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A COMPARISON OF BRAKING CHARACTERISTICS
BETWEEN PRE-PLANNED AND UNANTICIPATED CHANGING DIRECTION
TASKS IN FEMALE SOCCER PLAYERS: AN EXPLORATORY STUDY
Paul A. Jones, Sarah Stones, and Laura C. Smith
Directorate of Sport, Exercise and Physiotherapy, University of Salford
Introduction:
Changing direction is a common action involved in non-
contact anterior cruciate ligament injuries in female soccer
players (Faude et al., 2005). Most biomechanical studies
into changing direction focus on the final contact (‘turn’), but
little is known about the role of penultimate contact.
Previous research (Graham-Smith et al., 2009) found
significantly greater peak knee extensor moments, vertical
and horizontal ground reaction forces (GRF) during
penultimate compared to final contact during pre-planned
pivots in male soccer players. No previous research has
identified whether such deceleration strategies occur during
unanticipated cutting and pivoting. The aim of this study was
to compare braking characteristics (peak GRF’s and knee &
hip joint moments) between pre-planned (PP) and
unanticipated (UN) cutting (90⁰) and pivoting (180⁰turn).
Method:
•The study was approved by the University’s ethics
committee.
•Ten female soccer players (mean ±SD; age: 22.1 ±1.9
years, height: 1.62 ±0.06 m, mass: 62.6 ±8.5 kg)
performed 6 trials each of PP and UN cutting and pivoting.
•For each trial, three-dimensional motion data using
Qualisys Pro-Reflex infrared cameras (240 Hz) operating
through Qualisys Track Manager software v2.8 and GRF
data from two AMTI force platforms (1200 Hz) were
collected.
•This arrangement allowed data to be collected for both
penultimate & final contact during cutting & pivoting (Fig 1).
•Unanticipated trials were performed in response to a traffic
light system, which indicated the direction for subjects as
they passed through a gate 4 metres prior to the final
(‘contact’) force platform (Fig 1a).
•Joint coordinate and force data were smoothed with a
Butterworth low pass digital filter with cut-off frequencies of
12 Hz and 25 Hz, respectively.
•Internal joint moments were determined using an inverse
dynamics approach.
•A 2 ×2 factorial ANOVA for the factors of contact
(penultimate vs. final) and task (PP vs.UN) was used to
compare each dependent variable during cutting & pivoting.
Results:
•A significant interaction was revealed for peak vertical (cut:
η2= 0.76; pivot: η2= 0.48), horizontal (cut: η2= 0.59; pivot:
η2= 0.48) and resultant GRF (cut: η2= 0.70; pivot: η2= 0.49)
[Tables 1 & 2].
•Tukey’s post hoc analysis revealed significant (P< 0.05)
increases in peak vertical GRF from penultimate to final
contact during UN tasks, which remained unchanged during
PP tasks (Tables 1 & 2).
•More pronounced (P< 0.05) increases in horizontal (cut
46%; pivot 21%) and resultant (35%) GRF’s during UN
tasks compared to PP (HGRF cut 9%; pivot 10%; RGRF: cut
8%; pivot 16%) were observed.
Summary and Conclusion
The results fail to substantiate previous research (Graham-
Smith et al., 2009) that during PP changing direction greater
horizontal braking forces are witnessed during penultimate
compared to final contact. However, the results do illustrate
that less braking takes place during penultimate contact of
UN cutting and pivoting compared to PP; highlighting the
need to develop players’ anticipatory skills to allow more
time for technical adjustments prior to final contact to help
lower hazardous loading patterns during final contact.
References:
Faude, O., Junge, A., Kindermann, W. & Dvorak, J. (2005). Injuries in female
soccer players. A prospective study in the German national league. Am J Sports
Med .33 (11);1694-1700.
Graham-Smith, P., Atkinson, L., Barlow, R. & Jones, P. (2009). Braking
characteristics and load distribution in 180º turns. Poster presented at The 5th
Annual UKSCA Conference, 5-7 June 2009, Wyboston Lakes, Bedfordshire.
Figure 1. Qualisys motion analysis and AMTI force platforms
used to derive braking forces and joint moments in the
penultimate (b) and final contact (a).
a b
Table 1. Mean ± SD peak forces, knee & hip moments during the
weight acceptance phase of pre-planned & unanticipated cutting
Variable PRE-PLANNED UNANTICIPATED
PEN FINAL PEN FINAL
Peak VGRF
(BW)* 2.53 ±0.50 2.54 ±0.61 2.32 ± 0.53 2.95 ±0.61
Peak HGRF
(BW)* -1.16 ±0.33 -1.27 ±0.39 -1.06 ± 0.43 -1.55 ±0.35
Peak RGRF
(BW)* 2.69 ±0.55 2.80 ±0.69 2.55 ± 0.63 3.15 ± 0.68
Peak Knee Ext
Mom (Nm/kg) 2.94 ±0.47 2.69 ±0.39 2.82 ± 0.46 2.98 ± 0.46
Peak Hip Ext
Mom (Nm/kg) 2.66 ±0.71 2.99 ±0.70 2.25 ± 0.47 2.62 ± 0.64
Table 2. Mean ± SD peak forces, knee & hip moments during the
weight acceptance phase of pre-planned & unanticipated pivoting
Variable PRE-PLANNED UNANTICIPATED
PEN FINAL PEN FINAL
Peak VGRF
(BW)** 2.45 ±0.57 2.31 ±0.36 2.50 ± 0.44 2.74 ±0.52
Peak HGRF
(BW)** -1.46 ±0.31 -1.60 ±0.26 -1.45 ± 0.44 -1.76 ±0.34
Peak RGRF
(BW)** 2.74 ±0.77 2.79 ±0.42 2.90 ± 0.57 3.23 ± 0.60
Peak Knee Ext
Mom (Nm/kg) 2.84 ±0.70 2.15 ±0.32 2.87 ± 0.55 2.34 ± 0.33
Peak Hip Ext
Mom (Nm/kg) 2.55 ±0.83 2.39 ±0.87 2.54 ± 0.98 2.63 ± 0.96
* and ** Significant interaction (P < 0.01 and P < 0.05) between tasks and
contacts. VGRF = vertical GRF, HGRF = horizontal GRF, RGF = resultant GRF,
Ext Mom = Extensor Moment.
