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This work investigated the discomfort-time sequences of SPH tasks in an effort to determine the existing relationship between perceived discomfort and posture holding time. This study proposed the power function as an adequate representation of the discomfort-PHT relationship of SPH tasks. Additionally, An investigation was conducted on the inter-individual variation in perceived discomfort of static posture holding. The main findings from this dissertation work were as follows: (1) three distinct time increase patterns, namely, the linear, negatively accelerated and positively accelerated time increase patterns, characterize discomfort-time sequences of prolonged SPH trials (2) the relationship between PHT and perceived discomfort in SPH can be adequately described by the power function form (3) different individuals can experience significantly different postural stresses even in identical manual work tasks. A consequence of the inter-individual differences in work performance is that simple descriptive statistics become limited in describing such tasks, and (4) psychophysical perception of discomfort can be expressed in probabilistic terms. Re-design recommendations may now be based on the probability distribution of discomfort ratings. Discomfort levels os SPH tasks can be quantified by a metric/index predicated on the use of empirical discomfort distributions. Such index may be useful for decision making involved in ergonomics design interventions.