METHODS FOR COMPUTING A REAL-TIME STEP LENGTH AND SPEED OF A RUNNING OR WALKING INDIVIDUAL
FIG1 is a perspective view of an individual having a wrist-wearable device attached to the wrist  FIG2 is a schematic perspective view of a path followed by an individual during a walking (or running) session
On FIG1 is schematically drawn an individual on foot 1. The individual 1 is supposed to be healthy and have all his/her members, including legs and arms, the arms having wrists 2. The individual 1 defines a vertical sagittal plane P1 (which is the global symmetry plane of the individual 1) and a vertical front plane P2, which is perpendicular to the sagittal plane P1. As depicted on FIG1, a wrist-wearable device or "smartwatch" 3 is attached to at least one of the individual's wrists, here to the right wrist 2.  The smartwatch 3 is configured to monitor activity and infer various parameters of the individual 1 while he/she is moving on foot (i.e. either running or walking) on a path 4, the variations of altitude of which are voluntarily exaggerated on FIG2.
perspective view, schematic perspective view
3
smartwatch
2
wrist wrists
1
individual
["1. Method for computing an estimation of the step length  SL ^ n ′  of an individual (1) running along a path (4), over a time window  n',  n' being an integer higher than or equal to 1, said individual (1) being equipped with a wrist-wearable device (3) including: - a calculation unit (5), - a GNSS transponder (9) configured to deliver instant speeds of the device (3), - a barometer (8) configured to deliver instant atmospheric pressure measures (P), - an accelerometer (7) configured to deliver instant acceleration measures along three perpendicular axes, namely: ∘ a first acceleration  S x  along an  X  axis perpendicular to the wrist and parallel to a sagittal plane ( P 1) of the individual (1); ∘ a second acceleration  S y  along a  Y  axis parallel to the wrist and parallel to the sagittal plane ( P 1) of the individual (1); ∘ a third acceleration  S z  along a  Z  axis perpendicular to the wrist and parallel to a front plane (P2) of the individual (1); said method comprising the following steps, carried out by the calculation unit (5): - computing (208) a vector of features  X [ n ] over a time window  n ,  n  being an integer higher than or equal to 1, as follows:  X n = 1 F 1 n F 2 n F 3 n F 4 n F 2 2 n  where: ∘ feature  F 1 [ n ] is an instant cadence  cad ^ n  of the individual (1) over time window  n , computed from the norms of the instant acceleration measures  S x [ n ] ,S y [ n ] ,S z [ n ] delivered by the accelerometer (7) over time window  n , ∘ feature  F 2 [ n ] is an instant slope of the path computed from the instant atmospheric pressure measures ( P [ n ]) delivered by the barometer (8) over time window  n , ∘ feature  F 3 [ n ] is an instant energy of the second acceleration measures  S y [ n ] delivered by the accelerometer (7) over time window  n , ∘ feature F 4 [ n ] is an instant mean absolute jerk of the second acceleration measures  S y [ n ] delivered by the accelerometer (7) over time window  n , - computing (210) a coefficient vector β[ n ] over time window n as follows:  β n = β n − 1 + D n X n SL n − X n T β n − 1  where: ∘  D [ n ] is the dispersion matrix of the instant vector of features  X[n], ∘  SL n = V n cad ^ n , ∘  V [ n ] is a speed of the wrist-wearable device (3), measured by the GNSS transponder (9) over time window  n , ∘  β [0] is an initial parameter, - computing (302) a vector of features  X [ n' ] over time window  n',  as follows:  X n ′ = 1 F 1 n ′ F 2 n ′ F 3 n ′ F 4 n ′ F 2 2 n ′ - computing (304) the step length  SL[n']  as follows:  SL ^ n ′ = X n ′ β n ."]