Kristina Schüldt

Effects of changes in sitting work posture on static neck and shoulder muscle activity

Abstract In order to analyse the effect of changing the sitting posture on the level of neck and shoulder muscular activity, an electromyographic (EMG) study of ten healthy experienced female workers from an electronics plant was undertaken. A standardized, simulated task was performed in eight different sitting work postures. Using surface electrodes, the level of muscular activity was recorded as normalized, full-wave rectified low-pass filtered EMG. The results showed that the whole spine flexed sitting posture gave higher levels of static activity in several neck and shoulder muscles than the posture with a straight and vertical spine, which in turn gave higher levels than the posture with slightly backward-inclined thoraco-lumbar spine.

Load moments and myoelectric activity when the cervical spine is held in full flexion and extension

Abstract Sustained joint load in extreme positions (namely maximally flexed or extended positions) has been described as causing pain. The aim of the present study is to analyse eight different sitting work postures with respect to extreme positions, and to assess the mechanical load and the levels of muscular activity arising in defined extreme positions of the cervical spine. Ten healthy female workers from an electronics plant took part in laboratory experiments. For seven of these, levels of neck and shoulder muscular activity in sitting postures with the cervical spine in different manually-adjusted extreme positions were recorded using surface electrodes. Loading moments of force about the bilateral motion axis of the atlanto-occipital joint (Occ-C1) and the spinal cervico-thoractc motion segments (C7-T1) were calculated. Extreme or almost extreme positions occurred in sitting postures with the thoracolumbar back inclined slightly backwards or with the whole spine flexed. Electromyographic (EMG) act...

Influence of sitting postures on neck and shoulder e.m.g. during arm-hand work movements

The aim of the study was to analyze the effect of different sitting postures on the level of activity in some neck and shoulder muscles in a standardized work cycle involving movement of the arm/hand. Ten experienced female workers volunteered in a laboratory study. Full-wave rectified, low-pass filtered, time-averaged and normalized e.m.g. was used. Surface electrodes were applied unilaterally at six locations. The course of the level of muscle activity during the standardized work cycle is presented. There was a tendency to higher level of activity when the arm/hand was moving along the high part of the work object compared to along the low part. The level of activity during the standardized work movement with the arm/hand was significantly influenced by the sitting postures chosen. The highest activity levels were found in the posture with the whole spine flexed. A marked reduction of the level of activity was obtained when a posture with the thoraco-lumbar spine slightly inclined backward was used.

Maximum neck extension strength and relative neck muscular load in different cervical spine positions.

The aim of this project was to study how the isometrical neck extensor strength varies at different joint angles in the sagittal plane in order to calculate what fractions of the maximum strength are used in sitting postures to counteract the load moment induced by the weight of the head and neck segments. Ten female subjects sat with the torso fixed in a special device. The resistive force during maximum neck extension was recorded with a strain gauge in four different positions of the lower cervical spine; extended, vertical, slightly flexed and much flexed. For each of these four positions the upper cervical spine was kept in three positions-flexed, neutral and extended. Moments of force about the bilateral motion axes of the atlanto-occipital (Occ-C1) joint and the C7-T1 motion segment were calculated. Moment arms were measured from video images. The maximum muscular moment for Occ-C1 did not vary systematically, either with different positions of the lower or upper cervical spine. The mean neck extensor strength for C7-T, was lowest in the extended lower cervical spine position. In the vertical, slightly flexed or much flexed position little or no variation in strength was seen. However, the fraction of the strength (% MUR) utilized to counteract the load moment induced by the weight of the head and neck in the different postures showed higher utilization ratios when the head-and-neck was flexed (about 10 and 17% MUR, respectively) than when it was kept in a vertical position (about 2% MUR). The results strongly indicate that the flexed cervical spine position produces higher muscular load than vertical, even when taking muscular strength into account, and should thus be avoided during prolonged sitting.

E.m.g./moment relationships in neck muscles during isometric cervical spine extension.

The aim of the study was to describe the e.m.gJmuscular moment (torque) relationships for neck and shoulder muscles during cervical spine extension. Ten healthy women participated. Their average age was 25·6 years. The neck extension muscular moments exerted were measured isometrically in neutral and in flexed lower-cervical spine positions with a strain gauge connected to a sling around the back of the head. The moment about the bilateral axis of the C7 T1 spinal motion segment was calculated as the moment balancing the sum of the moment of the sling resistance force and the moment caused by the gravity forces of the head and neck. Video images were analysed for moment arm length measurements. Simultaneously with the force recording, the e.m.g. activity was recorded through surface electrodes applied unilaterally at six locations in the neck and shoulder region. The rectified low-pass filtered e.m.g. signals were normalized against the highest activity level obtained during a series of standardized isometric test contractions. The results show that a non-linear e.m.g./moment relationship exists in axial musculature of the cervical spine, with a slightly higher increase in e.m.g. levels at high muscular moment values.

Effects on work resumption of a co-operation project in vocational rehabilitation. : Systematic, multi-professional, client-centred and solution-oriented co-operation.

Purpose. The present aim was to evaluate the effect of systematic multi-professional co-ordinated rehabilitation (the Stockholm Co-operation Project) on the number of days’ sick leave during the first and second half-years after the rehabilitation co-ordination period, compared to the year before. Another aim was to evaluate the economic effects at national level. Method. A matched-pairs design was used. The study group was based on 64 rehabilitees employed by a public employer in Stockholm, who took part in a systematic multi-professional co-operation project. To obtain pairs, the 64 individuals were individually matched with 64 people who received conventionally organised rehabilitation. Thus, there were 128 subjects altogether. Results. The study group had substantially less sick leave days per month than the comparison group during the second half-year after the rehabilitation co-ordination period. The effect was even greater in a subgroup with more previous sick leave. During the first half-year after the intervention the comparison group had relatively more sick leave. No effect was found for a subgroup with less previous sick leave. The economic benefit of the intervention was estimated to €1,278 per month and person based on the whole group, and to €2,405 per month and person based on those with more sick leave. Conclusions. People who undergo co-ordinated rehabilitation have more working days after the intervention period than those with conventional rehabilitation. This way for rehabilitation actors to co-operate gives better outcomes for rehabilitation cases with long previous sick leave, but not for cases with less previous sick leave. It also generates economic gains at several levels.

Assessment of Jet Pilots' Upper Trapezius Load Calibrated to Maximal Voluntary Contraction and a Standardized Load

Electromyographic (EMG) recording of the myoelectrical activity level in the trapezius muscle is often used as one method of assessing neck and shoulder muscle workload. To analyse how the normalization value influences interpretation of upper trapezius load during a work task, two different reference values for normalization were applied - one obtained during a maximum voluntary contraction (MVE) and the other during a standardized muscular load (RVE). Nine jet pilots (ages 30-48 yr) flew two sorties in a 37 Viggen aircraft using either of two types of head garment while 3-D acceleration and muscular activity were recorded. In each sortie twice in the programme a steep left turn at 5-6 +G(Z) was performed. The highest activity level (MVE) obtained during shoulder elevation combined with an isometric heavy resistance (maximum) against arm flexion/abduction was used as one normalization value. Before, between, and after the two flights, 15 s EMG recordings (RVE) during a dumbbell test in the same arm position were also taken. The muscular activity in the upper trapezius during a given task varied a great deal between individuals, but the reliability of the amplitude levels on different occasions during a work day was good, given the same electrode location and application. If muscular activity during a standardized loading force (e.g. dumbbell test) is used to normalize the recordings for workload assessments related to utilized muscular capacity, a subject with high muscular strength and comparatively low workload might in some situations be assessed as having the same workload as, or a higher load than a subject with less strength and a comparatively high workload. While normalization using a standardized force can be used to assess changes in workload, for assessing workload related to the individuals capacity recording the myoelectrical activity during maximal contraction is preferable.

Cervical spine position versus e.m.g. activity in neck muscles during maximum isometric neck extension

The aim of the study was to describe the relationships between cervical spine positions and neck muscle activity during maximum isometric neck extension. Ten healthy women participated (mean age 25·6 years). Maximum isometric neck extensions were performed in 12 different neck positions with resistance applied againstthe back of the head. Surface e.m.g. was recorded from posterior neck muscles at six locations. The e.m.g. signals were rectified, low-pass filtered and normalized. The position of the upper cervical spine did not influence the e.m.g. levels, whereas the lower cervical spine positions did. The e.m.g. levels, in the cervical erector spinae/trapezius were higher in the slightly flexed lower cervical spine position than in the neutral (despite an approximately similar magnitude of muscular moment developed), when the upper cervical spine was in the neutral position. However, when the lower cervical spine was much flexed the e.m.g. level was about the same as that of the neutral lower cervical spine position (with upper cervical spine neutral). The e.m.g. levels of the splenius and the thoracic erector spinae/rhomboids varied in a similar way, but less pronouncedly. These findings are of interest for the method of normalization of e.m.g,. e.g. in studies of work postures and/or movements.

Work technique training for patients with chronic pain in neck, shoulder and arm. A questionnaire pilot study after a comprehensive exercise-oriented rehabilitation program

Syftet med denna studie var att följa upp hur patienter såg på sin arbetsmiljö och arbetsteknik samt hur föreslagna arbetsplatsanpassningar hade genomförts efter deltagande i ett multimodalt intensivträningsinriktat rehabiliteringsprogram. Programmet inkluderade en väsentlig del av individuell ergonomisk analys, individuell ergonomisk rådgivning och specifik arbeetsteknikträning på arbetsterapiavdelningen. Patienterna hade kronisk muskuloskelettal smärta i armen. Efter rehabiliteringsprogrammet skickades ett frågeformulär till 181 patienter, varav 135 patienter (109 kvinnor och 26 män) (75%) svarade. Mer än halften av patienterna rapporterade att de oftere än en gång i veckan tänkte tillbaka på den individuella ergonomiska rådgivningen som gavs i samband med att videofilmen tagen på deras arbetsplats presenterades. Deras skattningar visade på en hög medvetandegrad när det gällde att la mikropauser under arbetet (dvs atl räta upp ryggen kombinerat med muskelavslappning), att arbeta med armarna nära kroppen och att lyfta bördor nära kroppen. Hälften av patienterna hade använt sig av möjligheten att ändra arbetsställning mer än en gång per timme. Resultatet indikerar att patienterna var medvetna om sin arbetsteknik efter deltagandet i rehabiliteringsprogrammet.

Occupational Therapy Work Training Programs For Brain-Damaged Individuals

Work is mans chief occupation (Yerxa and Baum, 1986; Jacobs, 1990). Adults devote the majority of their time to work (Kemp and Kleinplatz, 1985; Bing, 1989). Individuals in a modern society such as Sweden have the right to a meaningful and productive life (The Association, 1980; Viktorin, 1988; Krafft, Rigner, and Wilhelmson, 1988). Work is an important, necessary activity that is assumed to fulfill and satisfy fundamental human needs (Reed, 1983; Karlsson, 1986; Jacobs, 1990). The concept of work cannot be reduced to a single, simple definition (Karlsson, 1986; Kielhofner, 1985; Bing, 1989; Kemp and Kleinplatz, 1983; Holmes, 1985). In existing definitions, two extremes can be discerned. In one, work is activity that gives the performer some form of reward (Karlsson, 1986). In the other, work is all forms of productive occupation, rewarded or not (Kielhofner, 1985). Productive occupation means the production of goods or services needed by others or that afford the individual and society new abilities, ideas, knowledge, and experience. Work gives the individual life roles. Work thus consists of activities that are of value for the individual, for others, and for society. Work is considered by many a precondition of physical, mehtal, and social health. Illness or injury that alters an individuals work ability has serious consequences (Kemp and Kleinplatz, 1985; Holmes, 1985) for that individuals work role, habits, and tolerance (Yerxa and Baum, 1986). Traditionally, occupational therapists work as team members in rehabilitation (Marshall, 1985; Smith and Bohmfalk, 1985/86), with the goal that the individual will retain or return to work. The occupational therapists role is to guide and support individuals in their endeavors to regain the necessary skills, control, and work endurance (Le Vesconte, 1970). The therapist needs to know how the individual handles tools and materials, the demands work tasks make on the individual, and how functional impairment affects work habits and work skill. The therapist