Definitions of Flexibility and Stability

Flexibility Definitions

• Flexibility can be defined in various ways, including statistical flexibility, adequate task flexibility, passive sufficiency of multi-articular links, and generalized hypermobility/laxity.

• Statistical flexibility refers to a joint having a range of motion (RoM) greater than the average for that joint.

• Adequate task flexibility refers to the necessary RoM for a specific task, which varies depending on the activity.

• Passive sufficiency of multi-articular links implies the links are long enough to not restrict passive motion of any joints they span.

Multi-Articular Links

• Multi-articular links, such as muscles, ligaments, fascia, nerves, and vessels, span multiple joints and influence motion.

Passive Sufficiency

• Passive sufficiency refers to the sufficient length of multi-articular links to not restrict passive motion across the joints they span.

Stability

• Postural stability is the ability to resist external perturbations without collapsing.

• Joint stability is the stability of positional equilibria in non-physiologic degrees of freedom (DoFs), and it is correlated with joint laxity, but not directly proportional.

Stabilization

• Passive stabilization: Results from forces and moments that do not require muscle activation, including gravity, inertia, tissue elasticity, and viscosity.

• Active stabilization: Involves muscle activation to maintain postural or joint equilibria, typically necessary for most positions and for maintaining stability in lax joints.

Stretch Types

• Static stretch: Held at the end of the range of motion (RoM) with a relatively low force over a period of time.
• Dynamic stretch: Involves movement through the RoM with variable force and velocity.
• Ballistic stretch: Rapid, forceful movements through the RoM, typically at a higher force and velocity.
• PNF (Proprioceptive Neuromuscular Facilitation) stretch: Involves a combination of active and passive stretching techniques.

Mechanical and Perceptual Effects of Stretching

• Short-Term Stretching: Causes temporary lengthening of tissues through viscoelastic stretching, increasing tolerance of tension but with no lasting effects on resting length or stiffness.

• Long-Term Stretching: May lead to an increase in RoM, likely due to increased tolerance of tension rather than structural changes in muscle tissue.

Costs of Active Stabilization

• Stiffness: Increased metabolic work, slower movement, and altered coordination.

• Compression: Possible damage to hyaline cartilage and intervertebral discs, and constraint of breathing if not trained.

Summary

• Range of motion (RoM): The extent of joint movement in a specific direction.

• Laxity: The amount of movement in a joint that is not considered normal or healthy.

• Flexibility is defined as the ability of a joint or muscle to move through its full range of motion, encompassing statistical flexibility, task-specific adequacy, and passive sufficiency.

• Equilibrium and stability are critical for optimal health and performance, and understanding the relationship between flexibility, laxity, and stability is crucial for developing effective exercise strategies for health and performance improvement.

Key Points

• Desirable flexibility and stability are interrelated and have different implications for health and performance.

• Flexibility is primarily related to performance (with some implications for health), while stability is primarily related to health (injury prevention) with some implications for performance.

• It is essential to understand the different stretch types and their effects to develop effective strategies for achieving desirable ranges of motion for optimal health and performance.