Participants
Two hundred thirty-four male basketball players aged 15 years (n=161; age: 14.78±0.02; basketball experience: 5.1±0.8 yrs), 16 years (n=73; age: 15.67±0.02; basketball experience: 6.7±1.3 yrs) took part of this study. All examined athletes belonged to the Caucasian ethnic group. The players were members of 34 sports clubs competing in the national championship in the age categories U-15 and U-17. This group included 18 basketball players who were members of the U-16 male national team. All participants had similar training volume (8 h 45 min per week - 3 technical training sessions [90 min. each], 3 strength and conditioning sessions [45 min. each], and 2 h weekly match). Data collection occurred in 2017-2020 during the regular season in the same periods of the year (from November to February) before the play-off phase.
Procedure
All the participants, legal guardians, clubs and Polish Basketball Association were informed in writing about the aims, benefits, and procedure of the research project, and about the possibility to withdraw from the study at any moment. The inclusion criterion was the written informed consent obtained from each participant, and the exclusion criteria were contraindications for basic anthropometric measurements. Other criteria included injuries or trauma were also the exclusion criteria. The research was approved by the local Ethics Committee for Scientific Research (SKE 01–28/2016), and the study was conducted according to the rules and regulations of the Declaration of Helsinki [30].
Biological maturation
The APHV of the male basketball players analyzed in the study was estimated by subtracting the maturity offset from chronological age at the time of measurement [31]. The predicted maturity offset (years) was calculated as , with standard errors of the equations of 0.542 years [32]. This equation was derived after calibrating the original equation proposed by Mirwald et al. [31]. Early maturers, average maturers, and late maturers were defined as players with an estimated APHV of less than 13.1 years, 13.1-15.1 years, and more than 15.1 years, respectively [14]. Since the average maturers accounted for 95.5% of the basketball players, it was decided to analyze only this group. Due to very low number, seven early maturing U15 players and five early maturing U16 players were excluded from the analysis. This was followed by grouping with respect to years before/after the observed PHV1 (0.50 to 1.49), PHV2 (1.50 to 2.49), PHV3 (2.50 to 3.49) [14].
Measurements
Body height (cm) was measured barefoot with the head positioned to the Frankfurt plane, using a stadiometer (Seca 264, Seca GmbH & co. kg, Germany) with a precision of 0.1 cm, as were standing reach measurements (Seca 216, Seca GmbH & co. kg, Germany). Body mass was measured using a JAWON Medical X-Scan Plus II device (Certificate No. EC0197 for medical devices) with a precision of 0.1 kg. The measurements were taken by an anthropometry expert who holds an ISAK Level 1 accreditation according to the standards proposed by the International Society for the Advancement of Kinanthropometry (ISAK) [33]. The basic anthropometric measurements and warm-up were followed by physical fitness tests performed each time in the same order (speed test, jumping ability test, agility test, endurance test). Fitness was evaluated in two stages: the morning session (to measure speed, jumping ability, and agility), and the evening session (evaluation of endurance) so that adequate rest periods were maintained. The FMS and technical tests (jump shot, free throw, dribbling) were conducted the following day.
Speed
Speed was measured using a 20 m sprint test with a split time recorded at 5 m (starting speed) and 10 m, when players ran at full speed. Each participant performed 2 trials with 5 min. rest interval between them. The better result was considered for further analysis [34]. The photoelectric cells Fusion Smart Speed photocells (Fusion Sport, Coopers Plains, QLD, Australia) were used to record time (s). The photocells were installed at the starting line, 5 m, 10 m, and 20 m into the trial. The time measurement was performed with an accuracy of 0.001 s. Player started from the standing position, with the preferred foot positioned in front (0,1m from starting line). No bouncing and backward movements were allowed before the sprint.
Jumping
The results of both standing jump (SVJ) and a vertical jump (VJ) were measured using a yardstick vertical jump device [35]. The device is used to measure the height to which a player can push away small sticks placed horizontally on a pole during a jump. Reaching height was subtracted from the height reached while jumping. The first step was to perform 2 standing jump tests. Next, the player had 6 attempts (2 jumps with the dominant leg, 2 with the non-dominant leg, and 2 with both legs), with 10 s rest intervals between jumps. The highest attempt scores were retained for analysis [35].
Agility
The design of the agility test was proposed by Gryko et al. [36]. The test was repeated twice, and a 10-minute rest interval was administered to minimize fatigue. Before the test, the participant was familiarized with the procedures by performing a trial (pre-test). The best time achieved during the test was recorded for the analysis of the results.
Endurance
The Yo-Yo Intermittent Recovery Test level 1 (Yo-Yo IR1) was used to evaluate endurance using a protocol presented in the literature [37,38]. The total distance covered (m) during the Yo-Yo IR1 was the main measure from which maximum oxygen uptake (VO2max) was calculated according to the formula: VO2max = IR distance (m) x 0.0084 + 36.4 [38].
Sport-specific skills – dribbling
An attempt to evaluate the movement of a player with the ball. The player started from a stance with the ball at the signal from point A. Then dribbled around points B,C,D,E,C,A around stands - flags with a height of 150 cm. Points A,B,D,E formed a rectangle with sides of 3 and 5 meters. The trial ended at the moment of touching the flag at point A after covering the above-mentioned running route three times (Fig. 1). The shortest time was considered for further analysis. Each athlete makes 2 attempts with 5 min. rest interval between trials.
Sport-specific skills – free throw
A test to evaluate the effectiveness of a the free throws. The subject stands at the free throw line. After receiving the ball from a partner (whether the throw is accurate or inaccurate, the partner collects the ball and passes it to the player), he makes a free throw from the appropriate spot. There were 10 free throws in a trial. The player makes 2 trials with 5 min. rest interval (better trial was considered). 12 points are awarded for each accurate free throw. A maximum of 120 points can be scored.
Sport-specific skills – jump shot
The test was used to evaluate the effectiveness of the jump shot. At the signal, the tested player attempted 10 jump shots from 10 spots (1 – 10) (Fig. 2). The trial starts on the spot, where the end line intersects with the centerline of the court. The test was performed by 3 players, using two balls. The tested player performed shots, the second collected the ball, and the third feed the shooter. There was a 60-s time limit for the trial. For each accurate shot from positions 1,3,5,7,9 was awarded 10 points, and for score from positions 2,4,6,8,10 - 14 points respectively. A maximum of 120 points can be scored. Each player made 2 attempts of the test with 5 min. rest interval (better trial was considered).
FMS
The Functional Movement Screen [FMS] test was used to assess musculoskeletal function and motor control in a global manner. Appropriately selected test items allowed to evaluate disorders in the kinematic chain to be highlighted during movement [38]. The Functional Movement Screen test includes 7 basic tests: deep squat (deep squat), lower limb transfer over hurdle (hurdle step), in-line lunge squat (in-line lunge), shoulder girdle mobility (shoulder mobility), active straight leg raise (active straight leg raise), trunk stability push up (shoulder flexion), and trunk rotational stability (rotational stability) [39]. All testing procedure were led and supervised by certified staff.
Statistical Analysis
The normality of distribution was verified by the Kolmogorov-Smirnov test, whereas the assumption of the equality of variance was verified using the Levene test. The reliability coefficient for the measurements was Cronbach’s α = 0.89. The analysis of variance (ANOVA) was used to examine significant differences between groups. Furthermore, ANCOVA analysis was used to demonstrate the differences in years after observed APHV, with chronological age, height, and mass used as covariates. Bonferroni adjustments were made for post-hoc comparisons. The effect size was evaluated using partial eta squared (η2) and classified as: no effect = 0 to .039, minimum effect = .04 to .24, moderate effect = .25 to .63, and strong effect = ≥ .64 [40].
Backward stepwise multiple regression was used to estimate the relative contributions of chronological age, maturity timing (stage of APHV), functional capacities (FMS), body height, body mass, and height x mass interaction (based on residuals) to the variability of individual physical fitness tests and basketball specific skills. The significance of the effects was set at p<0.05 for all the analyses. All calculations were performed using STATISTICA software (v.13.3, StatSoft, USA).