Wednesday, May 4, 2011

Can Strength Training Improve Kick Velocity or Distance?

Playing a quality long ball is an important piece of the soccer performance puzzle. Goalkeepers, defenders and midfielders routinely take free kicks and play direct balls where considerable distance on the kick is needed. Add to that, the need for attackers to strike high-speed shots and it is easy to see that kicking velocity and distance are critical to success. However, can this aspect of a player’s game be improved? Is it possible for a player to increase his or her kick distance through training? Leg strength and power are known to be important for many soccer skills such as sprinting, stopping, cutting and jumping. Can strength training, which improves leg strength and power, also benefit a player’s kick? Researchers at the University of Nevada Las Vegas found that players are able to improve kicking distance through a simple, low-intensity plyometric training program. They found that young girls, who engage in such a training program, can improve their kicking distance by more than 25%.

The players used in the study were 13-14 year old members of two local club teams. They all had a minimum of four years of competitive playing experience and the two teams were similar in terms of ability, experience and training. One team participated in regular soccer practices while the other also participated in a once-weekly plyometric training program.

The plyometric program was fairly low intensity. During weeks 1-6, training involved single- and double-leg hops over six- and ten-inch hurdles, lateral hops and shuffles over ten-inch hurdles and a 12-inch box. During weeks 8-14, training included 10-inch box and depth jumps and cutting drills.

All of the players were tested on their kicking distance and vertical jumping ability before the start of training and at weeks 7 and 14. For the kicking distance tests, a stationary ball was kicked and it was required to land within an 8-yard wide target lane. Distance was measured from the point where the ball was kicked to the first landing point.

The researchers found that kicking distance steadily improved in the polymeric training group. At 7 weeks, distance increased by 10% and at 14 weeks, it improved by more than 27%. In the group that did not undergo plyometric training, their kicking distance actually decreased over the course of the study.

Plyometric training also improved vertical jumping ability. In the trained group, vertical jump increased by 8% and 19% at 7 and 14 weeks. The control group’s vertical jump did not change.

The results of this study show that in teenage girls, a once-weekly program of low-intensity plyometric training can improve both kicking and vertical jumping ability. What is remarkable about this study is that the training program was fairly low-intensity and was performed just once per week. Yet, the gains in power and kick distance were quite impressive. This suggests that using plyometrics and adolescent female players can yield a considerable bang for the training buck.

Researchers at the University of Ballarat in Victoria, Australia reviewed the research on strength training and kicking. They found that a majority of studies report similar results - strength training in general and plyometric training specifically can improve lower body power as well as kicking velocity and distance. The key seems to be improving power of the hip flexors and, to a lesser extent, the knee extensors (quadriceps muscles).

Those studies that failed to find improvement in the player’s kick generally used elite players as subjects. At the elite level, it may be more difficult to achieve large improvements in performance with strength training. That is, they perform at such a high level that there may be very little room for improvement, especially over the course of a 12 to 14 week study. However, for the younger, less experience players, strength training does seem to be effective.

A word of caution about strength training focused on improving the kick. While knee extensors strength is important, focusing on developing the quadriceps muscles without increasing strength of the hamstrings (knee flexors) can raise the risk of knee injury. A key risk factor for anterior cruciate ligament injury is an imbalance of quadriceps and hamstring strength. Thus, during training, it is VERY important to train BOTH the quadriceps and hamstring muscle groups.

It is also important to point out that these studies focused on kick velocity and distance. They did not address accuracy. However, the Australian researchers note that there is a trade-off between velocity and accuracy. In general, as kick velocity increases, accuracy decreases. They argue that there is some sub-maximal kick velocity at which accuracy can be maintained. After which accuracy deteriorates. If strength training increases a player’s maximal kick velocity, it should also increase this sub-maximal velocity. Thus, training should increase the speed of the players most accurate shot. More research is needed, however to fully verify that idea.

The bottom line, when working with young players, a strength training program that includes plyometrics can benefit performance. Not only can it improve shot velocity, it can also improve other measures of soccer performance and reduce the risk of injury.

References:

Rubley MD, Haase AC, Holcomb WR, Girouard TJ, Tandy RD (2011) The effect of plyometric training on power and kicking distance in female adolescent soccer players. Journal of Strength and Conditioning Research, 25: 129-134.

Young WB, Rath DA (2011) Enhancing foot velocity in football kicking: the role of strength training. Journal of Strength and Conditioning Research, 25: 561-566.