ABSTRACT
A posture can be maintained for a limited period of time. The Maximum Holding Time (MHT) is the maximum time that a posture, with or without external force exertion, can be maintained continuously until maximum discomfort, from a rested state. Acute discomfort can be considered as an independent evaluation criteria for static postures (Miedema 1992; Dul et al. 1994; Miedema et al. 1996). Several studies have shown a linear relationship (at group level) between the duration of a continuous static task, and the level of discomfort as measured with the Borg rating scale (Manenica 1986; Bishu and Wei 1992). To avoid uncomfortable durations of static postures discomfort do not exceed score 2 or 3 on a 10 point rating scale (Hagerup and Time 1992; Douwes et al. 1993)
Due to the increment of discomfort in time, holding time (% MHT) can be taken as a measure for making recommendations concerning the maximum duration of static postures. In seven studies information was gathered about the MHT of 19 different standing postures which were maintained without rest pauses and without external load (Corlett and Manenica 1980; Hagberg 1981; Boussenna et al. 1982; Milner 1985; Taksic 1986; Manenica 1986; Meijst et al. 1995). All postures were defined by two parameters, i.e. the horizontal distance (% shoulder height) and vertical distance (% arm reach) of the position of the hands with
respect to the feet in upright standing posture. Shoulder Height (SH) is defined as the distance from acromion to the floor in the upright position. The Arm Reach (AR) is defined as the maximum distance from the knuckles to the wall when standing upright with the back against the wall and the shoulder in 90 degrees anteflexion. The 19 postures differ in the combination of 25, 50, 75, 100, 125 or 150% SH and 25, 50, 75 or 100% AR and are shown in Figure 1. In all studies the participants were asked to maintain the posture as long as they could. In almost all studies the subjects had to perform a task while holding the posture. These tasks implied television games, spot-tracking or tapping
tasks. During maintenance of the posture, location and amount of perceived discomfort was registered. The experiments ended when maximum discomfort was reached (score 10 on a 10 point rating scale; Borg 1990).
