The Science Behind SoterCoach

SoterCoach is designed to detect and reduce high-risk movements that lead to musculoskeletal disorders (MSDs). It uses wearable sensors—placed on the back or shoulder—to measure posture and motion in real time. These measurements are compared against scientifically defined thresholds to determine when a movement becomes hazardous. Here's what it measures and why.

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📍 Spine-Related Movements (Back Device)

1. Bending

• Measured angle: Spine flexion (forward bend)

• High-risk threshold: >85°

• Why this matters: Although bending beyond 60° is flagged in ergonomic tools like REBA and RULA, Soter chose 85° to reduce false positives in real-world settings. This ensures that the system alerts only for the most severe, potentially harmful bending.

2. Twisting

• Measured angle: Rotation of the spine

• High-risk threshold: >30°, or >45° when combined with bending

• Why this matters: Twisting combined with bending (especially beyond 50°) puts excessive load on spinal discs. That’s why the threshold is lowered when both movements occur together.

3. Static Posture

• Measured condition: Holding a bent posture >60° for ≥20 seconds

• Why this matters: Holding bent positions restricts blood flow and increases fatigue, making tissues more vulnerable to injury. 20 seconds is the maximum recommended duration in static postures before risk increases.

4. High-Intensity Movements

• Indicators: Jerky movements, fatigue-influenced technique, rapid bending/extension

• Why this matters: These movements are linked to decreased spinal stability. Soter infers high intensity when movements are fast, forceful, or likely affected by fatigue or poor technique.

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📍 Shoulder-Related Movements (Shoulder Device)

1. Arm Elevation

• Measured angle: Angle between the upper arm and vertical line

• High-risk threshold: >90°

• Why this matters: Most tasks can be safely done with arms below 90°. Exceeding this puts strain on the rotator cuff and stabilizing muscles. Limiting elevation reduces risk of tendonitis and shoulder pain.

2. Static Arm Elevation

• Measured condition: Holding arms above shoulder height for prolonged periods

• Why this matters: Continuous elevation leads to muscle fatigue and shoulder overuse injuries. The duration and repetition of this position are key indicators of risk.

3. Repetitive Arm Movements

• Measured metric: Number of arm elevations per minute/hour

• Why this matters: High repetition is a known contributor to upper limb disorders. Tracking frequency allows early detection of overuse risk.

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📊 Why These Thresholds Were Chosen

The thresholds used by SoterCoach are based on:

• Global ergonomic standards (REBA, RULA, LUBA)

• 3+ years of real-world usage data from 15,000+ workers across 210 companies

• Field testing and user feedback, to reduce false positives and increase user compliance

• The Pareto principle, used to group risk exposure levels into:

  • Low Risk: <10 hazardous movements per hour

  • Medium Risk: 10–20 per hour

  • High Risk: >20 per hour

These thresholds strike the right balance between scientific rigor and real-world usability—ensuring SoterCoach delivers alerts when they matter most, and avoids unnecessary interruptions.