The purpose of the study was to compare sex adaptations in hypertrophy, strength and contractile properties of upper and lower-body muscles induced by resistance training (RT). Eighteen RT untrained male (MG) and female (FG) students (aged 24.1 ± 1.7 years, height: 1.75 ± 0.08 m, weight: 70.4 ± 12.3 kg) undervent 7 weeks of biceps curl and squat training (2 days/week, 60–70% repetition maximum, 3–4 sets, 120 s rest intervals, reps until muscular failure). At baseline and final measurement, thickness and cross-section area, one-repetition maximum and tensiomyography parameters (contraction time − Tc and radial displacement − Dm) of elbow flexors (biceps brachii) and knee extensors (4 quadriceps muscles) were evaluated. Although MG tends to display greater absolute strength gains for upper- (p = 0.055) and lower-body (p = 0.098), for relative changes ANCOVA revealed no sex-specific differences for either of the tested variables. Significant hypertrophy was observed for all tested muscles, except for vastus intermedius in FG (p = 0.076). The Dm significantly decreased for biceps brachii (MG by 12%, p < 0.01 and FG by 13.1%, p < 0.01) and rectus femoris (MG by19.2%, p < 0.01 and FG by 12.3%, p < 0.05), while Tc values remain unchanged. These results indicate that initial morphological, functional and contractile alterations following RT are similar for males and females, and that there are no specific sex adaptations either for the upper- or lower-body muscles. The study was registered with ClinicalTrials.gov (NCT04845295).

The aim was to investigate the impact of a specific structured movement activities (SMA) program compared to free play activity (FRP) on the strength, speed, agility, coordination, and balance of motor fitness (MF) in 6-year-old boys and girls. A total of 53 children (24 boys, 29 girls) were randomly allocated to either the SMA group or the FRP group. Both group activities were administered three times a week over a 6-month period. MF variables were assessed before (pre-) and after (post-) using tests: the flamingo balance (FLA), the standing long jump (SLJ), plate tapping (PTT), the obstacle course backwards (OCB), and the shuttle run 4 × 5 m (SRT). At the post-test, the SMA program resulted in significant (p < 0.05) improvements in OCB, PTT, SLJ, and SRT tasks. For FRP, a noteworthy improvement was observed only in OCB (ES = 0.45, p < 0.05). An ANCOVA revealed a significant group × time interaction (F = 21.71–52.41, η² = 0.258–0.512, p < 0.01) for OCB, PTT, and SRT, favoring SMA over FRP. The present findings suggest that SMA may be more effective than FRP when aiming to develop motor coordination, agility, and speed of movement in children.

The present study investigated effects of squat resistance training on intermuscular hypertrophy of quadriceps femoris muscles (i.e., rectus femoris, RF; vastus intermedius, VI; vastus medialis, VM; and vastus lateralis, VL). Eighteen university students (age: 24.1 ± 1.7 years, 9 females) underwent 7 weeks of parallel squat training (2 days/week) preceded by a 2-week familiarization period. Squat strength (1RM) and cross-sectional area (CSA) of four quadriceps muscles were assessed at baseline and at the end of the study. At posttest, 1RM and CSA of quadriceps muscles significantly increased (p < 0.01), with moderate-to-large effect (ES = 1.25–2.11) for 1RM (8.33 ± 6.64 kg), VM CSA (0.12 ± 0.08 cm²), and VL CSA (0.19 ± 0.09 cm²) and small effect (ES = 0.89–1.13) for RF CSA (0.17 ± 0.15 cm²) and VI CSA (0.16 ± 0.18 cm²). No significant differences were found in the changes of CSA between muscles (F = 0.638, p = 0.593). However, the squat 1RM gain was significantly associated only with the changes in CSA of the VL muscle (r = 0.717, p < 0.001). The parallel squat resulted in significant growth of all quadriceps muscles. However, the novelty of this study is that the increase in strength is associated only with hypertrophy of the VL muscle.

The aim of this study was to investigate the association between morphological characteristics (body composition and anthropometric data) and gross motor coordination in preschool children (42 boys and 40 girls, aged 6.22 ± 0.43 years, height: 1.22 ± 0.48 m, body mass index: 20.22 ± 2.34 kg/m², muscle mass: 11.50 ± 2.08 kg, and fat mass: 5.43 ± 4.02 kg). Motor coordination was determined by the obstacle course backward test (OCB), while body composition was measured using the bioelectrical impedance (BIA) method. Sex differences in the OCB test and body morphology were determined by an independent t-test. Multiple linear regression was used to examine whether morphological characteristics could predict OCB scores. Boys were significantly taller, with greater muscle mass, protein mass, and total body water compared to girls (t = 2.01–3.73, p < 0.05). Inversely, mineral mass was greater in girls than in boys (t = 2.98, p = 0.01). No significant sex differences were observed in the results obtained for the OCB test (t = 0.74, p = 0.46). All morphological variables showed trivial-to-weak (r = 0.01–0.15) associations with the OCB results, without reaching statistical significance (p ≤ 0.16). The model of predictor variables did not have a statistically significant effect on the OCB scores in boys and girls (R² = 0.09, p = 0.91 and R² = 0.012, p = 0.92, respectively). These results indicate that sex dimorphism in body composition is present at an early age before puberty, while morphological characteristics have a negligible influence on motor coordination in 6-year-old children.