Want to jump higher or be faster out of the blocks? Squat (and deadlift) heavy weight. But jumping is explosive and lifting heavy is slow. Won’t those work at cross purposes? Not according to the best available research. In fact, the researchers trained their athletes using low repetitions of half squats at high weight, but also high velocity (or as high as players could manage when lifting their five-rep maximum). So the emphasis was on rapid force development, not just on getting the most weight off the ground as it were.
In detail, players were asked to work out twice a week, lifting a mere five repetitions per workout. After a week in which the player managed to successfully complete the weekly workload, weight was increased by 5 kilograms. The program lasted eight weeks.
The researchers found that those players who focussed on lifting heavy weights for few reps outperformed players with exercise programs that involved lifting lower weight for more reps. Vertical jump performance and sprint acceleration are all about the ability to generate maximal force quickly to explode off the ground or off the blocks. So a program that focusses on heavy weights in essential and these finding corroborate those from many earlier studies.
One other interesting detail from the study is that the researchers also tracked the V02max of the players. VO2max is associated with endurance and the ability to perform at a high level of output over a long time. This is obviously important for soccer players who run between 8 and 12 km (roughly 5-7 miles) during a game and tend to have very high levels of VO2max. We know from many studies that training for strength tends to inhibit endurance performance and training for endurance tends to inhibit strength development (world-class marathoners commonly have abysmal vertical leap ability). The researchers found no negative effects on VO2max among their players, which is good news. That said, in my opinion, an eight-week study is a very short time to see significant VO2max adaptation, and there are many factors that affect endurance besides VO2max.
Takeaway: There’s nothing surprising here. This study confirms what other studies have shown as well. Their goal was to show the precise relationship between max strength on the one hand and sprinting and jumping ability on the other. They show that heavy weight training, with a focus on rapid force development during the concentric phase (that is, during the “up” part of the half squat) tends to result in faster sprints and better leaping.
Source:U Wisløff, C Castagna, J Helgerud, R Jones and J Hoff, “Strong correlation of maximal squat strength with sprint performance and vertical jump height in elite soccer players,” British Journal of Sports Medicine, 2004 (vol. 38), pp. 285–288.