Effect of floor slope on submaximal lifting capacity

In order to reduce injuries due to lifting a box from the floor, maximal acceptable weights of lift (MAWL) have been established for a level surface. However, an inclined surface condition may be encountered on a jobsite. The purpose of this investigation was to determine if facing up or down a sloped surface affects MAWL. After obtaining university-approved informed consent, 20 apparently healthy men (age = 22.4 +/- 1.4 yrs) and 20 women (age = 22.0 +/- 1.9 yrs) determined floor to knuckle height MAWL using the psychophysical approach. After a familiarization day, two data collection days were completed with the uphill and level (+20, +10 and 0 degree) or downhill and level (-20, -10 and 0 degree) lifting capacities determined. A cadence of four lifts/min was used after starting with an unknown load that participants adjusted after each lift. No differences (p > 0.05) in level MAWL were found on the downhill day compared to the uphill day. While the men lifted significantly more than the women in every condition (p < 0.001), no differences were found across the lifting conditions (p > 0.05). The men averaged a MAWL of 24.7 kg across the five conditions (average standard deviation (SD) = 7.4 kg), the women averaged 14.8 kg (average SD = 3.1 kg). While these findings would suggest no changes in lifting guidelines for a sloped surface within 20 degrees of level, other factors such as lifting technique and the stress placed on the low-back should be examined to assess risk of injury in these different conditions.