Simple functional tests are essential tools in knee care, helping both clinicians and patients track joint health and mobility. Now, with the arrival of MAI Motion —a cutting-edge, AI-driven, markerless motion capture technology—the process is becoming even easier and more accurate. MAI Motion enables knee function assessment at home or in the clinic, without complex or costly equipment.

Traditionally, clinicians have relied on five-repetition versions of sit-to-stand (STS) and squat tests. Although effective, these tests can be too strenuous for some patients, particularly those with pain, weakness, or limited mobility. This article explores the growing evidence supporting a shorter, three-repetition version of these tests. With MAI Motion ’s precise analytics, three repetitions are enough to provide crucial information—such as movement smoothness and range of motion—helping inform better treatment decisions while putting less strain on patients.

Understanding MAI Motion in Knee Assessment

MAI Motion brings knee assessment into the digital age. Rather than relying on wearable markers or expensive force plates, it uses standard cameras or smartphones. Advanced AI algorithms construct a real-time digital skeleton, tracking joint movements and angles as the person performs each movement.

This approach is more affordable, easier to set up, and accessible beyond specialized labs. Immediate feedback allows clinicians to capture joint angles, movement quality, and smoothness instantly, streamlining the assessment process. Recent studies highlight that standard RGB cameras can reliably capture clinically relevant motion data (Armstrong et al., 2024). Importantly, research supports the accuracy of a three-repetition sit-to-stand test using MAI Motion , showing results comparable to the traditional five-repetition version. This means clinicians can rely on shorter, less demanding tests without sacrificing quality.

Streamlining the Sit-to-Stand Test: Five Reps Down to Three

The five-repetition sit-to-stand (STS) test has long been a trusted measure of leg power and balance, helping identify those at risk of falls—especially in older adults. However, for many patients, five repetitions can be tiring, or even unsafe.

Studies now show that the three-repetition version provides nearly all the same insights. Wen and colleagues found that key measures, like joint angles and movement consistency (measured by coefficient of variation), were almost identical between the three- and five-rep tests—a CV of 14.3% for three reps compared to 15.2% for five. Participants also reported that the shortened test was less physically taxing. These findings suggest that the three-rep test maintains essential metrics like range of motion and movement smoothness, all while making the process easier and more inclusive for a broader range of patients.

Squat Metrics: Deeper Insights into Knee Function

Squat tests provide another vital perspective on knee health, emphasizing deep knee bending and flexion—an area not fully captured by sit-to-stand movements. Using markerless technology like MAI Motion , researchers can identify specific knee flexion angles, both average and maximum, as reliable signals of joint function.

Combined data from the hip, knee, and ankle are used as “biomarkers” for overall movement quality. MAI Motion measures how smoothly someone lowers and rises in a three-repetition squat, as well as the total range of motion, delivering detailed and clinically valuable feedback.

Detecting subtle differences in these variables can flag early signs of functional decline, even before pain or noticeable symptoms arise. This provides an opportunity for timely intervention and more targeted care. Researchers note that these objective biomechanical measures, now obtainable without cumbersome markers, are more representative of natural movement and better suited to clinical and remote environments.

Clinical Benefits: Early Detection and Practical Monitoring

Implementing three-repetition sit-to-stand and squat tests has important implications for patient care. These tests can identify early warning signs of knee-related conditions such as osteoarthritis or muscle loss, and are also useful for monitoring rehabilitation progress after surgery.

Research shows that as people age or become frailer, their movements become less smooth and more variable—important signs of declining joint health. MAI Motion ’s detailed analytics allow clinicians to track these changes and personalize treatment plans accordingly. The streamlined test protocol is easier for older adults or those recovering from surgery, increasing both safety and participation.

Another advantage of MAI Motion is its support for remote assessments. Patients can perform these simple tests at home, allowing clinicians to monitor progress and update care plans without requiring frequent clinic visits—an especially valuable feature for those with limited mobility or tight schedules.

How to Safely Perform MAI Motion Tests at Home

If you’d like to use MAI Motion at home, follow these easy steps for safe and accurate results:

1. Choose a sturdy, armless chair of standard height for consistency.
2. Position your camera or smartphone about 1.5 to 2 meters away at knee height, ensuring your entire body is visible.
3. Wear fitted, comfortable clothing to help the AI accurately track your movements.
4. Perform three controlled sit-to-stand repetitions. Then, after a short pause, do three squats, keeping your torso upright and moving at a steady, comfortable pace.

If you feel unsteady, have a handrail or another person nearby for support. Warm up with light movement for a few minutes before starting. Afterwards, review the feedback from MAI Motion on movement smoothness and range of motion to help guide your exercise or rehabilitation routine .

Conclusion

Three-repetition sit-to-stand and squat tests using MAI Motion offer a practical, reliable, and patient-friendly way to assess knee health. By reducing the physical effort required without sacrificing the accuracy of biomechanical data , these tests make early detection and monitoring of knee issues more accessible to everyone.

As digital health tools like MAI Motion advance, knee care is becoming more precise, efficient, and convenient. Adopting these streamlined and markerless assessments empowers both clinicians and patients, helping drive smarter, more proactive orthopaedic treatment and rehabilitation .

References

• Wen, Y., Verma, T., Whitehead, J. P., & Lee, P. (2025). Empirical Validation of a Streamlined Three-Repetition Sit-to-Stand Protocol Using MAI Motion. Applied Sciences, 15, 5688. https://doi.org/10.3390/app15105688
• Armstrong, K., Zhang, L., Wen, Y., Willmott, A. P., Lee, P., & Ye, X. (2024). A marker-less human motion analysis system for motion-based biomarker identification and quantification in knee disorders. Frontiers in Digital Health. https://doi.org/10.3389/fdgth.2024.1324511
• Armstrong, K., Wen, Y., Zhang, L., Ye, X., & Lee, P. (2022). Novel clinical applications of marker-less motion capture as a low-cost human motion analysis method in the detection and treatment of knee osteoarthritis. Journal of Arthritis, 11. https://doi.org/10.4172/2167-7921.2022.11.053