The sit-to-stand (STS) test is a well-established way to measure a person’s ability to transition from sitting to standing, a movement that is fundamental for mobility and balance. This assessment is particularly important for older adults and individuals with musculoskeletal conditions, as it can help predict fall risk and monitor functional progress. Traditionally, the STS test involved several repetitions and was assessed mainly through observation. However, digital innovations like the markerless MAI Motion system are changing the way these tests are performed. MAI Motion uses digital motion capture to deliver detailed biomechanical and kinematic data—no markers or specialized equipment required. In this article, we look at how a streamlined three-repetition (3x) STS test, when combined with MAI Motion , can provide accurate results while reducing participant effort and discomfort.

The Biomechanics Behind the Sit-to-Stand

Standing up from a chair seems easy, but it’s actually a sophisticated sequence of coordinated motions. Biomechanics breaks this movement into four phases: flexion momentum (leaning forward), momentum transfer (shifting body weight forward), extension (straightening the hips and knees), and stabilization (achieving balance after standing).

During each phase, joint angles at the hips, knees, and ankles change to move the body’s center of mass safely and efficiently. By analyzing joint angles, range of motion, and the impulse (force generation at movement start), clinicians can pinpoint weaknesses or balance issues that may elevate fall risk. Using markerless motion capture , detailed movement features can be recorded non-invasively, giving clinicians robust insights into patient capabilities (Wen et al., 2025).

The Limits of the Five-Repetition Test

Traditionally, the STS test required participants to stand up and sit down five times in quick succession. While informative, this five-repetition (5x) approach can be too demanding for many—especially those recovering from surgery, living with chronic pain, or experiencing significant weakness. Completing five repetitions can lead to fatigue, increased discomfort, and, for some participants, incomplete or inconsistent test results.

Furthermore, more repetitions don’t always add value. Fatigue and changes in muscle control over several repetitions can introduce extra variability, making results harder to interpret. In practice, the additional strain on patients may outweigh the incremental benefits of the extra data.

Putting the Three-Repetition Method to the Test

To better balance data quality with patient comfort, researchers used MAI Motion ’s markerless technology to compare the traditional 5x STS with a shorter, three-repetition (3x) protocol in 20 participants. They measured key joint angles and calculated statistics like the coefficient of variation (CV, a measure of consistency) and mean differences between tests.

The results were encouraging. Differences between the 3x and 5x protocols were minimal, and the variability seen in movement patterns was not clinically significant. The three-repetition protocol delivered biomechanical data as precise as the longer test—while significantly reducing the effort required from participants (Wen et al., 2025).

Variability and Reliability: What the Numbers Say

Looking deeper, the study found that certain joint movements —such as the ankle or sideways (abduction) movements of the hips and knees—showed slightly more variability between repetitions. However, the average joint angles for both test formats were nearly identical.

In clinical biomechanics , a coefficient of variation under 10% is considered very reliable; 10–20% is still regarded as acceptable. The 3x STS protocol largely fell within these boundaries, confirming its consistency. Importantly, by reducing repetitions, the test is less likely to be affected by participant fatigue, increasing the likelihood that the results reflect genuine movement ability, not tiredness. This makes the 3x STS a reliable, efficient option.

Bringing the Three-Repetition STS into Practice

Shifting to a three-repetition STS test brings tangible benefits. The shorter protocol is quicker, less tiring, and better suited for people who may find repeated transitions difficult or uncomfortable. The MAI Motion system’s markerless design also means clinicians can use standard cameras—there’s no need for special suits, markers, or elaborate equipment—making the test easier to perform in clinics, homes, or via telehealth .

Participants themselves reported that three repetitions felt more manageable, suggesting that the shorter protocol could improve adherence and broaden participation, especially in remote settings or among frail populations. By blending precise data capture with less burden on the patient, the 3x STS can be seamlessly integrated into rehabilitation, ongoing monitoring, or self-assessment routines. Clinicians get trustworthy data, and patients experience less stress—an ideal outcome.

Looking Ahead: What’s Next for the 3x STS?

Although these results are promising, there are limitations. This study was conducted with a relatively small, homogeneous group, and only evaluated the sit-to-stand task. Future research should include larger and more diverse populations and evaluate the performance of the 3x protocol across other movement tasks—like single-leg stands or squats—to confirm its broad applicability.

Validation in specific clinical populations—such as those with osteoarthritis , muscle weakness, or post-stroke impairments—will be key to fully establishing clinical value. As technology and artificial intelligence continue to advance, digital motion capture will likely become more powerful, opening up even greater potential for personalized, long-term movement assessments .

In summary, the three-repetition sit-to-stand test , especially when paired with markerless motion capture like MAI Motion , strikes a smart balance between accuracy and ease. It makes functional mobility assessment more accessible, less taxing, and ideally suited for modern healthcare settings. As digital health tools continue to evolve, expect the 3x STS to become a new standard—helping more people maintain independence and quality of life with less effort.