Regular football training improves lung diffusion capacity in boys aged 6 to 10 years | BMC Sports sciences, medicine and rehabilitation

Attendees

The required sample size was calculated using G*Power (version 3.1, University of Düsseldorf, Germany) [21]. The a priori power analysis was calculated with an assumed power of 0.90, an alpha level of 0.01 and an effect size of Cohen’s f = 0.26 for pulmonary diffusion capacity (TL) [10]. The analysis showed that a total sample size of N=60 would be sufficient to detect a significant interaction effect by time. Accordingly, 80 participants were enrolled to account for possible dropouts due to injuries.

Eighty healthy prepubertal boys, aged 6 to 10 years, with normal lung volumes and regular flow-volume curves and no history of cardiovascular disease or allergies, volunteered to participate in the study. A respiratory functional examination was performed by a physician, including a health questionnaire to screen the participants’ medical history. The boys were randomly divided into two groups:

• The football group (SG, n = 40) participated in four weekly football sessions of 75 minutes each over a period of 28 weeks.
• The control group (CG, n = 40) matched to the SG in terms of age, body weight and height, participated only in regular physical education classes without any other extracurricular sports activities.

All participating boys went to the same school near the football training center. After providing written and verbal information about the risks and benefits of the study, written informed consent to participate in the study was obtained from all study participants and their parents or legal guardians before the start of the study. The ethics committee of Sousse Medical University (Tunisia) approved the study. The study was conducted in accordance with the latest version of the Declaration of Helsinki. The physical characteristics of the study participants at the time of inclusion are listed in Table 1.

Procedures

Baseline (Trial 1) anthropometric data (body height to the nearest 0.1 cm and body weight to the nearest 100 g) were collected using standard stadiometers (Seca™, Hamburg, Germany) and scales (Tefal, France). Maximum oxygen consumption (VO₂max) and maximum aerobic power (MAP) were determined using standard protocols, with the extensive testing performed on a bicycle ergometer (Monark cycle). The bicycle ergometer was chosen for safety reasons, because the participants are boys aged 6 to 10 years and the treadmill is also more stressful. Participants cycled unloaded at 60-65 revolutions/min (rpm) for the first minute, after which the work rate was increased every minute according to the Cooper and Weiler-Ravell procedure. [22] to VO₂the maximum had been reached. The examiners who performed the exercise test were blinded to group assignment.

Oxygen consumption (VO₂) and carbon dioxide (VCO₂) production were determined using a calibrated metabolic measurement system (MedGraphics CPX St Paul, MN, USA). The transfer of nitric oxide (NO) and carbon monoxide (CO) was measured simultaneously during a single breathing maneuver using an automated device (Medisoft, Dinant, Namur, Belgium), according to the latest ERS guidelines [23]. Each participant completed three validated transfer measurements [9, 10]: two at rest (before exercise) and one at the end of the maximum exercise test. After the test, the participants remained seated on the bicycle ergometer. An investigator attached the nose clip and mouthpiece to initiate the breathing maneuver under the experimenter’s guidance. Participants were informed about the importance of test standardization to achieve better test reproducibility. The validity of the test was visually checked by examining the trace showing the volume changes during the maneuver. In other words, the computer-generated trace should have no pause during the rapid inhalation, be flat during the breath-hold, and be continuous during the exhalation. The test was considered valid if these criteria were met. All participants were given three introductory trials to practice the maneuvers.

DM and Vc were determined from TL_NO and T.L_CO values ​​as previously described by Dridi et al. [9]. Since the reactivity of NO and hemoglobin was considered very high and its inverse was negligible, TL_NO was considered equivalent to DM_NO. DM_CO was determined using the coefficient of proportionality (a) and the DM values ​​of the two gases (aDM_NO = aDM_CO = 1.97) according to “Graham’s law.

Same tests (maximum O₂ consumption, maximum aerobic power and NO/CO transfer) were repeated 28 weeks later (Test 2). All tests and effort measurements were performed on the same equipment, calibrated using identical methods, and measured using identical laboratory techniques for the initial and follow-up tests.

Football training program

The training period was spread over 28 weeks (from October to April) (Table 2), with training taking place in four weekly sessions (between 5:00 PM and 6:15 PM on Tuesday, Wednesday, Friday and Sunday) (Table 3). During this time, only friendly matches were scheduled. Each training session included a 15-minute warm-up, followed by 20 minutes of physical work (jumping, wrapping, running) and 30 minutes of basic technical training (dribbling, juggling, passing, technical circuit), supplemented with active stretching exercises.

The SG was exposed to seven months (i.e. 28 consecutive weeks) of systematic football training with three sessions per week. The training sessions were carried out on a synthetic football field and were led by three professional coaches. During the first 6 weeks, the coaches emphasized training physical fitness components such as endurance, linear speed and speed of change of direction, coordination including balance to provide a foundation for subsequent football-specific training. From weeks 7 to 12, the exercise program mainly included football-specific technical exercises (passing, dribbling, ball control, etc.).

From weeks 13 to 18, the coaches ensured the development of motor skills such as movement coordination, speed, joint flexibility, basic endurance through circuits, slaloms, races, jumps, etc. From weeks 19 to 28, the coaches focused on technical and tactical aspects of training including ball possession, recovering the ball, transition… and proposing simple situations of reduced squads by limiting the opposition (3 × 2; 4 × 3; 5 × 4…) in addition to fun games and small games (3 × 3 ; 4 × 4; 5 × 5 in small to medium-sized places 12 × 20 m; 16 × 24 m; 25 × 35 m). The last 10 weeks were reserved for technical development, maintenance of physical qualities and tactical placement (mainly in player position). The model applied by the coaches followed the model proposed by the Tunisian Football Federation.

Exercise intensity was regulated and monitored using smartwatches (H.Tang, Model F6, China) that allowed monitoring heart rate during continuous running (i.e. 50–70% of maximum heart rate [HRmax]), high-intensity interval training (i.e. 90-100% of HRmax), specific football training with and without the ball, tactical training, technical training, small matches and aerobic training. In addition, a football match was scheduled every week on Sunday. The participating team played against other regional clubs, using a 7 × 7 format on a relatively small field (30 ≠ 40 m). The match lasted 15 minutes at halftime. SG played 20 matches during the experimental period.

The participating boys were part of the same football training center in the city of Sousse (Tunisia). Nine of the forty children played football in a private training center before the start of the study (maximum two years). All other participants started playing football when they entered the study. During the same period, CG attended a one-hour weekly physical education course at their primary school, the content of which was fundamentally playful and based on educational games. Boys did not participate in any other physical training activities during the study. The children in both groups completed all aspects of the training programs. The participation rate in training for the experimental group (e.g. the football group) was 91%. No test- or training-related injuries occurred during the study.

static analysis

All results are presented as means and standard deviations (SDs) after the normality distribution of the data was assessed and confirmed using the Shapiro-Wilk test. The intraclass correlation coefficient (ICC) and the coefficients of variation (CV) were used to determine the consistency of the measurements and their variation (test-retest reliability). Based on the 95% CI of the ICC estimate, values ​​less than 0.5, between 0.5 and 0.75, between 0.75 and 0.9 and greater than 0.90 were indicative of poor, moderate, good, respectively. and excellent agreement. Differences within and between groups were calculated using a two-way analysis of variance (ANOVA) for repeated measures. Bonferroni adjusted post hoc tests were calculated to assess any significant interactions by time period. Partial eta squared (η²p) are taken from the ANOVA output and Cohen’s d effect sizes (d) are calculated to quantify meaningful differences in the data [24, 25] with demarcations of trivial (<0.2), small (0.2–0.59), moderate (0.60–1.19), large (1.2–1.99) and very large (≥ 2, 0).

Pearson correlations were used to examine the relationship between variables. The magnitude of the correlations was determined using the modified scale proposed by Hopkins (2009). [26]. A stepwise multiple regression analysis was used to determine the best predictive independent variables. We attempted to use a stepwise regression between the VO₂max, MAP) and the lung parameters (TL_NOTL_COVA, Vc, DM).

All statistical analyzes were calculated using SPSS for Windows, version 16.0 (SPSS Inc., Chicago, IL, USA).