Isokinetics and Exercise Science 22 (2014) 273–278 273 DOI 10.3233/IES-140548 IOS Press Fat-free mass and bone mineral content positively affect peak torque production in Brazilian soccer players Daniel Leite Portella a,b,∗ , Marco Antonio Cossio-Bolaños b , Jefferson Eduardo Hespanhol c and Miguel de Arruda b a School of Health, School of Physical Education, University of São Caetano do Sul, São Caetano do Sul, Brazil b School of Physical Education, University of Campinas, Campinas, Brazil c School of Physical Education, Pontifical Catholic University of Campinas, Campinas, Brazil Received 2 October 2013 Accepted 18 May 2014 Abstract. BACKGROUND: Few studies thus far have investigated the relationship between body composition (in particular, bone com- ponents) and isokinetic strength performance. OBJECTIVE: To determine the relationship between bone mineral content (BMC), bone mineral density (BMD), and fat-free mass (FFM) with isokinetic strength performance variables in professional soccer players. METHODS: We recruited 20 elite male soccer players from the Brazilian league’s first division teams. Participants underwent a concentric isokinetic evaluation of knee flexor and extensor muscles. Dual-energy X-ray absorptiometry (DXA) was used to determine body composition. The relationships between variables were analyzed using Pearson’s product-moment correlation coefficient. RESULTS: Body composition variables were correlated with the strength output of knee flexor and extensor muscles in both lower limbs. FFM and BMC explained at least 50% of the variation in peak knee flexion and extension torque while BMD did not have the same effect. CONCLUSIONS: The relationships reported in this study indicate that the use of isokinetics and DXA in soccer players should be further investigated both for measuring athletic performance and for relevant clinical assessment. Keywords: Isokinetic, strength, fat-free mass, bone components, dual-energy X-ray absorptiometry (DXA) 1. Introduction Speed, power, and muscle strength performance are important physiological characteristics in soccer players, being required for running, moving, jump- ing, and kicking in soccer matches [1]. To perform * Corresponding author: Daniel Leite Portella, Rua Carlos Escobar 145/63, Santana, São Paulo, 02013-050, São Paulo, Brazil. Tel.: +55 11 95352 8441, +55 11 4239 3311; E-mail: dlportella@uol.com.br, daniel.portella@uscs.edu.br. these actions, muscle strength – particularly of the lower limbs – is significantly related to speed perfor- mance [2]. Moreover, the strength required for speed movements and direction changes is affected by body composition, as shown by the power produced by hockey players in motor actions [3]. Evaluations of body composition have evolved with the use of dual-energy X-ray absorptiometry (DXA), which provides information about fat mass, fat-free mass, and bone components [4]. In fact, several studies have used DXA for determining fat-free mass and in- ISSN 0959-3020/14/$27.50 c  2014 – IOS Press and the authors. All rights reserved AUTHOR COPY