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The news that cat purrs can heal bones have been circulating on the net for some time.

It started from Elizabeth von Muggenthaler's research, who used accelerometers to measure the frequencies of cat purrs. Paula Peterson interviewed Elizabeth and wrote about it in her web site Earthcode. Paula said: "Elizabeth has gone where no man (or woman) has gone before into the mysterious realm of the healing power of a cat's purring, the haunting whale-song of the Sumatran rhino, and about the sounds that we feel but never hear. She is also president of Fauna Communication Research Institute, where amazing breakthroughs are being made that may forever change the way we listen to the animals."

But is it true that cat purrs can heal bone injuries and osteoporosis, or is it just another old wives' tale, like "a cat has nine lives", or more like the folklore taught in veterinary schools: "Put a cat in a room with a bunch of broken bones — the bones will heal" ?

Why do cats purr?
Cats purr when being stroked by humans, leading to the idea they purr because they are content (In English, "purring with content" is a common expression). But they also purr when in pain or injured. Elizabeth believes that cat purrs must have a survival value for the cats in general.

Cats and dogs
It is a fact that cats suffer much less bone injuries than dogs. Cats have been known to fall from high rise buildings and survived. The record is a fall from the 45 th building level. The average height of cat falls studied is 5.5 floors, and 90% of them survived. (Whitney, W., and Mehlhaff, C., (1987) the Journal of the American Veterinary Medical Association).

Healing frequencies
Various researchers have found that low frequencies at low dB are helpful with regard to pain relief, and the healing of tendons and muscles.

Some of the reported results are:
50 - 150 Hz chronic pain
20 - 50 Hz increase bone density
120 Hz counters muscle atrophy
100 Hz decrease dyspnea in patients with chronic obstructive pulmonary disease

Elizabeth summarizes: "Vibrations between 20-140 Hz are therapeutic for bone growth/fracture healing, pain relief/swelling reduction, wound healing, muscle growth and repair/tendon repair, mobility of joints and the relief of dyspnea".

Cat harmonics
Returning to cat purrs, Elizabeth measures cat purr frequencies, including those of cheetah, puma, serval, ocelot and the domestic house cat. The dominant frequencies are 25 and 50 Hz, which are the best frequencies for bone growth and fracture healing. The harmonics are close to 120 Hz, found to repair tendons.

Another report by T.F. Cook mentioned: A dying cat who could not breath (they were considering euthanasia), was found to breath normally once it began purring. The purring opened up the cat's airway, and improvement was "remarkable and the next day commenced to eat...." Three species of cats have a strong harmonic at exactly 100 Hz, the vibrational frequency found to relieve dyspnea. One species within 2 Hz and one species within 7 Hz of 100 Hz. It could be that the cat's purr decreases the breathlessness by vibratory stimulation.

Putting two and two together
If we put the above together, about the healing frequencies, and the purr frequencies, can we then say that cat purrs heal bones? There are certainly indications in that directions, but a more thorough research is required.