Skip to contents

Detect gait events with the Zeni coordinate method

Source: R/events-zeni.R
detectEventsZeni.Rd

Implements the coordinate-based gait-event detector of Zeni, Richards & Higginson (2008). Heel strike (initial contact, IC) occurs when a heel marker reaches its most anterior position relative to a pelvis/COM reference; toe off (TO) occurs when a toe marker reaches its most posterior position relative to the same reference. Because events are keyed to the foot marker relative to the pelvis, the method works on treadmill trials where the body does not translate in the lab frame, and it returns per-stride IC/TO for both sides across a full trial.

Usage

detectEventsZeni(
  pe,
  markers,
  reference = "sacrum",
  ap_axis = NULL,
  direction = NULL,
  body_mass = NULL,
  min_separation = NULL,
  sampling_rate = NULL
)

Arguments

pe

A PhysioExperiment with marker position_x/position_y (and optionally position_z) assays (frames x markers).

markers

A named list of marker names (columns of the position assays) with entries heel_left, heel_right, toe_left, toe_right. A side is skipped if both its heel and toe entries are NULL/missing.

reference

Progression reference: a marker name (e.g. a sacral marker, the default "sacrum"), or "com" to use the whole-body centre of mass from calculateCOM() (requires body_mass).

ap_axis

Anterior-posterior (progression) axis: "x", "y", "z" or 1/2/3. NULL (default) auto-detects the axis with the largest heel-relative-to-reference excursion.

direction

+1 or -1 to orient the AP axis so anterior is positive; NULL (default) auto-detects it (the fastest relative foot motion, i.e. swing, points anterior).

body_mass

Body mass in kg, required only when reference = "com".

min_separation

Minimum number of frames between successive same-type events (refractory period). NULL (default) estimates it from the dominant stride period via autocorrelation.

sampling_rate

Sampling rate in Hz; defaults to samplingRate(pe).

Value

A detected_events data frame with one row per detected event (columns event, label, index, time, percent, method, confidence, side), sorted by frame index.

Details

The result is a detected_events data frame compatible with calculateGaitParameters(); heel-strike/toe-off rows are named left_heel_strike/right_heel_strike/left_toe_off/right_toe_off and carry an explicit side column.

References

Zeni JA, Richards JG, Higginson JS (2008). "Two simple methods for determining gait events during treadmill and overground walking." Gait & Posture 27(4):710-714.

See also

detectEvents() (use method = "zeni"), calculateGaitParameters(), calculateCOM().