Beetroot Juice and Neuromuscular Performance in Female Basketball Players

Isometric Mid-Thigh Pull (IMTP): Lower-body maximal isometric strength will be assessed using the isometric mid-thigh pull (IMTP) performed on VALD ForceDecks force platforms (VALD Performance, Brisbane, Australia). Participants will adopt a standardized mid-thigh pull position with the knees and hips slightly flexed and will be instructed to pull against an immovable bar as hard and as fast as possible. Ground reaction force will be recorded by the force platforms throughout each maximal effort. Peak force will be expressed both as absolute force (N) and relative to body mass (N·kg-¹). Participants will perform maximal trials separated by an appropriate recovery period, and the best trial will be retained for analysis.

Maximal Jump Height: Lower-body explosive performance will be assessed using the squat jump (SJ), countermovement jump (CMJ), and countermovement jump with arm swing (CMJ-AS). Jump performance will be measured using an OptoJump Next system (Microgate, Bolzano, Italy). Participants will perform maximal-effort trials for each jump condition following standardized instructions. Maximal jump height (cm) will be recorded for each jump type, and the best performance will be retained for analysis. Changes in maximal jump height following 5 days of supplementation will be compared between the nitrate-rich beetroot juice and placebo conditions.

Sprint performance will be assessed by measuring the time required to complete 10-m, 20-m, and 30-m sprints using Microgate photocell timing gates (Microgate, Bolzano, Italy). Participants will be instructed to sprint as fast as possible over the 30-m distance, with split times recorded at 10 m, 20 m, and 30 m. Sprint time will be recorded in seconds (s). Participants will perform maximal trials separated by an appropriate recovery period, and the best performance will be retained for analysis.

Modified T-Test Performance: Change-of-direction performance will be assessed using the modified T-test, with completion time measured using Microgate photocell timing gates (Microgate, Bolzano, Italy). Participants will be instructed to complete the standardized course as quickly as possible, incorporating forward sprinting, lateral shuffling, and backward running. Completion time will be recorded in seconds (s). Participants will perform maximal trials separated by an appropriate recovery period, and the best performance will be retained for analysis.

Saliva samples were collected 150 min after BJ or the placebo ingestion and were stored at -20°C for four months until subsequent analysis. To confirm the effectiveness of BJ supplementation on nitrate (NO3-) and nitrite (NO2-) levels, saliva concentrations were measured using a nitric oxide assay kit (EMSNO K195325, Thermo Fisher Scientific, Roskilde, Denmark) according to the manufacturer's instructions and as reported in previous literature (Richard et al., 2018). All samples and standards were measured in duplicate and averaged.

Immediately after each physical performance battery, participants were asked for providing her RPE using a Borg scale from 6 to 20 points

The morning after the supplementation and testing session, participants will complete a questionnaire assessing potential side effects associated with beetroot juice or placebo ingestion. The questionnaire includes gastrointestinal upset, red urine, gastric reflux, mild nausea, muscle pain, headache, increased urine excretion, increased fatigue, and nervousness. Each side effect will be assessed using a dichotomous Yes/No response scale (No = 0; Yes = 1). The incidence of each side effect will be reported as the number and percentage of participants reporting the symptom.