Sport Sci Health (2008) 2:101–105 DOI 10.1007/s11332-008-0047-5 Abstract The aim of the study was to investigate the ef- fect of a muscular training program on soccer players’ performance of which initially appeared imbalances or deficits. The study was conducte on 68 professional soc- cer players (age, 24.1±5.7 years; weight, 76.8±5.7 kg; height, 1.82±7 cm) participating in the championship of the first Greek national division over 2 years. During the preparation period, all the players performed an isokinetic test of knee flexors and extensors (60° s –1 and 180° s –1 ). These initial measurements detected muscular imbalances or deficits in 27 players (40%). The 27 players followed a specific isokinetic training program for 2 months, 3 times per week. After completion of the isokinetic train- ing program, the 68 players repeated the isokinetic test. The analysis revealed significant differences between the pre- and post-training measures at both angular veloci- ties in peak torque values, in differences from one limb to the other, and in peak torque ratios for flexors and ex- tensors. Consequently, the application of this specific isokinetic training program can restore imbalances in knee muscle strength efficiently. Key words Soccer · Isokinetic training · Muscle imbalance · Knee flexors · Knee extensors Introduction Soccer is one of the most popular sports and attracts many participants all over the world [1–3]. This partici- pation, however, leads to a considerable number of mus- culoskeletal injuries [4, 5]. Some of the factors respon- sible for soccer injuries are contact with an opponent or field conditions, but they may also be related to training, e.g. muscle-strength imbalances or deficits [1, 6]. Sahrmann [7] and, similarly, Caillet [8] defined muscle imbalance as a failure of the agonist-antagonist relation- ship. The terms balance and imbalance do not refer to equal or unequal torque values, but to the balance between the torque ratios of agonistic and antagonistic muscle groups. Practitioners have often used ipsilateral agonist- antagonist muscle ratios as standards by which to mea- sure the progress of rehabilitation or to assess muscle im- balance [9]. Concentric hamstring-to-quadriceps torque ratios have been studied extensively [10] with reported averages ranging from 0.5 to 0.75. Similarly, many researchers have supported that bilater- al differences (> 15%) in muscular performance (quadri- ceps and hamstring) detected with isokinetic measures are important predictors of soccer players’ injuries and signs of previous injuries and an incomplete rehabilitation program [9, 11, 12]. Since soccer frequently involves one-sided ac- tivities such as kicking with one leg, asymmetries in mus- cle strength between the two legs are possible [11, 13]. ORIGINAL ARTICLE Received: 18 July 2007 / Accepted: 15 October 2007 © Springer-Verlag 2008 Isokinetic strength training program for muscular imbalances in professional soccer players A. Gioftsidou · I. Ispirlidis · G. Pafis · P. Malliou · C. Bikos · G. Godolias A. Gioftsidou () · G. Pafis · P. Malliou · G. Godolias Department of Physical Education and Sports Science Democritus University of Thrace Campus, 69100 Komotini, Greece e-mail: agioftsi@phyed.duth.gr I. Ispirlidis Skoda Xanthi Football Club Xanthi, Greece C. Bikos Orthopedic Department General Hospital of Xanthi Xanthi, Greece 101_105_Gioftsidou:Sport 11-03-2008 14:23 Pagina 101