Standing on one leg may seem simple, but holding the position requires multiple systems in your body to work together to keep you upright, stable, and balanced.
The Single Leg Stance (SLS) test is a commonly used balance assessment that provides a simple way to measure this ability. Kinis uses the SLS test as part of its approach to measuring Movement Health™. This article explains the test, what research tells us about it, how Kinis analyzes your performance, and what your results can and cannot tell you.
Written by: Mary Bath, Doctor of Physical Therapy, Director of Balance Health, Kinis AI
Balance 101: How your body keeps you upright
To keep you upright, the brain continuously integrates sensory data from three distinct systems: your vision, which helps you understand where you are in relation to your surroundings; your vestibular system, located in your inner ear, which tracks the position and movement of your head; and your somatosensory system, which uses proprioception to sense where your joints and limbs are without having to look at them.
Depending on the balance task and environment, the brain dynamically adjusts how much it relies on each sensory source. The nervous system then processes this integrated information to trigger precise responses, while the musculoskeletal system provides the strength and joint control needed to make ongoing postural corrections.
What does the SLS test measure?
At its core, the SLS test assesses static balance and postural control. In the traditional clinical test, performance is typically measured by time: how long you can maintain the stance before losing the required position.
Is there a normal SLS time?
There is no single “normal” time that applies to everyone. SLS performance changes with age, and results can also be affected by how the test is performed — footwear, arm position, eyes open or closed, which leg is tested, the number of trials, and the maximum test duration.
Kinis uses a standardized protocol to help make results more consistent and comparable: barefoot, hands on hips, and the raised leg held in a specified position. Following the same protocol matters most when comparing results over time. Age also provides important context, which is why Kinis compares your hold time against age-based norms.
How Kinis analyzes the SLS
Kinis brings the SLS assessment directly to your clinic or home using a smartphone or tablet. You follow the instructions in the Kinis app and perform the stance while the camera captures your movement, analyzed with markerless visual skeleton tracking.
The traditional assessment primarily measures how long you can hold the stance. It can also be useful to understand how you maintain it. Kinis builds on that idea by looking at hold time along with four additional components of how your body moves while you balance:
For each component, Kinis calculates the average position across the entire trial and uses that as a baseline, then measures how much your movement deviates from it frame to frame. Ankle stability looks at the standing ankle, pelvis control uses tracked hip landmarks, trunk steadiness uses shoulder and hip landmarks, and whole-body stability combines all three. Results are reported separately for each leg.
Understanding your Kinis results
Your results give you a measurable starting point for understanding and tracking your balance: left and right legs, the individual movement components, and an overall score. Your first assessment shows where you are starting; you then receive an exercise program and repeat the assessment to see what has changed.
What can the SLS test tell you?
- Understand your current balance performance
- Compare your hold time with age-based reference values
- Look at how you maintain the position at the ankle, pelvis, and trunk
- Establish a baseline for future comparison
- Track changes when you repeat the assessment over time
What can’t the SLS test tell you?
- Diagnose a health condition
- Assess or diagnose an injury
- Predict whether you will fall
- Capture every aspect of balance you use in everyday life
- Replace an evaluation by a qualified healthcare professional
The SLS is best used as one piece of information about your balance performance — most useful when performed consistently and repeated over time.
Safety: who should not perform the test?
Do not perform the assessment if you need a cane, walker, or another person to stand safely, if you have had a recent fall, unexplained dizziness or vertigo, an acute injury or severe pain, post-surgical restrictions, or if you do not feel safe attempting it. If you are unsure, speak with a qualified healthcare professional first.