Load and speed effects on the cervical flexion relaxation phenomenon

Area of Science:

• Biomechanics
• Neuromuscular physiology
• Spinal kinematics

Background:

• The flexion relaxation phenomenon (FRP) is a known neuromuscular response in the spine.
• Cervical spine FRP, particularly its response to movement speed and load, is not well understood.
• This study aimed to characterize cervical FRP under varying conditions.

Purpose of the Study:

• To investigate the influence of load and movement speed on cervical FRP electromyographic (EMG) and kinematic parameters.
• To assess the repeatability of cervical FRP kinematic and EMG measurements.

Main Methods:

• Eighteen healthy adults performed standardized cervical flexion/extension movements under varied load and speed conditions.
• Kinematic and EMG data were collected, measuring angles of myoelectric silence onset/cessation and EMG RMS values.
• Repeatability was assessed within and between two sessions.

Main Results:

• Increased load significantly augmented FRP onset and cessation angles (P < 0.001).
• Load significantly affected EMG RMS values across all movement phases (P < 0.001).
• Higher loads and faster speeds during extension resulted in greater muscle activation, with good repeatability for all parameters.

Conclusions:

• Increased load enhances cervical FRP angles and muscle activation, potentially for spinal stability.
• Kinematic and EMG parameters demonstrate good repeatability for cervical FRP assessment.
• Further research is needed to compare findings in individuals with neck pain.