Electromyographic activity of rectus capitis posterior minor muscles associated with voluntary retraction of the head

Background context: The functional role of rectus capitis posterior minor (RCPm) muscles is not well defined. To the best of our knowledge, electromyographic (EMG) data from RCPm muscles in humans have never been collected and analyzed.

Purpose: To test the null hypothesis that there will be no difference in normalized levels of EMG activity measured from RCPm muscles with the head in a neutral position and with the head in a retracted position.

Study design: A repeated measures design intended to quantify normalized levels of EMG activity measured from RCPm muscles.

Methods: Disposable 25-gauge, bipolar fine wire hooked electrodes were used to collect EMG data from both right and left RCPm muscles from 17 asymptomatic subjects. Data were collected while subjects performed five trials with the head maintained in a neutral position; performed three maximal voluntary isometric contraction efforts; performed four trials with the head maintained in a retracted position. Mixed effects beta regression models were used to analyze the data.

Results: Normalized EMG activity of RCPm muscles collected with the subject's head held in a retracted position was significantly higher (p<.0001) than normalized EMG activity collected with the subject's head held in a self-selected, neutral position.

Conclusions: Rectus capitis posterior minor muscles are active when the head is held in a neutral position and show a significant increase in activity when the head is held in a retracted position.