Arm reflexes are tested by tapping specific tendons with a reflex hammer while the arm is relaxed and slightly flexed, then observing how strongly and quickly the muscle contracts. The three standard arm reflexes tested in a clinical exam each correspond to a different spinal nerve root, so the pattern of results can reveal where a problem sits along the nervous system. The technique itself is straightforward, but interpreting what a brisk, sluggish, or absent response actually means takes more context than most people realize.
The Three Main Arm Reflexes and Where to Tap
A neurological exam of the upper limbs typically includes three deep tendon reflexes. Each tests a different nerve root exiting the spinal cord in the neck, so together they map roughly three levels of the cervical spine.
- Biceps reflex (C5-C6): The examiner places a thumb or finger on the biceps tendon in the crook of your elbow and strikes that finger with the hammer. The expected response is a brief contraction of the biceps, causing a slight bend at the elbow.
- Triceps reflex (C7): Your arm is supported so the elbow hangs loosely at about 90 degrees. The examiner taps the triceps tendon just above the back of the elbow. The forearm should kick outward slightly as the triceps contracts.
- Brachioradialis reflex (C5-C6): The hammer strikes the lower end of the radius bone on the thumb side of your forearm, a few centimeters above the wrist. The normal response is a slight flexion of the elbow and a subtle rotation of the forearm.
Getting good results depends heavily on the person being genuinely relaxed. If you’re tensing your arm or gripping the chair, the reflex can be artificially dampened or exaggerated. Clinicians will often distract you with conversation or ask you to look away while they tap. Positioning matters too: the joint needs to be slightly flexed so the tendon is under a small amount of natural stretch, which puts the muscle spindles in the right state to fire.
How Reflexes Are Graded
Most clinicians use a simple scale from 0 to 4+, though the exact wording varies slightly between textbooks. The general framework looks like this:
- 0: No response at all, even with reinforcement techniques.
- 1+: A diminished response. The muscle contracts, but weakly, and you might need to look closely to see it.
- 2+: Normal. A brisk, clearly visible contraction without anything excessive.
- 3+: Brisker than average. The reflex is strong and easily elicited, but there’s no involuntary spread to other muscles.
- 4+: Very brisk, often with clonus, which is a rhythmic, involuntary bouncing of the joint after the tap.
The challenge with this scale is that it’s subjective. One study had three neurologists examine the same 20 patients using a nine-point reflex scale and found that in about 28% of the reflexes tested, the observers disagreed by two or more scale points. Even more striking, when looking at whether a pair of reflexes was symmetric between sides, the examiners disagreed about the presence of asymmetry nearly half the time.1PubMed. Reliability of the clinical and electromyographic examination of tendon reflexes That degree of variability is one reason clinicians rely on patterns across multiple reflexes rather than pinning too much on any single tap.
What Matters More Than the Number
The absolute grade of a reflex matters less than how it compares to the same reflex on the other side, and how it fits into the overall pattern of upper and lower body reflexes. A person whose reflexes are 3+ everywhere is often perfectly healthy, just someone with naturally brisk reflexes. A person who is 2+ on the right biceps and 0 on the left, however, has a meaningful asymmetry that warrants investigation.
Clinicians also look at the distribution. If arm reflexes are exaggerated while leg reflexes are normal, that narrows the problem to the cervical spinal cord or brain. If reflexes are reduced in one arm but normal everywhere else, the issue is likely in the peripheral nerve or nerve root serving that arm. The reflex exam is essentially a screening tool for localizing problems in the nervous system, not a standalone diagnostic test.
What Overactive Arm Reflexes Suggest
Hyperreflexia, where reflexes are exaggerated and the response seems too large or too easy to trigger, points toward an upper motor neuron problem. Upper motor neurons run from the brain down through the spinal cord, and when they’re damaged, the spinal reflex arc loses its usual braking signals. The result is reflexes that fire more readily and more forcefully than they should.
Common causes of hyperreflexia in the arms include cervical spinal cord compression (often from disc herniations or bone spurs narrowing the spinal canal), multiple sclerosis, stroke, and traumatic brain injury. In older adults, cervical spondylotic myelopathy, where age-related changes in the spine gradually squeeze the spinal cord, is a particularly common culprit. A study of 225 patients surgically treated for cervical myelopathy found that about 60% had hyperreflexia on examination.2Journal of Neurosurgery: Spine. Clinical Correlations of Cervical Myelopathy and the Hoffmann Sign
Hyperreflexia is rarely dangerous on its own. It’s a signpost. Its value lies in telling the examiner that the problem is upstream of the reflex arc itself, somewhere between the brain and the spinal cord segment being tested.
What Weak or Absent Arm Reflexes Suggest
Hyporeflexia, the opposite pattern, points toward damage in the lower motor neuron, the peripheral nerve, the nerve root, or the muscle itself. When the reflex arc is physically disrupted at any of these points, the signal can’t complete the loop and the reflex is diminished or lost entirely.
A compressed nerve root in the neck is one of the most common reasons a single arm reflex goes quiet. A herniated disc at C5-C6 might specifically knock out the biceps reflex while leaving the triceps reflex intact. That kind of isolated loss is a powerful localizing clue. More widespread loss of reflexes across multiple limbs can occur in conditions like Guillain-Barré syndrome, where the immune system attacks the peripheral nerves, or in diabetic neuropathy, which gradually erodes nerve function starting in the longest nerves and working inward.
It’s worth noting that some healthy people simply have reflexes that are hard to find. Older adults in particular may have naturally diminished reflexes without any pathology. A reflex graded at 1+ or even absent in an otherwise asymptomatic person doesn’t automatically signal disease, though it should be interpreted alongside the rest of the exam.
The Hoffmann and Trömner Signs
Beyond the standard tendon reflexes, clinicians sometimes test two additional responses in the hand that are particularly useful for detecting cervical spinal cord compression.
The Hoffmann sign is tested by holding the patient’s relaxed middle finger and flicking the fingernail downward. A positive result is an involuntary flexion of the thumb and index finger. The Trömner sign works similarly: the examiner flicks the pad of the middle finger upward and watches for the same thumb-and-finger flexion. Both are considered markers of upper motor neuron dysfunction, and both are especially associated with cervical myelopathy.
In a study of surgically treated cervical myelopathy patients, the Hoffmann sign was present in 68% of cases overall and was substantially more common than the Babinski sign, the well-known foot reflex that serves a similar diagnostic role. In patients with milder disease, the Hoffmann sign appeared about 46% of the time, while in severe myelopathy it was present in 81%.2Journal of Neurosurgery: Spine. Clinical Correlations of Cervical Myelopathy and the Hoffmann Sign That gradient makes it useful for catching cord compression even before symptoms become severe.
The same study also looked at patients who came in only for lumbar spine complaints and had no neck symptoms at all. About 12% of them had a positive Hoffmann sign. When the sign was present on both sides, MRI showed spinal cord compression in 91% of cases, suggesting the sign can flag occult cervical disease that the patient doesn’t even know about.2Journal of Neurosurgery: Spine. Clinical Correlations of Cervical Myelopathy and the Hoffmann Sign
The Trömner sign carries similar clinical weight. Research has shown that the amplitude of the muscle response during a Trömner test correlates with the degree of spinal cord compression seen on imaging, making it not just a yes/no test but a potential indicator of severity.3PubMed Central. Quantification of the Trömner signs: a sensitive marker for cervical spondylotic myelopathy
The Inverted Supinator Reflex
One arm reflex finding that can confuse both patients and clinicians is the inverted supinator reflex. Normally, tapping the brachioradialis tendon at the wrist produces elbow flexion. An inverted response is when the fingers flex instead, sometimes with no forearm movement at all. In textbooks, this is taught as a sign of cervical myelopathy, suggesting cord compression at the C5-C6 level.
In practice, it’s not always that clear. A study of asymptomatic patients found that an isolated inverted supinator reflex, without any other abnormal neurological findings, may simply be a normal variant. The researchers concluded that the finding on its own is not a reliable sign of myelopathy, though they cautioned that in older patients it deserves closer scrutiny.4PubMed. The evaluation of the inverted supinator reflex in asymptomatic patients The takeaway: context matters. A single unusual reflex finding in an otherwise normal exam doesn’t necessarily mean something is wrong, but it shouldn’t be ignored either.
What to Do When Reflexes Are Hard to Find
Sometimes reflexes genuinely appear absent, but the problem is technique or the patient’s level of relaxation rather than nerve damage. Before concluding that a reflex is truly gone, examiners use reinforcement maneuvers to amplify the response. The most common is the Jendrassik maneuver: the patient interlocks their fingers and pulls their hands apart while the examiner taps the tendon. For arm reflexes, the patient might be asked to clench their jaw or press their knees together instead, since the classic hand-pulling version occupies the upper limbs.
The mechanism behind reinforcement is more interesting than you’d expect. Research using sensitive electrophysiological measurements has shown that the Jendrassik maneuver doesn’t work by revving up the muscle spindles in the tested limb, and it doesn’t directly excite the motor neurons either. Those were the two leading theories for decades, and both turned out to be wrong.5PubMed. An investigation into mechanisms of reflex reinforcement by the Jendrassik manoeuvre The exact mechanism remains debated, but the practical point is clear: if a reflex only appears with reinforcement, it’s graded as 1+ (trace), not 0. A reflex that truly cannot be elicited even with reinforcement is more clinically significant.
Metabolic Conditions That Alter Reflexes
Not every reflex abnormality points to a structural problem in the nervous system. Several metabolic and systemic conditions change reflex behavior in characteristic ways.
Hypothyroidism is the classic example. The deep tendon reflexes in hypothyroid patients show a distinctive pattern: the initial contraction looks normal, but the relaxation phase is abnormally slow. The muscle seems to hang for a beat before letting go. This finding, known as the Woltman sign, is most easily seen at the ankle, but it can be observed in arm reflexes too. It was historically considered so characteristic that some clinicians used the reflex relaxation time as a rough screen for thyroid function before modern blood tests were available.6PubMed Central. A classic sign of hypothyroidism: a video demonstration
Hyperthyroidism pushes reflexes in the opposite direction, making them brisk and fast. Electrolyte disturbances, particularly abnormal calcium or magnesium levels, can also affect reflexes. Severe hypocalcemia tends to produce hyperreflexia, while hypermagnesemia (often from excessive magnesium supplementation or kidney failure) can suppress reflexes. Chronic alcohol use, vitamin B12 deficiency, and diabetes can all cause peripheral neuropathy that gradually erodes reflex responses over time.
The point is that finding abnormal arm reflexes doesn’t automatically send you to a neurosurgeon. Sometimes the answer is a blood test, not an MRI.
When Electrophysiology Fills the Gaps
The bedside reflex exam is a screening tool with real limitations, and sometimes the findings are ambiguous enough that more precise measurements are needed. One way to get there is through electrophysiological testing, particularly using what’s known as the H reflex. This is essentially a lab-based version of the tendon tap: an electrical stimulus is applied to a nerve, and the reflex response is recorded from the muscle with electrodes. Because the stimulus and the recording are both precisely controlled, the H reflex can reveal abnormalities that the hammer misses.
In the arms, the H reflex is most commonly tested in a forearm muscle called the flexor carpi radialis. One useful pattern: if the H reflex is absent at rest but appears when the patient voluntarily contracts the muscle, it may indicate low excitability of the motor neuron pool rather than structural nerve damage. On the other hand, if H reflexes can be recorded from muscles where they normally aren’t present at rest, that’s electrophysiological evidence of hyperreflexia.7PubMed Central. Clinical uses of H reflexes of upper and lower limb muscles These kinds of distinctions can be hard to make with a hammer alone.
A Brief History of the Reflex Exam
Deep tendon reflexes were introduced into the medical literature simultaneously by two German neurologists, Wilhelm Erb and Carl Westphal, in 1875. Erb described the knee jerk elicited by tapping the patellar tendon, while Westphal focused on its absence in certain diseases. Interestingly, there’s evidence that the knee jerk response was well known to the general public before either physician published on it; it just hadn’t been formalized as a medical test.8PubMed. Erb and Westphal: simultaneous discovery of the deep tendon reflexes Within a few years, deep tendon reflexes became one of the central features of the neurological exam, a status they still hold nearly 150 years later.
The remarkable thing about reflex testing is how little the basic technology has changed. The hammer got more refined over the decades, with different countries and traditions preferring different designs, but the underlying test is the same one Erb and Westphal described. You tap a tendon, watch the muscle, and think about what the response tells you about the wiring between the spine and the limb. It’s one of the few parts of the neurological exam that requires no electricity, no imaging, and no lab work, just a small hammer and a clinician who knows what to look for.