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Biomedical subjects

U P Arborelius

Publications and source records attributed to U P Arborelius.

At least 19 recordsLinked to original sources
PubMed1999

Effects of arm suspension in simulated assembly line work: muscular activity and posture angles.

The electromyogram and posture angles of the shoulder and arm were recorded during sitting manipulative work in three positions, with and without the forearm suspended by a balancer. A Selspot system was used to record movements. The results from 12 female subjects (mean age 29 yr) showed that the activity in deltoideus anterior decreased significantly by using a balancer. Lower mean values were also noted for deltoideus lateralis and the trapezius muscles. The neck inclination increased with higher work area position, but was independent of the use of a balancer.

Adult↗
PubMed1997

Effects of arm support on shoulder and arm muscle activity during sedentary work.

The aim of this study was to evaluate different arm supports by comparing the activity of shoulder and arm muscles during various work tasks, with and without the lower arm supported. Twelve female subjects, aged between 23 and 37 years, were asked to perform three types of tasks: typing, simulated assembly work (in two different positions), and pipetting. The supports used were: fixed arm support (FIX), horizontal movable arm support (HOR), and spring-loaded arm support (SLA). During the experiments, the electromyograms (EMG) of four muscles were simultaneously recorded: m. deltoideus anterior and lateralis, m. trapezius pars descendens and m. extensor carpi radialis brevis. Normalization was made against maximum isometric contraction. The mean values of the normalized EMG levels showed a reduced EMG level of the shoulder muscles when using arm supports in all the tasks, and for all muscles but the wrist extensor, compared to the EMG levels without arm supports. The horizontal movable support was more effective in reducing the EMG levels of the shoulder muscles than other arm supports, in tasks at table height. Thus, it is possible to reduce muscle activity of the shoulder region by using arm supports. Further research is needed to make biomechanical calculations to compare the EMG level of these muscles using suspension and the effects of inclination of work task.

Adult↗
PubMed1996

High- and low-bar squatting techniques during weight-training.

Eight Swedish national class weightlifters performed "high-bar" squats and six national class powerlifters performed "low-bar" squats, with a barbell weight of 65% of their 1 RM, and to parallel- and a deep-squatting depth. Ground reaction forces were measured with a Kistler piezo-electric force platform and motion was analyzed from a video record of the squats. A computer program based on free-body mechanics was designed to calculate moments of force about the hip and knee joints. EMG from vastus lateralis, rectus femoris, and biceps femoris was recorded and normalized. The peak moments of force were flexing both for the hip and the knee. The mean peak moments of force at the hip were for the weightlifters 230 Nm (deep) and 216 Nm (parallel), and for the powerlifters 324 Nm (deep), and 309 Nm (parallel). At the knee the mean peak moments for the weightlifters were 191 Nm (deep) and 131 Nm (parallel), and for the powerlifters 139 Nm (deep) and 92 Nm (parallel). The weightlifters had the load more equally distributed between hip and knee, whereas the powerlifters put relatively more load on the hip joint. The thigh muscular activity was slightly higher for the powerlifters.

Adolescent↗
PubMed1994

Power and work produced in different leg muscle groups when rising from a chair.

The aim of this study was to determine the power output and work done by different muscle groups at the hip and knee joints during a rising movement, to be able to tell the degree of activation of the muscle groups and the relationship between concentric and eccentric work. Nine healthy male subjects rose from a chair with the seat at knee level. The moments of force about the hip and knee joints were calculated semidynamically. The power output (P) and work in the different muscle groups surrounding the joints was calculated as moment of force times joint angular velocity. Work was calculated as: work = integral of P dt. The mean peak concentric power output was for the hip extensors 49.9 W, hip flexors 7.9 W and knee extensor 89.5 W. This power output corresponded to a net concentric work of 20.7 J, 1.0 J and 55.6 J, respectively. There was no concentric power output from the knee flexor muscles. Energy absorption through eccentric muscle action was produced by the hip extensors and hip flexors with a mean peak power output of 4.8 W and 7.4 W, respectively. It was concluded that during rising, the hip and knee muscles mainly worked concentrically and that the greatest power output and work were produced during concentric contraction of the knee and hip extensor muscles. There was however also a demand for eccentric work by the hip extensors as well as both concentric and eccentric work by the hip flexors. The knee flexor muscles were unloaded.

Adult↗
PubMed1993

The effects of a pneumatic stool and a one-legged stool on lower limb joint load and muscular activity during sitting and rising.

Nine healthy male subjects rose from four different stools. The 'ordinary' stool (K) was set at normal chair height, approximately 50 cm, and the 'low ordinary' stool (O), the one-legged stool (T), and the pneumatically-sprung stool (S) were all approximately 32 cm high. The moments of force in the hip, knee, and ankle joints were calculated with a semidynamic technique using a Kistler force plate and video. EMG in four leg muscles was recorded. The part of bodyweight carried by the different stools when the subjects were sitting was measured, and the subjects estimated the effort of rising, using the Borg scale. The low ordinary stool gave higher knee and hip moments than the ordinary stool. Use of the pneumatic stool reduced the knee and hip moments to a level comparable with that of the ordinary stool. The reduction in moment compared with the one-legged stool (T) and the low ordinary stool (O) was significant, both in the knee (p < 0.005) and the hip (p < 0.001). Rising from the three low stools gave no significant differences in mean maximum muscle activity in any of the muscles investigated. The subjects estimated that the pneumatic stool and the ordinary stool were the easiest to rise from. The part of bodyweight carried by the ordinary stool and the low ordinary stool, both around 80% when sitting, was significantly higher than for the two other stools (p < 0.005). It was concluded that a pneumatic stool can be a useful device to workers who work in low positions and rise frequently.

Adult↗
PubMed1993

Rising from a chair by a spring-loaded flap seat: a biomechanical analysis.

UNLABELLED: Nine healthy male subjects and 8 patients with unilateral knee osteoarthrosis were studied while rising from a chair with and without the aid of a spring-loaded flap seat. The seat force started at 216 N and decreased with increasing seat angle. Ground reaction forces and motion were recorded using a force plate and video. EMG of the left vastus lateralis muscle was recorded. The effort when rising was estimated by the Borg scale. The use of the flap seat reduced the mean peak knee moment for the healthy subjects from 73 to 41 Nm and for the patients from 55 to 33 Nm. The decreases were significant at a p < 0.001 level. The patients also reduced their hip moment significantly from 50 to 35 Nm (p < 0.005). The muscle activity in the vastus lateralis was also significantly lower when the flap seat was used (p < 0.005). When the theoretically maximal friction force between seat and subject was added, the effective seat force decreased more slowly, and the relation between its horizontal and vertical force components was more advantageous. The patients estimated greater effort reduction than the healthy subjects comparing the ordinary chair and the flap seat. CONCLUSION: a spring-loaded flap seat can reduce knee and hip load and can thus be useful for people with knee osteoarthrosis.

Aged↗
PubMed1992

The effects of armrests and high seat heights on lower-limb joint load and muscular activity during sitting and rising.

The loading moment of force on the hip, knee, and ankle joints of nine healthy men rising from four different types of stools were compared, together with the levels of myoelectrical activity (EMG) in four leg muscles. Two types of stool (stand stools) had higher seats than a normal chair. The other two were of ordinary seat height, but one also had armrests. The bodyweight carried by the different stools when sitting was also measured, and the subject estimated the effort required for each trial. The mean maximum knee moment was over 60% lower when rising from the high stool than from 'ordinary' seat height. The difference between the high and low stand stool was also significant (p less than 0.001). Using the high stool or help of the arms reduced the mean maximum hip moment by about 50%. The mean maximum ankle moment was only marginally influenced by the different stools. Knee moment was influenced more by seat height than was hip moment. Vastus lateralis activity was significantly higher when subjects rose from 'ordinary' height than when rising from either stand stool (p less than 0.001). The rectus femoris muscle was little activated and the semitendinosus muscle was activated earlier when rising from higher seat heights. All subjects estimated the effort of rising from the higher stand stool to be lower than from the lower stand stool or from 'ordinary' height without arm rests. It was concluded that stand stools are good alternatives for workers who change frequently between sitting and standing work.

Adult↗
PubMed1991

Inertial effects from single body segments in dynamic analysis of lifting.

Biomechanical calculations of loads on the locomotor system in lifting tasks are often based on static models. Several investigators have shown, though, that in a dynamic act like lifting, inertial effects are not generally negligible. A complete dynamic analysis includes the calculation of linear and angular accelerations of body segments and is rather complicated to carry out. So it was of interest to find out whether the contribution of single body segments to the dynamic effects of the whole body might be negligible. Ten male subjects lifted a 12.8 kg box using two different techniques and two speeds. Ground reactions and body segment movements were recorded and reaction forces and net moments at different joints were calculated with static, dynamic and 'semidynamic' methods. The latter method incorporated the ground reaction forces as measured from a force plate but was otherwise equal to the static method. The results from semidynamic analyses agreed well with those from complete dynamic analyses for the ankle, knee, hip, and L5/S1 joints. For example, the semidynamically calculated peak moments at L5/S1 differed on average less than 3% from the dynamically calculated values. The contributions of the lower extremities and the pelvis to the dynamic effects of the whole body seemed to be quite small. The less complicated semidynamic method offers a good alternative to a fully dynamic analysis for estimations of peak moments in the lower back, at least for the studied lifting techniques.

Adult↗
PubMed1987

Relative mechanical load on shoulder and elbow muscles in standing position when handling materials manually. A study of packing work.

When a patient with a musculoskeletal disorder returns to work after rehabilitation, the work-station should be designed so that the impaired muscle groups are less exposed to load. The work posture desirable for a particular muscle group might impose higher load on another muscle group. Since the shoulder muscles usually are stronger than the elbow muscles, a direct comparison of the loads is difficult. To make comparisons possible, the load moment about the investigated joints were divided by the counteracting maximum muscular moments, and a Muscular strength Utilization Ratio (MUR) was obtained. Using this principle, the muscular load on the shoulder and elbow was investigated in 72 different packing work postures. Different combinations of box size, box angle, edge height and weight of object handled were studied. There was a higher relative load on the shoulder than on the elbow. The concept of relating joint load to strength may serve as a guideline for how high a patient's strength should be before returning to work to avoid further injuries.

Adult↗
PubMed1987

Effects of arm support or suspension on neck and shoulder muscle activity during sedentary work.

The aim of this study was to evaluate the effects on the levels on neck and shoulder muscular activity of ergonomic aids used to support or suspend the arm in different sitting postures, both with and without movement of the arm-hand. Ten skilled women workers performed a standardized simulated work cycle similar to assembling printed circuit boards, in different sitting postures with and without ergonomic aids. The elbow was supported by a loosely-mounted, padded plate. For suspension, a new device, the K-block, was used giving an adjustable, constant suspending force. Full-wave rectified, low-pass filtered, time-averaged and normalized EMG was used. Surface electrodes were applied over six neck and shoulder muscles. The results show that a reduction in the level of activity in neck and shoulder muscles can be obtained with either aid. The reduction, whether caused by suspension or support of the arm, was related to the sitting posture. Elbow support might be more efficient than arm suspension in a sitting posture with the whole spine flexed, while arm suspension might be more efficient when the trunk is inclined slightly backward. Elbow support and, particularly, arm suspension may thus be recommended as technical aids in sedentary assembly work for patients with easily elicited cervical spine and/or shoulder pain. It is also suggested that arm suspension may be used to improve ergonomic conditions at workplaces.

Adult↗
PubMed1986

Power output and work in different muscle groups during ergometer cycling.

The aim of this study was to calculate the magnitude of the instantaneous muscular power output at the hip, knee and ankle joints during ergometer cycling. Six healthy subjects pedalled a weight-braked bicycle ergometer at 120 watts (W) and 60 revolutions per minute (rpm). The subjects were filmed with a cine camera, and pedal reaction forces were recorded from a force transducer mounted in the pedal. The muscular work at the hip, knee and ankle joint was calculated using a model based upon dynamic mechanics described elsewhere. The mean peak concentric power output was, for the hip extensors, 74.4 W, hip flexors, 18.0 W, knee extensors, 110.1 W, knee flexors, 30.0 W and ankle plantar flexors, 59.4 W. At the ankle joint, energy absorption through eccentric plantar flexor action was observed, with a mean peak power of 11.4 W and negative work of 3.4 J for each limb and complete pedal revolution. The energy production relationships between the different major muscle groups were computed and the contributions to the total positive work were: hip extensors, 27%; hip flexors, 4%; knee extensors, 39%; knee flexors, 10%; and ankle plantar flexors 20%.

Adult↗
PubMed1986

Shoulder joint load and muscular activity during lifting.

The aim of this study was to investigate load on shoulder joint and muscles in healthy adults during four different ways of lifting a moderate burden (12.8 kg) from floor to table level. The methods used were surface electrode EMG with linear envelope, and calculation of loading moments of force using a static biomechanical model. The shoulder load at the beginning of the lift was lowest for the straight knee lift. The peak load occurred in the late phase of all lifts. On completion of the lift, load and activation were considerably lower when the subject was allowed to step forward before putting the box down. The most activated shoulder muscles were the anterior and lateral parts of the deltoid, and the serratus anterior. Around 80% of the shoulder load moment was caused by the weight of the burden. Some 75% of maximum shoulder strength was required for lifting the burden.

Adult↗
PubMed1985

Muscular activity during ergometer cycling.

The aim of the study was to quantify the activity as recorded by electromyography during ergometer cycling in eleven different muscles of the lower extremity. Eleven healthy subjects rode in twelve different ways at different work-load, pedalling rate, saddle height and pedal foot position. Vastus medialis and lateralis, gastrocnemius medialis and lateralis and the soleus muscle were the most activated muscles. Changes in muscle activity during different calibrations were studied in eight of the eleven muscles. An increase in work-load significantly increased the mean maximum activity in all the eight muscles investigated. An increase of the pedalling rate increased the activity in the gluteus maximus, gluteus medius, vastus medialis, medial hamstring, gastrocnemius medialis and soleus muscles. An increase of the saddle height increased the muscle activity in the gluteus medius, medial hamstring and gastrocnemius medialis muscles. Use of a posterior pedal foot position increased the activity in the gluteus medius and rectus femoris muscles, and decreased the activity in the soleus muscle.

Adult↗