Evaluation of factors influencing the maintenance of static nonseated work postures: Assessment of age, gender, strength, and flexibility.

Abstract

This investigation of 60 subjects (age range 20--79 years) evaluated the effects of demographic (age and gender), physical (strength, range-of-motion, balance, and body mass) and task (postural angle of deviation from neutral) factors for maintaining 14 non-seated static work postures to the point of distracting discomfort---defined as the endurance time when subjects would take a brief break or momentary pause by changing position before continuing with their work task. The best predictor of endurance time was postural angle of deviation from neutral. None of the demographic or physical variables evaluated was a consistent predictor of endurance time. Quantitative rankings of body part discomfort were evaluated at trial termination (i.e. the threshold of distracting discomfort) using a visual analogue scale (VAS). Discomfort measures included both magnitude and summation of total body parts with reported discomfort. The overall average for the discomfort rating at the time of trial termination was 4.2 on a 10 cm VAS with a standard deviation of 2.6. The discomfort measures were significantly predictive of trial termination for test postures that were not near range-of-motion limits for torso flexion and shoulder flexion/abduction. The validity of subjective ratings of photographs as a postural stress assessment tool in both a laboratory and a field setting was evaluated. Rater (age and gender) and photograph model characteristics (age, gender, and work setting) were assessed to determine their effects on subjective postural stress ratings. Overall, raters assigned significantly higher estimates of postural stress as the angle of deviation from neutral increased. Photograph model age, gender, and work setting characteristics had varying effects on predictions. Laboratory raters consistently maintained test postures for longer periods of time than they predicted when looking at the photographs. Overall, strength was a more important predictive factor of postural endurance than balance for the postures assessed in this investigation. The active older subjects who volunteered for this study maintained high levels of strength and flexibility which enabled them to perform at a similar level as younger, less-active subjects. This finding suggests that physical activity training can be utilized to improve postural endurance.