Before administering a field sobriety test on the side of a Massachusetts roadway, law enforcement officers have to go through training to learn how to correctly administer them. Two of these are the walk-and-turn test and the one-leg stand test. These measure balance, which can be precarious for someone who has a blood alcohol concentration at or above the legal limit of 0.08 percent.

According to AAA, an officer may suspect that drivers are under the influence of alcohol if they have to put their arms out to catch their balance while taking heel-to-toe steps, or while standing on one foot and holding the other about six inches off the ground. If a driver also steps off the line in the first test, or puts the foot down in the other, the officer may determine that those two errors are enough reasonable proof that a person is impaired and can be required to take a breath or blood test.

The State University of New York warns that it is extremely common for drivers who have not had any alcohol or drugs to fail either or both of these tests. Although the administration of the tests is standardized, the officers use their personal discretion to interpret the results, adding another layer of fallibility.

A person who has a health problem should be given an opportunity to inform the officer that there is a valid reason to avoid the test. However, without a specific condition, a driver may not be able to explain the root of the balance issues. These may stem from factors as simple as posture, weight, height and even the length of the feet.