The single-leg stance test measures balance: the person stands on one leg, lifts the other, keeps their arms at their sides, and tries to hold that position for ten seconds without support and without the raised foot touching the ground.
A study published in the British Journal of Sports Medicine in 2022 followed 1,702 adults aged 51 to 75 in Brazil. People who couldn't hold the stance for ten seconds had roughly an 84% higher risk of death from any cause over the following decade than those who could - even after accounting for age, sex, BMI, and other health factors. In absolute numbers, mortality was around 17.5% in the group that failed the test versus 4.6% in the group that passed.
One explanation researchers point to is that neuromuscular coordination - the interplay of brain, nerves, and muscles needed for fine balance - tends to decline with age, often faster than raw muscle strength does. That may make single-leg balance a sensitive early signal, picking up changes before they show up elsewhere.
The result is also heavily shaped by protocol: whether the eyes are open or closed, which leg is standing, hard floor versus carpet, shoes on or off. A single home attempt isn't directly comparable to a number from a specific study.