Overview of Deep Tendon Reflexes
Doctors often use reflex tests as part of a routine check-up to understand the health of your nervous system. These tests are safe, inexpensive, quick, and can be done without any special medical equipment. They have been used for over 100 years and can give valuable information about your health.
This discussion will focus on a specific type of reflex test known as “deep tendon reflexes”. A more accurate name for these tests is muscle stretch reflexes (MSR).
When testing these reflexes, doctors assess how your muscles respond to stretches. It’s normal to see a wide range of responses – everyone is unique. These tests are particularly useful when the reflexes are not the same on both sides of your body or if they happen with other changes or issues. However, if the reflex is stronger or weaker than usual but there are no other health issues, it is typically not a concern.
Six particular muscle stretch reflexes are commonly tested and will be discussed here: reflexes in the biceps (upper arm muscle), triceps (back of the arm muscle), brachioradialis (forearm muscle), knee, ankle, and jaw.
Anatomy and Physiology of Deep Tendon Reflexes
The first five reflexes described are activated by the doctor lightly tapping a part of your body, like your knee, causing a small stretch in the muscle. The tap activates special sensors in your muscle that then carry a message up to your spinal cord. Once this message reaches the spinal cord, it quickly bounces back down to the muscle, leading it to contract or tighten up. This whole process is what makes your leg kick when a doctor taps your knee with a little hammer.
Importantly, during these reflex actions, there’s also a safeguard in place. As these messages bounce around, a signal is sent to a nearby muscle group that prevents them from activating. So when your knee jerk reflex causes your thigh muscles to tighten and your leg to kick, a message is also sent to your hamstring muscles, telling them to stay relaxed.
The way your body creates these reflexes involves a complicated dance of signals involving both your muscles and nerves, as well as your brain and spinal cord. Since there are lots of moving parts, if something goes wrong with any of these components, it can change how your reflexes work. This is why doctors often test your reflexes, as it can give them an idea of how well your nerves and muscles are working.
The jaw jerk reflex works in a similar way. When your chin is tapped, signals are sent up to your brain along a nerve located in your jaw, and quickly sent back down, causing your jaw muscles to tighten. This all happens in a flash, without you having to think about it!
Here is a breakdown of the six most common reflexes that are tested by your doctor:
- Biceps (C5-C6 nerve level): A tap just in front of your elbow triggers this reflex.
- Triceps (C7-C8 nerve level, mostly 7): This reflex is tested by a tap just behind your elbow.
- Brachioradialis (C5-C6 nerve level): Tapped about 10 cm above the wrist on the thumb side of the forearm to elicit this reflex.
- Knee (L2-L4 nerve level, mostly L4): Also known as the patellar reflex, it’s triggered by a tap just below the kneecap.
- Ankle (S1 nerve level): This is also known as the Achilles reflex, which is elicited by a tap behind the ankle joint on the Achilles tendon.
- Jaw Jerk (Pons level): A tap on your chin triggers this reflex.
There’s even a handy, nursery rhyme-style reminder of the reflexes: “One-two, buckle my shoe. Three-four, kick the door. Five-six, pick up sticks. Seven-eight, lay them straight. S1,2 ankle jerk; L3,4 knee jerk; C5,6 biceps and brachioradialis; C7,8 triceps.”
The Achilles reflex can also be tested by tapping under your foot while you lie flat on your back. This is a good option when you can’t easily have your ankle tapped, like if you’re invalid.
Equipment used for Deep Tendon Reflexes
Various tools are used to trigger a reflex response in the body, ranging from special devices to day-to-day items. Specialized hammers are generally more effective – these can come in different designs: with a triangular or tomahawk shape (type Taylor), T-shaped (type Tromner, Buck), or circular (type Queen Square, Babinski). All these hammers work well in triggering reflexes, although the Taylor type might not be as efficient with harder-to-trigger reflexes (also known as hyporeflexia).
Other everyday items that can be used for this purpose include doctor’s own fingers (which can work very well especially in patients with heightened reflexes), the edge of the chest piece of a stethoscope, or even the edge of a smartphone.
Preparing for Deep Tendon Reflexes
When a doctor tests your reflexes, it’s crucial that your body is positioned properly. This allows the muscles on both sides of the joint to be entirely calm and the joint itself to be at a nearly right angle. For instance, when the doctor tests your bicep reflex, your elbow needs to be in a relaxed state, not fully straight but around a 90-degree angle. This can be achieved by resting your arm on your thigh if you are seated or by the doctor supporting it. Babies being checked should have their heads positioned straight when any reflex is examined.
For the ‘jaw jerk’ test specifically, you need to be positioned with your jaw relaxed and slightly open. This is achieved by having your mouth slightly open, ensuring the jaw is not held tightly shut.
How is Deep Tendon Reflexes performed
During a physical examination, a doctor might test the reflexes in your muscles. This involves tapping certain areas with a special hammer. It’s a painless process that helps your doctor figure out if your nerves are working the right way.
Before starting the test, the doctor would usually ensure that their hands are clean and that the joint they’re looking at is relaxed. They hit the muscle with enough force to make it react but their attention isn’t on the movement you might see. Instead, they’re looking for a muscle contraction: a tensing up and releasing of the muscle that can be subtle.
To make sure your muscles are as loose as possible, your doctor might try to distract you. This can involve asking you to clench your jaw, or perhaps trying to engage you in conversation. For lower body reflexes, they might suggest you link your fingers together and try to pull your own arms apart. These little techniques, known collectively as “reinforcement,” aim to help get a better reaction.
The doctor won’t just test one reflex and move on. They’ll compare it to the same reflex on the other side of your body. This method helps them spot even very minor differences between the performance of similar muscles. They need to quickly switch around – elbow to elbow rather than elbow to knee, for example.
How the doctor uses the reflex hammer could vary slightly depending on the muscle they’re checking. It might look like they’re dropping the hammer passively when they’re testing the muscle just below your kneecap (patellar tendon), but seem to swing it more actively when they’re checking the muscle on your arm (biceps tendon). Regardless of how it looks, the aim is the same: to get the best muscle reaction without causing you any pain.
After all the tapping and observing, your doctor will grade your reflexes using a scale provided by the National Institute of Neurological Disorders and Stroke (NINDS). This Assessing scale ranges from 0 to 4, as follows:
- 0 – No reflex present
- 1 – A small reflex that is less than normal
- 2 – Reflex in the lower half of normal range
- 3 – Reflex in the upper half of normal range
- 4 – Reflex enhanced and better than normal
Plus or minus signs might be added to indicate the reflex lies between two whole grades. They might label a ‘5’ if there’s a long-lasting, repeated muscle contraction (clonus). Half points could indicate if they used those ‘reinforcement’ techniques we mentioned before.
What Else Should I Know About Deep Tendon Reflexes?
Reflexes are your body’s automatic reactions to certain types of stimulation, and they can tell doctors a lot about your nerves, spinal cord, and even your body’s general state. For example, whether or not you have a reflex when your ankle is tapped can actually tell doctors more about possible nerve damage from diabetes than other symptoms, how long you’ve had diabetes, or signs of diabetic eye disease.
Changes in your reflexes can even provide clues about the levels of certain chemicals, called electrolytes, in your body. These electrolytes are important because they help nerves send signals.
Depending on what pathway in the body is involved, having overactive reflexes (hyperreflexia) can suggest a problem in the brain or spinal cord, while underactive reflexes (hyporeflexia) can point to a problem with the nerves. So if you have an issue at the C5 level of your spinal cord, you might have decreased reflexes in the reflex that involves the C5 and C6 nerves (the biceps reflex), but increased reflexes in the reflex that involves the C7 and C8 nerves (the triceps reflex). This occurs because the problem is above the nerves for the lower reflex but affects the control of that reflex. Hence, underactive reflexes are considered a sign of nerve issues, and overactive reflexes are seen as a sign of brain or spinal cord issues.
Doctors grade your reflexes on a scale, although the specific values can vary based on the doctor’s experience and previous assessments. But reflexes that are rated from 1+ to 3+ and are the same on both sides are generally considered normal, unless you have other signs of nerve or brain/spinal cord issues. Also, if your reflexes become more pronounced as they move down your spinal cord, it could suggest damage to the spinal cord. Moreover, even if one side is a bit higher than the other, it is not usually a problem unless there are other concerning signs or symptoms. In some cases, even not having a reflex can be normal if it’s the same on both sides and there are no other issues.
