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The contribution of the flight phase in elite race walking

Abstract and Figures

Although race walkers are not permitted a visible flight phase, previous research has found that most competitors do experience very brief losses of contact. The purpose of this study was to assess the role of the flight phase in elite race walking. Seventeen international athletes race walked over two force plates recording at 1000 Hz. Video data were simultaneously recorded at 100 Hz and used to calculate kinematic variables such as step length. The mean flight time was 0.030 s (± .011) while the mean distance travelled during this phase was 0.12 m (± .05). It was calculated that without flight times, athletes would have slower mean velocities, particularly if mean cadence remained the same. However, the contribution of flight phases in race walking does not just allow for greater step lengths and faster speeds, but also more time for lower limb repositioning.
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THE CONTRIBUTION OF THE FLIGHT PHASE IN ELITE RACE WALKING
Brian Hanley
1
, Athanassios Bissas
1
and Andrew Drake
2
Carnegie Research Institute, Leeds Beckett University, Leeds, UK
1
National Centre for Race Walking, Leeds Beckett University, Leeds, UK
2
Although race walkers are not permitted a visible flight phase, previous research has
found that most competitors do experience very brief losses of contact. The purpose of
this study was to assess the role of the flight phase in elite race walking. Seventeen
international athletes race walked over two force plates recording at 1000 Hz. Video data
were simultaneously recorded at 100 Hz and used to calculate kinematic variables such
as step length. The mean flight time was 0.030 s .011) while the mean distance
travelled during this phase was 0.12 m .05). It was calculated that without flight times,
athletes would have slower mean velocities, particularly if mean cadence remained the
same. However, the contribution of flight phases in race walking does not just allow for
greater step lengths and faster speeds, but also more time for lower limb repositioning.
KEY WORDS: athletics, elite sportspeople, gait, kinematics.
INTRODUCTION: According to IAAF Rule 230.1, “Race walking is a progression of steps so
taken that the walker makes contact with the ground, so that no visible (to the human eye)
loss of contact occurs. The advancing leg must be straightened (i.e. not bent at the knee)
from the moment of first contact with the ground until the vertical upright position”. A flight
phase is one feature that distinguishes running from normal walking, and IAAF Rule 230.1 is
an attempt to maintain this conceptual difference. However, previous research on race
walking in competition and during laboratory testing has found that brief flight phases are
common to practically all elite race walkers (Hanley & Bissas, 2013; Hanley, Bissas & Drake,
2011, 2013). Previous mathematical models have been used to predict maximum race
walking speed in the absence of a flight phase. For example, in Figure 1, L
A
represents the
actual length of a race walker’s leg; while L
EFF
is the increased, ‘effective’ leg length
achieved with pelvic rotation (‘a’ represents the resulting distance between the hip joints
caused by this pelvic rotation). Step length can thus be calculated as [2 x (L
A
x cosθ) + a]
(Trowbridge, 1981). In the diagram, θ represents the angle between the leg and the ground
and is assumed to be the same for both legs at double support (and L
A
is assumed to be the
same for both the front and rear legs). While Trowbridge’s model has been used as evidence
that race walkers cannot possibly achieve their competitive speeds without loss of contact,
its weaknesses include an assumption that the push-off leg is straight (which is what allows
θ to be equal for both legs), even though race walkers need to maintain a straightened knee
until midstance only, and that it was not based on actual race walking measurements.
Figure 1: A model of calculating step length in race walking (Trowbridge, 1981).
While there is no prescribed limit of what constitutes loss of contact except as a subjective
‘visible’ occurrence, reporting typical flight times of elite athletes and those tested in
laboratory studies is invaluable to the coach (and judge) who is interested in appreciating
what actual flight durations occur, and to the researcher of race walking who is keen to
ensure external validity. The aim of this study was to measure and evaluate the role of the
flight phase in male and female elite race walkers.
METHODS: The study was approved by the Faculty Research Ethics Committee and 17
race walkers gave written informed consent. The athletes comprised 10 men (26 ± 3 yrs,
1.79 ± .05 m, 67.1 ± 7.9 kg) and seven women (26 ± 5 yrs, 1.66 ± .05 m, 55.8 ± 4.8 kg). All
athletes had competed at the Olympic Games or World Championships. All 10 men had
previously competed over 20 km (personal best time: 1:23:29 ± 1:59) with eight also
competing over 50 km (3:52:59 ± 6:23). The mean personal best time for the women over
their competitive distance of 20 km was 1:30:55 (± 1:47). Each athlete race walked along a
45 m indoor running track at a speed equivalent to their season’s best time (20 km or 50 km
for men dependent on specialism). Timing gates were placed 4 m apart around two force
plates (Kistler, Winterthur) that recorded both left and right foot contact phases and flight
time. Athletes completed at least ten trials and the three closest to the target time were
analysed (provided they were within 3% of the target time). The force plates recorded at
1000 Hz and were placed in a customised housing in the centre of the track. Contact time
was considered to begin when the vertical force trace exceeded 5 N and to end when it
decreased below 5 N again; flight time was calculated as the time between steps.
Video data were collected at 100 Hz using a high-speed camera (Fastec, San Diego, CA).
The shutter speed was 1/500 s, the f-stop was 2.0, and there was no gain. The camera was
placed approximately 12 m from and perpendicular to the line of walking. The resolution of
the camera was 1280 x 1024 pixels. The force plate software and the camera system were
synchronised using a Kistler connection box (Kistler, Winterthur). The GRF data were
smoothed using a recursive second-order, low-pass Butterworth filter at 50 Hz.
The video files were manually digitised by a single experienced operator to obtain kinematic
data (SIMI Motion, Munich). Digitising was started at least 10 frames before the beginning of
the stride and completed at least 10 frames after to provide padding during filtering. The
magnification tool in SIMI Motion was set at 400% to aid identification of body landmarks. De
Leva’s (1996) body segment parameter models were used to obtain data for the whole body
centre of mass and all body segments. Noise was removed using a Butterworth low-pass
filter, with the cut-off frequencies calculated using residual analysis (Winter, 2005).
Race walking speed was determined as the mean horizontal speed of the centre of mass
during one complete gait cycle (using the digitised data). Step length was measured as the
distance between successive foot contacts using the digitised data. Because of differing
standing heights of participants, step length was also normalised by expressing as a
percentage of the participants’ statures, and referred to as step length ratio. Cadence was
calculated by dividing horizontal speed by step length. The distance the whole body centre
of mass travelled during flight was measured from the instant of toe-off of one foot to the
instant of initial contact of the other and termed flight distance. With regard to angular
kinematics, the knee angle was calculated as the sagittal plane angle between the thigh and
leg segments and was considered to be 180° in the anatomical standing position. The hip
angle was defined as the sagittal plane angle between the trunk and thigh segments and
was also considered to be 180° in the anatomical standing position. The ankle angle was
calculated in a clockwise direction using the lower leg and foot segments and considered to
be 110° in the anatomical standing position. Pearson’s product moment correlation
coefficient was used to find associations between key spatiotemporal variables. In addition,
to further highlight the contribution of flight time to elite race walking, hypothetical values for
step length and cadence (and hence speed) were calculated based on the removal of flight
time with regard to its effect on these key spatiotemporal variables (‘No flight phase’) and in
terms the effect of absorbing flight time into contact time on these same variables (‘No flight /
cadence maintained’).
RESULTS: The main spatiotemporal results are shown in Table 1 (‘Actual’) along with
hypothetical values based first on the absence of flight time (but with no change in contact
time: ‘No flight phase’), and second with an absence of flight time (but with a contact time
that absorbs the original duration of flight: ‘No flight / cadence maintained’).
Table 1 Actual and hypothetical spatiotemporal variables of race walking (mean ± SD)
Actual
No flight phase
No flight / cadence
maintained
Flight time (s)
.030 (± .011)
-
-
Flight distance (m)
0.12 (± .05)
-
-
Step length (m)
1.16 (± .08)
1.04 (± .08)
1.04 (± .08)
Step length ratio (%)
132.8 (± 7.6)
118.8 (± 6.6)
118.8 (± 6.6)
Contact time (s)
.283 (± .018)
.283 (± .018)
.313 (± .012)
Cadence (Hz)
3.20 (± .12)
3.55 (± .21)
3.20 (± .12)
Speed (km/h)
13.37 (± .74)
13.25 (± .80)
11.95 (± .59)
In actual terms, flight distance contributed approximately 10% of total step length. Speed
was correlated with step length ratio (r = .73, p = .001), flight time (r = .52, p = .031) and
flight distance (r = .66, p = .004). Step length ratio was correlated with flight distance (r = .52,
p = .034). Cadence was negatively correlated with contact time (r = .81, p < .001), while
flight distance was positively correlated with flight time (r = .85, p < .001).The mean hip angle
at initial contact was 170° 2) while at toe-off it was 185° 3). The mean knee angle at
initial contact was 180° 2) while it was 149° 5) at toe-off. The mean ankle angles at
initial contact and toe-off were 90° (± 4) and 127° (± 6) respectively.
DISCUSSION: Flight times occurred in all 17 participants, with longer flight times associated
with higher walking speeds and longer steps. More importantly, the resulting longer flight
distances were therefore also a reason for overall greater step lengths. It is thus very clear
that the brief (but probably non-visible) flight phases that elite race walkers undertake are an
important factor in their performances. This was emphasised by the hypothetical values that
were predicted based on the removal of the flight phase; step lengths would have been an
average of 12 cm shorter, while the concurrent reduction in step time would have resulted in
mean cadences of 3.55 Hz (213 steps per minute) that are far higher than those reported of
world-class race walkers in competition (Hanley, Bissas & Drake, 2011). However, such an
eventuality would lead to decreases in walking speed of only 0.12 km/h. Nonetheless, the
high cadences required would be unachievable by most race walkers and maintenance of
the same cadence would be more likely (i.e. by spending the duration of flight time in double
support instead). This hypothetical eventuality would lead to very large decreases in speed
(by a mean of 1.42 km/h) in this group of athletes that would have considerable negative
consequences in competition. Modelling of race walking has suggested that it is difficult to
achieve speeds above 7.4 km/h without loss of contact (although pelvic rotation could
increase step length by increasing the functional length of the leg) (Trowbridge, 1981).
However, an increase in step length is possible beyond what was predicted in the model
because of knee flexion during late stance (the mean knee angle at toe-off was 149° in this
study). In this way, elite race walkers are able to achieve longer steps than those predicted
by Trowbridge (1981) who, by assuming the rear leg stayed straightened after midstance,
did not take into account the extra distance gained by either the small amount of knee
hyperextension at initial contact that sometimes occurs or the considerably greater degree of
knee flexion at toe-off (Figure 2). Therefore it is not the flight phases only that allow for
longer steps as joint kinematics also contribute.
Figure 2: Trowbridge’s model of step length with a digitised figure of an elite race walker
superimposed. The dashed lines are extrapolations of the original L
EFF
and L
A
lines because
the diagram has been rescaled to match the distance between the digitised hip joints (‘a’).
From a coaching viewpoint, flight time was an important contributor to step length by way of
flight distance, and there might be a temptation for athletes to deliberately increase it.
However, the risk of having too long a flight phase is clear and it is not sensible to explicitly
advise race walkers to increase its length in an attempt to improve performance. On the
contrary, it is preferable for them to develop their techniques in such a way that high speeds
are maintained with as little flight as possible. One way in which this might be achieved is
through increasing step length via the knee flexion movement that occurs in late stance.
CONCLUSION: The aim of this study was to measure and evaluate the role of the flight
phase in elite race walkers. Overall, it was clear that these elite race walkers relied on
relatively long flight times for a large component of step length, and without these flight
periods the athletes would have been considerably slower. In effect it is not possible for elite
race walkers to obtain the speeds required for world-class competition without some duration
of flight. It is possible that these flight phases, which if long enough to be visible can lead to
disqualification, would be even longer without the knee flexion that occurs during late stance.
REFERENCES:
de Leva, P. (1996). Adjustments to Zatsiorsky-Seluyanov’s segment inertia parameters.
Journal of Biomechanics, 29, 1223-1230.
Hanley, B., Bissas, A. & Drake, A. (2011). Kinematic characteristics of elite men’s and
women’s 20 km race walking and their variation during the race. Sports Biomechanics, 10,
110-124.
Hanley, B., Bissas, A. & Drake, A. (2013). Kinematic characteristics of elite men’s 50 km
race walking. European Journal of Sport Science, 13, 272-279.
Hanley, B. & Bissas, A. (2013). Analysis of lower limb internal kinetics and electromyography
in elite race walking. Journal of Sports Sciences, 31, 1222-1232.
Trowbridge, E.A. (1981). Walking or running - when does lifting occur? Athletics Coach,
15(1), 2-6.
... More recently, Hanley et al. 17 examined elite race walkers walking at their typical competition speeds and observed FTs of 30 ± 11 ms (mean ± SD),which suggests that some walkers used FTs > 40 ms. ...
... In addition, the constraints of the measurement set up may not have allowed all walkers to achieve a fully stable walking pattern at competition speed, although it should be noted that none of the walkers suggested that this was a problem for them. It is also possible that some elite walkers achieve higher speeds in competition by having flight periods >40 ms, 17 Since the human eye has a limited processing frequency of 16 Hz, 2 it is inevitable that very small FTs will pass undetected by coaches in training and judges in competition and this encourages and reinforces the walker to develop a walking pattern that employs a non-visible (in real time) flight phase. The results of this investigation showed that experienced walkers use this adapted walking style with flight phases ≤40 ms even at walking speeds slower than the predicted maximum walking speed. ...
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Zatsiorsky et al. (in Contemporary Problems in Biomechanics, pp. 272-291, CRC Press, Massachusetts, 1990a) obtained, by means of a gamma-ray scanning technique, the relative body segment masses, center of mass (CM) positions, and radii of gyration for samples of college-aged Caucasian males and females. Although these data are the only available and comprehensive set of inertial parameters regarding young adult Caucasians, they have been rarely utilized for biomechanical analyses of subjects belonging to the same or a similar population. The main reason is probably that Zatsiorsky et al. used bony landmarks as reference points for locating segment CMs and defining segment lengths. Some of these landmarks were markedly distant from the joint centers currently used by most researchers as reference points. The purpose of this study was to adjust the mean relative CM positions and radii of gyration reported by Zatsiorsky et al., in order to reference them to the joint centers or other commonly used landmarks, rather than the original landmarks. The adjustments were based on a number of carefully selected sources of anthropometric data.
Walking or running -when does lifting occur? Athletics Coach
  • E A Trowbridge
Trowbridge, E.A. (1981). Walking or running -when does lifting occur? Athletics Coach, 15(1), 2-6.