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

Suboccipital Muscles, Forward Head Posture, and Cervicogenic Dizziness

Dizziness or vertigo can be caused by dysfunction of the vestibular or non-vestibular systems. The diagnosis, treatment, and mechanism of dizziness or vertigo caused by vestibular dysfunction have been described in detail. However, dizziness by the non-vestibular system, especially cervicogenic dizziness, is not well known. This paper explained the cervicogenic dizziness caused by abnormal sensory input with references to several studies. Among head and neck muscles, suboccipital muscles act as stabilizers and controllers of the head. Structural and functional changes of the suboccipital muscles can induce dizziness. Especially, myodural bridges and activation of trigger point stimulated by abnormal head posture may be associated with cervicogenic dizziness.

Influence of forward head posture on muscle activation pattern of the trapezius pars descendens muscle in young adults

Forward head posture (FHP) is a serious problem causing head and neck disability, but the characteristics of muscle activity during long-term postural maintenance are unclear. This study aimed to investigate a comparison of electromyography (EMG) activation properties and subjective fatigue between young adults with and without habitual FHP. In this study, we examined the changes in the spatial and temporal distribution patterns of muscle activity using high-density surface EMG (HD-SEMG) in addition to mean frequency, a conventional measure of muscle fatigue. Nineteen male participants were included in the study (FHP group (n = 9; age = 22.3 ± 1.5 years) and normal group (n = 10; age = 22.5 ± 1.4 years)). Participants held three head positions (e.g., forward, backward, and neutral positions) for a total of 30 min each, and the EMG activity of the trapezius pars descendens muscle during posture maintenance was measured by HD-SEMG. The root mean square (RMS), the modified entropy, and the correlation coefficient were calculated. Additionally, the visual analogue scale (VAS) was evaluated to assess subjective fatigue. The RMS, VAS, modified entropy, and correlation coefficients were significantly higher in the FHP group than in the normal group (p < 0.001). With increasing postural maintenance time, the modified entropy and correlation coefficient values significantly decreased, and the mean frequency and VAS values significantly increased (p < 0.001). Furthermore, the forward position had significantly higher RMS, correlation coefficient, modified entropy, and VAS values than in the neutral position (p < 0.001). The HD-SEMG potential distribution patterns in the FHP group showed less heterogeneity and greater muscle activity in the entire muscle and subjective fatigue than those in the normal group. Excess muscle activity even in the neutral/comfortable position in the FHP group could potentially be a mechanism of neuromuscular conditions in this population.

Neural Basis of Etiopathogenesis and Treatment of Cervicogenic Orofacial Pain

(1) Background and Objectives: The aim of this narrative review was to analyze the neuroanatomical and neurophysiological basis of cervicogenic pain in cervico-cranial pain syndromes, focusing particularly on cervico-orofacial syndromes as a background for the proper diagnosis and non-surgical treatment. Relevant literature on the topic from past 120 years has been surveyed. (2) Material and Methods: We surveyed all original papers, reviews, or short communications published in the English, Spanish, Czech or Slovak languages from 1900 to 2020 in major journals. (3) Results: The cervicogenic headache originates from the spinal trigeminal nucleus where axons from the C₁–C₃ cervical spinal nerves and three branches of the trigeminal nerve converge (trigeminocervical convergence) at the interneurons that mediate cranio-cervical nociceptive interactions. The role of the temporomandibular joint in the broad clinical picture is also important. Despite abundant available experimental and clinical data, cervicogenic orofacial pain may be challenging to diagnose and treat. Crucial non-surgical therapeutic approach is the orthopedic manual therapy focused on correction of body posture, proper alignment of cervical vertebra and restoration of normal function of temporomandibular joint and occlusion. In addition, two novel concepts for the functional synthesis of cervico-cranial interactions are the tricentric concept of mouth sensorimotor control and the concept of a cervicogenic origin of bruxism. (4) Conclusions: Understanding the basis of neuroanatomical and neurophysiological neuromuscular relations enables an effective therapeutic approach based principally on orthopedic manual and dental occlusal treatment.

A risk assessment of health, production, and resource occupancy for 4 laying hen strains across the lay cycle in a commercial-style aviary system

Different strains of commercial laying hens have been molded by varying selection pressures, impacting their production, health, and behavior. Therefore, assumptions that all laying hen strains use the given resources within aviary systems similarly and maintain equal health and performance may be false. We investigated interactions among patterns of aviary resource use by 2 strains of white and 2 strains of brown laying hens (4 units per strain, 144 hens per unit) with daily egg production, location of egg laying, keel fractures, and footpad damage across the lay cycle. Hens' distribution among resources (litter, nest, wire floor, ledge, and perch) was recorded during light and dark periods at 28, 54, and 72 wk of age. Daily egg production and location were recorded, and 20% of hens per unit were randomly selected and assessed for keel bone damage, foot health, and plumage quality. Production and health risks associated with hens' resource use were assessed using multivariable regression. During the day, more brown hens occupied wire floors, while larger numbers of white hens were on perches and litter. More brown hens were on lower-tier wire floors in the dark, while more white hens occupied top tiers. Brown hens laid more eggs outside nests, showed lower incidence of keel fractures, and had better plumage quality than white hens. White hens had higher odds of keel fractures (4.2) than brown hens. Odds of keel fractures were 3.7 and 5.7 times higher at 54 and 72 wk than at 28 wk in all strains (P ≤ 0.05). Occupying the upper tier at night increased odds of keel fractures by 5.4 times. Occupying perches was associated with lower odds of foot lesions and poor plumage quality in all strains across the lay cycle (P ≤ 0.05). Finally, white hens were associated with lower odds of non-nest laying (0.76), whereas higher nest use by brown hens resulted in higher odds of non-nest egg laying (1.56) across the lay cycle (P ≤ 0.05). Distinct strain differences in resource use in an aviary were associated with different risks to hens' production, health, and welfare.

Implied Evidence of the Functional Role of the Rectus Capitis Posterior Muscles

Context

Osteopathic physicians often target the rectus capitis posterior minor (RCPm) and rectus capitis posterior major (RCPM) muscles when using muscle energy or soft tissue cervical techniques to treat patients with head and neck pain. The RCPm and RCPM muscles are located deep within the posterior occipitoatlantal and atlantoaxial interspaces, respectively.

Objective

To characterize the functional role of RCPm and RCPM muscles by comparing electromyographic (EMG) activation patterns of these muscles with EMG activation patterns of specific flexor and extensor muscles of the head and neck, the sternocleidomastoid (SCM), and the splenius capitis (SC) muscles, respectively.

Methods

Asymptomatic participants were recruited from the Michigan State University College of Osteopathic Medicine student body. Disposable 25-gauge, bipolar fine-wire intramuscular electrodes were used to collect EMG data from the right and left RCPm and RCPM muscles. Surface electrodes were used to collect EMG data from the right and left SCM and SC muscles. Data were collected as participants performed 4 cycles of flexion and extension with an external 4-lb force applied to the back of the head and the forehead.

Results

In RCPM muscles, EMG activity was significantly greater (P<.003) during flexion and extension of the head and neck when an external force was applied to the back of the head. EMG activity in SCM muscles was significantly greater (P<.0001) during flexion and extension of the head and neck when an external force was applied to the forehead. The authors observed that EMG activity in SC muscles was significantly greater (P<.015) during flexion and extension of the head and neck when an external force was applied to the back of the head. No significant difference was found in EMG activity in RCPm muscles (P<.834) during flexion and extension of the head and neck, regardless of whether the external force was applied to the back of the head or the forehead.

Conclusion

The EMG activation patterns of the RCPm muscles suggest that their functional role may be to stabilize the occipitoatlantal joint by helping maintain congruency of the joint surfaces. In contrast, the EMG activation patterns of the RCPM muscles suggest that their functional role may be to contribute to extension of the head, primarily at the occipitoatlantal and the atlantoaxial joints.

Forward Head Posture and Activation of Rectus Capitis Posterior Muscles

Context: Rectus capitis posterior (RCP) muscles have physical attachments to the pain-sensitive spinal dura. Atrophy of these muscles is associated with chronic headache in some patients. The authors suspect that the significance of atrophy in the RCP muscles has been undervalued because the functional role of these muscles is not well defined.

Objective: To determine whether a statistically significant change in normalized levels of electromyographic activity in RCP muscles occurs when the head is voluntarily moved from a self-selected neutral head position to a protruded head position.

Methods: Fine wire, intramuscular electrodes were used to collect electromyographic data as asymptomatic participants moved their head from a neutral head position into a forward head position and back into the neutral head position. This sequence was repeated 4 times. Normalized levels of electromyographic activity were quantified using a 2-head position × 2 sides of the body repeated measures design that incorporated mixed-effects β regression models.

Results: Twenty participants were studied. Electromyographic activity collected from RCP muscles was found to increase as the head was voluntarily moved from a self-selected neutral head position (11% of maximum voluntary isometric contraction [MVIC] in RCP minor, 14% of MVIC in RCP major) into a protruded head position (35% of MVIC in RCP minor, 39% of MVIC in RCP major) (P<.001).

Conclusion: Rectus capitis posterior muscles may contribute to segmental stabilization of the occipitoatlantal and atlantoaxial joints by helping to maintain joint congruency during movement of the head.