In-Season Strength Training for Youth Female Soccer Players

In-season lifting did not derail recovery in one youth soccer trial

The usual warning about lifting during soccer season is simple: extra strength work will leave players flat, sore, and less ready for the weekend match. The best direct study available offers a more measured answer. In elite adolescent female soccer players, two weekly moderate-intensity strength sessions added during a 12-week competitive-season period improved maximal strength and body composition without raising the resting blood markers the researchers measured for muscle damage and inflammation.

That finding comes from Bousselmi et al.'s 2026 randomized trial, which assigned 24 elite Tunisian U15 girls to strength training plus soccer or soccer alone. Twelve players entered each group, and the athletes averaged about 14.9 years old. It is a small study, but it directly tests a question that often gets answered with general gym advice rather than evidence from the people actually playing the sport.

The result does not mean every in-season lifting plan is harmless, or that normal blood work proves a player is ready to sprint, cut, and play 90 minutes. It does mean the blanket claim that moderate, supervised strength work inevitably breaks down young female soccer players does not fit this trial.

The players already had a full schedule

This was not an off-season experiment conducted in a vacuum. Before the added strength work, the players completed five 90-minute soccer sessions each week, a weekend match, and two school physical-education classes. The intervention integrated two moderate-intensity strength sessions per week with soccer training for 12 weeks. The control group continued soccer training without the strength program.

At the end of the intervention, the strength-training group improved maximal dynamic strength and body composition in a favorable direction. Resting creatine phosphokinase (CPK), lactate dehydrogenase (LDH), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha) did not increase. CPK and LDH can rise after muscle damage, while IL-6 and TNF-alpha are inflammatory markers. Their stability is reassuring within this setting, especially because the central concern was whether added lifting would create chronic physiological strain.

The publication excerpt does not report the exact between-group effect sizes, confidence intervals, p-values, detailed body-composition changes, or the precise strength-test variants. Readers therefore cannot judge the precision or practical size of the improvements from the available report. The study supports the direction of the result; it does not support a claim about how many kilograms stronger players became or how much body fat they lost.

What the trial can—and cannot—tell us

Random assignment strengthens the comparison between the strength-plus-soccer and soccer-only groups. The program also used a realistic frequency: two sessions per week, not a bodybuilding schedule dropped onto an already busy team calendar. For coaches and parents, that matters more than an abstract argument about whether soccer players should ever touch a barbell.

Still, the trial measured a limited set of outcomes. It did not document sprint performance, jumping, change of direction, match output, injury incidence, missed sessions, soreness, wellness, overreaching, or match availability. It also did not establish that unchanged resting biomarkers equal low injury risk or complete recovery. Blood markers are pieces of a readiness picture, not the whole picture wearing a lab coat.

The participants had not previously performed systematic overload strength training. Some of the gains may therefore reflect an early response to organized resistance training. The findings apply most closely to elite Tunisian U15 girls under a moderate, supervised program. They do not automatically extend to younger athletes, boys, adult women, recreational players, teams with crowded fixtures, or players who already train heavily in the gym.

Training order can change the outcome

Evidence from a related population gives a reason to care about programming details. In a 2024 randomized matched-pairs trial by Blechschmied et al., young male soccer players completed concurrent strength and endurance training in different sequences. The study found that selected physical-fitness outcomes depended on the order of training.

That trial does not contradict the female U15 result. It studied males, not elite adolescent girls, and it addressed sequencing within concurrent training rather than the same two-session in-season intervention. Its lesson is narrower and useful: "strength training" is not one exposure. Exercise selection, volume, timing relative to field work and matches, progression, and total load can change the balance between adaptation and fatigue. The female trial's available description does not provide its full exercise list, sets, repetitions, progression, session duration, or placement relative to matches, so it cannot function as a plug-and-play template.

Why resting biomarkers are not a complete recovery test

Soccer recovery has functional and neurological dimensions that a resting blood draw may miss. Cosio et al. in 2025 reported that early rate of torque development could monitor residual hamstring fatigue after football match-play. That finding is not evidence that the Bousselmi program caused hidden fatigue. It does show why stable resting CPK, LDH, IL-6, and TNF-alpha cannot settle every question about readiness.

Other experimental soccer studies point in the same direction. In a randomized study after simulated match-play, Bouchiba et al. found cold-water immersion improved recovery of central and peripheral fatigue compared with thermoneutral-water immersion over 72 hours. A separate crossover, double-blind trial in 13 semi-professional male players found that acute acetaminophen improved recovery of neuromuscular fatigue after simulated soccer match-play. These studies use different populations, interventions, and short-term recovery endpoints, so they do not validate an in-season strength program. They do show that recovery after soccer loading is modifiable and multidimensional.

Nutrition may also affect recovery kinetics. In 10 well-trained male soccer players, Kritikos et al. compared whey protein, soy protein, and placebo after speed-endurance training; the study examined performance, field activity, muscle-damage markers, and redox responses across a 72-hour recovery period. Again, that is not a study of female youth players lifting in season. It is evidence that muscle-damage markers and performance recover on their own timelines, and that neither should be assumed from the other.

The practical reading of the evidence

For an elite adolescent female soccer player, this evidence supports a cautious practical position. A coach can consider two moderate, supervised strength sessions per week during the season, especially for players without a history of systematic overload training. The goal should be to build strength while protecting the work that actually determines soccer performance: quality field training, match availability, and recovery.

• Keep the dose moderate rather than treating gym work as unlimited extra volume.
• Integrate sessions around the team's soccer schedule and adjust when match congestion changes.
• Track functional readiness and athlete feedback alongside any laboratory measures.
• Do not promise faster sprinting, fewer injuries, or better match output based on this study.

The strongest conclusion remains narrow. One small randomized trial found that a 12-week, twice-weekly moderate strength program improved maximal strength and body composition in elite U15 female soccer players without increasing four resting muscle-damage and inflammatory markers. That is enough to retire the myth that in-season lifting is automatically destructive. It is not enough to declare every lifting plan safe, effective, or performance-enhancing.