291, p=0.011) and non-dominant legs (F2,10=10.981, p=0.003). The HarmoKnee group also showed a significant difference between the NPT of quadriceps�� muscles in the dominant (F2,10=7.954, p=0.009) and non-dominant legs (F2,10=6.591, moreover p=0.015). The results did not show any significant differences in the control group (p>0.05). NPT of the hamstring muscles The mean values of strength of the hamstring muscles in pre- and post-tests of the groups are presented in Table 4. The mixed ANOVA indicated no significant differences between times (F1,33=2.67, p=0.111). There were also no significant interactions between time and angle (p>0.05). However, the results showed significant interaction between time and group (F2,33=3.764, p=0.034). The partial eta squared statistics indicated a large effect size (0.
19). In the 11+ group, hamstrings strength increased significantly (p<0.05) by 24.8% and 19.8% at 30�� and 60�� knee flexion in the dominant leg and by 28.7% and 13.7% at 30�� and 60�� in the non-dominant leg. The results indicated no significant differences in HarmoKnee and control groups (p>0.05) (Figure 2). Figure 2 Percentage of change from pre-test to post-test in hamstring strength (* p<0.05). Table 4 NPT of hamstrings muscle in dominant and non-dominant leg (values are mean �� SD), and percentage of change (��) [values are mean (95% CI)] from pre-test to post-test Hamstrings NPT between knee angles (30��, 60�� and 90��) The mixed ANOVA analysis showed significant main effect differences between angles (F2,32=121.37, p=0.001) with a large effect size (0.88).
Significant differences were shown only in the 11+ between the hamstring muscles of the non-dominant leg (F2,10=9.554, p=0.001). The results did not show any significant differences in HarmoKnee and control groups (p>0.05). Comparison of NPT between legs and groups The mixed ANOVA analysis showed no significant difference in the quadriceps strength between the dominant and non-dominant legs (F1,33=0.509, p=0.481). Therefore, a significant difference was observed in the hamstrings between the legs (F1,33=21.345, p=0.001). The results showed no significant difference between groups in the quadriceps and hamstrings (p>0.05). Discussion The aim of this study was to investigate the effect of the FIFA 11+ and HarmoKnee warm-up injury prevention programs on isometric strength in young professional male soccer players.
One of the main findings of our study was an increase in quadriceps strength in the HarmoKnee group at 90�� knee flexion by 85.7% and 73.8% in dominant and non-dominant legs, respectively. On the other hand, the 11+ program also showed increases in quadriceps strength Brefeldin_A in the dominant leg by 19.7% and 47.8% at 60�� and 90�� of knee flexion, respectively, and by 16%, 35.3% and 78.1% at 30��, 60�� and 90�� knee flexion, respectively, in the non-dominant leg. It seems that both programs have the potential of improving quadriceps�� strength.