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Journal of Sports Sciences
ISSN: 0264-0414 (Print) 1466-447X (Online) Journal homepage: http://www.tandfonline.com/loi/rjsp20
Field monitoring of sprinting power–force–velocity
profile before, during and after hamstring injury:
two case reports
J. Mendiguchia, P. Edouard, P. Samozino, M. Brughelli, M. Cross, A. Ross, N.
Gill & J. B. Morin
To cite this article: J. Mendiguchia, P. Edouard, P. Samozino, M. Brughelli, M. Cross, A. Ross,
N. Gill & J. B. Morin (2015): Field monitoring of sprinting power–force–velocity profile before,
during and after hamstring injury: two case reports, Journal of Sports Sciences
To link to this article: http://dx.doi.org/10.1080/02640414.2015.1122207
Published online: 09 Dec 2015.
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Field monitoring of sprinting power–force–velocity profile before, during and after
hamstring injury: two case reports
J. Mendiguchia
a
, P. Edouard
b,c
, P. Samozino
d
, M. Brughelli
e
, M. Cross
e
, A. Ross
e
, N. Gill
e,f
and J. B. Morin
g
a
Department of Physical Therapy, Zentrum Rehabilitation and Performance Center, Pamplona, Spain;
b
Laboratory of Exercise Physiology (LPE EA
4338), University of Lyon, Saint Etienne, France;
c
Department of Clinical and Exercise Physiology, Sports Medicine Unity, Faculty of medicine,
University Hospital of Saint-Etienne, Saint-Etienne, France;
d
Laboratory of Exercise Physiology (EA 4338), University of Savoy Mont Blanc, Le
Bourget-du-Lac, France;
e
Sports Performance Research Institute New Zealand (SPRINZ), Auckland University of Technology, Auckland, New
Zealand;
f
New Zealand Rugby Union, Wellington, New Zealand;
g
Laboratory of Human Motricity, Education Sport and Health, University of Nice
Sophia Antipolis, Nice, France
ABSTRACT
Very little is currently known about the effects of acute hamstring injury on over-ground sprinting
mechanics. The aim of this research was to describe changes in power–force–velocity properties of
sprinting in two injury case studies related to hamstring strain management: Case 1: during a repeated
sprint task (10 sprints of 40 m) when an injury occurred (5th sprint) in a professional rugby player; and
Case 2: prior to (8 days) and after (33 days) an acute hamstring injury in a professional soccer player. A
sports radar system was used to measure instantaneous velocity–time data, from which individual
mechanical profiles were derived using a recently validated method based on a macroscopic biome-
chanical model. Variables of interest included: maximum theoretical velocity (V
0
) and horizontal force
(F
H0
), slope of the force–velocity (F–v) relationship, maximal power, and split times over 5 and 20 m. For
Case 1, during the injury sprint (sprint 5), there was a clear change in the F–vprofile with a 14% greater
value of F
H0
(7.6–8.7 N/kg) and a 6% decrease in V
0
(10.1 to 9.5 m/s). For Case 2, at return to sport, the
F–vprofile clearly changed with a 20.5% lower value of F
H0
(8.3 vs. 6.6 N/kg) and no change in V
0.
The
results suggest that the capability to produce horizontal force at low speed (F
H0
) (i.e. first metres of the
acceleration phase) is altered both before and after return to sport from a hamstring injury in these two
elite athletes with little or no change of maximal velocity capabilities (V
0
), as evidenced in on-field
conditions. Practitioners should consider regularly monitoring horizontal force production during sprint
running both from a performance and injury prevention perspective.
ARTICLE HISTORY
Accepted 16 November 2015
KEYWORDS
Hamstring strain; sprint
mechanics; horizontal force;
injury prevention
Introduction
Hamstring muscle strains are the most prevalent injuries in team
sports, such as rugby and soccer, accounting for 12%–16% of all
injuries (Brooks, Fuller, Kemp, & Reddin, 2006;Ekstrand,
Hagglund, & Walden, 2011; Woods et al., 2004). The majority of
hamstring injuries (61%–68%) occur during high-speed sprinting
actions (Arnason, Gudmundsson, Dahl, & Jóhannsson, 1996;
Brooks et al., 2006; Woods et al., 2004), where the biarticular
muscles have simultaneous roles as hip extensors and knee
flexors. Namely, during the swing phase they act to decelerate
the shank (Chumanov, Schache, Heiderscheit, & Thelen, 2012),
and during the stance phase they act to pushing the body/
ground in the horizontal direction (Orchard, 2012). Forward
orientation of ground reaction force (GRF) has been shown to
be a stronger determinant of field sprint acceleration perfor-
mance than the overall magnitude of vertical or resultant GRF
(Morin, Edouard, & Samozino, 2011). These studies suggest that
hamstring plays an important role in sprint acceleration perfor-
mance as horizontal force producers.
While research surrounding horizontal force and its contri-
bution to performance has attained significant attention in
recent research, little is known about its relationship with
injury. In relation to the current study, how an athlete’s hor-
izontal propulsive force output changes as a potential cause
(pre) or consequence (post) of an acute hamstring injury
remains unknown. The reason for the current lack of knowl-
edge in this area is due to the practical difficulty of anticipat-
ing such an injury, and the limited ability of assessing
mechanical sprinting profiles during regular sprinting trials.
To date, complex computer-based musculoskeletal models
limited to instrumented treadmill sprinting and restricted to
the analysis of few step at top speed have usually been
utilised for understanding hamstring function during sprinting
(Heiderscheit et al., 2005; Schache, Dorn, Blanch, Brown, &
Pandy, 2012). Unfortunately, this renders their use in everyday
practice difficult, further restricts experimental measurements
on top level athletes, and limits the comprehension of sprint-
ing and hamstring injury relationship in this high risk injury
population (Heiderscheit et al., 2005; Schache et al., 2012).
Recently, a simple field method using a macroscopic biome-
chanical model was proposed and validated to quantify both
horizontal mechanical properties and performance measures
during the entire acceleration phase of an over-ground sprint
(Mendiguchia et al., 2014;Samozinoetal.,2015). As the method
requires only time and distance measurements during a single
CONTACT J. Mendiguchia jurdan24@hotmail.com
JOURNAL OF SPORTS SCIENCES, 2015
http://dx.doi.org/10.1080/02640414.2015.1122207
© 2015 Taylor & Francis
Downloaded by [88.136.29.36] at 06:47 09 December 2015
sprint, it could be considered an economical and practical field
alternative to lab-based assessments. This method feasibly
allows the implementation of consistent and regular monitor-
ing of mechanical sprint properties, both with regard to perfor-
mance and injury-prevention, potentially ensuring an optimal
return to normalised values (following rehabilitation) post-ham-
string strain. Moreover, such an assessment may increase the
opportunity to specifically assess top-level athletes in their daily
training tasks (ecological context), allowing, as in the present
study, to put forward clear differences in sprinting mechanics
between injured and non-injured athletes. Since it allows a
deeper investigation of the mechanisms underlying sprint
acceleration performance, this approach could help better and
more specifically design future hamstring prevention and reha-
bilitation research and likely lead to a better understanding and
consequent clinical application surrounding hamstring strains.
This information could be valuable in professional team sports,
given that these injuries no doubt constitute a significant
financial burden and can severely hamper player and team
performance (Hickey, Shield, Williams, & Opar, 2014).
Recently, Mendiguchia et al. (2014) reported significantly
lower maximal horizontal power output (P
max
)incurrently
competing soccer players who had previously suffered and
rehabilitated an acute hamstring injury. In particular, changes
in the slope of the linear force–velocity (F–v) relationship
(corresponding to the mechanical F–vprofile) (Jaskolska,
Goossens, Veenstra, Jaskólski, & Skinner, 1999;Morinetal.,
2011) indicated that the relative importance of force
(reduced at the time of return to sport) was greater than
velocity qualities (no change/s at the time of return to sport)
in determining the alteration in P
max
and individual F–v
profiles of previously injured players (Mendiguchia et al.,
2014). These individual F–vrelationships describe the
changes in external horizontal force generation with increas-
ing running velocity and may be summarised by two theore-
tical extremes: the theoretical maximal horizontal force
produced over one step at null velocity (F
H0
), and the theo-
retical maximal velocity produced during the same phase in
the absence of aerodynamic drag forces (V
0
). These integra-
tive parameters characterise the mechanical limits of the
entire neuromuscular system during sprint running, and
encompass numerous individual muscle mechanical proper-
ties as well as other morphological, neural and technical
factors (Cormie, McGuigan, & Newton, 2011). Since hip exten-
sors and knee flexors have important roles in producing
forward oriented GRF (Belli, Kyrolainen, & Komi, 2002;
Jacobs & van Ingen Schenau, 1992), we hypothesised that
horizontal mechanical properties could allow indirect evalua-
tion of hamstring muscle function.
The aim of this study was to examine whether the vali-
dated “simple”methodcouldbeusedtodetectworthwhile
changes in sprinting mechanics in relation to hamstring
injury management in two cases: (1) during on-field training
of maximal repeated sprint-ability directly prior to and during
an unexpected hamstring injury in an elite rugby sevens
player, and/or (2) as a means of regular assessment to serve
as a comparison during the undoubtedly critical period of
returning to sport post-hamstring injury in a professional
soccer player.
Case reports
Rugby player
The rugby player was a male professional rugby union and
international rugby sevens back (height: 187.0 cm; body mass:
94.0 kg; age: 23 years). At the time of testing, he had competed
at a professional level for 4 years, and had suffered from a left
hamstring strain 53 days prior to testing during a rugby sevens
tournament. Neither other history of hamstring strains nor
history of any associated medical problems was present. At
the time of the sprint tests, the rugby player was participating
fully in his usual training and competition activities. His training
consisted of whole body strength, speed, agility, aerobic endur-
ance, and rugby-specific skills training. His total training volume
was 10–12 hours per week (five days per week).
At the time of testing (24 February 2014), the rugby player
was performing a repeated sprint test over 40 m on a syn-
thetic track surface. The test consisted of ten 40-m all-out
sprints performed on a 30-s cycle, running back and forth in
a marked lane. During each sprint, the player’s instantaneous
speed was concurrently measured via a sports radar system
set to collect both incoming and outgoing data at one end of
the track. Four sprints were completed uninhibited, unim-
peded and symptom-free. However, during the 5th sprint the
participant suddenly decelerated and grasped his left ham-
string. Immediately following the injury, the rugby player was
examined by the team physiotherapist who identified palp-
able pain and weakness during contraction and assessed the
injury as a grade two hamstring strain. No magnetic resonance
imaging was performed. One week following the injury the
participant elected to have arthroscopic surgery on his left
shoulder, and as such his rehabilitation was directed at this.
The data comparison was performed between the data of
the first four sprints that were symptom-free and those of the
5th sprint during which the injury occurred, and with the data
from the player’s team. The rugby team included 20 interna-
tional rugby sevens players (height (mean (SD)): 188.0 (5.3) cm;
body mass: 96.4 (6.7) kg; age: 23.9 (4.0) years) free of any
musculoskeletal pathologies at the time of the test and parti-
cipating fully in their usual training and competition activities.
Soccer player
The professional soccer player (height: 173.2 cm; body mass:
64.3 kg; age: 25 years) was a forward and competed in the first
division of La Liga in Spain. He suffered from a right hamstring
injury 18 months prior, a right adductor injury 7 months prior,
and a left ankle sprain 2 months prior to the test presented
here. At the time of the sprint assessment, he was participat-
ing fully in his usual training and competition activities.
On 1 April 2014, the soccer player performed two 50-m
maximal sprints symptom-free. During the sprints, instanta-
neous speed was measured in order to determine the main
biomechanical characteristics and F–vprofile as part of his
usual training follow-up. Tests were preceded by a standar-
dised warm-up, consisting of 5 min of low-pace (~10 km h
–1
)
running, followed by 3 min of lower limb muscle stretching,
5 min of sprint-specific drills and three progressive 6-s sprints
separated by 2 min of passive rest. The soccer player was then
2J. MENDIGUCHIA ET AL.
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allowed 5 min of free cool down before performing the two 50-
m maximal sprints from a standing start on a natural grass field,
separated by 6-min passive rest. He wore his habitual football
boots and tests were performed at the same time of the day as
his normal football training. He was asked not to train or
exercise vigorously for at least 2 days prior to testing.
On 9 April 2014, the soccer player injured his left hamstring
during the acceleration phase of a maximal sprint, as part of a
standard match training session. The player immediately
ceased activity, and clasped at his left hamstring. Clinical
examination and MRI confirmed a hamstring strain (biceps
femoris injury grade 1). He rested and received massage treat-
ment the following 3 days. He then began progressive con-
ventional rehabilitation based in isometric then concentric
exercise. He then progressed to eccentric, balance and core
exercises, and at day 12 post-injury he started jogging, kicking
and returning to sprint activities after the eccentric training
was complete (Heiderscheit, Sherry, Silder, Chumanov, &
Thelen, 2010). He trained with the team progressively, and
returned to normal training without restrictions and with
medical permission on 12 May 2014. On 12 May 2014, the
player performed the second sprint test with the same proce-
dure as the 1 April 2014 assessment. He successfully competed
in the team’s last important season match for 90 minutes
without any complications. Data comparison was performed
between the first sprints 8 days before the injury (1 April 2014)
and those of the sprints 33 days after the injury (12 May 2014).
Methods
In both cases, instantaneous sprint velocity was measured by
means of a Stalker Acceleration Testing System (ATS) II radar
device (Model: Stalker ATS II, Applied Concepts, Dallas, TX,
USA). These devices measure the forward sprinting velocity
of the subject at a sampling rate of 46.8 Hz, and have been
previously validated in human sprint running experiments (di
Prampero et al., 2005). The device was placed on a tripod 10 m
behind the subjects at a height of 1 m corresponding approxi-
mately to the height of subjects’centre of mass.
From these measurements, speed–time curves were
plotted (di Prampero et al., 2005; Furusawa, Hill, & Parkinson,
1927; Henry & Trafton, 1951), and maximal running speed was
obtained. Additionally, horizontal external antero–posterior
GRF was computed using a recently validated computational
method from speed–time data measured during sprinting (see
Mendiguchia et al., 2014; Samozino et al., 2015 for more
details). F–vrelationships, its respective maximal theoretical
velocity (V
0
) and force (F
H0
) values, its slope and the corre-
sponding maximal power output (P
max
) were obtained
(Samozino et al., 2015). Split times at 2 m, 5 m, 10 m, 20 m
and 30 m were determined from the raw distance–time data
for the rugby player.
Results
Rugby player
The sprint values are presented in Table 1, and the changes in
the slope of the F–vrelationships according to the sprints (from
the 1st to the 5th sprints) are presented in Figure 1 for the
injured rugby players and the rugby group. For the injured
player, a change in the slope of the F–vrelationship (from
–0.76 to –0.92; +21.1%) was observed associated with an
increase in F
H0
(from 7.6 N/kg to 8.7 N/kg, +14%) and a minor
decrease in V
0
(from 10.1 m/s to 9.5 m/s, –6%) (Figures 1 and 2).
For the other players, there was a slightly change in the slope of
the F–vrelationship (from (mean (SD)) –0.97 (0.11) to –0.96
(0.08); 0.5 (11.7) %) with a decrease in F
H0
(from 8.9 (1.0) N/kg
to 8.2 (0.6) N/kg, –7.7 (10.8) %) and V
0
(from 9.6 (0.3) m/s to 8.8
(0.3) m/s, –8.3 (2.7) %) (Figures 1 and 2).
Soccer player
Between the pre- and post-injury sprints, a change in the
slope of the F–vrelationship (from –0.95 to –0.75; –21.1%)
was observed (Figure 3), representing a decrease in F
H0
(from
8.3 N/kg to 6.6 N/kg; –20.5%) without any change in V
0
(from
8.7 m/s to 8.7 m/s; 0%) (Table 2).
Table 1. Sprint values for the injured rugby players and the healthy rugby group (mean (SD)) for the five sprints (sprints 1–5).
Sprint 1 Sprint 2 Sprint 3 Sprint 4 Sprint 5
Injured
Rugby group
(mean (SD)) Injured
Rugby group
(mean (SD)) Injured
Rugby group
(mean (SD)) Injured
Rugby group
(mean (SD)) Injured
Rugby group
(mean (SD))
Split times
5 m (s) 1.30 1.23 (0.08) 1.15 1.22 (0.07) 1.37 1.30 (0.05) 1.23 1.26 (0.07) 1.26 1.32 (0.05)
20 m (s) 3.15 3.16 (0.10) 3.05 3.2 (0.08) 3.30 3.32 (0.07) 3.16 3.32 (0.09) 3.17 3.36 (0.09)
Top speed
(m/s)
9.85 9.31 (0.25) 9.27 8.84 (0.26) 9.50 8.76 (0.39) 9.23 8.42 (0.30) 9.17 8.56 (0.29)
Sprint horizontal
mechanical properties
V
0
(m s
−1
) 10.21 9.61 (0.28) 9.57 9.05 (0.30) 9.85 9.03 (0.44) 9.54 8.65 (0.34) 9.45 8.81 (0.32)
F
H0
(N) 787.35 855.00 (77.97) 789.70 944.53 (202.80) 720.55 806.69 (96.00) 770.30 856.17 (102.21) 835.06 785.22 (79.59)
F
H0
(N
kg
−1
)
8.20 8.91 (0.96) 8.23 9.92 (2.57) 7.51 8.30 (0.75) 8.02 8.92 (0.91) 8.70 8.15 (0.59)
P
max
(W) 2010.41 2052.70 (172.39) 1889.83 2132.82 (421.27) 1774.74 1818.35 (209.85) 1836.84 1849.44 (216.08) 1972.95 1730.11 (191.96)
P
max
(W
kg
−1
)
20.94 21.39 (2.12) 19.69 22.39 (5.31) 18.49 18.70 (1.42) 19.13 19.26 (1.77) 20.55 17.95 (1.47)
F–vprofile −77.09 −89.10 (9.43) −82.50 −104.68 (24.77) −73.13 −89.67 (12.55) −80.76 −99.23 (13.36) −88.36 −89.21 (2.60)
F–vprofile
(/BM)
−0.841 −0.97 (0.11) −0.896 −1.14 (0.31) −0.798 −0.96 (0.11) −0.877 −1.07 (0.13) −0.957 −0.96 (0.08)
Notes:V
0
= theoretical maximum velocity; F
H0
= theoretical maximum force; P
max
= peak power production; F–vprofile = slope of the force-velocity relationship; BM
= body mass.
JOURNAL OF SPORTS SCIENCES 3
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Discussion
The main result of this study was that the simple on-field sprinting
method was sensitive enough to indicate specific changes in
horizontal mechanical properties pre- or pro-ceding an acute
hamstring injury (the delay between the change observed in
mechanical outputs and the injury might be as short as one or
two sprints in the rugby player’s case). Until recently, complex lab-
testing methods were restricted to the measurement of flying top
speed, only able to be maintained for a few steps and irrespective
of the typically preceding acceleration phase (Schache et al., 2012;
Weyand, Sternlight, Bellizzi, & Wright, 2000). Indeed, acceleration
profiling better resembles how running speed is increased in real-
life sporting situations and has beenconsideredtobefundamen-
tal to team sports performance and injury risk. Moreover, since our
Figure 1. The figures present the slope of the F–vrelationship for the group of
rugby players (mean in bold grey line and standard deviation is the grey zone)
and the injured rugby player (black line) for the first (A), fourth (B), and fifth (C)
sprints. During this fifth sprint, the injured rugby player sustained his hamstring
injury (C).
Figure 2. Changes in the P
max
(A), F
H0
(B) and V
0
(C) for the injured rugby player
(black dots) and the healthy rugby group (grey dots) in relative value to the first
sprint.
4J. MENDIGUCHIA ET AL.
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present study reported that hamstring injury does not seem to
affect maximal velocity capabilities, assessing maximal flying top
speed without consideration of the acceleration phase might not
be appropriate for the investigation of this kind of injury. The
method used here allowed us to obtain horizontal external
force, velocity and power during specific conditioning (i.e. over-
ground on-field), which would have previously only been possible
using a 50-m long force plate system. This method was recently
validated in comparison to force plate measurements and pre-
sented very low bias (absolute bias <5%) and good test–retest
reliability (standard error of measurement <4% on force, velocity
and power parameters) (Samozino et al., 2015). This high reliability
led to low smallest worthwhile change values for both intra- and
inter-individual comparisons for each variable allowing sport prac-
titioners and clinicians to monitor sprinting mechanics over time
and accurately detect training or rehabilitation effects as in the
present study.
Furthermore, a consistent result in the two cases studied
here is that the change (pre- and post-injury) in horizontal
mechanical power associated with the injury is more related to
the ability to apply high levels of force into the ground at low
speeds (F
H0
), than to the ability to produce horizontal force a
high speeds (V
0
). This phenomenon may be explained by the
“motor”function of the muscles during early acceleration
phase (low velocity) in order to generate positive power out-
put and developed by the contractile component, compared
to the “spring”muscle function displayed during high speed
(25–34 km hr
–1
) in which an appreciable fraction of the power
is sustained by the mechanical energy stored in the “series
elastic elements”during stretching the contracted muscles
(negative work) and released immediately after in the positive
work (Cavagna, Komarek, & Mazzoleni, 1971).
Sprint mechanical properties before and during a
hamstring injury: rugby player
For the elite rugby player, the sprint during which injury occurred
(5th sprint in assessment battery of 10) exhibited similar split times
(performance index) compared with his preceding four sprints.
The injury sprint differed considerably in the balance between
force and velocity mechanical properties (athlete neuro-mechan-
ical muscular capabilities) during a repeated sprint task, both in
regard to the individual’s preceding four sprints, and that of the
rest of the group. Therefore, similar sprint acceleration perfor-
mance as monitored by split times can result from very different
underlying muscular F–vprofiles. In particular, the injury occurred
during a sprint where the horizontal power production was
defined by an “abnormal”increase in force compared to velocity
qualities. In this individual, the repeated sprint protocol induced a
change in F–vprofile towards a more force-oriented profile
(increase in F
H0
and decrease in V
0
),whichisincontrasttothe
rest of the group (Figures 1 and 2). Therefore, while the repeated
sprint protocol appears to affect velocity qualities (i.e. the
ability to develop horizontal force at high velocity) similarly
for the group and the injured player, the maximal force output
(F
H0
) and hence the maximal power were effected
Figure 3. For the soccer player, there was a change in the slope of the F–vrelationship between the pre-injury (black line) and the post-injury (dotted line) with
decrease in F
H0
without change of V
0.
Table 2. Pre- and post-injury sprint values for the soccer player.
Pre-injury Post-injury % change
Split times
5m (s) 1.31 1.45 7.0
20m (s) 3.33 3.56 4.8
Top speed (m/s) 8.44 8.36 –0.7
Sprint horizontal m mechanical
properties
V
0
(m s
−1
) 8.7 8.7 0.0
F
H0
(N) 532 432 −19.8
F
H0
(N kg
−1
) 8.3 6.6 −20.5
P
max
(W) 1155 933 −19.3
P
max
(W kg
−1
) 18.0 14.2 −21.2
F–vprofile −60.8 −49.3 −18.9
F–vprofile (/BM) −0.95 −0.75 −21.1
Notes:V
0
= theoretical maximum velocity; F
H0
= theoretical maximum force;
P
max
= peak power production; F–vprofile = slope of the force–velocity
relationship; BM = body mass.
JOURNAL OF SPORTS SCIENCES 5
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contrastingly between the injured player and the rest of the
group at the 4th and 5th (injury) sprints of the series. A recent
study by Morin, Samozino, Edouard, and Tomazin (2011)
showed that during a multiple-set repeated sprint series on
an instrumented treadmill, the concomitant decrease in the
technical ability to apply force (to apply force horizontally into
the ground) across repeated sprints indicates a faster “straigh-
tening up”of the resultant force vector orientation during the
acceleration with increasing fatigue. It can therefore be specu-
lated that in order to compensate for this fatigue-induced
decrease in V
0
and effectiveness of force application during
the injury sprint, the rugby player developed an “anticipatory”
strategy (conscious or not), resulting in a dramatic increase in
the level of force output at the beginning of the sprint (F
H0
). In
other words, knowing that maintaining maximal velocity
capacity would put his muscle structures at risk, the rugby
player may have put emphasis on his maximal force output
(the observed clearly higher F
H0
) to compensate and produce
an equivalent performance despite his altered maximal run-
ning velocity. This strategy allowed the player to achieve high
power and high speed sooner, and to improve his acceleration
capabilities compared to other sprints but probably resulted
in muscles facing an unusually high stress and strain that
eventually resulted in the hamstring injury later near maxi-
mum speeds where hamstring muscles requirement has been
proven to be even greater (Schache et al., 2012). Indeed, in the
present case study, raw radar speed–time data clearly show
that the moment of injury (speed–time curve drops) at the late
acceleration phase (~30.5 m) of the sprint, i.e. prior to the
maximal speed phase. (Figure 4)
Sprint mechanical properties before and after a
hamstring injury: soccer player
The main findings for the elite soccer player were that despite
being cleared to play after approximately 1 month post-injury,
decreased sprinting speed performance and mechanical
horizontal properties were observed compared with his baseline
sprint values. The 3–5 times higher change in F
H0
than in sprint
times could explain the underlying mechanisms of the decreased
performance. Specifically, the great magnitude of differences in
F
H0
(
≈
–20%) compared with no change of V
0
at return to play
suggested that the lower maximal horizontal power observed in
the injured player after rehabilitation was mainly related with the
reduced maximal horizontal force component during sprinting
(Table 1). These data can be used by clinicians to prescribe a
specific work to improve the horizontal forces at low speeds, such
as heavy sled towing and posterior chain strength training.
Horizontal force production and hamstring injury
Consistently between the two cases studied here, our results
extend previous findings showing a decrease in horizontal force
production, both in Australian Rules Football players and soccer
players with a previous hamstring injury (Brughelli, Cronin,
Mendiguchia, Kinsella, & Nosaka, 2010;Mendiguchiaetal.,2014).
The reduced horizontal force component (
≈
20%) in the present
study might be related to (1) the apprehension of pain or reinjury
for the injured athlete to produce high level of force and hence
forward momentum during sprinting (Warren, Ingalls, Lowe, &
Armstrong, 2002), or (2) the role of the hamstring muscles in the
initial contact phase where it is believed to be essential for produ-
cing posterior chain powerand therefore,a more forward directed
force with increasing running speed (Belli et al., 2002;Mann&
Hagy, 1980). Thus, the lower force component (i.e. F
H0
)atthetime
of return to sport observed in the present case study might be
related with the reported hamstring muscle weakness, hip exten-
sion (Sugiura, Saito, Sakuraba, Sakuma, & Suzuki, 2008)andknee
flexor functional strength (Lee, Reid, Elliott, & Lloyd, 2009;
Sanfilippo, Silder, Sherry, Tuite, & Heiderscheit, 2013), displayed
by athletes with previously injured hamstrings. One limitation of
this approach was that we only considered the changes in the
external outputs of the entire neuromuscular and tendinous sys-
tem, with no insight into the exact level of alteration. However,
Figure 4. Raw radar speed–time curves of the 5th sprint for the rugby player show the moment of injury (speed–time curve drops) at the late acceleration phase
(~30.5 m) of the sprint compared with his preceding four trials.
6J. MENDIGUCHIA ET AL.
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despite this limitation (which deserves further research) we sug-
gest that the proven possibility of “detecting”such an injury
occurrence on the sole basis of speed–time measurements
might be of interest for a comprehensive understanding of ham-
string strain injuries mechanism that should result in improved
training, rehabilitation and prevention processes.
Another practical application of the simple method used
in this study is, as shown in the soccer player case, to
evidence changes in sprint running mechanics (compared
to baseline data) following an acute hamstring injury during
the return to sport phase. Indeed, during this phase, speed
tests can be safely implemented and training/rehabilitation
processes can be adjusted according to the outcomes of
these tests.
Conclusions
As evidenced by the simple field method used, the capability to
produce horizontal force at low speed (F
H0
) (i.e. first metres of the
acceleration phase) is altered both before and after return to sport
from a hamstring injury in these two professional athletes. This
alteration has been observed in the direct and actual conditions of
practice (i.e. on-field maximal sprint acceleration). Therefore, prac-
titioners and researchers should collaborate towards a regular
monitoring of horizontal force production during sprint running
in order to extend the pilot analysis presented in this paper. This
could help verify whether or not this approach is useful from both
performance and injury perspectives.
Disclosure statement
No potential conflict of interest was reported by the authors.
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