Do Bits Cause Pain? Rein Tension and Bit Pressure in Horses

---

This 2025 study compared rein tension and bit pressure in horses to known human pressure pain thresholds. The key finding: most commonly reported rein pressures in equestrian sport exceed the level at which humans would perceive pain, and higher ranges could reach levels associated with severe pain or even tissue damage. Only the lowest rein tensions would likely be pain-free if applied to a human face or hand.

---

Bit pressure and rein tension are increasingly discussed in equine welfare science because the bit sits in the interdental space of the horse’s mouth, an area rich in nociceptors (pain receptors). Research has also documented oral lesions and pain-related behaviors associated with bit use, raising ongoing welfare questions in sport and training.

Because horses cannot verbally report pain and often mask discomfort as prey animals, researchers use comparative models to better estimate what certain pressures might feel like.

Overview: Comparing rein pressure to human pain thresholds

This article used a translational approach rather than a live experimental trial. Researchers:

• Reviewed published data on rein tension and bit pressure in equestrian sports

• Compared those values (in kPa) to established human pressure pain detection thresholds (PPDT) for the face, hand, and foot

• Used human quantitative sensory testing (QST) data as a reference, since pain physiology (nociception) is broadly similar across mammals

Reported rein tensions ranged widely—from about 91 kPa (low) to over 4000 kPa (maximum), while human pain detection thresholds are much lower (e.g., ~232 kPa for the face).

Comparing Rein Pressure to Human Pain Thresholds. This graph overlays reported rein tension values (red lines) against the human pain response function for pressure on the shin bone (black line). Notably, the maximum rein tensions recorded in some studies far exceed the pressure at which humans reach their pain tolerance threshold. These data suggest that "normal" rein aids can easily cross the line from a signal to a painful stimulus.

Key takeaways: What the research suggests about bit pressure and pain

• Most average and maximum rein tensions exceed human pain detection thresholds

• Only very light rein tensions would likely be considered non-painful if applied to humans

• Pressure levels commonly reported in riding could produce mild to severe pain sensations in a comparable mammalian system

• Some pressure ranges used in equestrian sport exceed limits considered ethically acceptable in human pain research

• Horses may suppress signs of pain, meaning quiet behavior does not equal comfort

The discussion also notes that prey animals like horses may tolerate or mask pain rather than express it openly, which complicates welfare assessment.

How to apply this to your riding, training and equipment choices

For riders, trainers, and owners, this research does not say “never use a bit.” Instead, it highlights the importance of pressure awareness and ethical contact.

• Aim for light, elastic rein contact rather than sustained pressure

• Watch for conflict behaviors (mouth opening, tongue activity, tension) as possible indicators of discomfort

• Prioritize training that improves self-carriage and balance, reducing reliance on rein pressure

• Reassess fit and function of bits, nosebands, and hands together, not in isolation

• Remember that bitless bridles also apply pressure (often on the nasal bone), so pressure management still matters

From an equine biomechanics and welfare perspective, the goal is not zero contact, but clear communication with minimal necessary pressure.

Read the original study

Musial F, Weiss T. What if Horses Were Humans? Comparing Rein Tension and Bit Pressures to Human Pressure Pain Thresholds. Animals. 2025; 15(20):2989. https://doi.org/10.3390/ani15202989