Quick Overview
A Fudan University team published a 12-week Sensors trial on 30 national male freestyle swimmers.
Half added 3 minutes of 50 Hz NMES, a form of EMS, before fin kick sets.
Underwater sEMG at 2000 Hz and 200-fps video tracked iEMG, RMS and synergies.
EMS lifted glute iEMG 60.08–72.85 and downward biceps iEMG 39.76–48.69.
Biceps propulsion weight rose 0.56–0.87. Posture synergy duration dropped 0.69–0.37.
Peer-reviewed work from a top Chinese lab, issued in Switzerland, is why this holds weight.
Those figures suggest EMS can help national swimmers and other trained athletes.
Read the full post for every protocol detail.
We always provide direct links to the original research at the end of every article so you can review the evidence yourself.
Electric Boost: Short EMS Sessions Helped National Swimmers Fire More Muscle in the Freestyle Kick
A new swimming study asked a simple training question.
Could a brief burst of EMS before kick work help elite swimmers use their legs better?
Researchers at Fudan University in Shanghai tested that idea.
Fudan is one of China’s leading research universities.
The paper was published in the peer-reviewed journal Sensors.
The publisher is MDPI, based in Basel, Switzerland.
The trial followed standard ethics rules and the Declaration of Helsinki.
This was not a gym advert.
It was a 12-week controlled training study in high-level athletes.
Who took part
Thirty national-level male freestyle swimmers joined the trial.
They were classed as highly trained under a published athlete framework.
Average age was 22.8 years.
Average height was 181.5 cm.
Average body mass was 72.3 kg.
They had about 10.5 years of training behind them.
All held National Class 1 status or higher.
Each had a top-three finish at China’s national long-course championships.
What the two groups did
The swimmers were split at random into two groups of 15.
Both groups trained three times a week for 12 weeks.
Every session included water-based resistance kicking with short-bladed fins.
They swam 4 x 25 m hard freestyle kick sets.
Rest was 2.5 minutes between sets.
Coaches stressed a hip-driven whip kick.
One group did that water work only.
The other group first received NMES, a form of EMS, on land.
The stimulator was a pad based (as described on the paper)
Pads sat on the vastus medialis, vastus lateralis, and biceps femoris.
Settings were 50 Hz and a 200 µs pulse width.
Each burst lasted 10 seconds on and 30 seconds off.
Total stimulation time was only 3 minutes.
Intensity sat at 80–90% of the highest level they could tolerate.
They then entered the water within 5 minutes.
How the scientists measured progress
This was not a guess from the pool deck.
The team recorded muscle activity underwater.
They used waterproof surface EMG sensors sampling at 2000 Hz.
A high-speed camera filmed the kick at 200 frames a second.
The systems started together with a shared trigger.
Each swimmer also did a maximum voluntary contraction test.
That let the team compare later kick signals against a true max.
They then measured two classic EMG scores.
iEMG tracks total electrical activity over time.
RMS tracks how hard the muscle is firing.
They also used non-negative matrix factorization.
That method finds muscle synergy patterns.
In plain terms, it shows which muscles work together, and when.
One full kick cycle was taken from the middle of a 25 m sprint.
That kept the data fast, clean, and away from the wall.
What the numbers showed
After 12 weeks, the EMS group showed bigger jumps in key leg muscles.
In the upward swing, iEMG rose more in the EMS group for several prime movers.
Gastrocnemius lateralis moved from 69.52 to 82.04.
Adductor longus moved from 69.73 to 86.12.
Adductor magnus moved from 66.54 to 88.31.
Gluteus maximus moved from 60.08 to 72.85.
Those group-by-time differences reached statistical significance.
The p-values were 0.010, 0.021, 0.011, and 0.035.
RMS told the same story in the up-swing.
Adductor magnus rose from 99.42 to 129.75 in the EMS group.
Gluteus maximus rose from 88.36 to 111.38.
On the downward kick, biceps femoris iEMG rose from 39.76 to 48.69 with EMS.
That interaction effect was significant at p = 0.013.
The tibialis anterior did the opposite in the EMS group.
Its downward iEMG fell from 68.50 to 56.19.
The authors read that as a cleaner, less fussy ankle pattern.
Coordination got sharper too
The kick still used about three main muscle synergies.
The number of synergies did not change much.
The inside of those synergies did change.
In the core propulsion synergy, muscle weighting rose for key drivers.
Biceps femoris weighting in that module rose from 0.56 to 0.87 with EMS.
The interaction effect was significant at p = 0.035.
The postural synergy got shorter and snappier.
Its activation duration in the EMS group fell from 0.69 to 0.37.
That change was significant at p = 0.020.
In the same postural module, tibialis anterior weighting dropped from 0.80 to 0.39.
The authors describe this as proximal drive going up.
Distal fuss went down.
That fits a stronger hip-led whip kick.
What this means in the pool
The study compared EMS plus water kick training with water kick training alone.
The extra EMS block was short.
It still tracked with higher measured activation in the big kicking muscles.
It also tracked with a tighter coordination pattern.
Prime movers carried more of the propulsion module.
The posture module switched on for less time.
The paper’s own conclusion is direct.
The combined plan “enhances muscle activation and optimizes neuromuscular coordination strategies.”
Who this may interest next
The athletes here were national-level men.
That is a high bar.
The measured changes were in muscle drive and timing, not medals.
Those building blocks matter in any serious kick set.
Club swimmers, age-group coaches, and other stroke specialists may still pay attention.
The protocol was specific.
It was brief EMS, then hard kick work in water, repeated for 12 weeks.
It does not prove the same numbers in every swimmer.
It does show a clear extra signal in elite freestylers when EMS was added to the same water plan.
The honest limit
The scientists flagged one design wrinkle themselves.
Post-testing in the EMS group followed a combined session.
The control group finished a water session only.
Some of the last readings may include an acute priming effect.
That does not erase the 12-week training record.
It does mean future trials should match the pre-test routine more tightly.
The bright takeaway
This paper did not sell a miracle.
It measured muscle electricity, timing, and synergy in the water.
National freestylers who added a 3-minute EMS primer to kick training showed stronger signals in key legs muscles.
They also showed a more focused propulsion pattern.
For coaches hunting a sharper flutter kick, that is the useful line.
Water work built the skill.
A short EMS burst before the set tracked with more measured fire in the muscles that drive the kick.
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Research Summary
| Detail | Summary |
|---|---|
| Full paper title | Effects of NMES Combined with Water-Based Resistance Training on Muscle Coordination in Freestyle Kick Movement |
| Original study links | Publisher page: mdpi.com/1424-8220/26/2/673 · DOI: https://doi.org/10.3390/s26020673 · PubMed: pubmed.ncbi.nlm.nih.gov/41600469 |
| Journal and publisher | Sensors 2026, 26(2), 673, published by MDPI, Basel, Switzerland |
| Research home | Fudan University, Shanghai: School of Mathematical Sciences and Faculty of Physical Education |
| Authors | Yaohao Guo, Tingyan Gao, and corresponding author Jun Liu |
| Study purpose | Test whether brief NMES (a form of EMS) before aquatic kick training changes muscle activation and coordination in the freestyle kick |
| Design | 12-week randomised controlled trial, 3 supervised sessions a week, experimental group versus control |
| Athletes studied | 30 national-level male freestyle swimmers; mean age 22.8 ± 3.2 years; height 181.5 ± 5.1 cm; mass 72.3 ± 4.7 kg; 10.5 ± 2.8 years of training |
| Training compared | Control: aquatic resistance kicking with short-bladed fins only. Experimental: 3 minutes of land NMES, then the same fin-kick sets |
| EMS protocol measured | Compex SP 8.0; 50 Hz; 200 µs pulse width; 10 s on / 30 s off; 80–90% tolerated intensity; pads on vastus medialis, vastus lateralis, and biceps femoris |
| How scientists measured | Waterproof sEMG at 2000 Hz, GoPro video at 200 fps, MVC normalisation, then iEMG, RMS, and NMF muscle-synergy analysis |
| Kick test | 25 m maximal freestyle kick with a kickboard; one mid-pool cycle from the fastest trial was analysed |
| Activation evidence | Experimental iEMG rose in key up-swing muscles, including gluteus maximus 60.08 to 72.85 and adductor magnus 66.54 to 88.31 |
| More activation evidence | Downward-phase biceps femoris iEMG rose 39.76 to 48.69 in the EMS group (interaction p = 0.013) |
| Intensity evidence | Up-swing RMS for adductor magnus rose 99.42 to 129.75; gluteus maximus RMS rose 88.36 to 111.38 |
| Coordination evidence | Core propulsion weighting for biceps femoris rose 0.56 to 0.87 (p = 0.035); postural synergy duration fell 0.69 to 0.37 (p = 0.020) |
| What did not change | Average number of synergies stayed near 3 (experimental 2.90 to 2.90; control 3.10 to 3.00) |
| Authors’ reading | Adding NMES to water kick training tracked with higher prime-mover firing and a tighter propulsion pattern than water training alone |
| Why the source is checkable | Open-access, peer-reviewed paper; ethics approval Fudan protocol 20251122; received 15 Dec 2025; published 20 Jan 2026 |
| Stated limit | Post-tests followed an NMES-plus-water session in the experimental group and water only in controls, so some readings may include an acute priming effect |
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