Leave the farm motorbike in the shed and walk as often as you can.

That is the blunt advice from Dr Stephan Milosavljevic from the University of Otago's School of Physiotherapy.

The rural-based clinician and researcher has become increasingly concerned about the effects of prolonged vibration exposure on farmers who are constantly using ATVs or quad bikes. His research shows that a farmer using an ATV for as little as an hour per day is exposed to maximum levels of low-frequency, whole-body vibration.

Dr Milosavljevic says the economic reforms of the 1980s brought changes to farming practices, with many farmers forced to get rid of workers and increase their own workload dramatically by using more equipment. "One of the big things they latched onto was quad bikes and a lot of farmers will tell you that they couldn't farm without their ATV because they've allowed them to increase productivity massively."

While farmers are most likely to injure their back by awkward lifting, Dr Milosavljevic looked at why recurring injury and pain was not fully subsiding. He realised farmers spent a lot of time on quad bikes – two-to-three hours most days and up to 10-hours during lambing.

Thirty South Otago farmers participated in the study. The researchers mounted sensors on the bike to measure vibration from the motor and the terrain; they mounted another on a helmet worn by the farmer.

"We can say that in one hour of constant riding an ATV on a farm, the farmers approach the international ISO threshold levels for maximum acceptable levels of vibration," Dr Milosavljevic says.

While the bike generated a whole spectrum of frequencies from zero to 100hz, it was the 2-12hz frequencies that travelled through the spine to the head. The body can't absorb these low-frequency vibrations and the spine actually starts shaking and vibrating in a way it cannot control.

Dr Milosavljevic says the vibration itself doesn't necessarily always do major damage. "It may be that the vibration cause changes in the physical capacity of the structure of the spine to handle load. So a farmer has been vibrated and shaken around on his bike, then he struggles with a sheep and hurts his back. It's a wicked combination. Exposure to vibration and then being asked to lift a substantial physical load is a recipe for disaster."

Research to date is based on field observations – meaning the spine can't be examined to see what damage is being done. The research team is now collaborating with Assoc Prof Jack Callaghan and Prof Stuart McGill at the world-renowned Spine Biomechanics Laboratory at the University of Waterloo in Canada, who have developed a successful model using pig spines. Parts of the pig's spine have similar structural and biomechanical properties to the human lumbar spine. Fresh specimens of pig spine can be put in a special jig and exposed to the same vibrations, loads and postures they have recorded in the field, to get an estimation of what is happening to the human spine when riding an ATV.

"From that we will get an indication of structural change and structural damage," says Dr Milosavljevic.

Meanwhile, they have also surveyed the farmers looking at a whole range of personal, physical and social factors in the way they farm that might be related to this exposure and the demands of work. That data is yet to be analysed.

Dr Milosavljevic says the best advice he can give farmers is to get off their bikes. "And the simplest thing is to walk. Walk to get your mail. Walk to get your paper. Walk to your woolshed. Walk some of the short distances," he says. "Walking does not cause any serious damage. In fact it is a healing activity - your spine enjoys it."

Dr Milosavljevic and co-researcher Dr Allan Carman are carrying out this research with support from a University of Otago Research Grant.