This was a randomized, double-blind, placebo controlled, crossover trial. The study aimed to assess the effect of sodium bicarbonate on the ability to perform a repeated sprint task by female football players. The researches hypothesis was that sodium bicarbonate increases the ability to remove lactic acid from muscle cells reducing its intracellular accumulation and increasing energetic efficiency resulting in the increase of peak power output, mean power output, or total work or in the decrease of the sprint decrement in each set of the repeated sprints task.

Experimental design: The study consisted of a randomized, double-blind, controlled, crossover trial where 11 female football players performed, in a randomized order, two repeated sprints tasks in a cycle ergometer, after having ingested either sodium bicarbonate (SB) or placebo (PL). Body composition of the athletes was characterized by bioelectrical impedance analysis with a single frequency (50 kHz) device (BIA 101 Anniversary, Akern, Florence, Italy) before the exercise sessions. Data collection was separated by a period of at least one week within a period of time not exceeding one month and performed at the same time of the day for each participant. Data regarding performance, blood lactate accumulation, pulmonary gas exchange, heart rate (HR), muscle oxygenation and neuromuscular fatigue were collected during these two sessions.

Supplementation protocol: The participants ingested capsules containing 0.3 g/kg of body weight of SB or cellulose as PL divided into two doses. The first intake (0.2 g/kg) occurred 2 h before the beginning of the protocol, and the second (0.1 g/kg) occurred 1 h later. Possible gastrointestinal symptoms associated with supplement ingestion were controlled with a questionnaire based on the questionnaire applied by Miller et al. (2016).

Repeated sprints protocol: The RSA protocol was performed in a cycle ergometer (Monark Ergomedic 894 E, Monark Exercise AB, Vansbro, Sweden) and was composed of 3 sets of 6 sprints with 6 s duration with a workload of 4% of the body mass. Repetitions were separated by 24 s of active recovery, and participants were conceded 5 min of passive recovery to rest between sets. The protocol was preceded by a 5-min warm-up in which athletes pedalled at a speed of 60 to 70 rpm.

Performance Measurements: Performance was evaluated by monitoring peak power output, mean power output, total work and the sprint decrement in each set of the two repeated sprints task.

Blood lactate accumulation: Lactate concentration was assessed (Lactate Pro 2, KDK Corporation, Kyoto, Japan) in capillary blood from the ear lobe before the beginning of each protocol, 1 min after the end of each set, and at min 1 and every 2 min after the tasks were completed, until the value started to decrease. At the end of the tasks, the maximal values achieved were considered for analysis.

Pulmonary gas exchange and heart rate: Oxygen uptake, carbon dioxide production and ventilation (VO2, VCO2, VE, respectively) were measured breath-by-breath, during the protocol, using a gas analyser (MetaMax 3B, Cortex Biophysik, Leipzig, Germany). Heart rate was continuously evaluated using an HR monitor (H7, Polar Electro Oy, Kempele, Finland). The integral of VO2 (L) and VCO2 (L) and the maximum 6-s moving average of relative VO2 (mL/kg.min), VE (L/min) and HR (bpm) were calculated for each set.

Muscle oxygenation: Throughout the protocol, oxygenated (O2Hb) and deoxygenated haemoglobin (HHb) were continuously monitored with a near-infrared spectroscopy device (Niro-200NX, Hamamatsu Phototonics, Hamamatsu, Japan) according with the manufacturer specifications. The integrals of O2Hb and HHb were calculated for each set of the protocol.

Neuromuscular fatigue assessment: Athletes executed a countermovement jump (CMJ) in a contact mat (Chronojump BoscoSystem, Software Version 2.2.0, Barcelona, Spain) before and after the exercise protocol, accessing values of jump height (JH). Three jumps were performed, separated by 30 s of rest, and the best jump was considered for analysis.

Data analysis: Power and sample calculations (G-Power, Version 3.1.9.2, Düsseldorf, Germany) were based on an effect size of 0.88 (McNaughton et al., 1997) for total work performed in the sprints, a power of 0.85 and a significance of 0.05. After the recruitment process, 12 athletes volunteered to participate in the study. One volunteer withdrew due to injury, leading to a sample size of 11 athletes. Statistical analysis was performed using the Statistical Package for the Social Sciences (IBM Corp, SPSS v27.0, Armonk, NY, USA) and R software (v4.2.0, Open-Source Code, General Public License). Normal distribution and sphericity were tested using Shapiro-Wilk's and Mauchly's tests, respectively. For variables with normal distribution, data was analysed using a two-way analysis of variance (ANOVA). Whenever a statistical significance was observed in the two-way ANOVA, post-hoc paired comparisons were performed with the Bonferroni correction. Statistical significance was set at p < 0.05. If normal distribution was not verified, the nparLD module of the R software was used to perform a non-parametric two-way ANOVA-type test and if any significant result was observed, a Friedman test and the post-hoc paired comparisons with the Bonferroni correction as well as a Wilcoxon test were performed. Statistical significance was adjusted according with the number of tests performed for each factor.

Inclusion Criteria:

• Football players
• Regularly training with a weekly microcycle consisting of 3 to 5 training sessions and 1 game at the weekend
• Able to provide informed consent

Exclusion Criteria:

• Injury occurrence in the month previous to data collection
• Ergogenic supplements consumption in the month previous to data collection
• Having known intolerance to sodium bicarbonate