Six weeks of knee extensor isometric training improves soccer related skills in female soccer players

Abstract

Objectives:Resistance training (RT) programs are often utilized to improve strength and power and thus enhance soccer performance. However, there is little research examining isometric knee extensor RTs effects upon soccer related skills. Design:The aim of this study was to examine the effects of knee extensor isometric training in female soccer athletes. Method: Sixteen female, university level, amateur soccer players (age 20.5 ± 1.1 years) were assigned to either a control or experimental group. The experimental group trained 1x/week for 6-weeks performing repeated maximal voluntary isometric contractions (MVIC) for the knee extensors alongside regular soccer training and the control group participated in soccer training alone. Knee extension MVICs were performed at seven joint angles and peak torque measured.Results: Outcome measures included, countermovement jump (CMJ), kicking distance (KD), straight sprint speed and zigzag sprint speed, with (SSB and ZSB, respectively) and without (SS and ZS, respectively) a ball. Significant increases (p < 0.05) in knee extensor MVIC (28.9%) occurred in the experimental group. Significant differences (p < 0.05) between the experimental group and control group were found for change in CMJ (2.24% vs -0.78% respectively) and KD (8.8% vs -2.5% respectively); however, change in SSB, ZSB, SS, or ZS were non-significant for both within-and between-group comparisons. Conclusions:Results indicate that a 6-week isometric knee extension RT intervention can improve jump height and kicking ability of amateur female soccer players.(Journal of Trainology 2017;6:52-56)

Brief Review: Effects of Isometric Strength Training on Strength and Dynamic Performance

“…However, Knapik et al [31] showed that performing 50 × 3 s isometric elbow extension at 90 ° elbow angle and 80 % MVC resulted in superior gain in isometric strength but inferior gain in isokinetic strength as compared to isokinetic strength training. Another study by Bimson et al [10] found that participants improved their countermovement jump height after performing 3 s maximal leg extension at 7 knee angles, while Kubo et al [36] found no improvement in participants who performed 10 × 15 s isometric leg press at 90 ° knee angle and 70 % MVC, even though the leg press would more likely fulfilled the training specificity principal for countermovement jump. Furthermore, the participants in the study by Bimson et al [10] were amateur female soccer players, while those in Kubo et al [36] were normal healthy adults, whose physical performance would have benefited more from any strength increment.…”

“…Another study by Bimson et al [10] found that participants improved their countermovement jump height after performing 3 s maximal leg extension at 7 knee angles, while Kubo et al [36] found no improvement in participants who performed 10 × 15 s isometric leg press at 90 ° knee angle and 70 % MVC, even though the leg press would more likely fulfilled the training specificity principal for countermovement jump. Furthermore, the participants in the study by Bimson et al [10] were amateur female soccer players, while those in Kubo et al [36] were normal healthy adults, whose physical performance would have benefited more from any strength increment. These 2 comparisons suggest that performing IST at multiple joint angles would benefit dynamic and functional performance more than just performing IST at single joint angle.…”

“…Some studies have shown that IST improved concentric only jump [12,36] but not countermovement and drop jump [4,33,37,47], indicating that IST does not benefit movements that require the use of stretch shortening cycle (SSC) [33]. However, the studies by Bimson et al [10], Bogdanis et al [11] and Goldmann et al [21] showed that performing IST led to improvement in countermovement and horizontal jump performances. In the study by Bogdanis et al [11], participants were required to perform maximal isometric leg press at either 85 ° or 145 ° knee angles, with each repetition executed explosively and held for 3 s. Participants were also required to perform a total of 6 countermovement jumps during the rest intervals.…”

“…Finally, another possible reason could be due to the joint angles adopted during IST. Although Bimson et al [10] used a single joint exercise with slow build up to maximal isometric force, the participants in this study had to perform IST at 6 different knee angles (12 °, 24 °, 42 °, 60 °, 78 °, 96 ° & 108 °). This method of IST was also previously shown to benefit dynamic performance [19].…”

“…Despite this believe, IST has been shown to be effective in improving isometric force production at the joint angle that the muscles were trained at [30,66], as well as joint angles that were not included in the training intervention [8,50]. Additionally, studies on IST have also shown positive effects on dyna mic strength [8,13,19,31,63,69], jump performances [10,11,21,33,36], various sports related dynamic performances including running [2,18], cycling [73], soccer related skills [10], Muay Thai strike [38] and bouldering grip [39], injury and pain management [17,22,42] and tendon properties [12,32,35,36].…”