title: Comparison of a standalone consumer grade smartphone with a specialist inertial measurement unit for quantification of movement symmetry in the trotting horse.
abstract: BACKGROUND
  Equine inertial measurement unit (IMU) gait analysis has gained in popularity for use in horses. Similar transducers are now found in consumer grade smartphones. However, to date there are no scientific data evaluating their use for assessment of movement (a)symmetry in the horse.
  
  
  OBJECTIVE
  To establish limits of agreement (LoA, mean difference ±2 s.d.) between a validated specialist IMU system and IMU data collected with a consumer grade smartphone for quantification of movement symmetry and range of motion (ROM) of pelvic movement in the trotting horse.
  
  
  METHODS
  Method comparison study based on quantitative gait data.
  
  
  METHODS
  Twenty horses were equipped with a specialist IMU (MTw, Xsens) and a consumer grade smartphone (Apple iPhone6), both securely attached immediately in front of one another in the midline over the sacrum. Horses were trotted in-hand and lunged on both reins on a soft arena surface. Median values for movement symmetry and ROM were determined over a series of strides for each exercise condition. Data collection was repeated in 6 horses to determine the effect of mediolateral sensor positioning on outcome parameters.
  
  
  RESULTS
  Valid data from 17 horses resulted in LoA values of -3.7 ± 9.2 mm for MinDiff (difference between left and right hind mid stance), -0.6 ± 6.0 mm for MaxDiff (difference between left and right hind propulsion) and -0.8 ± 7.4 mm for ROM across horses and exercises. LoAs were narrower for straight line exercise and the negative bias was considerably reduced when moving the smartphone to the right of the midline.
  
  
  CONCLUSIONS
  The consumer grade smartphone provided meaningful gait data in horses: LoAs in particular for in-hand exercise and when adjusting the mediolateral positioning are similar to published asymmetry thresholds. Owing to the sensitivity to mediolateral positioning, particular care should be taken when placing an IMU over the midline of the horse.
authors.affiliation: Department of Clinical Science and Services, Royal Veterinary College, Hatfield, UK.
authors.forename: T
authors.identifier: http://orcid.org/0000-0002-0702-4289
authors.initials: T
authors.lastname: Pfau
authors.affiliation: Department of Clinical Science and Services, Royal Veterinary College, Hatfield, UK.
authors.forename: R
authors.initials: R
authors.lastname: Weller
mesh_terms: D061725:Accelerometry / Q000295:instrumentation / Q000379:methods / Q000662:veterinary*; D000818:Animals; D005684:Gait / Q000502:physiology*; D006736:Horses / Q000502:physiology*; D009068:Movement / Q000502:physiology*; D010805:Physical Conditioning, Animal; D000068997:Smartphone
keywords: horse; inertial measurement unit; movement symmetry; smartphone