Table 1 Examples of Time Variation Pattern of Mechanical Exposure and its Relationship to Musculoskeletal Disorders (WMSD).

Risk Factor	Units	Body Region	Findings	Reference
Time OR Proportion of Time	% or s	Shoulder	Increased risk of shoulder disorders if arm above shoulder > 10% time	Punnet et al. (2000)
		Wrist	Increased risk of hand disorders with increased time in flexed or extended wrist postures	Hunting et al. (1981)
		Low Back	Increased risk of low back disorders if mild trunk flexion > 10% time	Punnett et al (1991)
Frequency of Performing Action OR Cycle Time	Min, s, hr OR day^-1, hr^-1, s^-1	Wrist	Increased risk with cycle times less than 30 seconds of with a fundamental subcycle occupying more than 50% of the time	Silverstein et al., (1986)
		Shoulder	Increased risk of shoulder disorders if arm above shoulder at least once per minute	Punnet et al. (2000)
		Low Back	Increasing risk of being in high risk group if number of lifts exceeds 120/hr	Marras et al., (1995)
Angular velocity/ accelera-tion of joint	Deg s^-1 OR Deg s^-2	Low Back	Increased risk of low back pain with increasing flexion/extension and lateral bend angular velocity	Marras et al., (1993), Norman et al (1998)
		Wrist	Increased risk of hand/arm disorders with increased angular wrist acceleration (and velocity)	Marras and Schoemarklin (1995)
Hand Activity Level (HAL)	-	Hand/ Arm	Greater risk of injury/discomfort with increasing Hand Activity Level^1	Latko et al., (1999)
Muscle Rest	min^-1	Shoulder/ Neck	Increased sick leave if low number of EMG gaps	Veiersted et al (1993)
Average Load^2	N or % MVC	Forearm/ Hand	Increased disorders with increased Median EMG amplitude of forearm musculature.	Malchaire et al (1997)
Cumulative load	N.s	Low Back	Increased risk of low back pain with increased cumulative spinal moment compression and shear load	Norman et al (1998), Kumar (1990)