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: It is well-established that strength training (ST) improves physical fitness in young athletes. However, its specific effects on hormonal changes in female soccer players are unresolved. Objectives: We examined the influence of a twelve-week ST program conducted twice per week on soccer-related measures of physical fitness and hormonal profiles in adolescent elite female soccer players. Methods: Twenty-four elite young female soccer players aged 15.3 ± 0.9 years (body-mass-index [BMI]: 20.8 ± 1.9 kg/m²) and Tier 4 training and performance caliber participated in this study. Players were randomly assigned to either an ST group (STG, n = 12) or an active control group (CG, n = 12). Several parameters were determined pre- and post-training including absolute and relative to kg body mass 1-RM in bench/leg press, countermovement jump (CMJ), linear sprint speed (5-m, 10-m, 30-m sprints), speed of changing directions (T-test with and without ball), sport-specific efficiency (Yo-Yo Intermittent Level1 [YYIRTL1]) and repeated shuttle sprint ability (RSSA). Cortisol (C), testosterone (T), growth hormone (GH), and insulin-like growth factor 1 (IGF-1) were assessed using blood samples collected after 12 h of fasting, before and after the ST program. Results: No significant baseline between-group differences were observed. Statistically significant group-by-time interactions were found for muscle strength measures (e.g., relative 1-RM leg press, p = 0.046, d = 0.59), vertical jump performance (e.g., CMJ, p = 0.007, d = 1.28), and soccer-specific performance (e.g., RSSA _Mean , p < 0.001, d = 2.67). Post-hoc tests demonstrated significant increases for 1-RM leg press ( p = 0.046, d = 0.59), CMJ ( p = 0.007, d = 1.28), and RSSA _Mean ( p < 0.001, d = 2.67) in STG. Furthermore, no significant group-by-time interactions were observed for hormonal markers (T, C, GH, and IGF-1; p > 0.05). Conclusion: While the ST program significantly improved physical fitness in adolescent female Tier 4 soccer players, no substantial changes were observed in hormonal markers. These findings suggest that ST-related physical adaptations observed in this population may not be directly linked to the hormonal markers measured in this study. Trial registration: Clinical trial number PACTR202504552619186 https://pactr.samrc.ac.za/Search.aspx Date of registration: 14/04/2025. “Retrospectively registered” Our study adheres to CONSORT guidelines.

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.

This study proposes to monitor the physical, immune and cognitive responses and adaptations of elite rugby players throughout the season based on the loads performed. Anthropometric measurements, physical fitness tests (e.g., muscle strength and power, linear and change-of-direction speed, cardiorespiratory fitness) and analyses of serum concentrations of markers of muscle damage (creatine kinase [CK] and lactate dehydrogenase [LDH]) and brain-derived neurotrophic factor (BDNF) were carried out over a sporting season (24 weeks) for 17 elite rugby players (10 forwards and 7 backs) aged 18.91 ± 0.76 years. The physical fitness test results show improvements in the performance of both forwards and backs over the season (p < 0.05), with an advantage for backs compared with forwards in most tests (p < 0.05). Muscle damage markers decreased at the end of the season compared with the baseline levels for forwards (p < 0.05). CK levels were unchanged for the backs, but there were increased LDH concentrations at the end of the season compared with baseline (p < 0.05). Serum BDNF levels decreased for the total group between the second and third sampling (p < 0.05). The muscular and physical capacities of rugby players differ according to their playing position. Immune responses and adaptations, as well as BDNF levels, vary throughout the season and depend on the physical load performed.