Heer Vyas

Influence of arm and wrist support on forearm and back muscle activity in computer keyboard operation

The effects of forearm and wrist supports on the upper extremity postures in computer keying tasks and associated EMG activity of arm and back muscles were examined (N = 8). Four positions were forearms unsupported (floating) and supported, wrists supported by bead packed (WR1) and gel-filled (WR2) wrist rest. The right and left elbow extensions were 65 degrees and 68 degrees , respectively, in unsupported forearms. Bilateral elbow extension increased with the forearm/wrist supports and mostly, the elbow was maintained at around 90 degrees or greater. The wrist extension decreased with forearm/wrist supports over the unsupported condition. The forearm support significantly reduced the activity of forearm extensor digitorum, i.e., right (F((1, 47)) = 12.19, p < 0.01) and left (F((1, 47)) = 5.38, p < 0.05) and upper trapezius muscles over the floating posture. Wrist rests, however, increased load on the upper trapezius; the activities of flexor digitorum superficialis and erector spinae were close to the resting EMG activity for both forearm and/or wrist support. The type of wrist rests was a concern and this study indicated that the gel filled wrist rest was advantageous in reducing the forearm muscle load, in comparison to the bead packed cushions.

Risk factors and musculoskeletal disorders among women workers performing fish processing

BACKGROUND The study examined the prevalence of musculoskeletal pain and discomfort (MSD) among workers engaged in fish processing activities and identified the occupational, environmental, and psychosocial factors contributing to the MSDs. METHODS An ergonomics checklist and questionnaire on general health and psycho-social issues were administered to women workers (N = 450). The relative risk for MSDs due to demographic factors, stress symptoms, and task variables were estimated. RESULTS Nearly 71% of the women (age 23.0 ± 6.4 years) reported MSDs, chiefly in upper back (54%), lower back (33%), knee (35%), and shoulders (27%). Workers engaged in mixed task (OR 13.8; CI 8.7-22.0), ring cutting (OR 18.3; CI 11.8-24.7), having job experience <3 years (OR1.9; CI1.3-2.9), being married (OR 1.5; CI 1.1-2.2), BMI18-25 (OR 1.7; CI 1.1-2.8) had increased risk of MSDs in the upper back. The severity of pain was high among the workers with elevated co-morbidity (pain in two or more regions). One third of the workers perceived the work environment to be cause of their MSDs. Multivariate analysis using binary logistic regression model indicated that highly specialized job (OR 13.0; CI 4.7-14.2), high physical activity (OR 11.7; CI 4.6-12.7), improperly designed tools (OR 8.1; CI 3.5-9.5), poor training (OR 7.0; CI 3.3-7.5), and poor job satisfaction (OR 1.5; CI 1.1-4.8) significantly increased the risk of MSDs. Almost all the psychosocial and work stress factors were associated with lower back MSD. CONCLUSION A cold and humid environment, awkward standing work posture for long hours, high physical activities, poor task clarity, and high mental overload are important risk factors for the development of MSDs.

Occupation, participation, inclusion, work role postural control in different load handling tasks.

BACKGROUND Manual material handling has been attributed as a major risk to human musculoskeletal system. Workers postural stability in these tasks is influenced by holding method, time and weight being handled. OBJECTIVES The study attempts to investigate postural balance in five different commonly adopted load handling methods amongst female volunteers. METHODS Ten women subjects performed manual material handling tasks by lifting 9 kg load in five different ways. Lifting tasks included (1) Upfront in palms (2) on head (3) sideways (left) (4) sideways (right) and (5) in bag at back. Normalized electromyography signals (back and leg) and center of pressure displacements parameters were investigated as measures of postural control. RESULT An increase in the medio-lateral and anterio-posterior center of pressure displacements and activity of back muscles was reported when subjects lifted the weight directionally. CONCLUSION There was a significant influence of load position on center of pressure displacements and muscle activity and thereby on postural stability. KEYWORDS Balance; center of pressure; electromyography.

Influence of footwear on stabilometric dimensions and muscle activity

Background: Properties of footwear exert an influence on centre of pressure (CoP) displacement parameters, muscle activity and users postural control. Thereby, selection of footwear aid to manage postural stability and fall problems. Objective: The study applies stabilometry, force exertion and electromyography when women stood and walked by donning footwear with different characteristics and in barefoot. Method: Women volunteers aged (30.2 ± 5.6 year), and having BMI (27.6 ± 7.4) participated in the study. The footwear included in the study were of four different designs, laced shoe (2.5 cm heel), flat heeled (9 cm heel), and pointed heel (7 cm and 13 cm heel). Female subjects (N = 15) stood and walked after putting on footwear and in bare feet. Results: The weighted force (kgf) distribution derived as the square root of the sum of squares of three forces at x, y and z coordinates was minimal in laced shoes, suggesting the relative stability in comparison to bare feet and other footwear. ANOVA showed that the footwear had discernible effect on the medio-lateral CoP displacement and CoP speed during standing, and anterior posterior CoP range while walking. The leg muscle activity, both soleus and tibaials anterior, was significantly higher in pointed heel (13 cm heel) while standing, suggesting that heels exert an influence on leg muscle activity and postural control mechanism. Conclusion: Laced shoes gave relatively better postural stability to the wearer. Potential implications: This work gives a valuable insight to consideration of biomechanical parameters for footwear manufacturers and wearers.

Disparity of a seat cushion and its influence on postural control

Properties of supporting surfaces of a seat have an influence on postural control. Centre of pressure (COP) displacement parameters reflect both the balance controlling process and movements of the centre of a mass of entire body. The subjects of the study were 9 healthy men. A seat cushion was examined with a 2-force platform setup. Force exertion at a seat pan and feet and COP displacement at a seat pan were measured to analyse postural control. Analysis of variance determined the differences in postural control depending on a cushion type among the subjects. Significant differences in COP displacement parameters were in COP trajectory length, medio-lateral COP displacement and COP velocity. The results of the study showed that foam cushion ensures better postural control.

Postural control in unstable sitting

We aimed to examine the influence of sitting instability, on the stabilometric dimensions and back and leg muscle with respect to postural control of women volunteers. Experimental seats with wooden hemispheres of distinct diameters were attached to achieve increasing levels of sitting instability. A two force plate experiment setup was assembled, where in one force plate served as seat pan and other plate as feet. The experimental seat was placed on a force plate and the participating volunteers were instructed to maintain their balance while sitting on the seat with their eyes open. Coordinates of centre of pressure (CoP) displacement, force distribution and electromyographic measurements of back and leg muscles were recorded and quantified with summary statistics. With an increase in seat instability, force distributions show a shift of load from seat pan to feet. Trajectory length and speed of CoP displacement significantly increased with increase in seat instability. Statistical analysis of the electromyography measurements indicated that leg muscle activities significantly increased in the unsupported sitting conditions.