Have you ever wondered why your doctor asks you to do odd things like touch your nose during an office visit, then scribbles notes in your chart? It's because there are many physical tests that can tell whether your body is functioning as it should. While we tend to leave it to doctors and medical tests to figure out if something's wrong, we can actually use many of these checks ourselves to determine whether all systems are go. Here, five odd medical tests you can do at home.

What it tests for: Cardiovascular, lung, or other diseases

How to do it: Hold up (or down) both index fingers and turn them so the nails are facing each other. Press the nails together and you should be able to see a tiny, narrow, diamond-shaped space between your nails where the nails come flat together but the nail beds don't touch each other.

What it means: If your nails are rounded over and can't press flat together, it's a sign of "clubbing," a thickening of the fingertips that occurs when not enough oxygen is circulating in the bloodstream. Clubbing can be a sign of cardiovascular disease, such as coronary artery disease or heart failure, or of lung disease, like COPD, lung infection, or lung cancer. In some cases, inflammatory bowel disease and cirrhosis of the liver also cause clubbing.

What to do if you fail: Look closely at your fingers for other signs of clubbing. Measure the thickness of your fingertips all the way around; if they're clubbing, you'll notice that they're noticeably thicker above the top knuckle than below it. Clubbing is important to bring to your doctor's attention to monitor your heart and lung health.

What it tests for: Degenerative diseases (or intoxication)

How to do it: Stand with your feet exactly together, arms by your sides. Now close your eyes and stay that way for a full minute. How do you feel: perfectly balanced, or as if you're swaying or falling forward? It's best to do this test with someone watching you to detect swaying. A variation of this test is to do it standing heel to toe on a straight line.

What it means: This test measures proprioception or positioning, considered the "sixth sense" that tells us where our bodies are in space. Proprioception requires accurate sensory input from our joints and muscles and healthy functioning of the dorsal columns of the spinal cord, which allow us to perceive the position of our limbs both in relation to other parts of our bodies and to the environment. When you can't balance with your eyes closed, it's considered a sign of sensory ataxia, or loss of motor coordination, which can be a sign of diabetic neuropathy, multiple sclerosis, inner ear problems, lumbar spinal stenosis, or another degenerative disease. Romberg's test is also sometimes used as a test of intoxication or drug use.

What to do if you fail: It is possible to fail this test when nothing is wrong with you, but -- because it can also indicate a serious condition -- it's worth discussing with your doctor. If you're also experiencing other symptoms, such as numbness, tingling in your arms or legs, or balance problems, ask your doctor for a referral to a neurologist.

What it tests for: Osteoarthritis, and other things. . . .

How to do it: Hold your hands flat and look closely at the lengths of your fingers in relation to each other. Is your index finger shorter than your ring finger?

What it means: A recent study at the University of Nottingham in England found that if a woman's index finger is shorter than her ring finger, she's more than twice as likely as others to develop osteoarthritis of the knee or hip. There's no scientific explanation yet for the connection between finger size and arthritis risk.

Several other studies have found another use for finger measurement: It can be used to guess at penis size. According to studies done in South Korea, if a man's ring finger is significantly longer than his index finger, he's likely to be well endowed, while a short ring finger indicates average to below-average size. Previous studies have shown that a long index finger is an indication of lower testosterone exposure in the womb.

What to do if you fail: Women: In this case, there's no immediate action to take. Just be on the alert for signs of osteoarthritis such as knee, hip, shoulder, or back pain. If you do develop pain and suspect osteoarthritis, you might mention the finger length research to your doctor. Guys: If you notice her looking at your ring finger, distract her by buying her a drink.

What it tests for: Neurodegenerative disease

How to do it: Hold your arm out, finger extended. Close your eyes and try to touch your nose with your finger. Then do it again with the other hand. You should be able to do this smoothly and accurately. Next, lie down and run the heel of one foot up and down the shin of the opposite extended leg.

What it means: These are two components of basic neurological testing, which evaluates coordination and fine motor movement indicative of the health of the cerebellum, the part of the brain that governs motor movement, coordination, balance, and muscle tone. Failure to do the nose and heel tests accurately can be one sign of a neurodegenerative disease such as multiple sclerosis or a brain tumor or lesion.

What to do if you fail: Try these tests several times before you conclude something's wrong, as many factors -- such as having had a glass of wine -- can affect it. If you regularly fail to get your finger anywhere near your nose, alert your doctor.