Research in Sport Medicine and Technology

The purpose of this research was to determine the acute effects of plyometric training with changing of height landing on the electromyographic activity during preparatory phase land-jump in male students. The population of this research were 10 physical education male students of Kharazmi University, which selected as sample. (21/10±1/286yrs, 173±6/467 height, 68/2±7/42 weight). In four different days subjects Performed as single leg one of four protocols plyometric training and land - jump from a height of 40 and 60 cm. EMG activity of the quadriceps and hamstring muscle group 150 milliseconds before foot contact with the ground was recorded. Analysis of variance with repeated measures and Bonferroni post hoc test was used. The results of this study showed that muscle activity after changing of height landing in preparatory phase (from 40 to 60 cm) has increased significantly (P=0/002, P=0/001, P=0/001) respectively. Activity of muscles (rectus femoris, vastus lateralis, biceps femoris) during landing after performing plyometric and changing of height landing in preparatory phase has increased significantly (P=0/039, P=0/001) (P=0/006, P=0/000) (P=0/001, P=0/014) respectively. Jump height has increased significantly (P=0/007, P=0/002) respectively. The results showed that acute perform plyometric training with changing of height landing result in significant changes in the electrical activity of muscles and also the height of the jump in the preparatory phase.

Various studies have shown that the external focus of attention is better than the internal focus of attention. But, so far no study has been investigated the level of electrical activity of the rectus abdominus muscle as a trunk stabilizer muscle. Therefore, the purpose of this study was to investigate the effect of focus of attention on electromyography activity of the rectus abdominus muscle during Different phases of vertical jump.Twelve male elite volleyball players from university of Tehran Participated in this research voluntary. They performed a vertical jump on the force plate in both internal and external focus of attention condition. Rectus abdominus Surface electromyography (SEMG) signals recorded by electromyography apparatus during vertical jump and The electrical activity of this muscle was calculated in the different phases of vertical jump motion.  Paired t-test results showed that height of jump under the external focus was higher than the internal focus. In addition, this  results showed that internal focus caused significant increasing in Rectus abdominus EMG in comparison to external focus during concentric phase. But, there was no significant difference in the eccentric phase between the external and internal focus of attention conditions. These results suggest that the external focus of attention effectively increases the efficiency of vertical jump. Therefor; we recommend using the external focus of attention instructions when executing vertical jump movement.