Acute Effects of Breathing Resistance During Exercise in Football Players

Prospective randomized-sequence, two-condition crossover study involving 35 active football players aged 18-30 years with regular football training over the preceding six months. The target allows for loss or incomplete data, with at least 32 completers sought based on a paired comparison with two-sided alpha 0.05, power 0.90, and standardized effect size 0.60.

Participants will provide written informed consent. Age, height, weight, dominant side, football experience, weekly training duration, and playing position will be recorded. Standardized preparation and familiarization will precede testing. Each participant completes a respiratory-resistance exercise-mask condition and a no-mask control condition. Condition order is computer randomized, with at least 72 hours between sessions. Participants will avoid strenuous exercise before test days and maintain comparable sleep and nutritional routines. All field testing will use the same surface, comparable environmental conditions, and standardized warm-up.

Maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP) will be measured before and after exercise using a calibrated mouth-pressure device and repeated acceptable and reproducible maneuvers. These are noninvasive measures of respiratory muscle function.

Heart rate and peripheral oxygen saturation (SpO2) will be monitored at standardized time points. Motion artifact, peripheral perfusion, sensor placement, and signal quality will be considered when recording pulse oximetry. Perceived exertion and breathlessness will be rated separately with the Borg category-ratio scale.

Repeated-sprint testing consists of five 30-meter linear sprints with 30-second active recovery intervals. Electronic timing records each sprint, with best, total/mean time, and performance decrement derived. The 505 change-of-direction test involves crossing the timing line, running 5 meters to a turning line, making a 180-degree turn, and returning through the timing line. Right and left turns will be standardized and electronically timed.

Testing will stop for chest pain, marked dizziness, presyncope, unusual breathlessness, or any finding judged unsafe by the researcher. No blood collection, invasive procedure, or therapeutic intervention is planned. Assessments will be conducted by the research team in an appropriate sports-field/laboratory setting.

Paired analyses will compare conditions. Repeated-measures analyses or linear mixed models will assess condition, time, and condition-by-time effects for pre/post variables including MIP and MEP. Heart rate, SpO2, perceived exertion, breathlessness, repeated-sprint performance and decrement, and 505 performance will be compared between conditions. Relationships between acute respiratory pressure changes and performance will be explored with Pearson or Spearman correlations. Sequence and period effects will be included where appropriate, and effect sizes and 95% confidence intervals will accompany inferential results. Two-sided p<0.05 will be used.

The mask condition uses the Elevation Training Mask 2.0 (Training Mask, Inc., USA), with the original manufacturer-labeled 9,000 ft valve configuration throughout field testing. This label identifies airflow resistance, not actual altitude or verified hypoxia. The same configuration is used across participants, with fit adjusted individually. The selected setting is based on published acute crossover research (Ozdemir et al., 2026; doi:10.1186/s13102-026-01892-6). Total repeated-sprint time is the primary outcome.