Design: Cross-sectional observational.
Setting: The Anglo-European College of Chiropractic.
Subjects: A convenience sample of 30 subjects who met the inclusion and exclusion criteria.
Main outcome measures: Each subject performed two sets of five repetitions of prone hip extension. To assess the within-subject consistency, the mean number of different activation orders used per set was calculated. As well, the “average” activation orders of both sets were compared for each subject to determine the amount of between-set consistency. To assess the between-subject consistency, the frequency that each of the possible activation orders was used as well as the frequency that each muscle became active first, second, third, and fourth were calculated for the entire sample.
Results: Subjects used an average of 3.3 (95% CI = 3.1 to 3.5) different activation orders per set of five repetitions. The between-set consistency ranged from 23.3% (95% CI = 12.0 to 41.8%) to 43.3% (95% CI = 27.9 to 62.0%), depending on the method used to determine the “average” activation order for each set. Six activation orders (HAM–IES–CES–GM, CES–IES–HAM–GM, IES–CES–HAM–GM, IES–HAM–CES–GM, HAM–CES–IES–GM, CES–HAM–IES–GM) accounted for 81.3% of the total repetitions. The proposed “normal” activation order (GM–HAM–CES–IES) was used once in 300 repetitions. The most prevalent muscles to become active first, second, third, and fourth were the HAM (34.3%; 95% CI = 29.8 to 40.7%), IES (42.7%; 95% CI = 38.0 to 49.3%), CES (36.7%; 95% CI = 32.1 to 43.1%), and GM (81.3%; 95% CI = 78.1 to 87.1%), respectively.
Conclusions: The results of this study indicate that the within-subject consistency in the motor patterns used to achieve prone hip extension in subjects without LBP is poor. The results seem to refute the “normal” activation order which has been proposed for this movement. As well, the GM was the final muscle to become active 81.3% of the time, which challenges the prevailing theory that a delayed onset of this muscle during the movement is associated with LBP. Despite this, research using LBP subjects must be performed before any comment can be made on whether “normal” or “abnormal” motor patterns exist for this movement.
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