This study aimed to compare the training load of a professional under-19 soccer team (U-19) to that of an elite adult team (EAT), from the same club, during the in-season period. Thirty-nine healthy soccer players were involved (EAT [n = 20]; U-19 [n = 19]) in the study which spanned four weeks. Training load (TL) was monitored as external TL, using a global positioning system (GPS), and internal TL, using a rating of perceived exertion (RPE). TL data were recorded after each training session. During soccer matches, players’ RPEs were recorded. The internal TL was quantified daily by means of the session rating of perceived exertion (session-RPE) using Borg’s 0–10 scale. For GPS data, the selected running speed intensities (over 0.5 s time intervals) were 12–15.9 km/h; 16–19.9 km/h; 20–24.9 km/h; >25 km/h (sprint). Distances covered between 16 and 19.9 km/h, > 20 km/h and >25 km/h were significantly higher in U-19 compared to EAT over the course of the study (p = 0.023, d = 0.243, small; p = 0.016, d = 0.298, small; and p = 0.001, d = 0.564, small, respectively). EAT players performed significantly fewer sprints per week compared to U-19 players (p = 0.002, d = 0.526, small). RPE was significantly higher in U-19 compared to EAT (p = 0.001, d = 0.188, trivial). The external and internal measures of TL were significantly higher in the U-19 group compared to the EAT soccer players. In conclusion, the results obtained show that the training load is greater in U19 compared to EAT.

Strength training (ST) is commonly implemented to enhance soccer-related fitness qualities such as sprinting, jumping, and changes-of-direction while also contributing to injury risk reduction. It is traditionally emphasized in the pre-season period. In-season ST may confer these benefits, but it can also induce muscle damage and inflammation. To examine the effects of a 12-week in-season ST program on maximal dynamic strength, muscle damage biomarkers, and inflammatory biomarkers, 24 elite young female soccer players (Tier 4 according to the McKay et al. classification) aged 14.9 ± 0.8 years and a maturity offset of +2.6 ± 1.1 years were randomly allocated to an ST group (STG, n = 12) or an active control group (CG, n = 12). Both groups followed the same soccer training program. However, in the STG, two weekly soccer sessions were replaced with ST. Overall training volume was comparable between groups. Maximal dynamic strength (1-RM tests for bench press, lat pull-down, and leg press), blood biomarkers of muscle damage (creatine phosphokinase [CPK], lactate dehydrogenase [LDH]), and inflammation (interleukin-6 [IL-6], tumor necrosis factor-α [TNF-α]) were assessed before (T1) and after (T2) the interventions. Analyses showed significant increases for STG for the 1-RM bench press, the 1-RM lat pull-down, and the 1-RM leg press (p < 0.001). No significant interactions were detected for any blood marker of muscle damage (LDH and CPK) or inflammation (IL-6 and TNF-α) (all p > 0.05). Results support a 12-week in-season ST program improved maximal dynamic strength in elite young female soccer players without altering resting levels of muscle damage or inflammatory markers measured 48 h after training compared to regular soccer training. These findings suggest that ST can be safely implemented during the competitive season in young female soccer players without overreaching or overtraining.

Background: Female soccer continues to gain global popularity. Selected components of physical fitness (e.g., muscle power, change-of-direction [CoD] speed) and cognitive function (e.g., attentional demand, training-induced) play an important role in soccer performance and should, therefore, be systematically developed. Objectives: In this study, we examined the effects of 12 weeks of strength training (ST) on selected measures of physical fitness, soccer performance, cognitive function, and selected markers of neuroplasticity in young female soccer players. Methods: Twenty-two highly-trained female soccer players with Tier 3 training and performance caliber aged 14.9±0.8 years were randomly assigned to a strength training group (SG: n = 11) or an active control group (CG: n = 11). During the training period, SG performed two weekly upper and lower body ST sessions (3 sets, 12 repetitions per set) at an intensity of 60–80% of the one-repetition-maximum (1-RM) and three soccer-specific training sessions (tactical–technical drills). Players from CG continued their regular soccer-specific training routine consisting of five weekly sessions. Training volumes were similar between groups. Pre- and post-training tests were conducted for the assessment of body composition (e.g., body mass, skinfold site measurements), muscle strength (1-RM bench press/Lat pull-down/leg press),the Loughborough Soccer Passing Test (LSPT), cognitive function (Stroop test), and selected markers of blood neurotrophins, such as basal brain-derived neurotrophic factor (BDNF) and insulin-like growth factor 1 (IGF-1) serum concentrations. Results: The following findings from post hoc analyses are based on significant ( p <.05) group-by-time interactions. Post hoc analyses revealed ST-related increases in muscle strength for 1-RM bench press ( p <0.001; η _p ² =0.41), lat pull-down ( p <0.001; η _p ² =0.43), and leg press ( p <0.001; η _p ² =0.36) and improvements in soccer-specific performance for the LSPT in the SG ( p =0.007; η _p ² =0.22). Post hoc tests indicated improved cognitive function (Stroop test) in the SG ( p 0.05; η _p ² =0.00–0.04). Conclusions: A 12-week in-season ST program with two weekly sessions improved measures of physical fitness, soccer-specific performance, and cognitive function but not biomarkers of neuroplasticity in young highly-trained female soccer players. Accordingly, we recommend ST should be implemented to improve physical fitness and cognitive function of young female soccer athletes.