential to improve coordination skills than tasks with freely chosen. Improved control skills resulted in the reduction of upper limb musculoskeletal load. It can be assumed that an increase in coordination skills with the use of appropriate training can help to reduce musculoskeletal load.

Assessment of load on the lumbar spine using two computerised packages and REBA method.

PURPOSE: The aim of the research was a comparative analysis of the back lumbar load assessment using three methods: two with continuous input data and evaluation procedures based on mathematical relationships (ShiftBack, 3DSSPP) and one method with categorized input data and tabular load estimation procedures (REBA). METHODS: For the analysis, work activities and the value of applied force were selected. Among the analyzed 24 work activities were those during which there was a symmetrical load, as well as those during which the applied force or the assumed position of the body caused a lack of load symmetry. RESULTS: The results show that the REBA method differentiates 24 cases of unit load into six levels, while the other two methods provide 24 different values between cases. Cases differing in load even over 100%, when assessed according to the 3DSSPP or ShiftBack do not differ in the assessment of REBA. Differences in the assessment of the same tasks between the results obtained from 3DSSPP and ShiftBack that were above 15% concern only 7 cases. CONCLUSIONS: A comparative analysis of the assessment of the lumbar part of the back using three methods indicates strong correlations between the results of the assessment carried out using 3DSSPP and ShiftBack. Smaller relationships were demonstrated by comparing these two methods with the REBA method.

Age-related changes in the range and velocity of postural sway.

The aim of this analysis was to compare values of centre of pressure (CoP) measures, which describe the ability to maintain static body balance (range of body sway and velocity in antero-posterior and medio-lateral directions), in two age groups on the basis of a systematic review and meta-analysis of available data published worldwide. After a systematic review of publications presenting values of selected CoP measures, a numerical database with means and standard deviations was created. Data were classified by eye condition (open or closed) and by age group (18-35 or ≥56). Allocation to each group was based on the mean value of age of each sub-group in the numerical database. The Mann-Whitney U test was used to test the statistical significance of differences between age groups and eyes-open and eyes-closed conditions. This article shows mathematical equations, which quantitatively express increases in body sway and its velocity with age. On the basis of those equations, higher values have been shown for both displacement and velocity measures for the EC vs. the EO conditions and for the elderly vs. the young. The differences between age groups are greater for the velocity measures.

Influence of type of MVC test on electromyography measures of biceps brachii and triceps brachii.

OBJECTIVE: This study aimed to investigate the amplitude and frequency measures of the electromyography (EMG) signal in agonistic and antagonistic muscles (biceps brachii, triceps brachii). METHODS: Fifteen males (22.9 ± 2.1 years old) took three isometric maximum voluntary contraction (MVC) tests. Two tests were typical MVC tests for biceps brachii and triceps brachii. The third was a test often used to obtain MVC for forearm muscles (arm and forearm hanging down). The EMG signal was recorded during three isometric MVC muscle contractions and during a relaxation test. RESULTS: There were no differences in amplitude between relaxation and MVC antagonist in static contraction, with higher values for frequency measures in relaxation. When biceps brachii and triceps brachii act as antagonists in an MVC test, frequency measures present lower values than when the muscles act as agonists. Biceps brachii shows much lower amplitude than during an agonist MVC contraction with similar spectral measures. Triceps brachii presents much higher values of spectral measures than during an agonist MVC test. CONCLUSION: The type of exerted force, i.e., if a muscle acted as an agonist, antagonist or stabilizer, affects the relationship between the time and frequency domain measures.

Influence of disability type on upper-limb motor skills.

This study was carried out in order to determine the effect of physical disability (paraplegia) and sensory disability (deafness) on motor skills of the upper limbs. Studies were distinguished by two parameters: the nature of the control curve (sine or random) and the magnitude of the isometric force exerted on the lever (10 N, 20 N, 40 N, 80 N). A comparison of the quality of manual force control in a visual detection task among groups of people with sensory disability (deaf), people with physical disability (paraplegic) and people without disability showed differences among those groups. Values of force above 20 N create conditions of lower quality of control and of direction of force exertion outside the body. At the same time, the study proved that people with some types of disability can perform certain work tasks as effectively as people without disability.

The influence of confounding factors on the relationship between muscle contraction level and MF and MPF values of EMG signal: a review.

The purpose of this article is to gather results of studies on the relationship between median frequency (MF) and mean power frequency (MPF) and the level of muscle contraction, and to use those results to discuss the differences in the trends according to factors related to measurement technique and subject. Twenty-one studies with 63 cases for upper limb muscles and nine studies with 31 cases for lower limb muscles were analysed. Most results showed an increase in parameters with an increased level of muscle contraction, only some studies showed a decrease. The influence on parameters of the level of muscle contraction and factors such as subjects, type of contraction, muscle length and electrodes was analysed for each muscle. It was concluded that when analysing the influence of different factors on MF and MPF, because those factors interact they should be considered together, not separately.

Trigger matters: an ergonomy analysis of insulin pens.

BACKGROUND: Excessive force required to deliver a set dose of insulin as well as a localization of the push button and its upwards extension may result in significant difficulties to safely perform insulin injection, including bending/breakage of the injector's needle. The GensuPen2 (Copernicus/Bioton, Warsaw, Poland) pen has a unique spring-assisted delivery system and a lateral trigger device for injection of insulin to improve its ergonomics. We tested the force required to administer insulin using three pens: GensuPen2, NovoPen(®) 4 (Novo Nordisk, Bagsværd, Denmark), and HumaPen Ergo(®) (Eli Lilly, Indianapolis, IN). MATERIALS AND METHODS: Using a certified dynamometer we tested injection force at three doses of insulin: 2, 30, and 60 U, using each of the three injectors (n=10) in triplicate. Area under the curve (AUC) and maximum force used were calculated for each series of injections. RESULTS: When administering doses of 2, 30, and 60 units of insulin, the GensuPen2 (6.55±1.09, 6.52±1.92, and 6.89±1.15 N, respectively) required significantly lower maximum force than the NovoPen 4 (9.04±0.61, 12.96±1.45, and 15.42±0.99 N, respectively) and the HumaPen Ergo (17.66±1.88, 32.14±6.08, and 40.39±7.64 N, respectively) (all P<0.0001). The AUC of force used for insulin injection with GensuPen2 did not differ between doses (P=0.82). At all dose levels, GensuPen2 required significantly lower force than the other two injectors. Moreover, the mode of holding of GensuPen2 was more similar to the natural arrangement of the hand while gripping a cylindrical item in comparison with NovoPen 4 and HumaPen Ergo. CONCLUSIONS: Usage of the GensuPen2 injector with a lateral trigger location and spring-assisted delivery system reduces the force required for drug administration, especially at high doses of insulin.

Assessment of muscle load and fatigue with the usage of frequency and time-frequency analysis of the EMG signal.

The aim of the study was to determine the effect of the muscle load and fatigue on the values of the parameters calculated on the basis of the time, frequency (Fourier transform) and time-frequency (wavelet transform) analysis of the EMG signal, for low levels of load. Fifteen young men took part in the study. The EMG signal was registered from right side biceps brachii (BB) and trapezius (TR) muscles in static conditions, at load 10%, 20% and 30% MVC (maximal voluntary contraction). On the basis of the analysis there were selected parameters sensitive to force (RMS) and parameters sensitive to fatigue but simultaneously insensitive to force (MPF--mean power frequency determined on the basis of Fourier transform, CMPFdb5--mean power frequency determined on the basis of the wavelet transform). The results indicate that CMPFdb5 can show similar (muscle BB) or greater (muscle TR) sensitivity to fatigue than MPF. It can suggest that, for low levels of load, the wavelet transform parameters can be more effective in assessing muscle fatigue than the parameters based on the Fourier transform. The obtained results can allow for a more precise analysis of muscle fatigue at low levels of load. Further analysis for a greater number of muscles activated at low levels of load, with the usage of the parameters tested is desirable.

Comparative study of upper limb load assessment and occurrence of musculoskeletal disorders at repetitive task workstations.

This study explored the relationship between subjectively assessed complaints of pain in the arm, forearm and hand, and musculoskeletal load caused by repetitive tasks. Workers (n=942) were divided into 22 subgroups, according to the type of their workstations. They answered questions on perceived musculoskeletal pain of upper limbs. Basic and aggregate indices from a questionnaire on the prevalence, intensity and frequency of pain were compared with an upper limb load indicator (repetitive task index, RTI) calculated with the recently developed Upper Limb Risk Assessment (ULRA). There was relatively strong correlation of RTI and general intensity and frequency of pain in the arm, and general intensity and frequency of pain in the arm and forearm or prevalence of pain in the arm. Frequency and intensity of pain in the arm were weakly correlated. An aggregate indicator of evaluation of MSDs, which was calculated on the basis of the prevalence, intensity and frequency of pain, was to a higher degree associated with the musculoskeletal load of a task than basic evaluative parameters. Thus, such an aggregate indicator can be an alternative in comparing subjectively assessed MSDs with task-related musculoskeletal load and in establishing limit levels for that load.

Comparison of concepts in easy-to-use methods for MSD risk assessment.

This article presents a comparative analysis of easy-to-use methods for assessing musculoskeletal load and the risk for developing musculoskeletal disorders. In all such methods, assessment of load consists in defining input data, the procedure and the system of assessment. This article shows what assessment steps the methods have in common; it also shows how those methods differ in each step. In addition, the methods are grouped according to their characteristic features. The conclusion is that the concepts of assessing risk in different methods can be used to develop solutions leading to a comprehensive method appropriate for all work tasks and all parts of the body. However, studies are necessary to verify the accepted premises and to introduce some standardization that would make consolidation possible.

Heart rate variability (HRV) and muscular system activity (EMG) in cases of crash threat during simulated driving of a passenger car.

OBJECTIVES: The aim of the study was to verify whether simultaneous responses from the muscular and circulatory system occur in the driver's body under simulated conditions of a crash threat. MATERIALS AND METHODS: The study was carried out in a passenger car driving simulator. The crash was included in the driving test scenario developed in an urban setting. In the group of 22 young male subjects, two physiological signals - ECG and EMG were continuously recorded. The length of the RR interval in the ECG signal was assessed. A HRV analysis was performed in the time and frequency domains for 1-minute record segments at rest (seated position), during undisturbed driving as well as during and several minutes after the crash. For the left and right side muscles: m. trapezius (TR) and m. flexor digitorum superficialis (FDS), the EMG signal amplitude was determined. The percentage of maximal voluntary contraction (MVC) was compared during driving and during the crash. RESULTS: As for the ECG signal, it was found that in most of the drivers changes occurred in the parameter values reflecting HRV in the time domain. Significant changes were noted in the mean length of RR intervals (mRR). As for the EMG signal, the changes in the amplitude concerned the signal recorded from the FDS muscle. The changes in ECG and EMG were simultaneous in half of the cases. CONCLUSION: Such parameters as mRR (ECG signal) and FDS-L amplitude (EMG signal) were the responses to accident risk. Under simulated conditions, responses from the circulatory and musculoskeletal systems are not always simultaneous. The results indicate that a more complete driver's response to a crash in road traffic is obtained based on parallel recording of two physiological signals (ECG and EMG).

Comparison of risk assessment procedures used in OCRA and ULRA methods.

The aim of this study was to analyse the convergence of two methods by comparing exposure and the assessed risk of developing musculoskeletal disorders at 18 repetitive task workstations. The already established occupational repetitive actions (OCRA) and the recently developed upper limb risk assessment (ULRA) produce correlated results (R = 0.84, p = 0.0001). A discussion of the factors that influence the values of the OCRA index and ULRA's repetitive task indicator shows that both similarities and differences in the results produced by the two methods can arise from the concepts that underlie them. The assessment procedure and mathematical calculations that the basic parameters are subjected to are crucial to the results of risk assessment. The way the basic parameters are defined influences the assessment of exposure and risk assessment to a lesser degree. The analysis also proved that not always do great differences in load indicator values result in differences in risk zones. PRACTITIONER SUMMARY: We focused on comparing methods that, even though based on different concepts, serve the same purpose. The results proved that different methods with different assumptions can produce similar assessment of upper limb load; sharp criteria in risk assessment are not the best solution.

The influence of wrist posture on the time and frequency EMG signal measures of forearm muscles.

This study investigates how altering wrist posture influences the relationship between the time and frequency measures of the electromyography (EMG) signal of extensor digitorum communis (EDC) and flexor carpi ulnaris (FCU). Thirteen participants exerted handgrip force related to maximum voluntary contraction (MVC) in four tests: 20%MVC and 50%MVC in neutral wrist posture and 20%MVC in full wrist flexion and extension. EMG measurements from EDC and FCU were used to calculate normalized values of amplitude (nRMS) and mean and median frequency of the power spectrum (nMPF, nMF). During muscle shortening (wrist flexion for FCU and wrist extension for EDC) nRMS was approximately twofold higher than in neutral posture for FCU and fourfold for EDC. All measures obtained at 20%MVC in neutral posture were significantly different from 20%MVC in wrist flexion for FCU and 20%MVC in wrist extension for EDC (p<0.05). Differences between 50%MVC and 20%MVC at neutral posture (nRMS) were significant for both muscles, although in nMPF and nMF for EDC only. Muscle shortening changed the pattern of statistical significance when the time and frequency domain measures were compared, whereas muscle lengthening did not. It can be concluded that muscle shortening caused by altering wrist posture influences the relationship between the time and frequency measures in both muscles. This suggests that in studies using EMG in different wrist postures, changes in the relationship between the time and the frequency measures should be considered.

Influence of upper extremity position on EMG signal measures calculated in time, frequency and time-frequency domains.

The aim of this study was to investigate the relationship between time-frequency, time and frequency measures when considering various upper extremity positions below the level of the shoulder and in trapezius as well as deltoideus muscles. During the experiment, 15 subjects performed a task that involved screwing and unscrewing a screw cap on a board in six different locations, i.e., there were six upper extremity positions. Variables were calculated in the time, frequency and time-frequency domains on a recorded EMG signal. The results showed that parameters analyzed in the time-frequency domain were more sensitive to changes in position than parameters analyzed in the frequency domain.

The influence of fatigue on muscle temperature.

The aim of the study was to investigate the possibility of using infrared (IR) thermography for assessing muscle fatigue during low effort. Three tests at constant levels of load 5, 15 and 30% of maximum voluntary contraction (MVC) lasting 5 min each were performed on a group of 10 men. Temperature and electromyographic (EMG) signal were registered from biceps brachii (BB). Analysis focused on the influence of load on the values and changes in time of muscle temperature. Correlations between temperature and EMG parameters (RMS, MPF and MF) were also analysed. Constant load sustained during the tests resulted in an increase in the temperature of BB. There were statistically significant correlations between temperature and EMG parameters for most subjects. Results of the study suggest that IR thermography can be an alternative or supplementary method for assessing muscle fatigue at low levels of contraction.

The influence of age and type of force on muscle strength capabilities in women.

The aim of this study was to assess handgrip and 5 other types of force in 52 women and to determine if handgrip force reflected general upper limb force capabilities correlated with age. The women were divided into subgroups according to age: 20-25, 45-50 and 55-65 years. Maximum forces of the right upper limb were measured in 6 types of force activities. In most tests the values of force showed statistically significant differences between the 20-25 group and the groups aged 45-50 and 55-64 years. The results did not show any differences related to age or to force activities that involved the small muscles of the forearms and hands. Thus handgrip force cannot always be considered an indicator of total force capabilities.

Social partners cooperation for reduction of musculoskeletal disorders in agriculture.

The European social partners in agriculture recognize the considerable frequency of musculoskeletal disorders (MSD) in the sector which has negative consequences for workers, employers, social security systems and hence for the whole society. They made an agreement in 2005 to tackle this problem and their main interest was finding good practices 'on the floor', with the involvement of the farmers and farming industries. A partnership with researchers from 4 different organisations across Europe, was created, taking into account both academic partners and/or partners experienced with the agricultural sector. GEOPA-COPA acted as a network partner with all the EU agriculture organisations. The project partners proposed a methodology how to collect the good practices. In total, 103 company visits were organised and 55 additional reports were collected. More than 140 good practices were defined going from easy, low-cost solutions to highly technological, more expensive solutions. All this information is disseminated via the project website (www.agri-ergonomics.eu) and summarised in 6 brochures. This paper focuses on the methodology to set up the ergonomic project with social partners.

Analysis of postural load during tasks related to milking cows-a case study.

The aim of this study was to analyse postural load during tasks related to milking cows of 2 farmers on 2 different farms (one with a manual milk transport system, the other with a fully automated milk transport system) as a case study. The participants were full-time farmers, they were both healthy and experienced in their job. The Ovako Working Posture Analyzing System (OWAS) was used to evaluate postural load and postural risk. Postural load was medium for the farmer on the farm with a manual milk transport system and high for the farmer working on the farm with a fully automated milk transport system. Thus, it can be concluded that a higher level of farm mechanization not always mean that the farmer's postural load is lower, but limitation of OWAS should be considered.