Deep Tendon Reflexes (Muscle Stretch Reflexes)

Deep tendon reflexes (DTRs) are reflexes that make certain muscles in your body squeeze or flex when a healthcare provider taps a tendon connected to them. That’s why they’re also known as muscle stretch reflexes.

A reflex is something that happens automatically, without you controlling it. Your body uses lots of different reflexes to help you react to the world around you and stay safe. Deep tendon reflexes keep your muscles ready to react and help you keep your balance.

DTRs get their name from how they work. They happen when something triggers nerves connected to tendons and muscles deep in your body. The nerves react instantly, and tell those muscles to move or twitch without you thinking about it.

There are five deep tendon reflexes:

• The biceps reflex: This makes your biceps in your upper arm flex.
• The brachioradialis reflex: You’ll squeeze the brachioradialis muscle in your forearm from this reflex.
• The triceps reflex: This makes you squeeze the triceps muscle on the back of your upper arm.
• The patellar reflex: Your quad muscles kick your lower leg forward when your provider taps your knee. This is probably the most famous reflex. It’s also known as the knee jerk reflex.
• The Achilles reflex: This makes your gastrocnemius and soleus muscles twitch your ankle. It’s also known as the ankle jerk reflex.

Why do healthcare providers test deep tendon reflexes?

A healthcare provider might test your DTRs if they’re checking for a neurological disorder. These conditions affect your nervous system, including your:

• Brain
• Spinal cord
• Nerves

Your reflexes might not work like they should if something is interrupting the connection between any of the parts in your nervous system.

Your provider may use a DTR test to help diagnose conditions like:

• Multiple sclerosis (MS)
• Amyotrophic lateral sclerosis (ALS)
• Spinal cord injuries
• Spinal muscle atrophy (SMA)

Your provider may also test some of your reflexes as part of a regular checkup.

How does the test work?

The specific steps will vary depending on which DTR your provider is testing. But these are the general steps:

1. Your provider will have you sit on an exam table.
2. You’ll need to relax into a comfortable, neutral posture. Try not to think too hard about moving the muscle they’re checking.
3. Your provider will tap gently on the tendon. They’ll use a small hammer made out of firm rubber. It might feel weird, especially when your body moves without you telling it to. But it won’t hurt.

Where your provider taps with a reflex hammer changes based on which reflex they’re testing:

• The biceps reflex: You’ll sit up straight with your arm bent and resting on your leg. Your provider will place their thumb on the inside of your elbow and gently press down with their fingers wrapped around your arm. They’ll tap on their thumb with the hammer. This should make your forearm twitch.
• The brachioradialis reflex: Your provider will hold your arm at the elbow with their thumb gently holding your biceps tendon. Then they’ll tap just above your wrist. This should make your forearm twitch and rotate open. Your fingers may jerk, too.
• The triceps reflex: You’ll sit up and rest your forearm on your provider’s arm. They’ll tap the hammer just above your elbow. Your forearm should flex when they do.
• The patellar reflex: You’ll sit on the edge of a table with your legs hanging over the edge. Your provider will rest their hand on your thigh and tap your knee. Your lower leg should kick out.
• The Achilles reflex: You’ll sit with your legs hanging off the edge of an exam table. Your provider will rest your foot in their hand and gently flex it up, toward your shin. They’ll tap the Achilles tendon on the back of your ankle above your heel. This should make you jerk your foot down, so your toes point toward the floor.

Jendrassik maneuver

Your provider might use the Jendrassik maneuver if typical tests aren’t triggering your patellar or Achilles reflexes. You will:

1. Sit with your legs hanging over the edge of the exam table.
2. Clench your teeth, like you’re biting down to hold something in your mouth.
3. Bend your elbows and lock your fingers together.
4. Pull your hands apart while keeping your fingers woven together.

Your provider will then tap on your knee or ankle after you’re clenching your teeth and pulling your hands apart.

This might feel silly, but it helps. Your brain sometimes interferes with your natural reflexes. If you know a tap is coming, your brain might anticipate it and stop you from reacting on pure reflex. The Jendrassik maneuver occupies your brain and nerves higher up in your body. This lets nerves and muscles in your legs react like they should, without interference.

What are the risks of this test?

There are no risks to having your deep tendon reflexes tested. All the tests are quick and painless. And your healthcare provider can do them as part of a regular office visit. They won’t need special equipment or a separate appointment.

What type of results do you get and what do the results mean?

Healthcare providers classify your DTRs with one of five grades. The higher the number, the more your muscle moved when your reflex was triggered:

• 0: No reflex at all
• 1+: A small reflex response, but noticeably less than it should be
• 2+: A normal response, but the reaction was slightly smaller than usual
• 3+: A normal response, but the reaction was slightly bigger than usual
• 4+: Too big of a reflex, possibly because something is making your nerves react much more than they should

"Normal" isn’t a very scientific word. In this case, it means typical compared to the average for most people. It also means that nothing has changed too much if your provider has tested your reflexes in the past.

You might have naturally bigger or smaller reflexes than usual, even if nothing is wrong. Your provider might test the same reflex on the other side of your body. This can help them know what’s normal for you, versus what might be a sign of an issue.

Your provider will probably suggest some other tests if your muscle stretch reflexes seem unusual. They'll tell you which tests you’ll need and why.

When should I call my healthcare provider?

It might be hard for you to feel something wrong with a specific deep tendon reflex. But you may notice signs of a neurological issue. Visit a healthcare provider if you feel like you can’t move or react like usual. You know what’s normal for you and when something isn’t quite right.