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BACKGROUND: Few studies have investigated mathematical characteristics of the discomfort-time relationship during prolonged static posture holding (SPH) on an individual basis. Consequently, the discomfort-time relationship is not clearly understood at individual trial level. OBJECTIVE: The objective of this study was to examine discomfort-time sequence data obtained from a large number of maximum-duration SPH trials to understand the perceived discomfort-posture holding time relationship at the individual SPH trial level. METHOD: Thirty subjects (15 male, 15 female) participated in this study as paid volunteers. The subjects performed maximum-duration SPH trials employing 12 different wholebody static postures. The hand-held load for all the task trials was a 'generic' box weighing 2 kg. Three mathematical functions, that is, linear, logarithmic and power functions were examined as possible mathematical models for representing individual discomfort-time profiles of SPH trials. RESULTS: Three different time increase patterns (negatively accelerated, linear and positively accelerated) were observed in the discomfort-time sequences data. The power function model with an additive constant term was found to adequately fit most (96.4%) of the observed discomfort-time sequences, and thus, was recommended as a general mathematical representation of the perceived discomfort-posture holding time relationship in SPH. CONCLUSION: The new knowledge on the nature of the discomfort-time relationship in SPH and the power function representation found in this study will facilitate analyzing discomfort-time data of SPH and developing future posture analysis tools for work-related discomfort control. [ABSTRACT FROM AUTHOR]

BACKGROUND: Realizing population-level discomfort evaluation and control of common static posture holding tasks requires an understanding of the inter-individual variation in discomfort perception. However, little research is available. OBJECTIVE: This study aimed to determine the types of mathematical probability distribution suitable for modeling population discomfort distributions of various static posture holding tasks and characterize how the magnitude of inter-individual variation in perceived discomfort varies across static posture holding tasks. SUBJECTS: Ten male and ten female subjects participated. METHODS: The participants conducted static posture holding for a set of 180 short-duration (20-second-long) static posture holding tasks and subjectively rated the overall perceived discomfort for each task using the Borg CR-10 discomfort scale. Statistical analyses were conducted according to the study objectives. RESULTS: The static posture holding tasks exhibited multifarious discomfort distribution patterns. Probability distribution identification analyses indicated that no single distribution type could represent population discomfort distributions universally across different static posture holding tasks. Sample standard deviation of discomfort ratings data quantifying the magnitude of inter-individual variation in discomfort perception varied considerably across static posture holding tasks. It seemed to have a positive relationship with sample mean within the range of the experimental conditions. CONCLUSIONS: Population-level evaluation of discomforts associated with static posture holding tasks must be based on careful examinations of empirical discomfort distributions. [ABSTRACT FROM AUTHOR]