This document summarizes two experiments that examined the coordination strategies during walk-run and run-walk transitions. Experiment 1 found that walking and running have distinct coordination patterns that remain stable at different speeds. Experiment 2 analyzed coordination in the transition stride and surrounding strides, finding that the transition stride adopts the coordination of the emerging gait. There was hysteresis in transition speeds between walk-run and run-walk. The data suggest gait transitions occur due to coordination thresholds rather than energy optimization.

1. CO-ORDINATION STRATEGIES DURING WALK-RUN AND RUN-WALK TRANSITIONS.
A. Moss
Department of Exercise and Sport Science, Manchester Metropolitan University, Hassall Road, Alsager
ST7 2HL, UK.
Abstract
Theories attempting to explain the transition from walking to running (W/R), and likewise running to
walking (R/W), postulate gait transitions occur as a result of a “mechanical trigger” (Farley & Taylor
1991), an “energetic trigger” or a mechanical limit in the current mode of locomotion (Alexander
1984). Diedrich & Warren (1995) proposed an explanation in line with dynamic theory that gait and
gait transitions behave like non-equilibrium phase transitions between preferred locomotor states or
attractors. One trained male subject aged 30, body mass 61.9 kg and height 1.74 m performed 2
experiments on a manually controlled powerjog treadmill.
Experiment 1 examined the kinematics and metabolic cost of walking and running at overlapping
velocities, specifically 1 m.s-1
, 1.5m.s-1
, 2 m.s-1
and 2.5 m.s-1
(walking) and 1.5 m.s-1
, 2 m.s-1
, 2.5 m.s-1
and 3 m.s-1
(running). A two dimensional video recording was made of the subject from a sagittal view
using a Panasonic F15 video camera and used for later analysis. Expired gas samples were collected
using Douglas bags during the 3rd minute of each 4-minute trial. Gas samples were analysed for
oxygen and carbon dioxide concentration (Servomex, series 1400) and these values used to determine
the metabolic energy cost of locomotion. Calculated energy expenditure values identified an equal
energy crossover (approx. 2.4 m.s-1
) after which walking has a greater metabolic cost than running.
Three full strides were digitised from the video recording for each speed of walking and running, using
an Archimedes 440 computer interfaced with an m-image video card. The hip-knee co-ordination
strategy was analysed using Conjugate Cross correlation analysis (Amblard et al., (1994, Journal of
Motor Behaviour, 26, 103-112). Analysis was performed using 15 phase lags from -0.28 s to + 0.28 s.
Different co-ordination strategies were used for walking and running with the strategy remaining stable
across all speeds for each mode of locomotion.
Experiment 2 examined the kinematics of W/R and R/W transitions brought about through linear
increases and decreases in treadmill belt velocity. Video data were collected and analysed as in
experiment one. Five strides each [T-2, T-1, T (Transition stride), T+1 and T+2] from 8 W/R and R/W
transitions were analysed. Analysis of the z-transformed cross correlation functions identified pre- and
post- transition strides to produce a similar co-ordination strategy to that seen in steady state
locomotion from experiment 1. The co-ordination strategy for the transitional stride was similar to that
of the motions towards which the transition was moving and significantly different (p>0.05) to the
previous mode.
Hysterisis was found upon examination of the treadmill belt velocity at the point of transition. The W/R
transition occurred at a mean of 1.86 + 0.12 m.s-1
and the R/W transition occurred at a mean of 1.93 +
0.21 m.s-1
. This finding suggests that there is an inertia to the change with the performer continuing
with the current pattern of motion before making a sudden jump to the new mode. Analysis of energy
cost data suggest that this transition is not prompted by a desire to optimise energy expenditure. These
data suggest that the transition between walking and running occurs at a critical threshold of the co-
ordination strategy and is not determined by energy expenditure.