ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

and angular rates were registered by 3-axis acceleration and orientation sensor
(MicroStrain Inc, 3DM-GX2 inertia-link). Full-length stride curves were computed by
resampling data segments spanned by one gait cycle. A total averaged signal was
computed over registers of 360 s. Orthogonality of axial accelerometry was assured by
correcting measured data with the instant rotation matrix.
Fig. 1 Phase plane of acceleration vs velocity in the vertical axis.
Fig. 1 shows representative phase plane portraits along the V axis, for two strides of one
subject; where gait progression occurs in the clockwise direction, some events of the
gait cycle are marked for reference. The patterns in the phase plane make evident the
differences between the dominant and non-dominant legs, the former presents higher
acceleration and velocity values than the latter. The second quadrant (negative velocity
and positive acceleration) in the plane allocates the contact. In the first quadrant the
body load is fully transferred to the supporting leg, and acceleration reaches its peak
value. Forefoot loading decelerates pelvic motion until reaching the negative peak value
in the fourth quadrant, where, after forefoot loading acceleration. Midstance events
elicit a smooth deceleration while velocity reaches equals zero; gait evolves towards the
swing phase with a gradual increment of acceleration in the third quadrant, at late swing
phase a smooth deceleration anticipates the next opposite heel contact. The
corresponding phase plane portrait along the AP axis is shown in Fig. 2. In the first
quadrant starts the contact phase, on heel strike, acceleration decreases at a high rate
becoming negative while velocity presents a short change. The response to forefoot
loading is shown in the fourth and third quadrant. In the second quadrant a gradual
acceleration develops propelling the body in preparation for the heel strike. The number
of trajectories in the phase plane, along the ML are half than in the planes of V and AP
axes; however variability is higher in the former, as shown in Fig. 2. After heel strike,
in the first quadrant, there is a stepped deceleration until midstance, as velocity
decreases from positive to negative values acceleration exhibits high variability up to
the heel strike of the opposite leg. Afterwards, early and middle swing phases take place
at the second quadrant with a gradual acceleration propelling the body in preparation for
the heel strike.