Body fat assessment in international elite soccer referees

Jou nal o Func ional Mo phology and Kinesiology A icle Body Fa Assessmen in In e na ional Eli e Socce Re e ees C is ian Pe i 1, F ancesco Campa 2, Vi o Hugo Teixei a 3,4, Pascal Izzicupo 5, Gio gio Galan i 1, Angelo Pizzi 6, Geo gian Badicu 7,* and Gab iele Masche ini 1 1Spo s and Exe cise Medicine Uni , Clinical and Expe imen al Depa men , Uni e si y o Flo ence, 50121 Fi enze, I aly; [email p o ec ed] (C.P.); [email p o ec ed] (G.G.); [email p o ec ed] (G.M.) 2 Depa men o Li e Quali y S udies, Uni e si y o Bologna, 47921 Rimini, I aly; [email p o ec ed] 3Facul y o Nu i ion and Food Sciences (FCNA), Uni e si y o Po o, 4200-465 Po o, Po ugal; [email p o ec ed] 4Resea ch Cen e in Physical Ac i i y, Heal h and Leisu e (CIAFEL), Facul y o Spo s, Uni e si y o Po o, 4099-002 Po o, Po ugal 5Depa men o Medicine and Aging Science, “G. D’Annunzio” Uni e si y o Chie i-Pesca a, 66100 Chie i, I aly; [email p o ec ed] 6A.I.A., I alian Re e ees Associa ion, 00187 Rome, I aly; [email p o ec ed] 7Depa men o Physical Educa ion and Special Mo ici y, T ansil ania Uni e si y o B aso , 500068 B aso , Romania *Co espondence: geo gian.badicu@uni b . o Recei ed: 14 Ap il 2020; Accep ed: 5 June 2020; Published: 6 June 2020   Abs ac : Socce e e ees a e a speci ic g oup in he spo s popula ion ha a e ecei ing inc easing a en ion om spo s scien is s. A lowe a mass pe cen age (FM%) is a use ul pa ame e o moni o i ness s a us and ae obic pe o mance, while being able o e alua e i wi h a simple and quick ield-based me hod can allow a egula assessmen . The aim o his s udy was o p o ide a speci ic p o ile o e e ees based on mo phological and body composi ion ea u es while compa ing he accu acy o di e en skin old-based equa ions in es ima ing FM% in a coho o socce e e ees. Fo y- h ee eli e in e na ional socce e e ees (age 38.8 ± 3.6 yea s), who pa icipa ed in he 2018 Russian Wo ld Cup, unde wen body composi ion assessmen s wi h skin old hickness and dual-ene gy X- ay abso p iome y (DXA). Six equa ions used o de i e FM% om skin old hickness we e compa ed wi h DXA measu emen s. The pe cen age o body a es ima ed using DXA was 18.2 ± 4.1%, whe eas skin old-based FM% assessed om he six o mulas anged be ween 11.0% ± 1.7% o 15.6% ± 2.4%. Among he six equa ions conside ed, he Faulkne ’s o mula showed he highes co ela ion wi h FM% es ima ed by DXA ( =0.77; R 2 =0.59 p<0.001). Addi ionally, a new skin old-based equa ion was de eloped: FM% =8.386 +(0.478 × iliac c es skin old) +(0.395 × abdominal skin old, =0.78; R 2 =0.61; s anda d e o o he es ima e (SEE) =2.62 %; p<0.001). Due o hese indings, na ional and in e na ional ede a ions will now be able o pe o m egula body composi ion assessmen s using skin old measu emen s. Keywo ds: an h opome y; body composi ion; DXA; equa ion; a mass; socce ; soma o ype; skin olds 1. In oduc ion No ma e he compe i ion le el, he e is no o icial socce game wi hou he p esence o he 23 d key elemen : he e e ee. The e a e mo e han 840,000 egis e ed e e ees who a bi a e socce games each week e i ying and en o cing he ules o he game [ 1 ]. Howe e , scien i ic li e a u e on e e ees J. Func . Mo phol. Kinesiol. 2020,5, 38; doi:10.3390/j mk5020038 www.mdpi.com/jou nal/j mk J. Func . Mo phol. Kinesiol. 2020,5, 38 2 o 10 in ela ion o physiological demands, body composi ion, and nu i ion- ela ed aspec s [ 2 – 4 ] is limi ed when compa ed o wha is a ailable on playe s. No only do eli e-class socce e e ees need o pe o m hei bes in pe cep ual-cogni i e abili ies and decision-making asks [ 5 ], bu hey mus also achie e an ele a ed ae obic pe o mance simila o a mid ield socce playe [ 6 ]. Al hough he e a e signi ican di e ences be ween games, e e ees co e on a e age a dis ance be ween 9 and 13 km pe game, depending on he le el o compe i ion [ 3 , 7 – 9 ]. Due o he high-in ensi y ma ches in ecen yea s [ 10 ] and as a consequence o he inc ease in physical demand he e is a end owa ds a dec ease in body mass index (BMI) and body a le els in eli e e e ees [ 11 ]. In ac , ecen s udies on eli e e e ees (FIFA) show lowe le els o BMI and body a han p e iously epo ed in P emie League e e ees [12,13]. In socce playe s, body a is gene ally es ima ed by skin old hickness assessmen , bioelec ical impedance analysis, and dual-ene gy X- ay abso p iome y (DXA). DXA is widely accep ed as a p ac ical me hod o assessing a mass in a hle es [ 14 – 16 ] and is becoming mo e popula in eli e spo s as an analysis used by bo h p ac i ione s and esea che s [ 17 ]. An h opome ic assessmen is ano he popula me hod used o p edic body a in a hle es [ 18 – 20 ]. The measu emen o skin olds is widely adop ed o moni o changes in body composi ion due o aining and/o die a y in e en ions. Skin old hickness measu emen s ha e long been u ilized o p edic body a and o e he yea s mul iple equa ions ha e been de eloped o his pu pose [ 21 – 26 ]. Howe e , o he bes o he au ho s’ knowledge, he e a e no s udies compa ing esul s ob ained by skin old-based measu emen s and DXA in socce e e ees. This s udy was designed o p esen body composi ion ea u es o socce e e ees called o he Russian Wo ld Cup in 2018 wi h wo main aims. The i s pu pose was o compa e di e en equa ions o es ima e a mass om skin old assessmen wi h da a de i ed om DXA. The second aim was o de elop a p edic ion equa ion o es ima ing he pe cen age o a mass (FM%) based on an h opome ic a iables speci ic o his coho . 2. Ma e ials and Me hods 2.1. S udy Popula ion Using a c oss-sec ional design, 43 eli e in e na ional socce e e ees (age 38.8 ± 3.6 yea s) om 6 con ede a ions we e en olled in he s udy du ing a semina held in he Fede al Technical Cen e o Co e ciano (I aly) in Ap il 2018, du ing he compe i i e season. They we e classi ied as eli e because hey we e ei he egis e ed a he maximum le el in he a hle ic ede a ion o ha e ecei ed inancial suppo o hei dedica ion o aining and games. The s udy was designed and conduc ed in acco dance wi h he Helsinki Decla a ion. The e hics commi ee o he I alian oo ball associa ion app o ed his s udy and all he pa icipan s signed w i en in o med consen p io o hei inclusion in he s udy (app o al code: 03032018). 2.2. P ocedu es Pa icipan s unde wen body composi ion assessmen s ea ly in he mo ning, in an o e nigh - as ed s a e, and a leas 12 h pos exe cise, wi h no long ips du ing he p e ious day. Fu he , he consump ion o alcohol and s imulan be e ages we e no allowed o a leas 15 h p io o es ing. The me hodology used o he assessmen o body composi ion was in acco dance wi h ou p e ious s udies [ 26 , 27 ], using he in eg a ion o an h opome y, skin old hickness, and DXA. An h opome ic measu emen s we e aken ollowing he p o ocol o The In e na ional Socie y o he Ad ancemen o Kinan h opome y (ISAK) [ 28 ] by he same esea che (an ISAK le el an h opome is ), whose echnical e o was 5% and 1.5% o skin olds and all o he measu emen s, espec i ely. Heigh (m) and body weigh (kg) we e measu ed o he nea es 0.1 cm and 0.01 kg, espec i ely, using a high-p ecision mechanical scale (SECA, Basel, Swi ze land). BMI was calcula ed using he o mula body mass/heigh 2 (kg/m 2 ). Biceps gi h, wais gi h, and hip gi h (cm) we e measu ed wi h a na ow, J. Func . Mo phol. Kinesiol. 2020,5, 38 3 o 10 me allic, and inex ensible measu ing ape (Lu kin ® model W606PM, London, UK; p ecision =1 mm). Skin olds we e measu ed wi h a skin old calipe (Hol ain L d., C ymych, UK; p ecision =0.2 mm) a nine ana omical si es ( iceps, subscapula , biceps, iliac c es , sup aspinal, pec o al, abdominal, high, and cal ). Hume us and emu b ead hs we e measu ed o he nea es 0.1 cm wi h a sliding calipe (GMP, Zü ich, Swi ze land). Soma o ype was calcula ed acco ding o he Hea h-Ca e me hod [29]. Body densi y was calcula ed om he Si i equa ion [ 30 ] adap ed o age [ 31 ], which was hen used o es ima e FM%. The ollowing six skin old-based equa ions we e used o es ima e FM%: •Yushaz [21]; •Faulkne [22]; •Es on e al. [24]; •Du nin and Wome sley [23]; •Reilly e al. [25]; •Sua ez e al. [26]. Addi ionally, he a e age FM% measu ed by all o hese equa ions was conside ed. Fa -F ee Mass (FFM) was calcula ed sub ac ing a mass om body weigh . A DXA scanne (Hologic QDR Se ies, Delphi A model, Bed o d, MA, USA) wi h Hologic APEX 13.3:3 so wa e e sion, was used o es ima e FM%. The ins umen was calib a ed wi h phan oms as pe he manu ac u e ’s guidelines each day p io o measu emen s. Pa icipan s assumed a s a iona y supine posi ion on he scanning able. All scanning and analyses we e pe o med by he same echnician o ensu e consis ency and in acco dance wi h s anda dized es ing p o ocols ecognized as bes p ac ice [17,32,33]. 2.3. S a is ical Analysis Da a we e exp essed as mean ± s anda d de ia ions (SD) and no mali y o dis ibu ion o he da a was e i ied by he Kolmogo o –Smi no es . Compa isons be ween FM% calcula ed wi h he di e en o mulas and hose measu ed by DXA we e made using linea eg ession analysis, as well as be ween he sum o skin old measu emen s wi h FM% ob ained by DXA. Gi en he ac ha di e en e hnic g oups pa icipa ed, he e ec o e hnici y on FM% was es ed using he K uskal–Wallis es . No in e ac ions we e ound be ween e hnici y and o he independen a iables; he e o e, we used he whole sample in he model de elopmen . The abili y o he ollowing a iables (age, s a u e, weigh , and skin olds) in p edic ing FM% in he in e na ional socce e e ees was assessed using s epwise eg ession analysis. Du ing model de elopmen , no mali y o esiduals and homogenei y o a iance we e es ed. Signi icance a p ≤ 0.05 was es ablished as he c i e ion o inclusion o a p edic o whe eas emo al c i e ia we e se a p ≤ 0.1. I mo e han one a iable emained in he model, and o assess mul icollinea i y, a a iance in la ion ac o ( h eshold as 5) was calcula ed o each independen a iable. The da a we e analyzed using he s a is ical package IBM SPSS S a is ics ( e sion 13.0) o Windows. (SPSS Inc., Chicago, IL, USA). 3. Resul s Gene al and an h opome ic cha ac e is ics and desc ip i e alues o FM% es ima ed om DXA and skin old-based equa ions a e shown in Table 1. The e e ees showed an a e age balanced mesomo ph soma o ype, cha ac e ized by a dominan mesomo ph componen and simila alues be ween endomo ph and ec omo ph componen s (no mo e han a di e ence o 0.5 uni s, Figu e 1). Co ela ion coe icien s and le el o signi ican di e ences be ween FM% wi h DXA and o he p ac ical es ima es in he socce e e ees a e shown in Table 2. Gi en ha no di e ence be ween e hnic g oups in FM% was ound (p=0.241), all he alues we e p esen ed oge he . J. Func . Mo phol. Kinesiol. 2020,5, 38 4 o 10 Table 1. Gene al and an h opome ic cha ac e is ics o he in e na ional-le el eli e e e ees. Va iable Mean SD Minimum Maximum Age (yea ) 38.8 3.6 29.5 44.1 Body Mass (kg) 75.7 6.5 61.0 94.0 Heigh (m) 1.8 0.1 1.7 1.9 Body mass index (kg/m2)23.1 1.3 20.6 25.8 Endomo phy 2.7 0.9 1.2 5.1 Mesomo phy 6.5 1.2 4.2 8.5 Ec omo phy 2.9 0.7 1.2 4.6 Fa Mass by DXA (%) 18.2 4.1 11.5 28.0 Fa Mass by Es on e al. [24] (%) 12.0 2.4 9.4 18.8 Fa Mass by Yuhasz [21] (%) 12.8 2.5 8.8 21.0 Fa Mass by Faulkne [22] (%) 12.7 2.1 9.2 18.5 Fa Mass by Reilly e al. [25] (%) 11.0 1.7 8.2 16.5 Fa Mass by Sua ez e al. [26] (%) 15.6 2.4 12.6 24.6 Fa Mass by Du nin and Wome sley [23] (%) 13.3 2.9 8.5 20.5 Fa Mass by Mean (%) 12.9 2.2 9.7 19.4 P2sk (mm) 14.1 5.0 7.8 29.6 P4sk-a (mm) 32.4 8.5 21.0 57.3 P4sk-b (mm) 38.6 11.4 21.6 75.6 P5sk (mm) 41.7 10.7 27.9 74.5 P6sk (mm) 59.6 16.4 34.0 112.6 P7sk (mm) 62.9 16.6 38.9 116.8 P9sk (mm) 73.7 18.2 46.5 130.8 Abb e ia ions: Σ 2sk =an e io high, medial cal ; Σ 4sk-a =biceps, iceps, subscapula , iliac c es ; Σ 4sk-b = iceps, abdominal; an e io high, medial cal ; Σ 5sk =biceps, iceps, subscapula , iliac c es , an e io high; Σ 6sk = iceps, subscapula , iliac c es , abdominal, an e io high, medial cal ; Σ 7sk = iceps, subscapula , iliac c es , sup aspinal, abdominal, an e io high, medial cal ; Σ 9sk =biceps, iceps, subscapula , iliac c es , sup aspinal, pec o al, abdominal, an e io high, medial cal . J. Func . Mo phol. Kinesiol. 2020, 5, x FOR PEER REVIEW 4 o 10 Table 1. Gene al and an h opome ic cha ac e is ics o he in e na ional-le el eli e e e ees. Va iable Mean SD Minimum Maximum Age (yea ) 38.8 3.6 29.5 44.1 Body Mass (kg) 75.7 6.5 61.0 94.0 Heigh (m) 1.8 0.1 1.7 1.9 Body mass index (kg/m 2 ) 23.1 1.3 20.6 25.8 Endomo phy 2.7 0.9 1.2 5.1 Mesomo phy 6.5 1.2 4.2 8.5 Ec omo phy 2.9 0.7 1.2 4.6 Fa Mass by DXA (%) 18.2 4.1 11.5 28.0 Fa Mass by Es on e al. [24] (%) 12.0 2.4 9.4 18.8 Fa Mass by Yuhasz [21] (%) 12.8 2.5 8.8 21.0 Fa Mass by Faulkne [22] (%) 12.7 2.1 9.2 18.5 Fa Mass by Reilly e al. [25] (%) 11.0 1.7 8.2 16.5 Fa Mass by Sua ez e al. [26] (%) 15.6 2.4 12.6 24.6 Fa Mass by Du nin and Wome sley [23] (%) 13.3 2.9 8.5 20.5 Fa Mass by Mean (%) 12.9 2.2 9.7 19.4 ∑2sk (mm) 14.1 5.0 7.8 29.6 ∑4sk-a (mm) 32.4 8.5 21.0 57.3 ∑4sk-b (mm) 38.6 11.4 21.6 75.6 ∑5sk (mm) 41.7 10.7 27.9 74.5 ∑6sk (mm) 59.6 16.4 34.0 112.6 ∑7sk (mm) 62.9 16.6 38.9 116.8 ∑9sk (mm) 73.7 18.2 46.5 130.8 Abb e ia ions: Σ2sk = an e io high, medial cal ; Σ4 sk-a = biceps, iceps, subscapula , iliac c es ; Σ4sk-b = iceps, abdominal; an e io high, medial cal ; Σ5sk = biceps, iceps, subscapula , iliac c es , an e io high; Σ6sk= iceps, subscapula , iliac c es , abdominal, an e io high, medial cal ; Σ7sk= iceps, subscapula , iliac c es , sup aspinal, abdominal, an e io high, medial cal ; Σ9sk = biceps, iceps, subscapula , iliac c es , sup aspinal, pec o al, abdominal, an e io high, medial cal . Figu e 1. Rep esen a ion o he soma o ype o he In e na ional eli e male socce e e ees. Figu e 1. Rep esen a ion o he soma o ype o he In e na ional eli e male socce e e ees. J. Func . Mo phol. Kinesiol. 2020,5, 38 5 o 10 Table 2. Co ela ion coe icien s and le el o signi icance be ween a mass pe cen age (FM%) es ima ed by dual-ene gy X- ay abso p iome y (DXA) wi h he sum o skin old measu emen s, and FM% ob ained om skin old-based equa ions. Va iable R2p-Value P2sk 0.41 0.165 0.007 P4sk 0.75 0.559 <0.001 P4sk 0.70 0.491 <0.001 P5sk 0.72 0.519 <0.001 P6sk 0.76 0.585 <0.001 P7sk 0.77 0.588 <0.001 P9sk 0.76 0.581 <0.001 Fa Mass by Es on e al. [24] 0.60 0.363 <0.001 Fa Mass by Yuhasz [21] 0.76 0.585 <0.001 Fa Mass by Faulkne [22] 0.77 0.598 <0.001 Fa Mass by Reilly e al. [25] 0.71 0.497 <0.001 Fa Mass by Sua ez e al. [26] 0.74 0.549 <0.001 Fa Mass by Du nin and Wome sley [23] 0.76 0.580 <0.001 Fa Mass by Mean 0.78 0.606 <0.001 All FM% alues ob ained by he skin old-based equa ions showed la ge o e y la ge posi i e co ela ions ( om 0.60 o 0.78) o hose measu ed by DXA. The FM% es ima ed om all o he equa ions showed signi ican di e ences (p<0.001) in compa ison o he DXA esul s. The sum o skin old measu emen s showed mode a e o e y la ge posi i e co ela ions wi h FM% ob ained by DXA, excep o he sum o wo skin old measu emen s. Rela ionships be ween DXA-de i ed FM% and skin old hicknesses o di e en ana omical si es a e shown in Table 3. The as majo i y o skin old measu emen s ci ed showed mode a e o e y la ge posi i e ela ionships wi h FM% ( om 0.57 o 0.71), excep biceps, pec o al, an e io high, and medial cal . Table 3. Rela ionships be ween DXA-de i ed FM% and di e en skin olds measu ed in he in e na ional- le el eli e e e ees. Va iable R2p-Value Biceps 0.25 0.060 0.113 T iceps 0.57 0.321 <0.001 Subscapula 0.63 0.394 <0.001 Iliac c es 0.71 0.510 <0.001 Sup aspinal 0.53 0.285 <0.001 Pec o al 0.02 0.001 0.885 Abdominal 0.68 0.464 <0.001 An e io high 0.37 0.135 0.016 Medial cal 0.39 0.154 0.009 BMI 0.10 0.011 0.505 Table 4shows he skin old-based model o FM% gene a ed o he in e na ional socce e e ees. Only a iables con ibu ing as signi ican p edic o s using backwa d s epwise app oach we e used in he model. The inal p edic ion model included: FM% =8.386 +(0.478 × iliac c es skin old) +(0.395 × abdominal skin old, =0.781; R2=0.610; SEE =2.62 %; p<0.001, Table 4; Figu e 2). J. Func . Mo phol. Kinesiol. 2020,5, 38 6 o 10 Table 4. De eloped models o FM% p edic ion. Va iable Coe icien R2SEE (%) Model 1 0.510 2.90 In e cep 9.727 Iliac c es skin old (mm) 0.714 Model 2 0.610 2.62 In e cep 8.386 Iliac c es skin old (mm) 0.478 Abdominal skin old (mm) 0.395 Abb e ia ions: R2, coe icien o de e mina ion; SEE, s anda d e o o he es ima e. J. Func . Mo phol. Kinesiol. 2020, 5, x FOR PEER REVIEW 6 o 10 Va iable Coe icien R 2 SEE (%) Model 1 0.510 2.90 In e cep 9.727 Iliac c es skin old (mm) 0.714 Model 2 0.610 2.62 In e cep 8.386 Iliac c es skin old (mm) 0.478 Abdominal skin old (mm) 0.395 Abb e ia ions: R 2 , coe icien o de e mina ion; SEE, s anda d e o o he es ima e. Figu e 2. The sca e plo illus a es he esul s o he eg ession analysis o FM% ob ained by he e e ence me hod (DXA) and p edic ed by he equa ion de eloped in he sample o in e na ional socce e e ees. 4. Discussion This s udy compa ed six skin old-based equa ions showing he di e en esul s in FM% es ima ion in in e na ional eli e socce e e ees, using DXA as a e e ence me hod. Addi ionally, ou s udy is he i s o ha e p o ided a speci ic equa ion o his pa icula sample g oup, as well as desc ip i e body composi ion pa ame e s. Ou esul s highligh ha he sum o skin old hickness measu emen s aken in se en ( iceps, subscapula , iliac c es , sup aspinal, abdominal, an e io high, and medial cal ) o in nine (biceps, iceps, subscapula , iliac c es , sup aspinal, pec o al, abdominal, an e io high, and medial cal ) si es show a high associa ion wi h he FM% es ima ed wi h DXA. Secondly, among he equa ions conside ed, ha o Faulkne [22] showed he bes sensi i i y in assessing FM% in he in e na ional eli e socce e e ees. Las ly, a new equa ion based on he an h opome ic measu emen s aken on he sample g oup was p oposed. While excessi e FM% may a ec pe o mance, body composi ion is an aspec o conside able in e es o scien is s, a hle es, and coaches [34]. Typical FM% alues ( anging om 5% o 19%) epo ed in male a hle es depends on he spo , playing posi ion, and me hodology used o he assessmen [35–37]. In pa icula , male socce playe s show a pe cen age o a mass anging be ween 11.7–13.7% [20,38]. Fu he mo e, he es ed e e ees in his s udy showed a balanced mesomo ph soma o ype. Figu e 2. The sca e plo illus a es he esul s o he eg ession analysis o FM% ob ained by he e e ence me hod (DXA) and p edic ed by he equa ion de eloped in he sample o in e na ional socce e e ees. 4. Discussion This s udy compa ed six skin old-based equa ions showing he di e en esul s in FM% es ima ion in in e na ional eli e socce e e ees, using DXA as a e e ence me hod. Addi ionally, ou s udy is he i s o ha e p o ided a speci ic equa ion o his pa icula sample g oup, as well as desc ip i e body composi ion pa ame e s. Ou esul s highligh ha he sum o skin old hickness measu emen s aken in se en ( iceps, subscapula , iliac c es , sup aspinal, abdominal, an e io high, and medial cal ) o in nine (biceps, iceps, subscapula , iliac c es , sup aspinal, pec o al, abdominal, an e io high, and medial cal ) si es show a high associa ion wi h he FM% es ima ed wi h DXA. Secondly, among he equa ions conside ed, ha o Faulkne [ 22 ] showed he bes sensi i i y in assessing FM% in he in e na ional eli e socce e e ees. Las ly, a new equa ion based on he an h opome ic measu emen s aken on he sample g oup was p oposed. While excessi e FM% may a ec pe o mance, body composi ion is an aspec o conside able in e es o scien is s, a hle es, and coaches [ 34 ]. Typical FM% alues ( anging om 5% o 19%) epo ed in male a hle es depends on he spo , playing posi ion, and me hodology used o he assessmen [ 35 – 37 ]. In pa icula , male socce playe s show a pe cen age o a mass anging be ween 11.7–13.7% [ 20 , 38 ]. Fu he mo e, he es ed e e ees in his s udy showed a balanced mesomo ph soma o ype. J. Func . Mo phol. Kinesiol. 2020,5, 38 7 o 10 Simila ly, high-le el socce playe s a e cha ac e ized by a balanced mesomo ph mo phology bu hei soma o ype can also be endomo phic mesomo ph, ec omo phic mesomo ph, mesomo ph ec omop h, and mesomo phic ec omo ph [ 39 ]; in all hese cases, he dominan componen is he mesomo phy, bu he e is a di e en balance be ween endomo phy and ec omo phy, p obably due o he di e en oles o he game. Ou esul s showed subs an ial disc epancies in FM% p edic ion depending on he me hod plied. The e o e, ca e mus be aken when eedback on FM% is p o ided o socce e e ees since alues a e likely o be me hod dependen . Wi h he excep ion o FM% ob ained using Sua ez’s equa ion [ 26 ] o es ima ed by DXA, mos o he da a ound was wi hin he ange desc ibed in he li e a u e. As opposed o Faulkne ’s equa ion [ 22 ], he new o mula sugges ed appea s o be a simple and as e al e na i e as i is speci ic o socce e e ees. Fu he mo e, he use o only wo skin old si es, p o ides an ad an age in he ield-based assessmen o FM%, ep esen ing a mo e e icien use o ime. Con a y o p e ious s udies o eli e socce playe s [ 25 , 26 ], da a collec ed in he p esen s udy showed ha measu emen s o he lowe body skin olds a e no accu a e when p edic ing FM%. In his s udy, high skin old hickness was no en e ed in he de eloped model ep esen ing s eng h in he new o mula because i has been acknowledged ha he an e io high skin old is one o he leas accu a e si es o measu e [ 23 , 24 ]. Fu he mo e, ou esul s showed ha di e en sums o skin olds measu ed on he e e ees showed mode a e o la ge co ela ions wi h DXA da a, used as a c i e ion me hod. The esul s o he p esen s udy showed e y la ge co ela ions be ween Σ4SKF-a, Σ4SKF-b, Σ 6SKF, Σ 7SKF, and Σ 9SKF wi h FM% es ima ed by DXA, simila o he associa ions wi h he da a ound in he li e a u e o eli e socce playe s [ 40 , 41 ]. Thus, conside ing he subs an ial di e ences obse ed be ween he di e en equa ions and hei simila and/o lowe co ela ions wi h he DXA-de i ed FM%, e en he sum o skin old measu emen s appea s o be a good al e na i e app oach in ob aining in o ma ion on body a dis ibu ion in eli e socce e e ees. Some o he s eng hs in his s udy include he selec ion o in e na ional-le el male socce e e ees, all wi h expe ience in in e na ional ma ches. Skin old measu emen is a p ac ical, low cos , and easily accessible al e na i e o mo e complex and expensi e me hods such as DXA. Consequen ly, he p esen s udy p o ides a nonin asi e, cos - ee, and as ool o accu a ely es ima e FM% in he in es iga ed coho . Mo eo e , he DXA me hod migh no be easible o use ul when inancial esou ces a e limi ed o when a whole g oup is epea edly measu ed, because up o 10 min o each pe son is equi ed. Howe e , he use o DXA as a e e ence me hod poses some limi a ions in he de elopmen and compa ison o new equa ions o assessing a mass. Mos o he equa ions in he li e a u e a e based on he e e ence o hyd os a ic weighing. This could p edispose ou equa ion o an o e es ima ion o body a . Addi ional limi a ions ega ding sample size should be add essed. The sample consis ed exclusi ely o male subjec s hus, u he s udies in ol ing eli e emale e e ees a e needed. Fu he mo e, he lack o a alida ion sample did no allow he es o he pe o mance o he new equa ion a a g oup le el (e.g., analysis o he eg ession coe icien s, line o iden i y, R 2 , RMSE) and a he indi idual le el using he Bland–Al man analysis. The p ac ical applica ion o his equa ion acili a es an inc easingly accu a e e alua ion o he a hle e. The socce e e ee can be conside ed in all espec s as an a hle e, e en spo s esea ch has deepened his pa icula popula ion. Fi s , he componen s o he physical load equi ed du ing a compe i ion [ 3 , 7 , 9 ] ha e been e alua ed, mo e ecen ly he nu i ional aspec s ha e had an inc ease in in e es [ 4 , 12 , 42 , 43 ]. In his con ex o ene gy balance, he de elopmen o a new equa ion o he e alua ion o he a mass wi h a speci ic e e ence o he analyzed popula ion allows a mo e accu a e, eliable, and epea able e alua ion du ing he compe i i e season o he socce e e ee h ough a ield me hodology. 5. Conclusions All he equa ions in es iga ed (Es on e al. [ 24 ], Yuhasz [ 21 ], Reilly e al. [ 25 ], Sua ez e al. [ 26 ], and Du nin and Wome sley [ 23 ]) showed posi i e co ela ions in compa ison wi h DXA da a. J. Func . Mo phol. Kinesiol. 2020,5, 38 8 o 10 In pa icula , he equa ions de eloped by Faulkne [ 22 ] showed he bes sensi i i y in assessing FM% compa ed o DXA. Addi ionally, he sum o se en skin olds, which included iceps, subscapula , iliac c es , sup aspinal, abdominal, an e io high, and medial cal measu emen s showed a high co ela ion wi h FM% measu ed by DXA, ep esen ing an al e na i e app oach in body composi ion assessmen . Finally, his s udy p o ides a new o mula o FM% es ima ion in in e na ional-le el male socce e e ees [FM% =8.386 +(0.478 ×iliac c es skin old) +(0.395 ×abdominal skin old)]. Au ho Con ibu ions: Concep ualiza ion, C.P. and G.M. me hodology, C.P., F.C., and P.I.; o mal analysis, C.P., F.C., and P.I.; in es iga ion, A.P., G.G., and C.P.; da a cu a ion, C.P., F.C., and P.I.; w i ing—o iginal d a p epa a ion, V.H.T., C.P., F.C., and G.B.; isualiza ion, G.B., V.H.T., and G.M.; supe ision, F.C., G.B., and G.M. All au ho s ha e ead and ag eed o he published e sion o he manusc ip . Funding: This esea ch ecei ed no ex e nal unding. 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