The Desk Height and Keyboard Design as Determinants of Posture and Trapezius Tension

ABSTRACT

OBJECTIVE: To test the hypothesis that changing the desk height or keyboard design with fixed neck posture will change posture of the upper extremity and the trapezius tension, and to suggest the appropriate the desk height and the keyboard design to relieve the tension of the trapezius. METHOD: Five men volunteered. Four desk heights (5 cm below, same as, 5 cm above, 10 cm above the olecranon) and three keyboard designs (flat, wrist support, natural) were set up. The posture of the upper extremity was analysed by 3 dimensional Ariel performance analysis system. The tension of trapezius was measured by surface EMG. RESULTS: The trapezius tension was low when the desk height was below the olecranon in 'flat' keyboard, and was low when the desk height was no higher than 5 cm above the olecranon in 'wrist support' and 'natural' keyboard. The trapezius tension went with the change of the shoulder flexion, abduction, elevation and the elbow flexion in 'flat' keyboard, and went with the change of the shoulder flexion and elevation in 'wrist support' and 'natural' keyboard. CONCLUSION: To lessen the tension of the trapezius, the desk height should be below the olecranon in 'flat' keyboard and no higher than 5 cm above the olecranon in 'wrist support' and 'natural' keyboard. The keyboard design should include the wrist support which relieved the tension of trapezius by giving the resting point.