Most studies on strength training for young soccer players run six to twelve weeks. That is not long enough to learn much. Six weeks mostly shows a kid getting better at the exercise itself. It says little about athlete training over the long run. It says nothing about a full season.
A group of researchers in Germany decided to do it the hard way. Over the last decade they ran four studies. Each one lasted six months to two years. They followed real teams through real seasons, with real games on the weekend. About 230 players took part in total (Sander et al., 2013; Keiner et al., 2022; Skratek et al., 2024; Kadlubowski et al., 2025).
Put those four studies next to each other. Together they say something clearer about sports performance training than any one of them says alone.
The most useful study for most families comes from Skratek and colleagues (2024). Those kids started where most kids start. They were 12 to 15 years old. They played four soccer practices a week at an elite academy. None of them had ever lifted a weight.
Half of them added two lifting sessions per week. Each session ran thirty minutes. One day they squatted with the bar on their back. The next day they squatted with the bar in front. They did five sets of ten reps, and they added a little weight whenever technique held up. That was the entire program.
The other half kept playing soccer and did nothing else. Both groups were tested for a full year.
Coaches measure squat strength as a ratio to bodyweight. It lets you compare a small kid to a big kid fairly. If you weigh 100 pounds and squat 100 pounds, that is 1.0.
Over the year, the kids who lifted went from 0.70 to 1.60. The kids who only played soccer went from 0.66 to 0.92.
Both groups improved, which makes sense. Kids get stronger as they grow, and both groups grew about the same amount (Skratek et al., 2024). But the lifting group got far stronger than growth alone can explain.
Jumping followed a few months behind. The lifting group added 3.7 centimeters to their jump. The soccer-only group added 0.9.
Speed is where the study gets interesting. The kids who lifted got about a tenth of a second faster over 30 meters. That sounds like almost nothing.
But the kids who only played soccer got slower over the same year.
The clearest way to see it is in how many players improved at all. Of the kids who lifted, 19 out of 27 got meaningfully faster. Of the kids who did not lift, only 2 out of 21 did (Skratek et al., 2024).
So lifting did not turn these kids into sprinters. Instead, it stopped a long season from taking their speed away. Seasons wear players down. By spring, most players are slower than they were in July. Strength is what protects against that.
If you are an athlete wondering why the weight room matters in November, that is your answer.
The study people quote most often comes from Keiner and colleagues (2022). It is usually quoted badly.
That study followed 48 players aged 17 and 18 for ten months. It split them four ways. One group lifted barbells. One did jumping and sprinting. One did band and bodyweight work. One just played soccer. Only the barbell group improved on anything.
Online, that gets shared as proof that band work is useless. Read the study more carefully, though, and it says something narrower.
The band group did mini band walks, planks, and twists with a three kilogram medicine ball. Meanwhile, those same athletes already squatted 1.2 to 1.8 times bodyweight. Picture a kid who squats 200 pounds, then ask him to do band walks. Nothing will happen. The exercise is simply not hard enough for him.
The jumping group had a related problem. Researchers measured a jump that starts from a dead stop. But the program trained the fast bounce off the ground instead (Keiner et al., 2022). In other words, they tested a quality the program never practiced.
A pattern shows up when you line all four studies up by starting strength.
In the weakest athletes, squatting improved everything by around 0.7 times bodyweight (Skratek et al., 2024). In trained athletes near 1.4 times bodyweight, squatting still built strength while the alternatives did not (Keiner et al., 2022). And in the strongest group, at 1.5 and above, squat strength stopped separating the groups at all.
In the Kadlubowski study (2025), two groups ran the exact same squat program. Their squat numbers came out identical. So what distinguished them was what they added on top of it.
The right answer changes depending on where the athlete starts. That is the whole puzzle. A study on beginners and a study on strong athletes answer two different questions. People quote both as though they answer the same one.
One more detail is worth noticing. The study with the largest results used the shortest sessions. Thirty minutes, twice a week, for a year (Skratek et al., 2024).
The two studies using hour-long sessions produced smaller results (Keiner et al., 2022; Kadlubowski et al., 2025). That is not a fair comparison, because those athletes were already much stronger. Still, it establishes something useful.
Two half-hour sessions a week is a real dose. It is enough to change an athlete across a season. For a family driving between school, four practices, and a weekend tournament, that matters more than any number in a results table.
These are good studies. They also have real problems.
First, the groups were not picked randomly. In each study, one club trained and a different club served as the comparison (Keiner et al., 2022; Skratek et al., 2024; Kadlubowski et al., 2025). Those clubs had different coaches, schedules, and facilities. Some of the difference may come from that instead.
Second, the huge numbers in the youngest athletes mislead a little. A 13 year old squatting 0.70 times bodyweight is mostly showing you how well he knows the movement. The researchers say so themselves (Skratek et al., 2024).
Third, the injury result does not hold up. The lifting group had one injury and the soccer-only group had eight. But 13 players had already been cut from that soccer-only group for being hurt or ill on testing days (Skratek et al., 2024). You cannot compare injury counts after removing injured players from one side.
Finally, every athlete in all four studies was male, European, and in an elite academy. None of this has been tested on girls. That is a real gap, and it is the one I spend most of my research time working in.
If you are a parent, your athlete does not need a complicated program. Two supervised sessions a week of about thirty minutes is enough. Expect strength to change first, jumping to follow, and speed to move last. Give it a year before you judge it.
If you are a coach, the squat is the highest-value exercise for a developing player. The research is not close on that point. Once an athlete passes roughly 1.2 to 1.5 times bodyweight, though, the squat alone stops paying the same returns (Kadlubowski et al., 2025). Most youth athletes never get there, and that is the actual problem in youth sports.
If you are an athlete, the version that matters is simple. The players who lifted got faster while their teammates got slower. Not because lifting is magic, but because a season is long and takes something out of you. Strength is what you use to fight that.
None of these studies say strength training is a shortcut. They say it takes a year, it takes showing up, and it works.
This is the framework we build every program around at Prepare for Performance in Rockville, Maryland. PFP athletes squat. They progress. They train through the season rather than around it.
The research on sports performance training has been clear about this for a decade, even if the internet has not caught up. If you coach a team in Montgomery County, or you have a player who has plateaued, that is the conversation worth having.
Kadlubowski, B., Keiner, M., Wirth, K., & Csapo, R. (2025). Effects of traditional strength vs. combined strength and plyometric training on sprint, jump, and maximum strength performance in elite youth soccer players: A 6-month controlled trial. Journal of Strength and Conditioning Research, 39(7), e878–e889.
Keiner, M., Kadlubowski, B., Sander, A., Hartmann, H., & Wirth, K. (2022). Effects of 10 months of speed, functional, and traditional strength training on strength, linear sprint, change of direction, and jump performance in trained adolescent soccer players. Journal of Strength and Conditioning Research, 36(8), 2236–2246.
Sander, A., Keiner, M., Wirth, K., & Schmidtbleicher, D. (2013). Influence of a 2-year strength training programme on power performance in elite youth soccer players. European Journal of Sport Science, 13(5), 445–451.
Skratek, J., Kadlubowski, B., & Keiner, M. (2024). The effect of traditional strength training on sprint and jump performance in 12- to 15-year-old elite soccer players: A 12-month controlled trial. Journal of Strength and Conditioning Research, 38(11), 1900–1910.
