WHEN DOES A GAIT TRANSITION OCCUR DURING HUMAN LOCOMOTION?
California State University, Department of Kinesiology and Health Science,
Sacramento, CA, USA
09 August 2006
Journal of Sports Science and Medicine (2007) 6, 36 - 43
Google Scholar for Citing Articles
|When a treadmill accelerates continuously, the walk-run transition
has generally been assumed to occur at the instant when a flight phase
is first observed, while the run-walk transition has been assumed
to occur at the instant of the first double support period. There
is no theoretical or empirical evidence to suggest that gait transitions
occur at the instant of these events, nor even whether transitions
are abrupt events. The purpose of this study was to determine whether
the gait transitions during human locomotion occur abruptly, and if
so, to determine the instant during a stride at which a transition
occurs. The time history of the vertical velocity of the hip (vhip)
and the angular velocity of the ankle (ωankle) were
compared between constant speed strides (walking or running) and strides
at and near the walk-run and run-walk transitions to determine if
and when the transition strides resemble the stride of the corresponding
constant speed strides. For both the walk-run and run-walk transitions,
the stride prior to the transition resembled the original gait pattern,
while the stride following the transition resembled the new gait pattern.
The transition stride, however, did not resemble either a walking
or a running stride during either of the transition directions. It
was concluded that gait transitions are initiated at about midstance
of the transition stride, but the transition is not completed until
after an adjustment period of between one step and one stride. Thus,
gait transitions are not abrupt events during human locomotion.
WORDS: Gait changes, walking, running, treadmill locomotion.
A gait has been defined as "a pattern of locomotion characteristic
of a limited range of speeds described by quantities of which one
or more change discontinuously at transitions to other gaits"
Several researchers (Abernethy et al., 2002;
Beuter and Lefebvre, 1988;
Biewener and Taylor, 1986;
Collins and Stewart, 1993;
Diedrich and Warren, 1998;
Raynor et al., 2002)
have based conclusions related to gait transitions on the assumption
that gait transitions are abrupt events, as suggested by this definition.
There is, however, some evidence which suggests that gait transitions
are not abrupt events. Argue and Clayton, 1993
noted that the walk-trot and trot-walk gait transitions of highly
trained dressage horses generally occurred abruptly, but intermediate
steps were usually detected in the transitions of novice dressage
horses. Gatesy and Biewener, 1991
observed that the gait transitions of ground dwelling birds were
difficult to discern since they occurred over a number of steps.
For humans, Li and Hamill, 2002
reported differences in the ground reaction forces of the steps
leading up to the walk-run gait transition, suggesting that this
transition occurs gradually. Other researchers (Segers et al., 2006)
reached a similar conclusion based upon the observation of differences
in spatialtemporal characteristics in the steps leading to both
the walk-run and run-walk transitions.
When studying gait transitions, researchers have primarily relied
upon two different protocols to determine the preferred transition
speed (PTS). In the "incremental" protocol (Hreljac et
Prilutsky and Gregor, 2001;
Raynor et al., 2002),
researchers who control the treadmill speed, increase or decrease
speed incrementally, with a decision period (usually about 30 s)
given to subjects to determine whether walking or running is the
preferred gait at the selected speed. Because constant speeds are
utilized, and subjects are allowed a fairly lengthy decision period
when using this protocol, the PTS is able to be assessed accurately
and easily. When using this protocol, however, an actual spontaneous
transition does not occur, and an analysis of the steps leading
up to a spontaneous transition is not possible (Li and Hamill, 2002).
This problem is overcome by utilizing a "continuous" protocol,
in which a constantly accelerating treadmill is used to determine
the transition speed. With this protocol, a spontaneous gait transition
occurs, but the determination of the exact instant of the transition
is not always obvious.
When using the continuous protocol, many researchers (Beuter and
Diedrich and Warren, 1995;
Li and Hamill, 2002;
Segers et al., 2006;
Thorstensson and Roberthson, 1987;
Turvey et al., 1999)
have defined the time of the walk-run transition (WR) as the instant
at which a flight phase first occurs as treadmill speed increases,
and the time of the run-walk transition (RW) as the instant at which
double support is first observed as speed decreases. These definitions
imply that WR occurs at a toeoff, and RW occurs at a heelstrike.
There is no theoretical or empirical evidence to suggest that gait
transitions occur at the instant of these events, nor even whether
gait transitions are abrupt events. In addition, defining walking
and running by the presence or absence of a double support phase
is not always correct. As examples of situations in which these
classical definitions of walking and running do not apply, McMahon
et al., 1987
pointed out that when running in tight circles, running on very
compliant surfaces, and running with exaggerated knee flexion (Groucho
running), subjects do not have a flight phase. It has also been
demonstrated that during slow speed running, subjects may have a
short period of double support (Hreljac, 1995;
Hreljac et al., 2002).
Since running at speeds near the PTS could be defined as slow speed
running, it is possible that the true transition time determined
when using the continuous protocol may occur one or more steps prior
to the first flight phase for WR, or after the emergence of double
support during RW.
A more robust and unambiguous means of distinguishing walking from
running is the use of two different simple models. Walking has been
characterized by an inverted pendulum model (Alexander, 1984;
while running could be described by a bouncing ball model (Alexander,
In the inverted pendulum model, the pivot point of the pendulum
is the stance foot, while a kneeless lower extremity represents
the arm of the pendulum, with the hip or body's center of mass (CM)
as the endpoint. In this model, the maximum height of the hip or
CM during the stance phase occurs at approximately midstance. In
the bouncing ball model of running, the minimum height of the hip
or CM during the stance phase occurs at approxi-mately midstance.
Using these two models as a guide, a more accurate estimate of the
instant of gait transitions may be formulated from observations
of the body's position at midstance. In the current study, lower
extremity segment positions at midstance of the transition step
were used as criteria for determining whether a subject was walking
The primary purpose of this study was to determine whether gait
transitions observed while using the continuous protocol occur abruptly,
or over a number of steps. If the gait transitions were found to
occur abruptly, then an attempt would be made to determine the relative
timing of the transitions, which would be compared between WR and
RW. Determination of the timing of gait transitions would allow
future researchers to more confidently assess gait transition speeds
when using a continuous protocol. Because of the obvious kinematic
differences between walking and running, a kinematic analysis was
considered to be the most appropriate means of making these assessments.
Participants in this study were 11 (six males, five females) young,
healthy college students (height = 1.70 ± 0.08 m; mass = 71.9 ±
11. 9 kg; lower extremity length = 88.0 ± 5.2 cm), who were free
from musculoskeletal injury or disease at the time of the study.
Prior to participation, subjects signed informed consent forms,
reiterating the basic procedures and intent of the study, as well
as warning of any potential risks involved. All subjects wore their
own running footwear during each testing session. Subjects who
were inexperienced in treadmill locomotion were habituated by walking
and running at a variety of speeds on the treadmill for a period
of at least 15 minutes prior to the initiation of data collection.
This time period has been shown to be sufficient to allow for accommodation
to treadmill locomotion (Charteris and Taves, 1978;
Wall and Charteris, 1980).
The PTS of each subject was determined with two protocols; incremental
and continuous. For all trials, an ex-perimenter controlled the
speed of the treadmill, and the treadmill controller panel was not
visible to the subject. The PTS found using the incremental protocol
was subse-quently used as the speed for the constant speed walking
and running trials.
To determine WR using the incremental protocol, the treadmill was
initially set to a speed at which subjects would walk comfortably
(approximately 1.2 m·s-1). Subjects were instructed to mount the
treadmill and utilize the gait which felt most natural. After a
decision period of approximately 30 s, the treadmill was stopped
and subjects dismounted. If subjects indicated that walking was
the preferred gait at that speed (as was the case for all subjects
at the initial speed), the treadmill speed was increased by approximately
0.1 m·s-1 before the subject remounted. Again, after a 30 s decision
period, subjects were instructed to indicate the gait which felt
most natural at the new speed. This process continued until a speed
was reached at which subjects indicated that running was the most
natural gait at that particular speed. That speed was defined as
the speed of WR. By starting the treadmill at a high enough speed
to ensure that subjects ran (> 3.0 m·s-1), then decreasing the
treadmill speed incrementally (in a similar manner as done when
finding WR), the speed of RW was determined. The entire process
was repeated three times in random order. The PTS was defined as
the average of the speeds at WR and RW.
For the continuous protocol WR trials, the tread-mill was initially
set to a slow walking speed (approxi-mately 1.0 m·s-1). After subjects
were comfortably walk-ing at this speed, the treadmill was continuously
acceler-ated by applying constant pressure to the "increase
speed" button of the treadmill controls until after the subject
began running. The instant of WR was determined from observation
of a sagittal plane video recording (see be-low), and defined to
occur at midstance of the step during which the subject switched
from an inverted pendulum to a bouncing ball model. Since the vertical
position of the hip at midstance is largely determined by the amount
of hip and knee flexion at midstance, and the amount of knee flexion
at midstance is quite easy to observe, this was the criterion used
to determine whether a subject was walking or running. When walking,
the knee is close to the anatomical position at midstance (Öberg
et al., 1994).
During running, however, there is approximately 50º of knee flexion
at midstance (Milliron and Cavanagh, 1990).
Because these differences are quite large, and easily distinguishable
by an observer, no measurements of knee angles (or hip heights)
were used to determine the step during which a transition occurred.
To make this assessment, frame by frame observations of knee angles
at mid- stance were independently made by two researchers. If there
would have been disagreement between observers for any trial (which
did not happen), then the trial would not have been accepted. Treadmill
speed at WR was determined by averaging the subject's heel marker
speed while the foot was completely in contact with the treadmill.
Heel position was determined from the digitized records, as described
below. In the RW trials, the process was repeated in reverse, with
the treadmill initially set to a
speed at which subjects could run comfortably (about 3.5 m·s-1).
The treadmill speed was then continuously decreased until the subject
began walking. Transition direction conditions were randomly ordered,
and repeated twice, with rest periods provided between trials to
data collection and processing
Kinematic data were collected during all continuous protocol trials
for each subject, and two constant speed walking and running trials.
The speed of the constant speed trials was the PTS determined when
using the incremental protocol. All kinematic data were collected
with a single JVC GR-DVL 9800u digital video camera positioned approximately
seven meters from the treadmill. Data were recorded in the sagittal
plane (from the right side) at a frequency of 240 Hz. Two-dimensional
position coordinates were obtained by digitizing markers placed
on appropriate anatomical landmarks, including the hip (greater
trochanter), knee (estimated knee joint center), ankle (lateral
malleolus), heel (calcaneus), and toe (head of fifth metatarsal).
Before processing, all coordinate data were smoothed using a fourth
order zero-lag Butterworth filter with cutoff frequencies uniquely
chosen for both coordinates of each marker. The choice of a cutoff
frequency was based on the residual method (Wells and Winter, 1980).
Data were collected for three strides during each trial, with an
additional 10 to 20 frames digitized prior to the first heelstrike,
and after the fourth heelstrike to help avoid endpoint smoothing
errors (Vint and Hinrichs, 1996).
During constant speed trials, the three consecutive strides chosen
for analysis always occurred after subjects had been walking or
running for at least 30 s. For the continuous protocol trials, the
strides analyzed included the transition stride (WRTS or RWTS),
one stride before the transition stride (WRTS-1 or RWTS-1), and
one stride after the transition stride (WRTS+1 or RWTS+1).
Prior to analysis, all strides were normalized in time, so that
all time variables were expressed as a percentage of stride time,
with consecutive heelstrikes marking the beginning and ending of
a stride. Heelstrike timing was determined using previously developed
algorithms (Hreljac and Marshall, 2000;
Hreljac and Stergiou, 2000).
In an initial analysis, the two variables that had the greatest
average root mean square (RMS) difference between walking and running,
and thus distinguished walking from running better than all other
variables, were the vertical velocity of the hip (vhip)
and ankle angular velocity (ωankle). Differences
were compared throughout the curves for an entire stride at one
percent intervals, giving a total of 101 points of comparison. Since
the vertical velocity of the hip is a fairly good representation
of the vertical velocity of the body's CM, this variable, vhip,
was considered to be a global variable that could distinguish between
walking and running. Ankle angular velocity has been demonstrated
to be associated with the walk- run gait transition (Hreljac, 1995),
so this variable, ωankle, was considered to be an
appropriate localized variable. Representative graphs of vhip
and ωankle during constant speed walking and running
are illustrated for a single stride in Figures 1a
For both of the selected dependent variables (DVs), the average
RMS difference between each unique pair of the three constant speed
walking strides (WS1, WS2, and WS3) and running strides (RS1, RS2,
and RS3) were calculated for each subject. The mean of the three
average RMS differences for each gait (W-RMSavg and R-RMSavg) was
determined and used in subsequent comparisons.
The RMS difference between WRTS-1 and WS1, WS2, and WS3 was then
calculated for each DV. The minimum RMS difference found between
WRTS-1 and the constant speed walking trials (WR1-RMSmin) was compared
to W-RMSavg to determine whether this stride could fit the profile
of a constant speed walking stride. Similarly, the RMS difference
between WRTS+1 and RS1, RS2, and RS3 was calculated for each DV.
The minimum RMS difference found between WRTS+1 and the constant
speed running trials (WR3-RMSmin) was compared to R-RMSavg to determine
whether this stride could fit the profile of a constant speed running
stride. The RMS difference between WRTS and WS1, WS2, WS3, RS1,
RS2, and RS3 was also calculated. The minimum RMS difference between
WRTS and the constant speed walking trials (WR2W-RMSmin) was compared
to W-RMSavg, and the minimum RMS difference between WRTS and the
constant speed running trials (WR2R-RMSmin)
was compared to R-RMSavg. These comparisons were made to determine
whether the transition stride fit the profile of either a constant
speed walking trial or a constant speed running trial.
For the run-walk transition trials, similar compari-sons were made.
The minimum RMS difference found between RWTS-1 and the constant
speed running trials (RW1-RMSmin) was compared to R-RMSavg to determine
whether this stride fit the profile of a constant speed running
stride. The minimum RMS difference found between RWTS+1 and the
constant speed walking trials (RW3- RMSmin) was compared to W-RMSavg
to determine whether this stride fit the profile of a constant speed
walk-ing stride. The minimum RMS difference between RWTS and the
constant speed running trials (RW2R-RMSmin) was compared to R-RMSavg,
and the minimum RMS difference between RWTS and the constant speed
walking trials (RW2W-RMSmin) was compared to W-RMSavg to determine
whether the run- walk transition stride fit the profile of either
a constant speed running trial or a constant speed walking trial.
If any of the comparisons showed that a specific stride during the
transition trials did not fit one of the constant speed profiles
for either DV, then a further analysis of this stride was conducted
by breaking the stride down into 20% increments. Since the stance
phase of a slow running is approximately 40% of the stride time,
and the stance phase of a walking stride is approximately 60% of
the stride time, 20% increments were considered appropriate. The
minimum RMS difference between each of these 20% increments and
the average RMS difference found within the corresponding increment
of the constant speed walking and/or running were compared to determine
whether the specified increment fit the profile of the corresponding
increment of either a constant speed walking or running stride.
In this way, the time of the actual transition could be determined
more specifically. All RMS stride comparisons were made using a
repeated measures ANOVA with the level of significance set at p
Because the data were collected on the right side of the body in
this two-dimensional analysis, only trials in which the transition
was determined to occur with the right side of the body were analyzed.
Since the determination of transition foot was made after data
were collected, trials in which the transition was determined to
occur with the left foot were subsequently excluded from the analysis.
Due to the exclusion of trials, the analysis of RW trials included
nine subjects, while the analysis of WR trials included eight subjects.
average rate of treadmill acceleration for the WR trials was 0.18
± 0.02 m·s-2, while the average rate of-treadmill acceleration for
the RW trials was -0.20 ± 0.03 m·s-2. The average PTS found using
the incremental protocol was 1.88 ± 0.11 m·s-1. This was the speed
selected for all constant speed trials. Using the continuous protocol,
the average speed of WR was 1.93 ± 0.14 m·s-1, and the
average speed of RW was 1.85 ± 0.10 m·s-1.
For both DVs analyzed, WR1-RMSmin was significantly
less than W-RMSavg (Table
1), indicating that WRTS-1 fit the profile of a constant speed
walking stride. Similarly, WR3-RMSmin was not significantly
different than R-RMSavg for either of the variables (Table 1), indicating that WRTS+1 fit the profile of a constant
speed running trial. For both DVs, WR2R-RMSmin was significantly
greater than R-RMSavg, and WR2W-RMSmin was
significantly greater than W-RMSavg (Table
1). This indi-cates that WRTS did not fit the profile of either
a constant speed walking or running trial (Figures 2a
and 2b). Fur-ther analyses
were conducted on this stride to determine whether differences occurred
at any sections of the stride.
For both vhip and ωankle, RW1-RMSmin was significantly less than
R-RMSavg, indicating that RWTS-1 fit the profile of a constant speed
running stride (Table 2). Also for both DVs, RW3-RMSmin was
not significantly different than W-RMSavg, indicating that RWTS+1
fit the pro-file of a constant speed walking trial. For both variables,
RW2W-RMSmin was significantly greater than W-RMSavg, and RW2R-RMSmin
was significantly greater than R-RMSavg (Table
2). This indicates that the run-walk transition stride did not
fit the profile of either a constant speed walking trial or a constant
speed running trial (Figures 3a and 3b). Further analyses were
conducted on this stride to determine whether differences occurred
at any sections of the stride.
When the transition stride was subdivided into 20% increments, it
was found that WRTS resembled a walking stride for vhip until the
last 20% increment, and ωankle, resembled a constant speed walking
stride for the entire stride. The WRTS, however, never did resemble
a running stride for either variable (Table
For RW trials, ωankle for RWTS resembled a constant speed running
stride until the last 40% of the stride, while vhip did not differ
from a running stride until the last 20% increment. It was only
for vhip that RWTS ever resembled a walking stride. This occurred
during the last 20% increment of the stride (Table 4).
only three strides were analyzed in the constant speed walking and
running trials, the amount of variability found within both vhip
and ωankle between these strides was similar to
that reported in other studies in which a greater number of strides
were analyzed (Milliron and Cavanagh, 1990;
In addition, the time histories of vhip and ωankle
(Figures 1a and 1b)
are similar to those shown by others (Winter, 1989).
Thus, using the constant speed walking and running trials as a basis
for determining whether the strides of the transition trials fit
the profile of a walk or a run appears to be justified.
The results of the stride by stride analysis suggest that it is
possible to identify the stride during which a gait transition occurs,
although WRTS is not as obvious as RWTS. The exact instant of the
transition, however, is not necessarily apparent. Since the criterion
used to determine the transition stride occurred at midstance of
stride, it was expected that WR would become apparent after approximately
40% of WRTS since mid stance of a walking stride occurs at approximately
30% of stride time. It was also expected that RW would become apparent
after approximately 20% of RWTS since midstance for a running stride
occurs at approximately 20% of stride time. In actual fact, WR did
not become apparent until the heelstrike of WRTS+1, and RW did not
become apparent until the last 20% to 40% of RWTS. There are several
possible explanations for these observations.
From Figures 1a and 1b,
it could be seen that a large amount of the difference between walking
and running for both variables lies in the relative timing of the
maxima and minima. When a gait transition occurs, the relative timing
may actually shift during the stride. If the gait transitions occurred
prior to the swing phase, as expected, this would decrease the
duty factor (ratio of time between stance and swing phases) for
WR and increase the duty factor for RW. For WR, decreasing the duty
factor would effectively shift the swing phase portion of the curve
for both variables to the right. For RW, increasing the duty factor
would effectively shift the swing phase portion of each curve to
the left. This would mean that for vhip, the difference
between walking and running would increase during WR, and would
decrease during RW. The opposite would be true for ωankle.
This may partially explain why vhip displays a difference
between WRTS and walking, while ωankle did not.
The walk-run transition does not appear to be completed until the
heelstrike of WRTS+1. During the latter part of the swing phase
of WRTS, stride kinematics begin to differ from the kinematics of
a walking stride (Table 3),
but these kinematics do not resemble the kine matic pattern of
a run until the heelstrike of the following stride. This would actually
be about 1½ steps after the instant that many previous authors (Beuter
and Lefebvre, 1988;
Diedrich and Warren, 1995,
Li and Hamill, 2002;
Segers et al., 2006;
Thorstensson and Roberthson, 1987;
Turvey et al., 1999)
have estimated the transition to occur (instant of first flight
phase), and approximately 1¾ steps after the transition was expected
to occur in the current study. Thus, WR does appear to be a gradual
transition, as suggested by previous researchers (Li and Hamill,
Segers et al., 2006),
rather than an abrupt transition, as suggested by Alexander, 1989.
The run-walk transition also does not appear to be an abrupt event.
The evidence from this study suggests that RWTS begins to deviate
from the kinematic pattern of a run early in the swing phase (Table
4). The stride begins to partially resemble a walking stride
in the latter stages of the swing phase, but the transition is not
completed until the heelstrike of RWTS+1 (Table
4). This transition would therefore take place about one step
after the instant that previous authors have estimated the transition
to occur (instant of first double support), and approximately 1¼
steps after the time predicted in the current study.
It was believed that vhip would be more likely to exhibit
an abrupt change at the transition since this variable is a good
representation of the movement of the body's CM, and thus should
provide a good representation of the walking and running models.
It is possible that even after a decision is made by a subject to
change gaits, that the body requires some finite time period to
adjust or recalibrate in terms of position, velocity, and acceleration
coordination patterns. The results of this study suggest that a
period of between one step and one stride may be required for these
adjustments to fully take effect. This supports the hypothesis of
researchers (Diedrich and Warren,
who have used dynamical systems theory to explain gait transitions,
since this theory suggests that there would be increased variability
in variables such as relative phase angles at speeds near the gait
|It appears that for a continuously accelerating treadmill, the
initiation of a gait transition (walk-run and run-walk) occurs at
about midstance of the transition stride, but the transition is not
complete until the next heelstrike of the ipsilateral foot. The time
period between the initiation of the gait transition and the completion
of the transition exhibits some aspects of kinematic behavior that
could not be classified as being either a walk or a run.
transitions are not abrupt events.
of a gait transitions occur at about midstance of the transition
transitions are completed approximately at the next heelstrike
of the ipsilateral foot.
period between initiation and completion of transition does not
resemble either a walk or a run.
Employment: Associate Professor of Biomechanics, Department
of Kinesiology and Health Science, California State University,
Research interests: Gait transitions, running injuries.
Employment: Assistant Professor of Biomechanics, Department
of Kinesiology and Health Science, California State University,
Research interests: Biomechanics of judo, gait, and weight
Employment: Associate Professor of Physical Therapy, Department
of Physical Therapy, California State University, Sacramento.
Research interests: Exercise rehabilitation, throwing
mechanics, squat lifting.
Employment: PhD Student, Iowa State University.
Research interests: Impact force, mechanical loading
and bone adaptation, signal processing and wavelet analysis