Understanding CRAC Stretching in Mobility+ Programming: Why It Works and How to Apply It
With Mobility+, our mission is to help you not just move better, but move stronger. One of the cornerstone methods we use to improve flexibility, mobility, and joint resilience is the CRAC method — Contract-Relax-Agonist-Contract stretching.
This technique is simple in concept but incredibly powerful in practice, and today, we’ll break down why it works so well, the science behind it, and how we apply it in our Mobility+ sessions.
What is CRAC Stretching?
CRAC is a form of PNF (Proprioceptive Neuromuscular Facilitation) stretching, a highly effective approach to improving range of motion (ROM).
The steps in CRAC stretching involve:
Contract the muscle you are trying to stretch (isometrically, without movement) against some resistance for a few seconds.
Relax that same muscle after the contraction.
Agonist Contract: Immediately contract the opposing (agonist) muscle group, trying to move deeper into the new range of motion.
In short:
Contract → Relax → Contract the Opposite Side → Gain more range.
Example:
If you are stretching your hamstrings:
First, contract the hamstrings hard against resistance.
Then, relax them.
Immediately, actively use your hip flexors (agonists) to pull your leg even higher.
Why CRAC Stretching Works So Well (The Science Behind It)
CRAC stretching is incredibly effective because it leverages neuromuscular physiology to bypass your body’s natural protective mechanisms and create lasting improvements in range of motion and control. Here's a deeper look at the science behind it:
1. Autogenic Inhibition
During the initial contraction phase (where you contract the target muscle), your body activates special receptors called Golgi Tendon Organs (GTOs) located in the tendons near the muscle junctions.
GTOs are sensitive to tension.
When a strong contraction is held (typically 5–8 seconds), the GTOs send a signal to the spinal cord to reduce muscle tension to protect the muscle from injury.
This response, called autogenic inhibition, temporarily reduces the muscle’s resistance to stretching, allowing a deeper and safer stretch afterward.
Key Point:
The longer and stronger (within reason) the isometric contraction, the greater the activation of GTOs — and the greater the window for deeper flexibility.
2. Reciprocal Inhibition
In the agonist contract phase, you immediately contract the muscle opposite to the one you're stretching.
For example, when stretching the hamstrings, you contract the hip flexors.
Contracting the agonist (hip flexors) triggers a neurological response that inhibits the antagonist (hamstrings)
This process, known as reciprocal inhibition, allows smoother and safer joint movement by automatically relaxing the opposing muscle.
Key Point:
Reciprocal inhibition reduces the tension in the muscle being stretched, deepening the stretch naturally and safely.
3. Neurological "Re-education" and Increased Motor Control
CRAC doesn't just stretch tissue — it reprograms your nervous system.
Most mobility restrictions are not purely mechanical but are neurological—your brain limits movement into unsafe ranges.
Contracting muscles into new ranges and using opposing muscles to deepen the range teaches your nervous system that the new position is safe, strong, and controllable.
Over time, this expands your "motor map" — your brain’s internal control over wider ranges of motion.
Key Point:
You’re not forcing flexibility — you’re building it into your nervous system’s safe movement patterns.
4. Strengthening at End Range
Unlike passive stretching, CRAC involves active muscular effort throughout the stretching sequence.
Contracting muscles in a lengthened position builds strength at the end range — the outer limits of your mobility.
Strength at end ranges is essential for joint stability, injury prevention, and high-performance movement.
Key Point:
Flexibility without strength is fragile. CRAC creates durable, usable mobility by reinforcing end-range strength.
5. Improved Tissue Health and Elasticity
Over time, CRAC-style stretching may positively influence the viscoelastic properties of connective tissues:
Regular loaded stretching and contracting can promote better collagen fiber alignment within muscles and fascia.
Improved tissue structure enhances elastic recoil, joint support, and overall tissue health.
Key Point:
CRAC stretching doesn’t just change how far you can move — it improves the quality of the tissues that allow you to move.
At Mobility+, we don't stretch just to feel good — we train flexibility the same way we train strength: systematically, purposefully, and with physiological precision.
CRAC Stretch Example in Practice: Hamstring Stretch
Here's a simple CRAC drill we often use in Mobility+ classes:
Setup:
Lie on your back with one leg extended on the floor.
Lift the other leg straight up toward the ceiling, holding it with a strap or your hands.
Step 1 - Contract:
Gently press your leg down into your hands or strap as if trying to bring it back to the floor (but resist, keeping it still).
Hold the contraction for 5-8 seconds at about 50-70% effort.
Step 2 - Relax:
After the contraction, completely relax the hamstrings for 2-3 seconds.
Step 3 - Agonist Contract:
Actively use your hip flexors to pull the leg higher, gaining a new end range.
Hold this new position for 10-15 seconds.
Repeat for 2–3 rounds to maximize the effect.
Why We Use CRAC So Often in Mobility+
Unlike basic passive stretching, CRAC makes you work for your mobility — and that's exactly what you need for real, long-term gains.
In Mobility+, our goal isn't just "feel good" stretching.
It’s building usable, resilient, and strong mobility that supports your lifting, running, jumping, or simply better daily living.
By reinforcing flexibility with strength and neurological control, you’re not only gaining more range of motion — you're making that range functional.
