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This pilot randomized controlled trial evaluates whether combining lower-body electrical muscle stimulation (EMS) with resistance training is feasible and beneficial for physically inactive postmenopausal women, who experience concurrent declines in muscle strength, body composition, arterial elasticity, and cardiac autonomic balance.
Sixteen physically inactive postmenopausal women aged 50-70 years are randomly assigned (1:1) to either (A) supervised resistance training combined with lower-body EMS (applied to 6 muscle groups: lower back, lower abdomen, glutes, quadriceps, hamstrings, and calves) or (B) supervised resistance training alone. Both groups complete twelve 50-minute sessions (consisting of a 10-minute warm-up, 30-minute main exercise, and a 10-minute cool-down) over 6 weeks (twice weekly). Assessments before and after the intervention include body composition, lower-body muscle function, arterial stiffness, and 5-minute heart rate variability.
The primary aim is to determine the feasibility of the protocol(recruitment, retention, session attendance, and intervention dose delivery) to inform a future definitive trial. Preliminary estimates of intervention effects on the measured outcomes are reported as secondary aims.
BACKGROUND AND RATIONALE Postmenopausal women often experience physiological declines in muscle function, body composition, and cardiovascular health. While resistance training is an established countermeasure, maximizing its efficiency and adherence remains a challenge. Applying lower-body electrical muscle stimulation (EMS) during resistance training may enhance physiological adaptations and overall training effectiveness. This study aims to evaluate the feasibility of combining lower-body EMS with resistance training in physically inactive postmenopausal women to inform the design of a future definitive trial.
STUDY DESIGN This is a pilot randomized controlled trial. Participants will be randomly assigned to either an intervention group receiving combined lower-body EMS and resistance training or a control group receiving resistance training alone. Clinical and physiological outcomes will be assessed before and after the intervention period to evaluate preliminary effects.
PRIMARY FEASIBILITY OUTCOMES
The primary objective is to evaluate the feasibility of the study protocol. Feasibility will be determined by assessing several key components, including:
Recruitment: The ability to recruit the target population within the planned timeframe.
Retention: The proportion of participants who complete the study and post-intervention assessments.
Adherence: Participant attendance and compliance with the scheduled exercise sessions.
Intervention Fidelity: The successful delivery of the exercise intensity and EMS protocol as intended.
These components will be evaluated against pre-established progression criteria to determine whether the protocol can proceed to a larger trial or requires modification.
STATISTICAL APPROACH Feasibility outcomes will be summarized primarily using descriptive statistics. For secondary physiological and clinical outcomes, appropriate statistical methods will be utilized to estimate the preliminary effects of the intervention, comparing changes between the groups while adjusting for baseline measurements. Effect sizes and confidence intervals will be calculated to provide preliminary evidence and to assist with sample size calculations for future large-scale trials.
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| Label | Type | Description | Intervention Names |
|---|---|---|---|
| A Group: EMS + Resistance Training | Experimental | Lower-body EMS combined with 8 machine-based resistance exercises for 6 weeks, 2 sessions per week. |
|
| B Group: Resistance Training | Active Comparator | 8 machine-based resistance exercises for 6 weeks, 2 sessions per week without EMS. |
|
| Name | Type | Description | Arm Group Labels | Other Names |
|---|---|---|---|---|
| Lower-Body EMS combined with Resistance Training | Device | Electrical muscle stimulation (85 Hz, 350 μs, cycle 11, duty approx 1:2) applied to 6 muscle groups: lower back (erector spinae), lower abdomen, glutes, quadriceps, hamstrings, and calves. |
| Measure | Description | Time Frame |
|---|---|---|
| Composite Feasibility Outcome (Recruitment, Retention, Session Attendance, and Intervention Dose Delivery) | The primary outcome is the feasibility of the study protocol, assessed via recruitment rates, participant retention, session adherence, and targeted intervention delivery. These indicators will be evaluated against pre-defined progression criteria using descriptive statistics to determine whether to proceed with or modify the protocol for a future definitive trial. Unit: Percentage | Baseline and Week 6 |
| Measure | Description | Time Frame |
|---|---|---|
| Skeletal Muscle Mass Index (SMI) | Appendicular skeletal muscle mass divided by height squared. Unit: kg/m². | Baseline and Week 6 |
| Total Body Muscle Mass | Total skeletal muscle mass of the whole body. Unit: kg |
| Measure | Description | Time Frame |
|---|---|---|
| Dominant Knee Extensor Fatigue Index at 180°/s | Percentage decline in knee extensor torque across the repetition set at 180°/sec on the dominant limb. Unit: % | Baseline and Week 6 |
| Non-dominant Knee Extensor Fatigue Index at 180°/s |
Inclusion Criteria:
Exclusion Criteria:
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| Name | Affiliation | Role |
|---|---|---|
| Yeon Soo Kim, MD, Prof | Seoul National University | Principal Investigator |
| Facility | Status | City | State | ZIP | Country | Contacts |
|---|---|---|---|---|---|---|
| Seoul National University | Seoul | Seoul | 08826 | South Korea |
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| ID | Term |
|---|---|
| D009043 | Motor Activity |
| ID | Term |
|---|---|
| D001519 | Behavior |
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| ID | Term |
|---|---|
| D055070 | Resistance Training |
| ID | Term |
|---|---|
| D005081 | Exercise Therapy |
| D012046 | Rehabilitation |
| D000359 | Aftercare |
| D003266 | Continuity of Patient Care |
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| Resistance Training | Behavioral | A 50-minute session consisting of a 10-minute warm-up, 30 minutes of main exercise (8 machine-based lower-body resistance exercises, 3 sets of 8-12 repetitions), and a 10-minute cool-down. |
|
| Baseline and Week 6 |
| Total Leg Muscle Mass | Combined left and right leg skeletal muscle mass. Unit: kg | Baseline and Week 6 |
| Body Fat Percentage | Body fat mass expressed as a percentage of total body weight. Unit: % | Baseline and Week 6 |
| Total Body Fat Mass | Absolute total body fat in kilograms. Unit: kg | Baseline and Week 6 |
| Estimated Visceral Fat Area (eVFA) | Estimated visceral fat area at the umbilical level. Unit: cm² | Baseline and Week 6 |
| Waist Circumference | Circumference measured at the level of the umbilicus. Unit: cm | Baseline and Week 6 |
| Waist-to-Hip Ratio (WHR) | Waist circumference divided by hip circumference. Unit: ratio | Baseline and Week 6 |
| Body Mass Index (BMI) | Body weight in kilograms divided by the square of height in meters. Unit: kg/m² | Baseline and Week 6 |
| Phase Angle | Whole-body bioimpedance phase angle derived from the arctangent of the reactance-to-resistance ratio. Marker of cellular membrane integrity and overall nutritional/health status. Unit: degrees | Baseline and Week 6 |
| Dominant Knee Extensor Peak Torque per Body Weight at 60°/s | Peak concentric knee extensor torque normalized to body weight, measured at 60°/sec angular velocity on the dominant limb. Unit: Nm/kg | Baseline and Week 6 |
| Non-dominant Knee Extensor Peak Torque per Body Weight at 60°/s | Peak concentric knee extensor torque normalized to body weight at 60°/sec on the non-dominant limb. Unit: Nm/kg | Baseline and Week 6 |
| Dominant Knee Flexor Peak Torque per Body Weight at 60°/s | Peak concentric knee flexor (hamstring) torque normalized to body weight at 60°/sec on the dominant limb. Unit: Nm/kg | Baseline and Week 6 |
| Non-dominant Knee Flexor Peak Torque per Body Weight at 60°/s | Peak concentric knee flexor torque normalized to body weight at 60°/sec on the non-dominant limb. Unit: Nm/kg | Baseline and Week 6 |
| Dominant Hamstring-to-Quadriceps (H/Q) Ratio at 60°/s | Ratio of knee flexor peak torque to knee extensor peak torque at 60°/sec on the dominant limb. Unit: ratio | Baseline and Week 6 |
| Non-dominant Hamstring-to-Quadriceps (H/Q) Ratio at 60°/s | Ratio of knee flexor peak torque to knee extensor peak torque at 60°/sec on the non-dominant limb. Unit: ratio | Baseline and Week 6 |
| Dominant Total Work Done by Knee Extensor per Body Weight at 180°/s | Total work performed by knee extensors across the test set, normalized to body weight, at 180°/sec angular velocity on the dominant limb. Unit: Nm/kg | Baseline and Week 6 |
| Non-dominant Total Work Done by Knee Extensor per Body Weight at 180°/s | Total work performed by knee extensors normalized to body weight at 180°/sec on the non-dominant limb. Unit: Nm/kg | Baseline and Week 6 |
| Dominant Total Work Done by Knee Flexor per Body Weight at 180°/s | Total work performed by knee flexors normalized to body weight at 180°/sec on the dominant limb. Unit: Nm/kg | Baseline and Week 6 |
| Non-dominant Total Work Done by Knee Flexor per Body Weight at 180°/s | Total work performed by knee flexors normalized to body weight at 180°/sec on the non-dominant limb. Unit: Nm/kg | Baseline and Week 6 |
| Average Brachial-Ankle Pulse Wave Velocity (baPWV) | Mean of left and right brachial-ankle pulse wave velocity; primary indicator of large-artery stiffness. Unit: cm/s | Baseline and Week 6 |
| Highest Brachial-Ankle Pulse Wave Velocity (baPWV) | The higher of left and right baPWV values, reflecting the most affected limb. Unit: cm/s | Baseline and Week 6 |
| Brachial Systolic Blood Pressure (SBP) | Brachial systolic blood pressure. Unit: mmHg | Baseline and Week 6 |
| Brachial Diastolic Blood Pressure (DBP) | Brachial diastolic blood pressure. Unit: mmHg | Baseline and Week 6 |
| Pulse Pressure (PP) | Pulse pressure calculated as systolic minus diastolic blood pressure. Unit: mmHg | Baseline and Week 6 |
| Mean Arterial Pressure (MAP) | Mean arterial pressure derived from systolic and diastolic blood pressure. Unit: mmHg | Baseline and Week 6 |
| Average Ankle-Brachial Index (ABI) | Mean of left and right ankle-brachial systolic blood pressure ratio. Unit: ratio | Baseline and Week 6 |
| Augmentation Index (AI) | Augmentation index derived from second-derivative photoplethysmography. Unit: unitless | Baseline and Week 6 |
| Root Mean Square of Successive Differences (RMSSD) | Root mean square of successive differences between adjacent normal-to-normal RR intervals. Unit: ms | Baseline and Week 6 |
| High-Frequency (HF) Power | Spectral power in the high-frequency band (0.15-0.4 Hz); index of parasympathetic (vagal) activity. Unit: ms² | Baseline and Week 6 |
| Standard Deviation of NN Intervals (SDNN) | Standard deviation of all normal-to-normal RR intervals; time-domain index of overall heart rate variability. Unit: ms | Baseline and Week 6 |
| Low-Frequency (LF) Power | Spectral power in the low-frequency band (0.04-0.15 Hz). Unit: ms² | Baseline and Week 6 |
| LF/HF Ratio | Ratio of low-frequency to high-frequency spectral power. Unit: ratio | Baseline and Week 6 |
| High-Frequency Normalized Units (HFnu) | HF power expressed in normalized units = HF / (LF + HF) × 100. Unit: n.u. | Baseline and Week 6 |
| Low-Frequency Normalized Units (LFnu) | LF power expressed in normalized units = LF / (LF + HF) × 100. Unit: n.u. | Baseline and Week 6 |
| Total Power (TP) | Total spectral power up to 0.4 Hz. Unit: ms² | Baseline and Week 6 |
| Very-Low-Frequency (VLF) Power | Spectral power in the very-low-frequency band (≤0.04 Hz). Unit: ms² | Baseline and Week 6 |
Percentage decline in knee extensor torque across the repetition set at 180°/sec on the non-dominant limb.
Unit: %
| Baseline and Week 6 |
| Dominant Knee Flexor Fatigue Index at 180°/s | Percentage decline in knee flexor torque across the repetition set at 180°/sec on the dominant limb. Unit: %. | Baseline and Week 6 |
| Non-dominant Knee Flexor Fatigue Index at 180°/s | Percentage decline in knee flexor torque across the repetition set at 180°/sec on the non-dominant limb. Unit: % | Baseline and Week 6 |
| Bilateral Deficit of Knee Extensors at 60°/s | Percentage asymmetry of knee extensor peak torque between dominant and non-dominant limbs at 60°/sec. Unit: % | Baseline and Week 6 |
| Bilateral Deficit of Knee Flexors at 60°/s | Percentage asymmetry of knee flexor peak torque between dominant and non-dominant limbs at 60°/sec. Unit: % | Baseline and Week 6 |
| Dominant Total Work Done H/Q Ratio at 180°/s | Ratio of knee flexor to knee extensor total work done at 180°/sec on the dominant limb. Unit: ratio | Baseline and Week 6 |
| Non-dominant Total Work Done H/Q Ratio at 180°/s | Ratio of knee flexor to knee extensor total work done at 180°/sec on the non-dominant limb. Unit: ratio | Baseline and Week 6 |
| Arterial Elasticity (AE) | Arterial elasticity index derived from second-derivative photoplethysmography. Unit: unitless | Baseline and Week 6 |
| Peripheral Elasticity (PE) | Peripheral elasticity index derived from second-derivative photoplethysmography. Unit: unitless. | Baseline and Week 6 |
| D005791 |
| Patient Care |
| D013812 | Therapeutics |
| D026741 | Physical Therapy Modalities |
| D064797 | Physical Conditioning, Human |
| D015444 | Exercise |
| D009043 | Motor Activity |
| D009068 | Movement |
| D009142 | Musculoskeletal Physiological Phenomena |
| D055687 | Musculoskeletal and Neural Physiological Phenomena |