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.

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.

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.