Objective To evaluate the acute effect of four inspiratory warm-up intensities (15%, 40%, 60%, and 80% of maximal inspiratory pressure \[MIP\]) on 100 m freestyle performance, and to analyze their impact on heart rate, blood lactate concentration, perceived exertion, and dyspnea in trained swimmers. Methods A randomized, crossover, double-blind experimental study was conducted. Participants were swimmers aged ≥18 years, with no respiratory or musculoskeletal pathology. Each participant completed, in sessions separated by at least three days, an inspiratory muscle warm-up consisting of 30 breaths against resistive loads set at 15%, 40%, 60%, and 80% of their MIP, previously determined using standardized procedures. Following each intervention, participants performed a maximal 100 m freestyle test. The following variables were recorded: Swimming time Heart rate (during and post-exercise) Post-exercise capillary blood lactate concentration Rating of perceived exertion (Borg scale) Dyspnea (Dyspnea-12) Conclusions This study will help identify the optimal inspiratory warm-up intensity to enhance swimming performance.
Inspiratory warm-up An intervention performed prior to exercise consisting of breathing against resistance to activate the inspiratory muscles (mainly the diaphragm and accessory respiratory muscles) with the aim of enhancing their performance during subsequent effort. Maximal Inspiratory Pressure (MIP) The maximum pressure that an individual can generate during a forceful inspiration against an occluded airway. It is an indicator of inspiratory muscle strength and is used to prescribe training intensity. Relative intensities (15%, 40%, 60%, 80% of MIP) Percentages of MIP representing different levels of respiratory workload. They allow graded inspiratory resistance to investigate dose-response effects on performance. Inspiratory Muscle Training (IMT) A specific training method targeting the inspiratory muscles through controlled resistive breathing loads, aimed at improving strength, endurance, and ventilatory efficiency. Crossover design An experimental design in which each participant completes all experimental conditions, acting as their own control, thereby reducing inter-subject variability. Double-blind design A methodological approach in which neither participants nor evaluators are aware of the assigned condition, minimizing bias in performance and outcome assessment. Swimming performance A functional outcome measured primarily through time to complete a fixed distance, in this case 100 meters freestyle. Cardiovascular response The physiological response of the cardiovascular system to exercise, typically assessed through heart rate and post-exercise recovery dynamics. Blood lactate concentration A marker of metabolic stress during high-intensity exercise, reflecting the contribution of anaerobic glycolysis to energy production. Perceived exertion A subjective assessment of exercise intensity, commonly measured using standardized scales such as the Borg scale. Respiratory discomfort (dyspnea) A subjective sensation of breathing difficulty associated with exertion, reflecting ventilatory demand and exercise tolerance.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
TREATMENT
Masking
DOUBLE
Enrollment
52
It is a crossover study in which the different exercise intensities are investigated.
swimming time (100 meters)
After the respiratory interventions, participants will perform a maximal 100-meter freestyle swimming test under supervision. The total time will be recorded using a digital stopwatch, starting with the starting signal and ending when the swimmer touches the wall upon completing the distance.
Time frame: This measurement will be carried out from the randomization process until 8 weeks after the start of the inspiratory training program.
Maximal Inspiratory Pressure and Maximal Expiratory Pressure
Maximal Inspiratory Pressure (PIM/MIP) and Maximal Expiratory Pressure (PEM/MEP) are indicators of global respiratory muscle strength. PIM reflects the maximal negative pressure generated during a forced inspiratory effort against an occluded airway, mainly assessing diaphragmatic and external intercostal muscle function, whereas PEM reflects the maximal positive pressure produced during a forced expiratory effort, mainly involving abdominal and internal intercostal muscles. Both variables are expressed in centimeters of water (cmH₂O) and are widely used to quantify inspiratory and expiratory muscle performance, as well as to evaluate respiratory muscle fatigue and training adaptations in clinical and sports settings.
Time frame: This measurement will be carried out from the randomization process until 8 weeks after the start of the inspiratory training program.
Lactate
Immediately after the test, blood lactate will be measured using a Lactate Pro 2 portable analyzer, from a capillary blood sample obtained from the fingertip.
Time frame: This measurement will be carried out from the randomization process until 8 weeks after the start of the inspiratory training program.
Perceived exertion.
Perceived exertion will be assessed using the Borg scale (6-20), previously explained to ensure proper understanding, and will be recorded immediately after exercise through a direct interview.
Time frame: This measurement will be carried out from the randomization process until 8 weeks after the start of the inspiratory training program.
Dysnea
The Dyspnea-12 (D-12) scale is a multidimensional questionnaire used to assess the severity and qualitative perception of dyspnea (breathlessness). It evaluates both the physical and emotional components associated with breathing discomfort. The questionnaire consists of 12 items: My breath does not go in all the way My breathing requires more work I feel short of breath I have difficulty catching my breath I cannot get enough air My breathing is uncomfortable My breathing is exhausting My breathing makes me feel depressed My breathing makes me feel miserable My breathing is distressing My breathing makes me agitated My breathing is irritating Each item is scored using a 4-point Likert scale: 0 = None 1. = Mild 2. = Moderate 3. = Severe Therefore, the total score ranges from 0 to 36 points. Interpretation: A low score indicates little or no perceived dyspnea. A moderate score reflects clinically relevant breathing discomfort. A high score indicates severe dyspnea with an important
Time frame: This measurement will be carried out from the randomization process until 8 weeks after the start of the inspiratory training program.
Heart rate.
Heart rate will be continuously monitored during the test and for up to five minutes post-exercise using a Polar H10 chest strap, placed on the anterior thoracic region just below the xiphoid process. The device will be calibrated before each session, and data will be analyzed using Polar Flow software to obtain parameters such as mean heart rate, maximum heart rate, which are key indicators of autonomic and cardiovascular response to exercise.
Time frame: This measurement will be carried out from the randomization process until 8 weeks after the start of the inspiratory training program.
Recovery time
Recovery time will be defined as the period required for heart rate to decrease following the cessation of exercise. This parameter reflects autonomic nervous system recovery, particularly parasympathetic reactivation after physical exertion. Heart rate recovery will be analyzed during the first five minutes post-exercise using data collected from the Polar H10 device. Faster recovery times are generally associated with better cardiovascular fitness and autonomic regulation, whereas delayed recovery may indicate increased physiological stress or fatigue.
Time frame: This measurement will be carried out from the randomization process until 8 weeks after the start of the inspiratory training program.
Heart rate variability
Heart rate variability (HRV) refers to the variation in the time intervals between consecutive heartbeats (R-R intervals). HRV is considered a non-invasive marker of autonomic nervous system activity and reflects the balance between sympathetic and parasympathetic modulation. HRV data obtained from the Polar H10 sensor will be analyzed using Polar Flow software, and parameters such as RMSSD and SDNN may be extracted. Higher HRV values are typically associated with better autonomic adaptability and recovery capacity, while lower values may reflect fatigue, stress, or reduced physiological adaptability.
Time frame: This measurement will be carried out from the randomization process until 8 weeks after the start of the inspiratory training program.
Forced Vital Capacity and Forced Expiratory Volume in 1 second
Forced Vital Capacity (FVC/CVF) and Forced Expiratory Volume in 1 second (FEV₁) are spirometric measures used to assess ventilatory capacity and pulmonary function. FVC represents the total volume of air that can be forcibly exhaled after a maximal inspiration, expressed in liters (L), while FEV₁ represents the volume exhaled during the first second of that maneuver, also expressed in liters. The FEV₁/FVC ratio is commonly used to identify ventilatory limitations, particularly obstructive patterns. Together, these variables provide key information on airway function, expiratory flow limitation, and overall pulmonary performance.
Time frame: This measurement will be carried out from the randomization process until 8 weeks after the start of the inspiratory training program.
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