R J Parker Sports & Remedial Therapy

But what is actually happening inside your body when you stretch?

Modern research shows that stretching is not just about making muscles longer. It involves a combination of changes in your tissues and how your nervous system responds to movement (Behm et al., 2016; Freitas et al., 2018).

What Do We Mean by Stretching?

Stretching is simply the act of lengthening a muscle and the tissues connected to it (known as the muscle–tendon unit) to improve movement and flexibility.

When you become more flexible, this is usually due to two things:

1. Your body becomes more comfortable moving into that position
2. Your tissues become slightly more adaptable over time (Freitas et al., 2018; Warneke et al., 2023)

What Happens Inside Your Body When You Stretch?

Stretching affects more than just muscle. It involves:

• Muscles
• Tendons (which connect muscle to bone)
• Fascia (connective tissue around muscles)
• Your nervous system

What Do We Mean by Stretching?

Stretching is the process of lengthening a muscle–tendon unit—this includes:

The muscle itself

The tendon (which attaches muscle to bone)

Surrounding connective tissues (fascia)

The goal is usually to:

Improve flexibility

Increase range of motion (how far a joint can move)

Reduce stiffness or discomfort

What’s important to understand is that flexibility gains come from both:

Physical changes in the tissue

Your nervous system allowing more movement

(Freitas et al., 2018; Warneke et al., 2023)

What Actually Happens When You Stretch?

1. Your Muscles and Tendons Behave Like Elastic Materials

Your soft tissues act a bit like a combination of a spring and putty:

Like a spring → they can stretch and return to shape

Like putty → they slowly change shape if held long enough

When you hold a stretch:

The tissue gradually lengthens (creep)

The resistance you feel reduces (stress relaxation)

This is why a stretch feels tight at first, then eases after 20–30 seconds (Freitas et al., 2018).

2. The “Stretch Feeling” Comes from Your Nervous System

That pulling or tight feeling isn’t just the muscle—it’s largely your nervous system protecting you.

Your body uses sensors to monitor stretch:

Muscle spindles → detect quick stretch and trigger tightening

Golgi tendon organs → help muscles relax when tension is high

At first, your brain interprets stretch as a potential threat.

But over time, with regular stretching:

Your brain becomes more comfortable with that position

The feeling of tightness reduces

You can move further without discomfort

This is called increased stretch tolerance, and it plays a major role in flexibility (Behm et al., 2016; Freitas et al., 2018).

3. Long-Term Changes in Muscle Structure

If you stretch consistently over weeks:

Muscles may adapt by increasing their usable length

The muscle–tendon unit may become less stiff

However, these changes are gradual and require regular input—occasional stretching won’t produce lasting effects (Warneke et al., 2023).

4. Fascia Also Plays a Role

Fascia is the connective tissue that surrounds and links muscles.

It helps:

Transfer force

Provide structural support

Influence how freely tissues move

When you stretch, fascia is also being loaded and may contribute to the feeling of stiffness or restriction (Wilke et al., 2019).

Types of Stretching (With Practical Use)

Passive Stretching

This is when an external force creates the stretch.

Examples:

A therapist moving your limb

Using a strap or towel

Letting gravity assist (e.g. bending forward)

When it’s useful:

If movement is limited

During rehabilitation

When muscles are very tight or painful

What it does:

Allows you to reach a deeper stretch

Reduces resistance in the tissues over time

(Freitas et al., 2018)

Static Stretching

A type of passive stretching where you:

Hold a position for 15–60 seconds

Best used:

After exercise

For general flexibility

Important:

Doing long static stretches immediately before sport may slightly reduce strength or power output (Behm et al., 2016).

Active Stretching

This is when you use your own muscles to create the stretch.

Example:

Lifting your leg and holding it there without support.

Benefits:

Builds strength and control

Improves flexibility in a more functional way

(Behm et al., 2016)

Dynamic Stretching

This involves controlled movement through range.

Examples:

Leg swings

Arm circles

Walking lunges

Why it’s effective:

Increases blood flow and temperature

Prepares muscles for activity

Improves mobility without reducing strength

(Opplert and Babault, 2018)

PNF Stretching (Contract–Relax)

This combines muscle contraction with stretching.

How it works:

Stretch the muscle

Contract it (push against resistance)

Relax and stretch further

Why it works:

Encourages the muscle to relax more deeply

Improves range of motion effectively

Often used in therapy settings (Behm et al., 2016)

Ballistic Stretching

This involves bouncing or swinging movements.

Example:

Bouncing to touch your toes

Considerations:

Less controlled

Can increase injury risk

Generally not recommended for most people

(Opplert and Babault, 2018)

Short-Term vs Long-Term Effects

Short-Term (After One Session)

Increased flexibility

Reduced stiffness

Muscles feel “looser”

However:

Long static stretching may temporarily reduce strength

(Behm et al., 2016)

Long-Term (With Consistency)

Improved range of motion

Better movement quality

Reduced perception of tightness

Most of these improvements come from your body becoming more tolerant and efficient in those ranges, not just physically “longer” muscles (Freitas et al., 2018).

Common Misconceptions About Stretching

“Tight muscles need aggressive stretching”

→ Not always. Gentle, consistent stretching is more effective and safer.

“Stretching prevents all injuries”

→ Stretching alone does not prevent injury, but it can support overall movement and function (Behm et al., 2016).

“If it hurts, it’s working”

→ Pain is not necessary. Stretching should feel like tension, not sharp discomfort.

Practical Advice

Stretch regularly, not just occasionally

Hold static stretches for 20–30 seconds

Use dynamic stretching before activity

Avoid forcing painful positions

Match the type of stretching to your goal

Final Thoughts

Stretching is not just about flexibility—it’s about improving how your body moves and feels. By understanding both the physical and neurological sides of stretching, you can use it more effectively and safely.

If you have ongoing stiffness, pain, or injury, a personalised approach—guided by a professional—will give you the best results.

Reference List (Harvard Style)

Behm, D.G., Blazevich, A.J., Kay, A.D. and McHugh, M. (2016) ‘Acute effects of muscle stretching on physical performance, range of motion, and injury incidence in healthy active individuals: a systematic review’, Applied Physiology, Nutrition, and Metabolism, 41(1), pp. 1–11.

Freitas, S.R., Mendes, B., Le Sant, G., Andrade, R.J., Nordez, A. and Milanovic, Z. (2018) ‘Can chronic stretching change the muscle-tendon mechanical properties? A review’, Scandinavian Journal of Medicine & Science in Sports, 28(3), pp. 794–806.

Moltubakk, M.M., Magulas, M.M., Villars, F.O., Seynnes, O.R. and Bojsen-Møller, J. (2018) ‘Specialized properties of the muscle–tendon unit: implications for stretch and performance’, Journal of Applied Physiology, 125(3), pp. 768–778.

Opplert, J. and Babault, N. (2018) ‘Acute effects of dynamic stretching on muscle flexibility and performance: an analysis of the current literature’, Sports Medicine, 48(2), pp. 299–325.

Warneke, K., Keiner, M., Lohmann, L.H. and Wirth, K. (2023) ‘The influence of long-lasting static stretching on maximal strength, muscle thickness and flexibility’, Frontiers in Physiology, 14, 1058733.

Wilke, J., Krause, F., Vogt, L. and Banzer, W. (2019) ‘What is evidence-based about myofascial chains: a systematic review’, Archives of Physical Medicine and Rehabilitation, 100(3), pp. 454–461.