Validity of Slow Unpredictable Movements for Neck Movement Testing
Slow unpredictable movements of short duration are NOT valid for measuring neck movement because movement smoothness is strongly velocity-dependent—slow movements are inherently jerky and irregular even in healthy individuals, making them unreliable for distinguishing normal from pathological movement patterns. 1
The Velocity-Smoothness Relationship
The fundamental problem with slow movements as a measurement tool is their inherent irregularity:
Healthy individuals demonstrate non-smooth, jerky movements during slow neck motion, with a strong inverse relationship between movement velocity and normalized jerk cost (a measure of smoothness) across all movement directions and amplitudes 1
Fast movements are smooth while slow movements are jerky by nature, meaning that irregular movements observed during slow testing cannot reliably indicate motor impairment 1
Movement smoothness varies with both velocity and amplitude, with larger amplitude movements showing higher jerk cost for any given velocity compared to smaller movements 1
Optimal Testing Parameters
For valid neck movement assessment, specific parameters should be used:
Self-paced movements at natural speeds provide more reliable kinematic data, as they allow subjects to move at velocities that produce interpretable smoothness patterns 2, 1
Peak velocity measurements show high reliability (ICC 0.86-0.93) when movements are performed at natural speeds in response to external stimuli rather than artificially slowed 2
Mean velocity demonstrates good global reliability (ICC 0.84) when movements are task-oriented rather than constrained to slow speeds 2
Clinical Implications for Movement Testing
When evaluating neck movement disorders:
Angular velocity and acceleration should be primary assessment parameters rather than range of motion alone, as chronic neck pain patients show significantly decreased cervical angular velocity and acceleration even when range of motion appears preserved 3
Movement coordination between cervical and thoracic spine regions provides more clinically relevant information than isolated slow movements, with cross-correlation analysis revealing coordination deficits in neck pain patients 3
The majority of daily neck motions are less than 15 degrees with flexion-extension being twice as frequent as other axes, suggesting functional testing should emphasize these natural movement patterns 4
Common Pitfalls to Avoid
Do not interpret irregular movements during slow testing as pathological, since healthy individuals naturally exhibit jerky movements at slow velocities 1
Avoid using short-duration movements without considering the velocity-amplitude interaction, as this relationship fundamentally affects smoothness measurements 1
Do not rely solely on range of motion assessment, as this fails to reveal movement dysfunctions that become apparent through velocity, acceleration, and coordination analysis 3
Recommended Alternative Approach
Use interactive, task-oriented assessments with external stimuli that elicit natural-speed movements rather than slow, constrained protocols. Virtual reality-based systems that require responsive movements to targets have demonstrated high inter-tester reliability (ICC 0.64-0.93) and provide ecologically valid kinematic data including peak velocity, mean velocity, and movement coordination patterns 2, 5