Hoover’s sign refers to two different clinical tests, both named after Dr. Charles Franklin Hoover, a physician in Cleveland, Ohio, who described them in 1908. The neurological version detects whether leg weakness is functional (meaning the nervous system is structurally intact) rather than caused by nerve damage or a stroke. The pulmonary version identifies a problem with how the diaphragm moves in people with severe lung disease. Despite sharing a name, the two tests examine completely different parts of the body and serve different diagnostic purposes.
The Neurological Hoover’s Sign
This is the more commonly referenced version. It takes advantage of a simple principle: when you lift one leg while lying on your back, your other leg automatically pushes down into the surface beneath it. This happens involuntarily. You don’t have to think about it. Hoover realized that this automatic response could reveal whether someone’s leg weakness had a structural neurological cause or not.
The test works like this. You lie flat on your back with your legs straight. The examiner places their hands under both of your heels. First, they ask you to press both legs down into their hands to establish a baseline of your strength. Then they run two sequential tests. In the first, they ask you to lift your unaffected leg while paying attention to how hard your affected (weak) leg pushes down. In the second, they ask you to lift your affected leg while checking how hard your unaffected leg pushes down.
The sign is considered positive when the examiner feels strong downward pressure from the weak leg during the first test (when you’re lifting the good leg), but that same weak leg produces little or no voluntary force when you’re asked to lift it directly. In other words, the leg clearly has the strength to push down automatically, but that strength disappears when you try to use it on purpose. This inconsistency between involuntary and voluntary movement is the hallmark of what’s called functional weakness.
What a Positive Result Means
A positive neurological Hoover’s sign is one of the key indicators of Functional Neurological Disorder, or FND. This is a real condition where the brain’s ability to send and receive signals works differently, even though there’s no structural damage visible on scans. It’s not malingering or faking. The weakness is genuine from the patient’s perspective, but it doesn’t follow the patterns seen in stroke, spinal cord injury, or nerve damage.
Hoover’s sign is considered the most extensively studied and validated bedside technique for identifying functional leg weakness. Its mechanism has been confirmed using computerized force-measurement tools that show significant differences between functional weakness and weakness caused by identifiable nerve damage. Hoover himself originally developed the test because he found existing methods for distinguishing organic from non-organic weakness unsatisfactory. His 1908 paper, based on just four patients seen over two years, introduced a principle that remains central to neurological examinations more than a century later.
The Pulmonary Hoover’s Sign
The pulmonary version is an entirely separate observation. It refers to an abnormal inward movement of the lower rib cage during breathing, seen in people with obstructive lung disease like COPD or emphysema. Normally, when you breathe in, your lower ribs flare outward as the diaphragm contracts and pulls downward. In people with severely hyperinflated lungs, the opposite happens.
The reason is mechanical. In healthy lungs, the diaphragm is dome-shaped and sits against the inner chest wall. When it contracts, it pulls the ribs outward and upward. But in advanced COPD, the lungs become chronically overinflated with trapped air. This pushes the diaphragm flat. A flattened diaphragm loses its normal contact with the chest wall, and when it contracts, the force it generates pulls the lower ribs inward instead of outward. The result is a visible, paradoxical indrawing of the lower rib margins every time the person takes a breath in.
Pulmonary Hoover’s Sign and COPD Severity
The presence of this sign tracks with disease severity. Studies have found it appears in about 36% of people with moderate COPD, 43% with severe COPD, and 76% with very severe COPD. People who show the sign tend to be older, have a higher BMI, and have more severe airflow obstruction.
Research into patients with severe and very severe COPD found that those with Hoover’s sign had significantly weaker inspiratory muscle strength and more air trapping compared to those without it. Interestingly, overall lung hyperinflation as measured by standard breathing tests wasn’t significantly different between the two groups, suggesting the sign reflects diaphragm dysfunction specifically rather than just how inflated the lungs are. The ratio between expiratory and inspiratory muscle pressures was higher in people with Hoover’s sign, pointing to a mismatch in how the breathing muscles generate force.
How the Two Signs Connect
Both signs were described by the same physician, Charles Franklin Hoover, who trained as a Methodist minister before studying medicine at Harvard, Vienna, and Strasbourg. He went on to become a professor of medicine at Western Reserve University in Ohio, specializing in lung and liver disease. The neurological sign appeared in his 1908 paper. The pulmonary sign was described in 1920. Both rely on the same core insight: observing what the body does automatically can reveal problems that direct testing might miss. In the neurological version, it’s involuntary leg extension exposing preserved motor pathways. In the pulmonary version, it’s the visible rib movement exposing a diaphragm that has lost its mechanical advantage.