The goal of this randomized clinical trial is to investigate whether vocal exercises or breathing exercises improve respiratory function and trunk stability in healthy adult women aged 18-65. The main questions it aims to answer are:

Do vocal exercises improve respiratory function, respiratory muscle strength, endurance, and trunk stability? Do breathing exercises improve respiratory function, respiratory muscle strength, and endurance? Researchers will compare the vocal exercises group to the breathing exercises group to determine if one intervention has a superior effect on lung function, respiratory muscle performance, and trunk stability.

Participants will:

Perform a 6-week program of either vocal exercises or breathing exercises, with sessions twice per week, 30 minutes each.

Complete pre- and post-intervention assessments including thoracic excursion, breath-hold tests, spirometry, Dynamic Neuromuscular Stabilization (DNS) tests, and trunk stability tests using the Stabilizer pressure biofeedback device.

Engage with instructional videos and guidance through a closed social media group, allowing questions and feedback to ensure correct technique.

Study Design This study was a randomized controlled trial designed to evaluate the effects of vocal exercises versus breathing exercises on respiratory function and trunk stability in adult women. Ethical approval was obtained from the [name of ethics committee] (Approval No.: 2024 12 09 MNL-KIN (M)-2024-726). All participants provided written informed consent prior to enrollment, in accordance with the Declaration of Helsinki.

Participants Fifty healthy women aged 18-65 years were recruited via an online questionnaire distributed on social media. Inclusion criteria were female sex, age 18-65 years, no prior engagement in structured breathing or vocal training in the previous six months, and absence of acute or chronic respiratory infection. Exclusion criteria included inability to attend in-person assessments or failure to meet age or health criteria. Baseline demographic characteristics (age, weight, height, BMI) were comparable between groups.

Randomization and Allocation Eligible participants (n = 50) were randomly assigned in a 1:1 ratio to either the Vocal Exercises Group (VE, n = 25) or the Breathing Exercises Group (BE, n = 25) using a computer-generated random sequence. Both interventions lasted six weeks, with participants completing sessions twice per week for 30 minutes each.

Intervention

Breathing Exercises Group

Participants were provided access to a 30-minute instructional video demonstrating the following exercises:

Conscious Breathing: Seated observation of chest and abdominal wall movement.

Humming Bee (Bhramari Pranayama): Exhalation with a humming sound and ears gently occluded.

Kapalabhati: Rapid forceful exhalations with passive inhalations; intensity increased over time.

Alternate Nostril Breathing (Nadi Shodhana): Cycles of inhalation and exhalation through alternate nostrils.

Square Breathing (4x4x4x4): Seated breathing with equal durations of inhalation, breath-hold, exhalation, and breath-hold.

Diaphragmatic Breathing: Supine breathing with lateral rib expansion.

Vocal Exercises Group

Participants received access to instructional videos emphasizing diaphragmatic breathing and contemporary singing techniques. Exercises included:

Initial Exercises (Weeks 1-2): Sustained "s" sounds, lip trills, humming, melodic vowel sequences, and short vocal phrases.

Solo Vocal Exercises (Weeks 3-6): Short and long "S" sounds, humming on single and multiple notes, "mum" vocalization sequences, "Cha-cha-cha" sequences, melodic humming, and counting exercises without inhalation.

Both groups had access to a closed social media group for guidance and questions. Intensity adjustments were recommended after two weeks based on participant tolerance.

Outcome Measures Assessments were conducted at baseline and after six weeks.

Respiratory Function

Thoracic Excursion (CE): Measured at Th3-4, Th7-8, and Th11-12 using a tape measure. CE was calculated as the difference between maximal inspiration and expiration.

Spirometry: FEV₁, FVC, and PEF were measured using a handheld wireless spirometer (Contec SP80B). Three trials were performed, and the mean value was used.

Breath-Hold Tests: Stange (after maximal inspiration) and Genchi (after maximal expiration) tests were conducted in a seated position.

Trunk Stability

Dynamic Neuromuscular Stabilization (DNS): Three tests were used-diaphragm function, head/neck/trunk flexion, and head/neck/trunk extension. Tests were scored on a 4-point scale (1 = failed, 4 = excellent).

Stabilizer Pressure Biofeedback Device: Four tests assessed trunk stability: prone, supine, bent-leg lift, and straight-leg lift. Mean pressure differences over three repetitions were calculated for each leg.

Statistical Analysis Data were analyzed using IBM SPSS Statistics 29.0. Normality was confirmed using the Shapiro-Wilk test (p > 0.05). Within-group comparisons were performed with paired-samples t-tests, and between-group differences were assessed using independent-samples t-tests. Statistical significance was set at p < 0.05. Effect sizes were interpreted according to Cohen's d: 0.00-0.20 = no effect, 0.21-0.50 = small, 0.51-0.80 = medium, 0.81-1.30 = large, >1.30 = very large.

Flow of Participants Eighty-six participants were initially screened; 26 were excluded (19 due to recent training, 6 unable to attend in-person, 1 outside age range). Fifty participants were randomized and completed the six-week intervention with no attrition.

Inclusion Criteria:

• female sex;
• age 18-65 years;
• no engagement in breathing exercises for at least six months;
• no engagement in vocal training for at least six months;

Exclusion Criteria:

• acute respiratory diseases.
• chronic respiratory diseases