The purpose of the present study was to examine the importance of the agonist muscle activity of the post-impact 30 ms phase during drop jump (DJ) for effective rebound performance by comparing those of sprint runners and swimmers. The eight sprint runners (SPRINT) and twelve swimmers (SWIM) were participated in this study. They performed DJ from a 0.3-m height box with maximal rebound efforts. Electromyograms (EMG) of the lower leg muscles (medial gastrocnemius [MG], soleus [SOL] and tibialis anterior [TA]), and vertical ground reaction force together with kinematic data were measured simultaneously during DJ. In addition, the onsets of fascicle stretching of the MG and SOL muscles were measured by using high-speed ultrasonography (521Hz) during DJ. The onsets of the fascicle stretching of SOL during DJ were not significantly different between SPRINT and SWIM (15 ± 7 ms and 16 ± 6 ms, respectively). During DJ, SPRINT showed onset of the SOL EMG before the ground contact (-26 ± 19 ms). Meanwhile, SWIM showed the onset of the SOL EMG after the ground contact of DJ (16 ± 19 ms). These results suggest that the SOL muscles for SWIM cannot be fully-activated during the braking phase. Consequently, the rate of force development during the braking phase of DJ and subsequently rebound height could be reduced in SWIM.

In this study, we searched the relevant literature for studies involving the number of tackles and wins/losses in a rugby match, the movement of the tackler and ball carrier, the momentum of tackles, the technique and physical fitness of tacklers, and the risk of injury in order to examine the factors contributing to a successful tackle. As a result, it was found that professional players had a higher success rate of tackles than amateur players younger than 20 years of age. However, the number of tackles per match and the relationship between the success rate of tackles and the results of the match differed depending on the competitive level and the country/region. Regarding tackle movements, the success rates of shoulder tackles were higher than those of other types of tackles. High-level players performed shoulder tackles with both shoulders and both hips facing the ball carrier (body position square), with their trunk roughly parallel to the ground. Furthermore, high-level players had a high body mass; thus, they tackled with high momentum (velocity × mass). Regarding physical fitness, high-level tackling techniques required maximum strength and power in the lower and upper limbs, and also improving the maximal aerobic capacity and overall agility may help prevent fatigue and thus positively contribute to successful tackling. This review suggested that young rugby players need to improve their tackling techniques, including adopting a posture with a straight spine and leg-drive, as the risk of concussion among novices was higher than that among experts.