EMG vs. EMS — Why the Electrode Positions Are Not the Same
EMG and EMS use electrodes on the skin over the same muscles — and that is where the similarity ends. Surface EMG records the microvolt-sized electrical activity a muscle produces when it contracts voluntarily; EMS/NMES delivers milliampere currents to make the muscle contract. Because the aims are opposite, so are the placement rules: EMG uses small electrodes 20 mm apart, parallel to the fibres, deliberately away from the innervation zone; NMES uses large pads, one of them over the motor point, to excite the nerve endings as efficiently as possible. The positions on EMG Guide are recording positions. They are not a pad chart for a stimulator.
Two techniques, opposite direction of current
Konrad's definition of kinesiological EMG: the study of muscle activation during voluntary posture, movement and training — the muscle is the source, the amplifier the listener. In electrical stimulation the device is the source and the muscle the receiver. Everything about electrode design follows from that:
| Surface EMG (recording) | EMS / NMES (stimulation) | |
|---|---|---|
| Signal | µV from the muscle to the amplifier | mA from the stimulator into the tissue |
| Electrode size | small (≤ 10 mm conductive diameter, SENIAM) for selectivity | large pads (several cm²) to spread current and stay comfortable |
| Number and geometry | bipolar pair, 20 mm centre-to-centre, parallel to fibres, plus reference | typically two pads per muscle: one over the motor point, one distal or proximal along the muscle |
| Relation to innervation zone / motor point | avoid it — amplitudes cancel there | target it — lowest threshold, strongest contraction |
| Goal of positioning | reproducible, selective, artifact-free measurement | efficient, comfortable, strong contraction |
| Skin preparation | abrasion + alcohol to lower impedance for a clean signal | clean skin; abrasion less critical, comfort more |
| Standard | SENIAM (Hermens et al. 2000), Cram's atlas | motor-point maps (Botter et al. 2011), manufacturer charts |
What the motor point is — and why EMG stays away from it
The motor point is the skin location where an electrical pulse elicits a visible muscle twitch at the lowest current — the point closest to where the motor nerve enters and branches into the muscle, usually over the innervation zone. Gobbo and colleagues showed that placing the NMES electrode on the motor point, rather than on a "standard" position, gives stronger contractions at lower and more comfortable currents; Botter et al. mapped the motor points of the lower-limb muscles for exactly this purpose.
For EMG the same spot is the worst possible place. Over the innervation zone the action potentials travel away in opposite directions and partly cancel at the bipolar pair — the amplitude is small and unstable (why the electrode must not sit on the innervation zone). Cram's, following Fridlund & Cacioppo: avoid straddling the motor end-plate region. SENIAM's landmark fractions are chosen to keep the pair between innervation zone and distal tendon.
So for the Rectus Femoris, an NMES pad chart puts one electrode over the motor point in the proximal-to-mid thigh and a second more distally; the SENIAM EMG pair sits at 50 % of the line from the anterior superior iliac spine to the superior patella border, 20 mm apart, both electrodes on the same side of the zone. Similar for the Vastus Lateralis, Gastrocnemius (Medial Head), Gluteus Maximus and Tibialis Anterior: same muscle, different logic, different spot.
Can EMG and EMS be combined?
Yes, in two ways — and both need the positions kept apart:
- EMG-triggered stimulation. The patient initiates a voluntary contraction, the EMG detects the onset above a threshold, and the stimulator adds current to complete the movement. The detection pair and the stimulation pads sit on the same muscle but in different places, and the amplifier is blanked during the pulse.
- Assessment before/after NMES training. EMG documents voluntary activation (e.g. % MVC, timing) between stimulation sessions. Record with the SENIAM pair, stimulate with the pads — do not reuse one set of electrodes for both.
Recording during stimulation is a special case (stimulation artifacts dwarf the EMG by orders of magnitude) and needs dedicated hardware and artifact-blanking algorithms.
Where to find each
- EMG recording positions: the 106 muscle pages on EMG Guide — position, orientation, starting posture and test movement, following SENIAM or a named peer-reviewed source, plus the crosstalk and artifact notes.
- NMES motor points: motor-point maps such as Botter et al. 2011 for the lower limb, and the pad charts supplied with the stimulator. Do not derive them from an EMG guide.
Muscles referenced in this article
From placement to measurement
EMG Guide shows where the electrodes go. easyEMG with PicoBlue sensors visualises the signal live afterwards — SENIAM-conform, in real time, with a signal check on screen.
Frequently asked questions
Can I put my EMS pads where EMG Guide shows the electrodes?
You can — it will not harm — but it will not be the optimal stimulation position. EMG positions are chosen to avoid the motor point; NMES pads work best on it. Use a motor-point map or the stimulator's chart.
Can I record EMG with EMS pads?
No. Stimulation pads are large and usually carbon or hydrogel with high impedance; they average over a big area, pick up neighbouring muscles and give no reproducible bipolar geometry. Use small Ag/AgCl electrodes 20 mm apart.
Are the electrodes themselves interchangeable?
Not in practice. EMG electrodes are small pre-gelled Ag/AgCl snaps optimised for low, stable impedance; NMES pads are large, reusable, designed for current density and comfort. Some clinical systems accept both on separate channels — the electrodes remain different.
Is "electrode placement" on EMG Guide the same as in the EMS app I use?
No. The words are the same; the intent is opposite. If your app shows two large pads with one "on the belly", it is a stimulation chart. EMG Guide shows a bipolar recording pair off the innervation zone.
Sources
- Konrad P. The ABC of EMG. Noraxon; 2005 — p. 4 (definition: kinesiological vs. neurological EMG), p. 18 (motor point regions).
- Hermens HJ et al. SENIAM sensor and sensor placement recommendations. J Electromyogr Kinesiol. 2000;10:361–374.
- Gobbo M, Maffiuletti NA, Orizio C, Minetto MA. Muscle motor point identification is essential for optimizing neuromuscular electrical stimulation use. J NeuroEng Rehabil. 2014;11:17.
- Botter A, Oprandi G, Lanfranco F, Allasia S, Maffiuletti NA, Minetto MA. Atlas of the muscle motor points for the lower limb. Eur J Appl Physiol. 2011;111:2461–2471.
- Criswell E. Cram's Introduction to Surface Electromyography. 2nd ed. 2011 — Ch. 4 (p. 70, motor end-plate region).
Read next
EMG Electrode Placement — The Practical Guide
How to place surface EMG electrodes correctly — SENIAM rules, skin prep, 20 mm spacing, fibre direction, reference electrode, signal check and common mistakes.
Why the Electrode Must Not Sit on the Innervation Zone
What the innervation zone is, why a bipolar pair over it gives small, unstable EMG amplitudes, how SENIAM avoids it, notorious muscles, and how to spot it.
Surface EMG Glossary
54 terms of surface electromyography explained in one sentence each — from amplitude cancellation to volume conduction. With sources (SENIAM, Cram's, Konrad).
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