Q 250 D 310 BW: body weight, N/R: not reported, D: dynamic, S: static, Q: quasistatic. L3–L4 = between the third and fourth lumbar vertebrae. L4–L5 = between the fourth and fifth lumbar vertebrae. L5–S1 = between the fifth lumbar and first sacral vertebrae. (From Hooper, 1996).

The cascading degenerative process is often the result of cumulative damage to the spinal components induced by chronic loading (Goel and Weinstein, 1990). Many situations may cause chronic loading. For example, during the heavy physical work prevalent among blue collar workers, lifting not only induces large axial compressive forces across the motion segment, but tends to be associated with twisting and bending of the trunk (Andersson, 1981; Brinckmann and Porter, 1994; Chaffin and Andersson, 1984; Chaffin and Park, 1973; Damkot et al., 1984; Frymoyer et al., 1983; Kelsey and White, 1980). The other major class of loading situations associated with low -back pain is static loading influenced by posture (Anderson, 1987; Wood and Badley, 1987). Backache appears to occur with increased frequency in those with sedentary occupations (such as jobs involving

Table 14.3 Review of asymmetric lifting tasks.