Erector spinae activity during three methods of lifting a baby car seat in postnatal women and matched controls
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Objectives The lifting of baby car seats could be a contributing factor in persistent back pain experienced by many postnatal women. The purpose of this study was to compare the activity of the erector spinae muscles of postnatal women and a control group during three methods of lifting a baby car seat. Design A repeated measures design was used to compare three methods of lifting a baby car seat: symmetrical, asymmetrical and cradling. Setting Ante-natal clinic, Victoria Mansionhouse Unit, Glasgow. Participants Convenience sample of nine postnatal mothers and nine matched controls. Main outcome measure Surface electromyography was used to record erector spinae muscle activity. Results Independent two-sample t-tests revealed no statistically significant difference in resting erector spinae activity between the two groups. Analysis of covariance suggested a significant difference between the two groups for both sides and between the different lifting methods. For example, for symmetrical lifting, activity in the right erector spinae was 353 mV [95% confidence interval (CI) 253-453 mV] in the postnatal group and 458 mV (95% CI 339-577 mV) in the control group. For the cradling lift, these values rose to 443 mV (95% CI 340-546 mV) for the postnatal group and 568 mV (95% CI 452-684 mV) for the control group. Asymmetrical lifting evoked the least erector spinae activity, and the cradling method evoked the most activity. However, electromyographic activity was most evenly distributed during symmetrical lifting. Conclusions Symmetrical lifting is recommended as the preferred method of lifting baby car seats due to the even distribution of load between left and right erector spinae activity. Further research is required to investigate the activation of other muscle groups and to discriminate between the lifting and the stabilising phases of the lifting manoeuvre.