Background: Back muscles simultaneously drive spinal movements and stabilize the trunk. Paraspinal muscle activity is presumed to be symmetric and gender-insensitive, and more activated with aging to protect the spine during functional tasks.
Research question: Does over-activated and asymmetric behaviors exist in the pain-free elderly population which is affected by their physical activity levels?
Methods: Forty healthy participants (aged 64.8 ± 9.9 years, 20 males and 20 females) were recruited for this cross-sectional study. They completed the International Physical Activity Questionnaire (IPAQ) to quantify their self-reported physical activity measures including the total physical activity in MET-min/week and time spent sitting. Surface electromyographic activity of bilateral paraspinal muscles at L3 level was measured. Subjects were instructed to perform functional tasks including symmetric movements as well as right- and left-side rotation/bending. Asymmetry in muscle activation between the two sides was calculated. A multiple linear regression model was used to assess the association of muscle activations with age and gender. Pearson correlation analysis was used to verify the relationship between the asymmetry and physical activity measures.
Results and significance: The results showed a downtrend of paraspinal muscle activations with aging and the decreasing rate could differ between genders. Left-side muscle activations were generally higher than those of the right-side muscles. Muscle asymmetrical activation correlated with sitting time but not total physical activity. This study highlighted aging and gender effects on the paraspinal muscle activations as well as muscle imbalance during different movement paradigms. Future work is needed to verify the underlying mechanism for declining and asymmetrical muscle activation and its link to back disorders.
Keywords: Asymmetry; Electromyography; Physical activity; Spinal control; Spinal movements.
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