Influence of an Inspiratory Muscle Fatigue Protocol on Healthy Youngs on Respiratory Muscle Strength and Heart Rate Variability

Influence of an Inspiratory Muscle Fatigue Protocol on Healthy Youngs on Respiratory Muscle Strength and Heart Rate Variability

Respiratory muscle training represents an effective method increasingly utilized in both sports and healthcare domains, employing various devices, among which threshold devices are prominent. The aim of this study is to determine the relationship between inspiratory muscle fatigue and maximal inspiratory pressure, diaphragmatic strength (guided by ultrasound image) and heart rate variability.

According to our hypothesis, the execution of a protocol inducing inspiratory muscle fatigue in healthy youngs could influence cardiorespiratory function.

In this study, subjects will be divided into three groups: the experimental group , the activation group and the control group.

Measurements of variables, such as maximal inspiratory pressure, heart rate variability and diaphragmatic strength (ultrasound image), will be conducted.

This is a randomized control trial. The experimental group (EG) will perform the diaphragmatic fatigue protocol using a specific inspiratory endurance test, in which volunteers, one-on-one, and in a single session, will breathe against submaximal inspiratory loads equivalent to 60% of their Maximum Inspiratory Pressure (MIP) through a threshold valve device. The participants will follow a free pattern of breathing until they are unable to establish flow during at least 3 maximum inspiratory efforts.

The activation group (AG) will perform the protocol of 2 sets of 30 repetitions at 40% of their MIP, one-on-one, and in a single session, using a threshold valve device.

The control group will do a seat and wait.

The interventions will be supervised by a physiotherapist. The primary outcomes will be

Respiratory muscle strength will be assessed using a respiratory pressure meter or manometer designed, and with ultrasound image measuring the cross sectional area of the diaphragm at 8-9th rib level and speed of contraction with a deep and fast inspiratory manoeuver. This will be done immediately before intervention and immediately after intervention

Heart rate variability (HRV) will be assessed using a heart rate sensor Polar H10.

Inclusion Criteria:

• Aged between 18-45 years.
• Non-smoker.
• Engaged in sports activity at least 3 times a week for a minimum of one year.

Exclusion Criteria:

• Having a medical condition that impedes engaging in physical activity.
• Individuals with compromised cognitive capacities.
• Subjects with any chronic disease (cardiorespiratory, neurological, metabolic, oncological, etc.).
• Subjects with tympanic perforation or middle-inner ear pathology.
• Subjects who have undergone lower limb surgery within the past 12 months.
• Subjects experiencing an active episode of lower limb pain.