Analysis of the Lumbar Spine During a Lifting Task with and without an Infant Carrier

Abstract

In the United States, 15–40% of people experience low back pain during a given year leading to loss of wages, decreased productivity and increased health care costs. Many people do not require manual lifting as part of their employment, and their low back pain is caused by performing daily activities, such as lifting while holding a child. PURPOSE: To investigate the torque and compression force at L5/S1, and the muscle recruitment of the erector spinae and upper rectus abdominus during a lifting task while holding an infant model (3.41 kg). METHODS: Ten healthy subjects (2 male, 8 female), ages 18–30, performed three trials of three velocity controlled lifting conditions. The lifting task consisted of lifting a shoulder bag (4.55 kg) and placing it on a platform 72.4 cm in height and 50 cm from the subject's feet. The lifting conditions were 1) a self-selected lift with no infant model (control), 2) manually hold the infant model (infant), and 3) carry the infant model in an anterior mounted Baby Bjorn® Original Infant Carrier (carrier). Lift Trak software was used for two-dimensional videography data collection and processing, to determine peak torque and peak compression at L5/S1. Electro my ography (EMG) data were collected with Noraxon Myovideo and processed with Noraxon Myoresearch software. A one-within factor repeated measures ANOVA was used for all comparisons, and a paired samples t-test for post hoc analysis. RESULTS: There was a significant difference (p < .05) within the three lifting conditions for torque (p = .000) and compression force (p = .000) atL5/S1. Post hoc analysis showed significantly less torque during the infant lift (103.25 Nm ± 22.76) when compared to the control lift (158.58 Nm ± 38.09) and carrier lift (155.38 Nm ± 43.85). There was significantly less compression force during the infant lift (2191.2 N ± 436.35) when compared to the control lift (3164.61 N ± 680.77) and carrier lift (3107.85 N± 776.95). No significant differences were found within the integrated EMG data for the erector spinae (p =.119) and rectus abdominus (p = .996). CONCLUSION: The torque and compression findings were consistent with previous research. The EMG data were not consistent with changes in torque and compression that were found in previous research. When using the infant carrier, subjects utilized a lifting strategy more similar to their self-selected (control) strategy. These strategies resulted in higher torque and compression force at L5/S1. Repetitive lifting that produces high lumbar torque and compression force is a mechanism for low back injury. Manually carrying an infant during a lifting task may reduce the risk of low back injury compared to using an infant carrier.