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The purpose of this research was to determine if there were any differences in (1) lumbar spine flexion moments or (2) activity of the lumbar erector spinae or external oblique muscles while varying (1) lumbar postures and (2) hand heights used to lift a load. A completely randomized design with repeated measures was used. 20 male workers (32.9 (+OR-) 12.4 years, 178.3 (+OR-) 6.8 cm, 81 (+OR-) 14.7 kg) employed in positions requiring manual lifting assumed specific lumbar spine postures (subject preferred, kyphotic, straight or lordotic), lifted a 157 N crate to three different hand heights (25, 50, 76 cm), paused for 1-2 seconds while a photograph was taken, and lowered the crate. Two replicates of each lifting combination of posture and hand height were performed. Linear envelope EMG signals from the erector spinae and external oblique muscles bilaterally were recorded, and flexion moments about L5-S1 were estimated when the load was held at the specific hand height of each lift. Moments were largest using the preferred method of lifting and became successively lower for the postures of kyphosis, straight and lordosis (p < 0.05). Moments were largest in the lowest hand height position and became successively lower for the middle and highest hand heights (p < 0.05). Average erector spinae muscle activity was highest in lordosis and lower for the postures of straight, preferred and kyphotic. However, the differences were not significant with a mixed effects design. In spite of the lack of significance across postures, the kyphotic posture commonly reduced the activity of the erector spinae to bursts of activity while lifting and caused more discomfort during the lifting tasks than any other posture. External oblique muscles were most active during kyphosis, lower in preferred and lordosis and lowest in the straight posture (p < 0.05). The external oblique muscles were more active at the lowest hand height with decreasing amount of activity as the hand height increased (p < 0.05). The following hypotheses were supported: (1) flexion moments were affected by lumbar posture with the lowest moments estimated in the lordotic posture, particularly at the lowest hand height; (2) the average erector spinae muscle activity was not affected by either lumbar posture nor hand height of the lift; and (3) the external oblique muscles were most active for the kyphotic posture at the lowest hand height.