In e na ional Jou nal o
En i onmen al Resea ch
and Public Heal h
A icle
Sp in Va iables A e Associa ed wi h he Odds Ra ios o
Non-Con ac Inju ies in P o essional Socce Playe s
Hadi Noba i 1,2,3,4,* , Elena Maine -Pa dos 5,* , Angel Denche Zamo ano 2, Thomas G. Bowman 6,
Filipe Manuel Clemen e 7,8 and Jo ge Pé ez-Gómez 2
Ci a ion: Noba i, H.; Maine -Pa dos,
E.; Denche Zamo ano, A.; Bowman,
T.G.; Clemen e, F.M.; Pé ez-Gómez, J.
Sp in Va iables A e Associa ed wi h
he Odds Ra ios o Non-Con ac
Inju ies in P o essional Socce Playe s.
In . J. En i on. Res. Public Heal h 2021,
18, 10417. h ps://doi.o g/10.3390/
ije ph181910417
Academic Edi o : Paul B. Tchounwou
Recei ed: 12 Augus 2021
Accep ed: 1 Oc obe 2021
Published: 3 Oc obe 2021
Publishe ’s No e: MDPI s ays neu al
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Copy igh : © 2021 by he au ho s.
Licensee MDPI, Basel, Swi ze land.
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A ibu ion (CC BY) license (h ps://
c ea i ecommons.o g/licenses/by/
4.0/).
1Depa men o Physical Educa ion and Spo s, Uni e si y o G anada, 18010 G anada, Spain
2HEME Resea ch G oup, Facul y o Spo Sciences, Uni e si y o Ex emadu a, 10003 Cáce es, Spain;
[email p o ec ed] (A.D.Z.); [email p o ec ed] (J.P.-G.)
3Depa men o Exe cise Physiology, Facul y o Educa ional Sciences and Psychology,
Uni e si y o Mohaghegh A dabili, A dabil 56199-11367, I an
4Spo s Scien is , Sepahan Foo ball Club, Is ahan 81887-78473, I an
5Heal h Sciences Facul y, Uni e sidad San Jo ge, Au o A23 km 299, 50830 Villanue a de Gállego, Spain
6Depa men o A hle ic T aining, College o Heal h Sciences, Uni e si y o Lynchbu g,
Lynchbu g, VA 24501, USA; bowman. @lynchbu g.edu
7
Escola Supe io Despo o e Laze , Ins i u o Poli écnico de Viana do Cas elo, Rua Escola Indus ial e Come cial
de Nun’Ál a es, 4900-347 Viana do Cas elo, Po ugal; [email p o ec ed]
8Ins i u o de Telecomunicações, Delegação da Co ilhã, 1049-001 Lisboa, Po ugal
*Co espondence: [email p o ec ed] (H.N.); [email p o ec ed] (E.M.-P.)
Abs ac :
Signi ican e idence has eme ged ha a high olume o sp in ing du ing aining is
associa ed wi h an inc eased isk o non-con ac inju ies in p o essional socce playe s. T aining
load has been epo ed as a modi iable isk ac o o successi e inju y in socce . Sp in wo kload
measu es and non-con ac inju ies we e eco ded weekly in wen y-one p o essional socce playe s
o e a one season pe iod. Odds a io (OR) and ela i e isk (RR) we e calcula ed based on he weeks
o high and low load o o al dis ance (TD), high-speed dis ance (HSD), sp in dis ance (SPD). and
epea ed sp in s (RS). The Poisson dis ibu ion es ima ed he in e al ime be ween he las inju y and
he new inju y. The weeks wi h high-load le els inc eased he isk o non-con ac inju y associa ed
wi h TD (OR: 4.1; RR: 2.4), HSD (OR: 4.6; RR: 2.6), SPD (OR: 6.9; RR: 3.7), and RS (OR: 4.3; RR: 2.7).
The ime be ween inju ies was signi ican ly longe in weeks o low-load in TD ( a e a io ime (RRT)
1.5 s. 4.2), HSD (RRT: 1.6 s. 4.6), and SPD (RRT: 1.7 s. 7.7) compa ed o weeks o high-load. The
indings highligh an inc eased isk o non-con ac inju ies du ing high weekly sp in wo kloads.
Possibly, TD, HSD, and SPD measu ed ia a wea able ine ial measu emen uni could be modeled
o ack aining and o educe non-con ac inju ies. Finally, he in e al ime be ween he las inju y
and he new inju y a he high-load is sho e han he low-load.
Keywo ds:
oo ball; inju y isk; high load; ex e nal moni o ing; pe o mance; high-speed dis ance;
global posi ioning sys em
1. In oduc ion
Socce is conside ed an in e mi en spo and i demands a wide a ie y o skills a
high in ensi y wi h pe iods o es o low in ensi y [
1
]. P o essional socce playe s ha e
a conges ed calenda which usually equi es playing successi e ma ches wi h h ee days
o eco e y [
2
]. These playe s a e exposed o high aining load due o he poo eco e y
pe iods be ween yea s o long aining and high ma ch equencies. These compe i i e
demands could inc ease inju y isk and educe pe o mance; he e o e, hey could be
de imen al o eam success [2–4].
In ecen imes, he e has been an inc ease o high-speed dis ance (HSD) and unning
du ing compe i i e socce ma ches [
5
]. Mo eo e , he abili y o p oduce HSD seems o be a
signi ican quali y o pe o mance [
6
]. Socce playe s need imp o ed de elopmen o high
In . J. En i on. Res. Public Heal h 2021,18, 10417. h ps://doi.o g/10.3390/ije ph181910417 h ps://www.mdpi.com/jou nal/ije ph
In . J. En i on. Res. Public Heal h 2021,18, 10417 2 o 10
speed and sp in unning abili y o gain ad an age in a acking and de ensi e si ua ions [
7
].
Malone e al. [
8
] epo ed ha exposing playe s o la ge and apid inc eases in HSD and
sp in dis ances (SD) inc eased he odds o inju y. Bowen e al. [
9
] demons a ed ha h ee
weekly accumula ions o accele a ions >9254 we e ela ed o an ele a ed isk o non-con ac
inju y. Ne e heless, om an inju y pe spec i e, mo e s udies a e wa an ed ha allow
coaches o unde s and he dose- esponse o HSD wi hin aining en i onmen s.
Mic o- echnology use, such as global posi ion sys ems (GPS) which measu e ex e nal
aining loads o playe s, has become p e alen in p o essional socce [
10
]. The ool is used
o iden i y he ac i i y p o ile o playe s du ing aining and ma ches [
10
]. Also, GPS is
able o quan i y he dis ance co e ed along wi h high accele a ion e o s, sho du a ion,
high eloci y sp in s and epea ed sp in (RS) exe cise bou s [
11
]. Angelidis e al. [
12
]
examined he link be ween GPS a iables and non-con ac inju ies in socce playe s in
a ecen sys ema ic e iew. They ound eigh a iables, o al dis ance (TD), high-speed
unning, o al load, accele a ions, decele a ions, new body load, me e pe minu e, and
sp in ing, ha dese e pa icula a en ion when moni o ing socce playe s’ ex e nal load
o he pu pose o inju y p e en ion. A each aining and compe i ion, playe s a e exposed
o a gi en wo kload [
13
]. An inapp op ia e wo kload du ing hese pe iods can inc ease
inju y isk. An inc eased acu e GPS-de i ed wo kload in eam spo s p oduced a highe
associa ion wi h inju y isk [
14
,
15
]. In p o essional socce playe s, when he ch onic loads
we e low wi h e y high acu e spikes, non-con ac inju y isk inc eased [
16
]. Howe e ,
mo e s udies a e needed o conside he e ec o he accumula ion load o es ablish s onge
conclusions be ween GPS aining load measu emen and non-con ac inju y in p o essional
socce playe s.
Time loss due o inju y is one o he bigge p oblems du ing socce playe s’ ca ee s [
3
].
Mos inju ies occu in he lowe ex emi ies [
17
]. In addi ion, inju ies o p o essional
socce playe s ha e a conside able impac on he spo s indus y [
18
], he eco e y and
ehabili a ion o playe s is associa ed wi h a conside able cos [
19
]. A non-con ac inju y
is an inju y wi h no physical con ac wi h o he playe s, and a conside able p opo ion
o inju ies in socce a e non-con ac [
17
]. Talukde e al. [
20
] p oposed ha he mos
ele an cha ac e is ics o p edic ing inju ies a e he a e age speed, he numbe o pas
compe i ions played, he a e age dis ance co e ed, he numbe o minu es played o da e,
and he a e age ield goals a emp ed. Hence, esea che s and coaches a e in e es ed
in educing he likelihood o inju ies o hei socce playe s and consequen ly, inju y
o ecas ing is engaging mo e in e es wi hin he spo ing en i onmen .
T aining load has been epo ed as a modi iable isk ac o o successi e inju y in
socce [
21
]. Gabbe and Ullah [
22
] obse ed a co ela ion be ween high in ensi y unning
and inju y isk du ing aining sessions. Wi hin eli e socce playe s, main aining hea a e
(HR) abo e 85% HRmax du ing aining was associa ed wi h inc eased isk o inju y [
23
].
Malone e al. [
8
] ecen ly showed ha highe ch onic loads and highe ae obic condi ioning
appea o o e a be e p o ec i e e ec agains inju y o p o essional socce playe s,
and hey should be conside ed media o s o inju y isk. I is impo an o p ac i ione s
o unde s and he op imal aining load a which adap a ion occu s wi hou aising he
isk o inju y. Howe e , he e a e no s udies ha ha e in es iga ed he ela ionship be-
ween non-con ac inju y incidence and sp in a iables h ough GPS wi hin p o essional
socce playe s.
Gi en he need o coaches and p ac i ione s o know he ela ionship be ween GPS-
de i ed wo kload and non-con ac inju y isk in p o essional socce playe s, he aims o
he cu en s udy we e o in es iga e, (i) he ela ionship be ween he o al dis ance, HSD,
sp in dis ance (SPD), and RS wi h non-con ac inju ies in p o essional playe s h oughou
a ull socce season; (ii) he inju y isk associa ed be ween high- e sus low-load le el
o each o he a o emen ioned pa ame e s wi h odds a ios (OR) and ela i e isk (RR),
espec i ely; and (iii) ul ima ely, a Poisson es o ob ain lambda alues (i.e., numbe o
inju ies pe week o each le el o cases lis ed), wi h he p edic ed ime be ween inju ies o
new inju y o calcula e he a e a io.
In . J. En i on. Res. Public Heal h 2021,18, 10417 3 o 10
2. Ma e ials and Me hods
2.1. Pa icipan s
Twen y-one socce playe s [age (yea ), 28.3
±
3.8; heigh (cm), 181.2
±
7.1; weigh (kg),
74.5
±
7.7] om a p o essional eam in he Pe sian Gul P o League we e analyzed du ing a
ull season (2018–2019 yea s). These playe s had mo e han 8 yea s o p o essional playing
expe ience. The c i e ion o en e ing he pa icipan s’ in o ma ion in o he analysis was
ha hey had pa icipa ed in a leas h ee aining sessions pe week. The c i e ion o
excluding pa icipan s’ da a in he analysis was ha da a was no a ailable o 2 consecu i e
weeks o hey had no pa icipa ed o les 2 consecu i e weeks in he aining. Also,
goalkeepe s’ da a we e elimina ed in his s udy. Based on a powe analysis o esul s om
p e ious s udies, we belie ed a sample size o 21 was adequa e o educe he isk o a
Type 2 e o [
8
,
22
]. This esea ch was conduc ed by he aining coaches o he club a e
app o al wi h he ele an au ho i ies and he head coach in he club. P io o commencing
he s udy, he app o al o he esea ch e hics commi ee om he Uni e si y o Is ahan
(IR.UI.REC.1399.064) was also ecei ed. All playe s we e in o med o he pu pose o
he s udy be o e signing he in o med consen . All s ages o his s udy we e ca ied ou
acco ding o he human s udies in he Helsinki Decla a ion.
2.2. S udy Design
The design o he p ospec i e coho s udy was pe o med in a ull season du ing
he Pe sian Gul P o League and knockou ou namen . Ex e nal load moni o ing was
pe o med by GPS (GPSPORTS sys ems P y L d, Model: SPI High Pe o mance Uni (HPU),
Canbe a, Aus alia) a each aining and ma ch session o e he whole season. All non-
con ac inju ies ( ha is, occu ing wi hou con ac wi h o eign ma e ial o a hle es) we e
eco ded du ing he season. Du ing he ull season, 7-weeks conges ed play (i.e., wo o
mo e ma ches wi hin 7-days), 30-weeks non-conges ed play; 44 ma ches, 11-weeks wi h no
compe i ions, 200 aining sessions, and 14,126.9 minu es o ime play and sessions we e
held. Almos all aining sessions and compe i ions we e held on a na u al g ass ield.
The eam be ween weeks 26 o 32 (mid-season b eak) was a he In e na ional Camp in
Tu key. The unning a iables eco ded, du ing he season, o his s udy included: TD,
HSD (18–23 km/h
−1
) [
24
,
25
] SPD, and me e s o RS. A e wa d, each a iable was di ided
in o wo le els, uppe and lowe , and subsequen ly, he ela ionship be ween he a iables
was measu ed.
2.3. P ocedu e
2.3.1. Wea able Ine ial Measu emen Uni Recei e
All playe s’ ac i i ies in aining sessions and ma ches we e eco ded wi h GPSPORTS
sys ems P y L d, Canbe a, Aus alia. The GPS-based acking sys ems o p o essional
a hle es, model SPI HPU ea u es included: 15 Hz posi ion GPS, dis ance, and speed
measu emen ; accele ome e : 100 Hz, 16 G T i-Axial-T ack impac s, accele a ions, and
decla a ions as well as da a sou ce body load (BL); Mag: 50 Hz, T i-Axial; dimensions:
74 mm ×42 mm ×16 mm
; wa e esis ance and da a ansmission: in a- ed and weighed
56 g. P e ious s udies ha e shown ha he GPS uni had e y high accu acy and demon-
s a ed excellen alidi y and in e -uni eliabili y [
26
]. All da a we e collec ed du ing
aining and ma ch sessions wi h a o able wea he and GPS sa elli e s a us.
2.3.2. Da a Collec ion
Da a collec ion was comple ed as in p e ious s udies [
27
,
28
]. As in du ing p e-session
we placed up igh acking uni s in he pouch o he manu ac u e p o ided bel , hen
ensu ed he g een ligh s (GPS acking) and ed ligh s (hea - a e acking) we e lashing.
Pos -session, acking uni s we e collec ed om playe s and placed on he docking s a ion.
Da a om he uni s we e au oma ically downloaded hen dele ed om he uni s o p epa e
o he nex session. A e 10 min, he uni s u ned o au oma ically. The GPS sys em was
uned o he de aul SPI IQ Absolu es in his s udy.
In . J. En i on. Res. Public Heal h 2021,18, 10417 4 o 10
2.3.3. Sp in Va iables Calcula ed
TD was calcula ed as he mean numbe o weekly me e s un by he eam’s playe s
o e he 48 weeks o he season.
HSD was calcula ed as he mean o weekly me e s un a high speed by he eam’s
playe s o e he 48 weeks o he season.
SPD was calcula ed as he mean numbe o weekly me e s un by he eam’s playe s
du ing he 48 weeks o he season.
RS was calcula ed as he mean weekly me e s o epea ed sp in s pe o med by he
eam’s playe s h oughou he 48 weeks o he season.
TD le el di ision was he di e ence be ween “high-load” and “low-load” weeks
acco ding o he a e age weekly TD o he eam. “High-load” was de ined as
TD ≥21,900
and “low-load” was de ined as TD < 21,900, bo h in me e s. The cu -o poin was es-
ablished in he TD alue, in which a g ea e di e ence was ound be ween he mean
o inju ies be ween weeks o highe and lowe load (clus e s wi h mo e han 11 weeks),
ha ing p e iously o de ed he weeks in acco dance wi h highe o lowe TD.
I.
Mean o inju ies du ing he 12 weeks o highes TD–Mean o inju ies du ing he es o
he weeks.
II.
Mean o inju ies du ing he 13 weeks o highe TD–Mean o inju ies du ing he es o
he weeks.
III.
Mean o inju ies du ing he 36 weeks o g ea e TD–Mean o inju ies du ing he es o
he weeks.
HSD le el di ision was he di e ence be ween “high-load” and “low-load” weeks
acco ding o he a e age weekly HSD o he eam. “High-load” was de ined as
HSD ≥288
and “low-load” was de ined as HSD < 288, bo h in me e s. The cu -o poin was es ablished
a he HSD alue in which a g ea e di e ence was ound be ween he mean o inju ies
be ween weeks o highe and lowe load (clus e s wi h mo e han 11 weeks), ha ing
p e iously o de ed he weeks in acco dance wi h highe o lowe HSD.
I.
Mean o inju ies du ing he 11 weeks o highes HSD–Mean o inju ies du ing he es o
he weeks.
II.
Mean o inju ies du ing he 12 weeks o highe HSD–Mean o inju ies du ing he es o
he weeks.
III.
Mean o inju ies du ing he 36 weeks o highe HSD–Mean o inju ies du ing he es o
he weeks.
SPD le el di ision was he di e ence be ween “high-load” and “low-load” weeks
acco ding o he a e age weekly SPD o he eam. “High-load” was de ined as
SPD ≥1601
and “low-load” was de ined as SPD < 1601, bo h in me e s. The cu -o poin was es-
ablished a he SPD alue in which a g ea e di e ence was ound be ween he mean
o inju ies be ween weeks o highe and lowe load (clus e s wi h mo e han 11 weeks),
ha ing p e iously o de ed he weeks in acco dance wi h highe o lowe SPD.
I.
Mean o inju ies du ing he 11 weeks o highes SPD–Mean o inju ies du ing he es o
he weeks.
II.
Mean o inju ies du ing he 12 weeks o highe SPD–Mean o inju ies du ing he es o
he weeks.
III.
Mean o inju ies du ing he 36 weeks o highe SPD–Mean o inju ies du ing he es o
he weeks.
RS le el di ision was he di e ence be ween “high-load” and “low-load” weeks
acco ding o he a e age weekly RS o he eam. “High-load” was de ined as RS
≥
60 and
“low-load” was de ined as RS < 60, bo h in numbe s. The cu -o poin was es ablished a
he RS alue in which a g ea e di e ence was ound be ween he mean o inju ies be ween
weeks o highe and lowe load (clus e s wi h mo e han 11 weeks), ha ing p e iously
o de ed he weeks in acco dance wi h highe o lowe RS.
In . J. En i on. Res. Public Heal h 2021,18, 10417 5 o 10
I.
Mean o inju ies du ing he 11 weeks o highes RS–Mean o inju ies du ing he es o
he weeks.
II.
Mean o inju ies du ing he 12 weeks o highe RS–Mean o inju ies du ing he es o
he weeks.
III.
Mean o inju ies du ing he 36 weeks o highe RS–Mean o inju ies du ing he es o
he weeks.
2.3.4. How o Reco d and calcula e Inju y
In o ma ion on inju ies was upda ed daily by he eam’s specialized medical s a .
All inju ies we e eco ded by ype, loca ion o he inju y, and iming o inju y based on
p e ious s udies. The in o ma ion used o he inju ies was as ollows:
1.
The numbe o egis e ed inju ies was he o al numbe o non-con ac inju ies pe
week o he eam o e he 48 weeks o he season.
2.
Weekly inju y eco ded he exis ence o no o a non-con ac inju y in each o he
48 weeks o he season.
2.4. S a is ical Analysis
IBM SPSS 25 and R S udio 3.6.2 (S a is ical Compu ing, Vienna, Aus ia). we e used
o he s a is ical analyses. A desc ip i e s a is ical analysis was pe o med, indica ing
he mean alues and SD o he “high-load” and “low-load” le els o he a iables “TD”,
“HSD”, “SPD”, and “RS”, as well as he o al alues. Non-pa ame ic Mann–Whi ney U
es s we e used o compa e he median o he load le els o he p e ious a iables, checking
he exis ence o s a is ically signi ican di e ences be ween hem. A es o no mali y,
Kolmogo o –Smi no , e i ied ha he a iable “Numbe o inju ies”, did no ollow a
no mal dis ibu ion. Addi ionally, a desc ip i e analysis o he numbe o inju ies p oduced
in he weeks o high and low load o each one o he a iables was comple ed, as well as
he calcula ion o he means o each one o hem, bo h o he wo le els o load, as well
as o he o al. In o de o de ec s a is ically signi ican in e -g oup di e ences be ween
he means o inju ies a he “high-load” and “low-load” le els o he “TD”, “HSD”, “SPD”,
and “RS” a iables, non-pa ame ic es s we e used, conside ing, as ac o s, he load le els
o each a iable. A con as o p opo ions de e mined i signi ican di e ences exis ed
be ween he le els o “high-load” and “low-load” o each a iable and he weeks wi h
inju y. To es ima e he isk o ha ing a high-load le el compa ed o a low-load le el,
espec i ely, o each a iable, OR and RR we e calcula ed, in addi ion o he espec i e
con idence in e als (CI) 95%. Finally, he a iable “Numbe o inju ies” ollowed a Poisson
dis ibu ion, allowing he pe o mance o a Poisson es , ob aining he lambda alues
(a e age numbe o inju ies pe week o each le el o load o each a iable), and he
expec ed ime un il a new inju y occu ed, once one had occu ed. Possible signi ican
di e ences be ween load le els we e examined ia calcula ing Ra e Ra ios, as well as
espec i e CI 95%. The le el o signi icance was se a p< 0.05 and p< 0.001 o all s ages.
3. Resul s
A desc ip i e analysis o he high- and low-load le els o he TD, HSD, SPD, and RS
a iables a e p esen ed in Table 1. S a is ically signi ican di e ences be ween “high-” and
“low-” load le els we e obse ed in all a iables.
Table 2de ails he ela ion be ween sp in a iables wi h non-con ac inju ies. Mean
inju ies we e signi ican ly highe in he high load weeks compa ed o he low load weeks
o TD, HSD, SD, and RS.
Signi ican di e ences we e ound (p< 0.05) in he p opo ion o inju y- ee weeks
be ween high- and low-load weeks in all a iables s udied. The OR and RR o p oducing
some inju y wi hou con ac was signi ican ly highe in he weeks o high load compa ed
o he weeks o low load in each one o he a iables o in e es . Simila ly, signi ican RR
we e ound o all a iables excep o he “RS” a iable (Table 3).
In . J. En i on. Res. Public Heal h 2021,18, 10417 6 o 10
Table 1. Desc ip i e in o ma ion o sp in a iables based on high- and low-load le els.
Va iables High-Load
Median (IQR)
Low-Load
Median (IQR) pTo al
Median (IQR)
TD (m) 23,757 (21,073–26,367) 20,006 (21,667–25,828) ≤0.001 *** 21,595 (19,211–25,046)
HSD (m) 360.2 (289.5–387.8) 207.7 (157.9–235.2) ≤0.001 *** 288.2 (210.4–361.7)
SPD (m) 1962 (1854–2473) 1429 (1189–1590) ≤0.001 *** 1845 (1518–2182)
RS (m) 77.6 (65.1–85.2) 48.6 (37.9–57.6) ≤0.001 *** 65.5 (55.9–81.0)
IQR: In e qua ile ange; m: me e s; To al dis ance (TD): High load (weeks wi h TD
≥
21,900 m); Low load (weeks wi h TD < 21,900 m);
High-speed dis ance (HSD): High load (weeks wi h HSD
≥
288 m); Low load (weeks wi h HSD < 288 m); Sp in dis ance (SPD): High load
(weeks wi h SPD
≥
1601 m); Low load (weeks wi h SPD < 1601 m); Repea ed sp in s (RS): High load (RS
≥
60). Low load (RS < 60); p
(p alue); *** (p< 0.001).
Table 2. Rela ion be ween TD, HSD, SPD, and RS wi h non-con ac inju ies (mean).
Va iables High-Load Low-Load pTo al
Inju ies Weeks M Inju ies Weeks M Inju ies Weeks M
TD (m) 15 23 0.65 6 25 0.24 0.017 * 21 48 0.44
HSD (m) 16 25 0.64 5 23 0.22 0.013 * 21 48 0.44
SPD (m) 19 33 0.58 2 15 0.13 0.013 * 21 48 0.44
RS (m) 18 32 0.56 3 16 0.19 0.034 * 21 48 0.44
m: me e s; To al dis ance (TD): High load (weeks wi h TD
≥
21,900 m); Low load (weeks wi h TD < 21,900 m); High-speed dis ance (HSD):
High load (weeks wi h HSD
≥
288 m); Low load (weeks wi h HSD < 288 m); Sp in dis ance (SPD): High load (weeks wi h SPD
≥
1601 m);
Low load (weeks wi h SPD < 1601 m); Repea ed sp in s (RS): High load (RS ≥60). Low load (RS < 60); M: mean; p(p alue); * (p< 0.05).
Table 3. Inju y isk ela ed o di e en load le els and sp in a iables wi h OR and RR (mean).
Va iables
High Load Low Load
OR
CI 95%
RR
CI 95%
Inju y
(No Inju y) To al Inju y
(No Inju y) To al Min Max Min Max
TD (m) 13 (10) 23 6 (19) 25 4.1 1.2 14.1 2.4 1.1 5.2
HSD (m) 14 (11) 25 5 (18) 23 4.6 1.3 16.3 2.6 1.1 6.0
SPD (m) 17 (16) 33 2 (13) 15 6.9 1.3 35.5 3.7 1.0 14.6
RS (m) 16 (16) 32 3 (13) 16 4.3 1.0 18.2 2.7 0.9 7.8
m: me e s; n: numbe s; To al dis ance (TD): High load (weeks wi h TD
≥
21900 m); Low load (weeks wi h TD < 21900 m); High-speed
dis ance (HSD): High load (weeks wi h HSD
≥
288 m); Low load (weeks wi h HSD < 288m); Sp in dis ance (SPD): High load (weeks wi h
SPD
≥
1601 m); Low load (weeks wi h SPD < 1601 m); Repea ed sp in s (RS): High load (RS
≥
60). Low load (RS < 60); Inju y (weeks wi h
inju ies). No inju y (weeks wi hou inju ies). To al ( o al weeks). OR (Odds Ra io) RR ( ela i e isk). CI95% (con idence in e al); Min
(minimum); Max (maximum).
Ul ima ely, i was obse ed ha he ime be ween inju ies was educed in weeks
o high-load and longe in weeks o low-load in he ou a iables s udied, al hough
signi ican di e ences we e ound in all a iables, excep in he a iable RS. Simila ly, he
a e a ios we e signi ican in all a iables o he expec ed weeks be ween inju ies excep
o he a iable RS (Table 4).
Table 4. Rela ionship be ween inju ies and di e en le els o load o ind he expec ed ime un il new inju ies (mean).
Va iables High Load Low Load pRa e Ra io CI 95%
λExpec ed Time Inju y λExpec ed Time Inju y Min Max
TD (m) 0.65 1.5 0.24 4.2 0.046 * 2.7 1.0 8.6
HSD (m) 0.64 1.6 0.22 4.6 0.029 * 2.9 1.0 10.3
SPD (m) 0.58 1.7 0.13 7.7 0.033 * 4.3 1.0 38.2
RS (m) 0.56 1.8 0.19 5.3 0.067 3.0 0.9 15.9
Poisson: m: me e s; n: numbe s; To al dis ance (TD): High load (weeks wi h TD
≥
21,900 m); Low load (weeks wi h TD < 21,900 m);
High-speed dis ance (HSD): High load (weeks wi h HSD
≥
288 m); Low load (weeks wi h HSD < 288 m); Sp in dis ance (SPD): High load
(weeks wi h SPD
≥
1601 m); Low load (weeks wi h SPD < 1601 m); Repea ed sp in s (RS): High load (RS
≥
60). Low load (RS < 60); p
(
p alue
); * p< 0.05; CI 95% (Con idence in e al); MIN (minimum); MAX (maximum); Ra e a io (Expec ed ime inju y low load/Expec ed
ime inju y high load).
In . J. En i on. Res. Public Heal h 2021,18, 10417 7 o 10
4. Discussion
This s udy in es iga ed he ela ionship be ween GPS-de i ed wo kload and non-
con ac inju ies in p o essional socce playe s. The p esen da a highligh ha he weeks
o high-load le els inc ease he isk o non-con ac inju y wi hin socce playe s. Based on
ou esul s, TD, HSD, and SPD a iables could po en ially ack aining and may allow
exe cise p esc ip ion o educe non-con ac inju ies. Finally, acco ding o he a e a ios
calcula ed, he in e al ime be ween he las non-con ac inju y and he new inju y du ing
high-load aining in TD, HSD, and SPD) is sho e han du ing low-load aining.
The ela ionship be ween non-con ac inju ies and di e en le els o load o ind
he expec ed ime un il a new non-con ac inju y was p esen ed ia ORs and RRs. All
a iables we e signi ican excep o he RS a iable in RR (Table 3). TD and HSD we e
ound p e iously o be he bes a es o non-con ac inju ies [
12
]. In he cu en s udy and in
p e ious s udies, inc eased inju y occu ed when ORs and RRs we e g ea e han 1 [
12
,
29
].
TD (OR: 4.1, RR: 2.4) and HSD (OR: 4.6, RR: 2.6) we e signi ican ly di e en be ween high-
and low-load weeks. The e o e, pa icipan s had a highe odds and isk o a non-con ac
inju y du ing high-load weeks compa ed o low-load weeks. P e ious s udies did no
in es iga e SPD and RS, al hough hese ha e been ound o be associa ed wi h non-con ac
inju y occu ence [
12
]. In he cu en s udy, when playe s co e ed
SPD ≥1601 m
du ing a
week, hey we e a signi ican ly highe isk o inju y compa ed o weeks wi h
SPD < 1601 m
(OR: 6.9; RR: 3.7 m; p< 0.05). Howe e , RS epo ed a signi ican OR (4.3; p< 0.05) bu no
signi ican RR (2.7; p> 0.05). The e o e, TD, HSD, and SPD a iables could po en ially be
associa ed wi h non-con ac inju ies and he expec ed ime un il new inju y and may help
p ac i ione s and coaches adjus aining load in an e o o p e en non-con ac inju y.
Ou s udy is one o he i s o in es iga e he e ec s o GPS-de i ed wo kload on
subsequen non-con ac inju y isk in an eli e coho o socce playe s. We obse ed ha
he weeks in which playe s eached TD < 21,900 m, HSD < 288 m and SPD < 1601 m,
hey educed inju y isk compa ed o highe week loads (OR: 4.1 o 6.9). In addi ion, ou
indings sugges ha weeks in which playe s epea ed <60 sp in s, hey we e a educed
inju y isk compa ed o high-load weeks (OR: 4.3). The cu en da a sugges ha low
load exposu e o sp in a iables can p o ec p o essional socce playe s om subsequen
non-con ac inju y isk. These esul s could p o ide coaches and p ac i ione s wi h ini ial
guidelines o op imal wo kload o educe non-con ac inju y occu ence.
P e ious li e a u e has ound ha mode a e and highe ch onic aining loads can o e a
p o ec i e e ec agains lowe limb inju y isk o eam spo playe s [
8
,
28
].
Malone e al.
[
30
]
obse ed ha playe s wi h mode a e exposu es o maximum eloci y (>6–10) we e a
educed inju y isk compa ed o playe s who expe ienced lowe (<5) exposu es (OR: 0.24).
Also, he au ho s [
30
] ound ha playe s wi h highe 21-day ch onic loads (
≥
2584 AU)
comple ed inc eased high-speed and sp in unning dis ances ha indica ed a p o ec i e
e ec agains inju y (OR: 0.24–1.22). The eason o hese obse a ions may be because he
playe s a e usually exposed o a ch onic aining load pe iod. Hence, hey a e used o ole -
a ing high-speed unning wo kload which educes inju y isk. In con as ,
Malone e al.
epo ed ha eli e socce playe s we e a inc eased isk o inju y when hey expe ienced
high one-week cumula i e aining loads (
≥
1500 o
≤
2120 AU) [
8
]. Gabbe and Ullah [
22
]
demons a ed ha g ea e amoun s o HSD a e associa ed wi h an inc eased inju y isk
o lowe body so - issue inju y in eli e ugby playe s (RR: 2.7). These indings can be
explained by highe acu e loads ha a e associa ed wi h an inc ease in a igue s a us in
playe s and esul an inc eases in inju y isk [
21
]. In his ega d, con o e sy s ill exis s
ega ding he impac o sp in s in non-con ac inju ies and u he s udies a e needed in
he eli e socce en i onmen .
F om a pe o mance poin o iew, ca e ul hough should be aken o unde s and and
apply he p esen indings o eli e pe o mance socce . Ou da a sugges ha educing he
amoun o sp in ing in p o essional socce aining could o e a p o ec i e e ec agains
non-con ac inju y. In his con ex , a ine balance exis s be ween aining load es ic ion
(i.e., p e en ing inju y) and inc eased aining loads (i.e., imp o ing pe o mance)
[4,8,22].
In . J. En i on. Res. Public Heal h 2021,18, 10417 8 o 10
Consequen ly, keeping in mind he need o an app op ia e s imulus o imp o e pe o -
mance, we used he cu en da a o a y sp in ing loads du ing he socce season. Ou
da a sugges ha playe s will be exposed o inc eased isk o non-con ac inju y when he
amoun o TD, HSD, SPD, and numbe o RS is highe . Planning a dec ease o mean sp in
a iables in some high-load weeks may o e he balance be ween inju y p e en ion and
pe o mance enhancemen . The inding could be an impo an conside a ion o co ec ly
manipula e wo kloads du ing he season, no only o educe non-con ac inju y bu also o
enhance physical pe o mance wi hin p o essional socce playe s.
A me hod o measu ing in e nal aining load, such as a ing o pe cei ed exe ion
(RPE) using he ca ego y a io scale (CR10-scale) pe session [
31
], could be used o assess
how he playe s a e coping wi h aining loads e e y day. This me hod has been shown
o be he mos alid indica o o exe cise in ensi y [
32
]. The collec ion o weekly GPS
(ex e nal load) and session-RPE (in e nal load) a iables allows he calcula ion o ch onic
aining loads [
2
], enabling educ ion o u u e loads based on hese a iables. P e iously,
Gallo e al.
[
33
] demons a ed mode a e o e y la ge associa ions be ween session-RPE
and bo h HSD ( = 0.51) and TD ( = 0.81) in eam spo a hle es. The e o e, including
his pa ame e in u u e esea ch could assis p ac i ione s and coaches in inding he
app op ia e s imulus and balance be ween inju ies and pe o mance.
Recen s udies obse ed ha non-con ac inju ies had a high equency o e-inju y
and pe sis en complain s a e e u n o socce compe i ion [
3
,
34
]. Acco ding o he esul s
o he a e a ios, he in e al ime be ween he las non-con ac inju y and he new inju y a
he high-load in TD, HSD, and SPD is sho e han he low-load (Table 4). Socce inju ies a e
de ined by an in e -indi idual a iabili y o lexo and ex enso muscle pe o mances [
35
].
One o he majo isk ac o s ha has been iden i ied is s eng h asymme y, and he
asymme y index has been conside ed as a alid and use ul ool o de ec playe s a high
inju y isk (e.g., 4- old in playe s wi h >10% asymme y) o lowe ex emi y inju y [
36
].
S eng h asymme y has been conside ed in ela ion o mo emen speed in eam-spo
a hle es [
37
]. The e o e, he majo numbe o sp in s du ing high load weeks may induce
an inc ease o s eng h imbalances in he lowe limbs, and a g ea e p edisposi ion o inju y
may be possible. Consequen ly, in e -limb asymme y es s and s eng h aining p og ams
may allow a p e en i e app oach o educe he isk o e-inju y in p o essional socce .
4.1. Limi a ions
Se e al limi a ions a e impo an o men ion om he cu en s udy. Inju y isk in
socce playe s can also be a ibu ed o mul iple ac o s such as p e ious inju y, pe cei ed
muscle a igue, nu i ion and hyd a ion, mood, sleep a ings, and physiological s esso s,
none o which we e included in his s udy [
18
,
27
]. Resea ch inco po a ing objec i e
measu es o GPS wi h RPE- alues may p o ide addi ional insigh in o he aining load–
inju y ela ionship. In addi ion, he p esen in es iga ion was de eloped in one p o essional
socce eam du ing one season. Consequen ly, ou esul s canno be di ec ly ex apola ed o
o he spo s, eams, o ac oss mul iple seasons. The e o e, we ecommend u he s udies
o be e unde s anding o he wo kload–inju y ela ionship in eli e socce .
4.2. P ac ical Applica ions
The cu en s udy is he i s o p o ide an indica ion o how playe s’ weekly aining
load is associa ed wi h non-con ac inju ies in p o essional socce playe s. Team socce s a
should measu e weekly he in e nal and ex e nal load o playe s o plan and implemen
op imal ainings ha imp o e hei pe o mance and educe hei inju y isk. Gi en
ha hese indings sugges ha a high load o sp in s inc eases he isk o sus aining
non-con ac inju ies, a emp ing o adjus aining load o sp in a iables du ing high
load weeks is ecommended. Howe e , his obse a ion equi es u he in es iga ions.
One possibili y o achie e his in p ac ice is o es ic he amoun o sp in ing and p esc ibe
s able and consis en weekly loads du ing he season o p e en any spikes in acu e
wo kload. Ou esul s also sugges ha TD, HSD, and SPD measu ed ia GPS could be
In . J. En i on. Res. Public Heal h 2021,18, 10417 9 o 10
modelled o ack aining and o educe non-con ac inju ies. Ne e heless, u he s udies
a e ecommended o imp o e he accu acy o hese a iables in educing non-con ac
inju ies. Finally, he indings may p omo e an e idence-based app oach o coaches and
p ac i ione s in planning and moni o ing weekly aining load h esholds o educe a igue
du ing socce pa icipa ion and consequen ly, p e en non-con ac inju ies.
5. Conclusions
The esul s o his s udy demons a ed ha he high olume o sp in ing du ing
high-load weeks is associa ed wi h non-con ac inju y occu ence. In addi ion, TD, HSD,
and SPD o GPS a iables could ack aining and may allow exe cise p esc ip ion o
educe non-con ac inju ies. Finally, he in e al ime be ween he p e ious inju y and a
new inju y du ing high load aining is sho e han du ing low load aining. The cu en
da a p o ide an impo an con ibu ion ha may be aluable o suppo he decisions o
coaches and p ac i ione s when hey ha e o choose he bes GPS a iables o obse e
non-con ac inju ies, o educe he amoun o sp in ing du ing p o essional socce seasons,
and o adjus aining loads o sp in a iables. Howe e , hey could also con empla e he
consequences o educing aining loads du ing he season on playing pe o mance.
Au ho Con ibu ions:
Concep ualiza ion, H.N., E.M.-P., A.D.Z. and J.P.-G.; me hodology, H.N.,
E.M.-P., A.D.Z., F.M.C. and J.P.-G.; so wa e, H.N., T.G.B. and J.P.-G.; o mal analysis, H.N and A.D.Z.;
in es iga ion, J.P.-G., H.N., E.M.-P., A.D.Z., F.M.C. and T.G.B.; w i ing—o iginal d a p epa a ion,
H.N., E.M.-P., A.D.Z. and J.P.-G.; w i ing— e iew and edi ing, H.N., E.M.-P., A.D.Z., F.M.C., T.G.B.
and J.P.-G. All au ho s ha e ead and ag eed o he published e sion o he manusc ip .
Funding: The e is no ex e nal und.
Ins i u ional Re iew Boa d S a emen :
The s udy was conduc ed acco ding o he guidelines o
he Decla a ion o Helsinki and app o ed by he E hics Commi ee o he Uni e si y o Is ahan
(IR.UI.REC.1399.064).
In o med Consen S a emen :
In o med consen was ob ained om all subjec s in ol ed in he s udy.
Da a A ailabili y S a emen :
The da ase s used and/o analyzed du ing he cu en s udy a e
a ailable om he co esponding au ho on easonable eques .
Acknowledgmen s:
The au ho s would like o hank he Sepahan Foo ball Club, eam’s coaches, and
playe s o hei coope a ion du ing all da a collec ion p ocedu es.
Con lic s o In e es : The au ho s decla e no con lic o in e es .
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