Comparison of a standalone consumer grade smartphone with a specialist inertial measurement unit for quantification of movement symmetry in the trotting horse.
Authors: Pfau T, Weller R
Journal: Equine veterinary journal
Summary
# Editorial Summary: Smartphone-based gait analysis in horses Pfau and Weller investigated whether readily available smartphone accelerometers could replace expensive specialist inertial measurement units (IMUs) for detecting movement asymmetry in trotting horses—a question of considerable practical importance given that IMU technology is increasingly used in equine practice for objective lameness assessment and rehabilitation monitoring. In a method comparison study, they fitted 17 horses with both a validated specialist IMU system and an Apple iPhone 6 positioned side-by-side over the sacrum, collecting symmetry and range-of-motion data during in-hand trotting and lunging on soft ground. The smartphone proved reasonably accurate, with limits of agreement of ±9.2 mm for mid-stance differences and ±6.0 mm for propulsion phase differences—margins that align with published asymmetry thresholds relevant to clinical decision-making, particularly during straight-line work. However, the system showed critical sensitivity to mediolateral positioning, with lateral displacement of the smartphone substantially reducing measurement error and bias, suggesting that practitioners using smartphone-based analysis must exercise careful standardisation of sensor placement. For farriers, physiotherapists and veterinarians seeking objective gait data on a budget, this work suggests smartphones merit consideration as a supplementary tool, though consistency in mounting technique would be essential to ensure reliable longitudinal monitoring.
Read the full abstract on PubMed
Practical Takeaways
- •Smartphones can provide useful gait symmetry data in horses comparable to specialist IMU systems, particularly for in-hand trotting assessment — potentially offering a more accessible diagnostic tool
- •Precise, consistent mediolateral placement of any IMU over the sacrum is critical for reliable measurements; even small positioning shifts can substantially alter results
- •In-hand exercise produces more reliable data than lunging, so standardise assessment protocols accordingly if using smartphone IMU for clinical decision-making
Key Findings
- •Consumer grade smartphone IMU provided clinically meaningful gait data with limits of agreement of -3.7 ± 9.2 mm for MinDiff, -0.6 ± 6.0 mm for MaxDiff, and -0.8 ± 7.4 mm for ROM compared to specialist IMU system
- •Limits of agreement were narrower for straight-line in-hand exercise than for lunging, suggesting exercise type affects measurement reliability
- •Mediolateral positioning of the smartphone sensor significantly affected outcome parameters, with negative bias considerably reduced when positioned to the right of midline
- •Agreement between devices was sufficiently close to published asymmetry thresholds to make smartphone IMU a potentially viable alternative for gait analysis in some applications