TENS While Stretching: Does It Improve Range of Motion?

Using a TENS unit while you stretch probably will not increase your range of motion beyond stretching alone—at least not in the one direct trial we have. In a 2025 randomized controlled trial, healthy active adults improved hamstring flexibility after one session of static stretching whether they stretched alone, stretched with TENS, or stretched with NMES. The groups did not differ significantly (P=0.255; partial η²=0.063).

That result disappoints a tidy biohacking theory. TENS might reduce discomfort at the end of a stretch, allowing a person to tolerate more range. NMES might alter reflex-driven resistance through muscle activation and fatigue. Both ideas have plausible physiology behind them. Plausibility, however, is not a substitute for a larger range on the goniometer.

The direct test found no acute bonus

Gunaydin et al. (2025) randomly assigned 45 healthy, physically active participants to one of three groups: static stretching alone, static stretching plus transcutaneous electrical nerve stimulation (TENS), or static stretching plus neuromuscular electrical stimulation (NMES). Each group had 15 participants, and the study measured immediate hamstring range-of-motion changes after a single session.

All three groups improved within the session (P<0.001; η²=0.356). That is the useful finding for anyone trying to become less stiff today: the static stretching itself worked. Adding either form of electrical stimulation did not produce a statistically significant difference between groups. The study also found no significant between-group difference in performance outcomes (P=0.062).

The partial η² of 0.063 sits around the conventional lower boundary for a medium effect, so the trial cannot rule out a small added effect. But the study did not show one, and it gave no evidence of an added change large enough to justify calling TENS or NMES a flexibility accelerator.

The best direct evidence says that one bout of TENS or NMES does not make static hamstring stretching work better in healthy active adults.

Why electrical stimulation seemed like a reasonable idea

The hypothesis was never absurd. Saito et al. (2023) studied patterned electrical sensory nerve stimulation paired with static stretching and provides a useful framework for how electrical input could affect range of motion and passive torque. The proposed pathways include reduced muscle-tendon-unit stiffness, greater stretch tolerance through sensory pain modulation, and altered stretch-reflex sensitivity.

TENS is often discussed through gate-control theory: activating large sensory fibers may reduce the unpleasantness of end-range discomfort. If discomfort limits a stretch before tissue resistance does, less discomfort could let someone move farther. NMES creates muscle contractions, so it could theoretically influence motor-unit recruitment, fatigue, or reflex-mediated resistance.

But Saito's protocol used patterned electrical sensory nerve stimulation, or PESNS. It was designed specifically to engage sensory pathways and is not interchangeable with the waveform from a consumer TENS unit. Consumer devices differ in frequency, pulse width, intensity, and electrode placement. Mechanistic findings from PESNS therefore explain a possibility; they do not validate every device with two adhesive pads and an optimistic product listing.

Positive NMES-plus-PNF findings do not settle the question

A second randomized trial, Sos-Tirado et al. (2025), reported short-term hamstring-flexibility improvements when youth basketball players used NMES with proprioceptive neuromuscular facilitation (PNF) stretching. This result is interesting, but it does not overturn the static-stretching trial.

PNF differs from passive static stretching because it includes an active contraction. Its proposed effect on flexibility includes autogenic inhibition through Golgi tendon organ pathways. PNF itself can improve hamstring range of motion; a 2023 randomized trial in amateur athletes found that PNF and foam rolling both improved hamstring flexibility. When NMES and PNF appear together in one intervention, the design cannot isolate how much, if any, of the benefit came from NMES.

The two trials also studied different populations, stretching methods, and intervention packages. Treating a positive NMES-plus-PNF result in young basketball players as proof that NMES enhances ordinary static stretching would answer a question neither study directly tested.

Stretching has evidence; the add-on does not

Static stretching remains the part of the routine with demonstrated acute value in the direct trial. Broader evidence also supports stretching as a way to improve range of motion, although outcomes depend on context. Afonso et al. (2021) systematically reviewed randomized trials of post-exercise stretching and assessed range of motion alongside strength recovery and delayed-onset muscle soreness.

Repeated stretching can also produce changes that a one-session study cannot capture. In older adults, Nakamura et al. (2024) reported that a 10-week static-stretching program performed at least three times weekly improved ankle dorsiflexion range of motion and reduced medial-gastrocnemius tissue hardness. The protocol used four 30-second stretches. A separate 2021 study by Nakamura and colleagues found training and detraining changes in ankle dorsiflexion range of motion and medial-gastrocnemius stiffness after a five-week high-volume static-stretching program.

Those studies matter because they show that consistent stretching can change flexibility-related outcomes over weeks. They do not show that electrotherapy speeds those adaptations. No controlled multi-week trial has tested TENS or NMES added to a structured stretching program against stretching alone.

What the evidence does not cover

Gunaydin and colleagues studied a single session in healthy, physically active people. It cannot tell us whether using TENS or NMES for several weeks changes cumulative range-of-motion gains. The study was also small for a three-arm comparison, with 15 people per group. A larger trial might detect a small difference, but a detectable difference still needs to be large enough to matter in practice.

The available publication details also do not report the stimulation frequency, pulse width, intensity, electrode placement, or session duration. That prevents replication and makes it impossible to know whether a different parameter set would produce another result. Low- and high-frequency TENS do not engage the body in identical ways, and NMES effects depend heavily on intensity and duty cycle.

Just as important, all controlled electrical-stimulation-plus-stretching evidence here concerns hamstrings. It does not establish benefits for ankle dorsiflexion, plantar flexors, hip flexors, or lumbar muscles. Static stretching has been studied at the ankle—for example, a randomized trial in children with spastic cerebral palsy found acute ankle range-of-motion gains after static or PNF plantar-flexor stretching—but that is clinical stretching research, not evidence for pairing ankle stretching with TENS or NMES.

A practical verdict

If you already use TENS while stretching because it feels more comfortable, the current evidence does not show that this is harmful or pointless as a comfort practice. It may help some people tolerate an end-range position or spend more time stretching. That remains a hypothesis, not a demonstrated electrotherapy effect on range of motion.

Do not buy a TENS or NMES unit expecting extra flexibility from a single stretching session. Stretch consistently, use a tolerable intensity, and judge the device separately by whether it improves comfort or symptom management for you. The only direct randomized trial found that the stretch—not the electrical add-on—accounted for the immediate hamstring range-of-motion gains.