Water-Inertia-Based Dynamic Stability Training for Balance and Postural Control in Healthy Young Women

Effects of Water-Inertia-Based Dynamic Stability Training on Dynamic Balance and Single-Leg Postural Control in Healthy Young Women: A Randomized Controlled Trial

This randomized controlled study evaluated the effects of a 10-week dynamic stability training program using a mobile water load compared with a mass-matched stable load in healthy young women. Thirty participants were randomly assigned to either water-inertia-based unstable-load training or stable-load training. Both groups completed the same supervised exercises three times per week, using vests with the same total external mass; the main difference between groups was whether the load inside the vest was mobile or stable. Outcomes were assessed before training, after 5 weeks, and after 10 weeks. The study evaluated dynamic balance, postural sway during single-leg stance, and other physical-performance outcomes to determine whether mobile water loading produced different training adaptations from stable loading.

Study Overview

• Status: Completed
• Conditions: Postural Control and Dynamic Balance in Healthy Young Women
• Intervention / Treatment: Behavioral: Water-Inertia-Based Dynamic Stability Training; Behavioral: Stable-Load Dynamic Stability Training

Detailed Description

This study was designed to examine whether dynamic stability training performed with a mobile water-based external load produces different physical and postural adaptations from the same training performed with a mass-matched stable external load in healthy young women. The study used a randomized, parallel-group design.

Healthy female university students aged 19-25 years who had not participated in resistance training during the previous 12 months were recruited. After baseline assessment, 30 eligible participants were randomly assigned in a 1:1 ratio to an unstable-load training group or a stable-load training group.

Both groups completed the same supervised dynamic stability training program three times per week for 10 weeks, for a total of 30 training sessions. Each session lasted approximately 50 minutes. The exercise content, training frequency, session duration, set-repetition structure, rest intervals, vest mass, and any additional prescribed exercise loads were matched between groups. During the main training block, participants completed three sets of each exercise, with 12 repetitions per set during weeks 1-5 and 15 repetitions per set during weeks 6-10.

The unstable-load group trained while wearing an Aqua Vest containing a total external load of 5 kg, consisting of approximately 4 kg of water and a 1-kg vest. Because the water pouches were partially filled, the internal water could move during exercise and change the distribution of the external load. The stable-load group wore a mass-matched weighted vest containing approximately 4 kg of steel rods and a 1-kg vest. The steel rods were arranged to approximate the spatial distribution of the water pouches. Thus, the primary experimental difference between groups was the mobility of the external load rather than total vest mass or prescribed exercise content.

Assessments were conducted at baseline, after 5 weeks of training, and after 10 weeks of training. Dynamic postural control was evaluated using the Y-Balance Test. Participants completed reaching tasks in the anterior, posteromedial, and posterolateral directions while standing on one limb. The maximum valid reach distance in each direction was retained and normalized to limb length, and a composite score was also calculated.

Postural sway was evaluated during single-leg stance using force-platform-derived center-of-pressure measures under eyes-open and eyes-closed conditions. Eyes-open trials lasted 30 seconds and eyes-closed trials lasted 20 seconds. Center-of-pressure outcomes included total path distance and direction-specific root-mean-square displacement in the anteroposterior and mediolateral directions.

The broader study protocol also included lower-extremity physical-performance assessments. The registration record is intended to describe the original study protocol and design; individual publications arising from the study may focus on specific subsets of the collected outcomes.

The purpose of the comparison was to determine whether introducing load mobility through a water-filled vest, while keeping the prescribed exercise program and external mass closely matched, resulted in different adaptations from training with a stable weighted vest.

• Study Type: Interventional
• Enrollment (Actual): 30
• Phase: Not Applicable

Contacts and Locations

Study Locations

• South Korea
  • Busan, South Korea
    • Busan University of Foreign Studies

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• Female undergraduate students aged 19 to 25 years.
• Generally healthy at the time of enrollment.
• No surgery within the previous 6 months.
• No congenital, neurological, vestibular, or musculoskeletal disorder affecting the foot, pelvis, or spine.
• No participation in resistance training during the previous 12 months. Able and willing to participate in the 10-week supervised exercise intervention and study assessments.
• Provided written informed consent to participate.

Exclusion Criteria:

• Did not meet any of the inclusion criteria.
• Participated in resistance training or functional training outside the study intervention during the 10-week study period.
• Developed a health condition, injury, or other circumstance during the study that prevented safe participation in the prescribed exercise program or outcome assessments.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Other
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Single

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Water-Inertia-Based Unstable-Load Training; Participants assigned to this arm completed a supervised 10-week dynamic stability training program three times per week while wearing an Aqua Vest with a total external load of 5 kg, consisting of approximately 4 kg of water and a 1-kg vest. The partially filled water pouches allowed internal water movement during exercise, creating a mobile external load. Exercise content, session duration, set-repetition structure, rest intervals, and any additional prescribed exercise loads were matched to the stable-load training arm.	Behavioral: Water-Inertia-Based Dynamic Stability Training; Participants completed a supervised dynamic stability training program three times per week for 10 weeks (30 sessions), with each session lasting approximately 50 minutes. During training, participants wore a vest providing a total external load of 5 kg, consisting of approximately 4 kg of water in partially filled pouches and a 1-kg vest. Internal water movement allowed the external load distribution to change during exercise. Exercises were performed for three sets, with 12 repetitions per set during weeks 1-5 and 15 repetitions per set during weeks 6-10, with 30 seconds of rest between sets. Exercise content and any additional prescribed implement loads were matched to the stable-load intervention.; Other Names: Unstable-Load Training (ULT); Aqua Vest Training
Active Comparator: Stable-Load Training; Participants assigned to this arm completed the same supervised 10-week dynamic stability training program three times per week while wearing a mass-matched stable weighted vest with a total external load of 5 kg, consisting of approximately 4 kg of steel rods and a 1-kg vest. The steel rods were arranged to approximate the spatial loading configuration of the water pouches. Exercise content, session duration, set-repetition structure, rest intervals, and any additional prescribed exercise loads were matched to the unstable-load training arm.	Behavioral: Stable-Load Dynamic Stability Training; Participants completed the same supervised dynamic stability training program three times per week for 10 weeks (30 sessions), with each session lasting approximately 50 minutes. During training, participants wore a stable weighted vest providing a total external load of 5 kg, consisting of approximately 4 kg of steel rods and a 1-kg vest. The steel rods were arranged to approximate the spatial loading configuration of the water pouches used in the water-inertia intervention. Exercises were performed for three sets, with 12 repetitions per set during weeks 1-5 and 15 repetitions per set during weeks 6-10, with 30 seconds of rest between sets. Exercise content and any additional prescribed implement loads were matched between groups.; Other Names: Stable-Load Training (SLT); Weighted Vest Training

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Normalized Anterior Reach Distance on the Y-Balance Test	Dynamic postural control was assessed using the lower-quarter Y-Balance Test. Participants performed three valid anterior reach trials while maintaining single-leg stance. The maximum reach distance was retained and normalized to the corresponding limb length: normalized reach distance (%) = maximum reach distance / limb length × 100. Higher values indicate greater normalized reach performance.	Baseline, Week 5, and Week 10
Normalized Posteromedial Reach Distance on the Y-Balance Test	Participants performed three valid posteromedial reach trials during the lower-quarter Y-Balance Test. The maximum reach distance was retained and normalized to the corresponding limb length: normalized reach distance (%) = maximum reach distance / limb length × 100. Higher values indicate greater normalized reach performance.	Baseline, Week 5, and Week 10
Normalized Posterolateral Reach Distance on the Y-Balance Test	Participants performed three valid posterolateral reach trials during the lower-quarter Y-Balance Test. The maximum reach distance was retained and normalized to the corresponding limb length: normalized reach distance (%) = maximum reach distance / limb length × 100. Higher values indicate greater normalized reach performance.	Baseline, Week 5, and Week 10
Y-Balance Test Composite Score	The composite score was calculated from the maximum valid anterior, posteromedial, and posterolateral reach distances normalized to limb length: composite score (%) = (maximum anterior + maximum posteromedial + maximum posterolateral reach distance) / (3 × limb length) × 100. Higher values indicate greater overall Y-Balance Test performance.	Baseline, Week 5, and Week 10
Center-of-Pressure Total Distance During Eyes-Open Single-Leg Stance	Postural sway was assessed using a force platform during 30-second eyes-open single-leg stance. Total CoP distance (cm) represented the cumulative path length of the center-of-pressure trajectory during each valid trial. Three trial-specific values were averaged for analysis. Lower values represent a shorter CoP trajectory during the test condition.	Baseline, Week 5, and Week 10
Anteroposterior CoP RMS During Eyes-Open Single-Leg Stance	Anteroposterior root-mean-square (AP RMS) displacement of the center of pressure was calculated during 30-second eyes-open single-leg stance and expressed in centimeters. AP RMS represents the dispersion of CoP displacement about its mean position in the anteroposterior direction. Three trial-specific values were averaged for analysis.	Baseline, Week 5, and Week 10
Mediolateral CoP RMS During Eyes-Open Single-Leg Stance	Mediolateral root-mean-square (ML RMS) displacement of the center of pressure was calculated during 30-second eyes-open single-leg stance and expressed in centimeters. ML RMS represents the dispersion of CoP displacement about its mean position in the mediolateral direction. Three trial-specific values were averaged for analysis.	Baseline, Week 5, and Week 10
Center-of-Pressure Total Distance During Eyes-Closed Single-Leg Stance	Postural sway was assessed using a force platform during 20-second eyes-closed single-leg stance. Total CoP distance (cm) represented the cumulative path length of the center-of-pressure trajectory during each valid trial. Three trial-specific values were averaged for analysis. Lower values represent a shorter CoP trajectory during the test condition.	Baseline, Week 5, and Week 10
Anteroposterior CoP RMS During Eyes-Closed Single-Leg Stance	Anteroposterior root-mean-square (AP RMS) displacement of the center of pressure was calculated during 20-second eyes-closed single-leg stance and expressed in centimeters. AP RMS represents the dispersion of CoP displacement about its mean position in the anteroposterior direction. Three trial-specific values were averaged for analysis.	Baseline, Week 5, and Week 10
Mediolateral CoP RMS During Eyes-Closed Single-Leg Stance	Mediolateral root-mean-square (ML RMS) displacement of the center of pressure was calculated during 20-second eyes-closed single-leg stance and expressed in centimeters. ML RMS represents the dispersion of CoP displacement about its mean position in the mediolateral direction. Three trial-specific values were averaged for analysis.	Baseline, Week 5, and Week 10
Knee Extension Peak Torque Relative to Body Weight at 60°/s	Concentric knee extension strength was assessed using an isokinetic dynamometer at an angular velocity of 60°/s. Peak torque was normalized to body weight and expressed as a percentage of body weight (PT/BW, %). Higher values indicate greater knee extensor torque relative to body weight.	Baseline, Week 5, and Week 10
Knee Flexion Peak Torque Relative to Body Weight at 60°/s	Concentric knee flexion strength was assessed using an isokinetic dynamometer at an angular velocity of 60°/s. Peak torque was normalized to body weight and expressed as a percentage of body weight (PT/BW, %). Higher values indicate greater knee flexor torque relative to body weight.	Baseline, Week 5, and Week 10
Ankle Inversion Peak Torque Relative to Body Weight at 60°/s	Concentric ankle inversion strength was assessed using an isokinetic dynamometer at an angular velocity of 60°/s. Peak torque was normalized to body weight and expressed as a percentage of body weight (PT/BW, %). Higher values indicate greater inversion torque relative to body weight.	Baseline, Week 5, and Week 10
Ankle Eversion Peak Torque Relative to Body Weight at 60°/s	Concentric ankle eversion strength was assessed using an isokinetic dynamometer at an angular velocity of 60°/s. Peak torque was normalized to body weight and expressed as a percentage of body weight (PT/BW, %). Higher values indicate greater eversion torque relative to body weight.	Baseline, Week 5, and Week 10
Ankle Inversion Peak Torque Relative to Body Weight at 120°/s	Concentric ankle inversion strength was assessed using an isokinetic dynamometer at an angular velocity of 120°/s. Peak torque was normalized to body weight and expressed as a percentage of body weight (PT/BW, %). Higher values indicate greater inversion torque relative to body weight.	Baseline, Week 5, and Week 10
Ankle Eversion Peak Torque Relative to Body Weight at 120°/s	Concentric ankle eversion strength was assessed using an isokinetic dynamometer at an angular velocity of 120°/s. Peak torque was normalized to body weight and expressed as a percentage of body weight (PT/BW, %). Higher values indicate greater eversion torque relative to body weight.	Baseline, Week 5, and Week 10

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Knee Extension Test Range of Motion at 60°/s	Range of motion recorded by the isokinetic dynamometer during the knee extension test performed at 60°/s, expressed in degrees. This measure represents the angular range recorded during the corresponding isokinetic testing condition.	Baseline, Week 5, and Week 10
Knee Flexion Test Range of Motion at 60°/s	Range of motion recorded by the isokinetic dynamometer during the knee flexion test performed at 60°/s, expressed in degrees.	Baseline, Week 5, and Week 10
Ankle Inversion Test Range of Motion at 60°/s	Range of motion recorded by the isokinetic dynamometer during the inversion test performed at 60°/s, expressed in degrees. This measure represents the angular range recorded during the corresponding isokinetic testing condition.	Baseline, Week 5, and Week 10
Ankle Eversion Test Range of Motion at 60°/s	Range of motion recorded by the isokinetic dynamometer during the eversion test performed at 60°/s, expressed in degrees. This measure represents the angular range recorded during the corresponding isokinetic testing condition.	Baseline, Week 5, and Week 10
Ankle Inversion Test Range of Motion at 120°/s	Range of motion recorded by the isokinetic dynamometer during the inversion test performed at 120°/s, expressed in degrees. This measure represents the angular range recorded during the corresponding isokinetic testing condition.	Baseline, Week 5, and Week 10
Ankle Eversion Test Range of Motion at 120°/s	Range of motion recorded by the isokinetic dynamometer during the eversion test performed at 120°/s, expressed in degrees. This measure represents the angular range recorded during the corresponding isokinetic testing condition.	Baseline, Week 5, and Week 10

Collaborators and Investigators

• Sponsor: Yuanyan Huang

Study record dates

Study Major Dates

• Study Start (Actual): July 5, 2024
• Primary Completion (Actual): September 20, 2024
• Study Completion (Actual): September 20, 2024

Study Registration Dates

• First Submitted: September 4, 2026
• First Submitted That Met QC Criteria: September 4, 2026
• First Posted (Actual): September 10, 2026

Study Record Updates

• Last Update Posted (Actual): September 10, 2026
• Last Update Submitted That Met QC Criteria: September 4, 2026
• Last Verified: September 1, 2026

More Information

Terms related to this study

• Keywords: postural control; dynamic balance; center of pressure; dynamic stability training; Y-Balance Test; water-inertia loading; unstable-load training; healthy young women; single-leg stance
• Other Study ID Numbers: 2024-0666-001; P01-202407-01-004 (Other Identifier: Public Institutional Bioethics Committee, Republic of Korea)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES
• IPD Plan Description: De-identified individual participant data that support the findings of the study may be shared with qualified researchers upon reasonable request, subject to applicable ethical and data-protection requirements.
• IPD Sharing Time Frame: Beginning after publication of the primary study results, with no predetermined end date.
• IPD Sharing Access Criteria: De-identified individual participant data may be shared with qualified researchers upon reasonable request for scientifically appropriate purposes. Requests should include a brief research proposal and planned analyses and will be reviewed for ethical, privacy, and data-protection considerations. Approved data will be provided by the study investigator.
• IPD Sharing Supporting Information Type: STUDY_PROTOCOL

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No