Shearing through the back pain

Dr Stephan Milosavljevic: Using a back harness reduces the forces on a shearer’s spine by a significant 25-30%.

17-03-2010 | Robert Pattison

As shearers expertly remove another fleece the toll on their backs is probably the last thing on anyone's mind.

However, University of Otago research confirms traditional sheep shearing is one of the most physically demanding occupations in New Zealand. Recent research shows the cumulative load on shearers' backs is six times greater than rest-home workers and four times greater than automotive assembly plant workers.

This study of 80 shearers pointed to a gradual deterioration of their spines. The loss of flexibility averages about 7.6%/year, meaning their risk of lower back injury is four to six times greater than other industrial workers.

Senior Lecturer at the university's Centre for Physiotherapy Research, Dr Stephan Milosavljevic, says it was a jaw-dropping moment when he presented his research findings for the first time to spinal researchers in Canada in 2004. "They could not believe a physically demanding job such as sheep shearing existed."

A shearer shearing 300 sheep a day, each weighing 60-80kg, is catching, lifting and dragging on average 20,000kg in eight hours. "That is a huge load and stress on a person's body."

It is common for shearers to have a high prevalence of occupational lower back pain (LBP) and musculo-skeletal injury. The two main risk factors are the forces required to control unco-operative sheep and the prolonged period of forward trunk flexion. A third factor is that shearers tend to cope with back pain.

They are paid per sheep shorn which motivates them to ignore the LBP and get on with the job. Continuing to shear while in pain continues to produce considerable stress on the lower back.

Woolhandlers have similar stresses, but at about half the cumulative load compared to shearers.

Milosavljevic says that between 1994 and 2006, claims for back injury compensation in NZ cost $5 million for a working population of about 2000 full-time shearers. It has been calculated that back injuries to shearers cost the Australian wool industry A$76.4m/year, or 15.9% of the labour cost of shearing (Bentley 1993).

He says that to minimise the risk of back injury when bent over shearers should keep their spine symmetrical (in line) and walk around the sheep - obviously using their legs as much as possible. Research also shows that using a back harness reduces the forces on a shearer's lower back by 25-30% and also helps reduce injury risk.

Shearers do adapt to the job. They lose about 30% of their ability to extend backwards after about 10 years, but they also gain 30% more flexibility when leaning forward. They also often experience discomfort when standing in one position for long periods. "The problem is that there is only one joint at the base of the spine. The large lumbar vertebrae and the L5/S1 disc is exposed to all the risk. It's like a big-end bearing in a motor, it's the one thing that will fail if it isn't maintained and looked after," Milosavljevic says.

The aim of the research was to determine what effect shearer skill level has on cumulative spinal loads over time.

Milosavljevic and his team monitored the time shearers spent in different trunk postures throughout a working day. They also surveyed shearers, asking if they had a history of LBP that had required treatment from health professionals. The responses showed 46% had suffered from back pain before seeking treatment, implying 54% hadn't.

Milosavljevic says young people tend to think they are bullet proof. They do things that expose them to a higher risk of musculo-skeletal injuries. "Young males, for example, will drive four wheelers over rough terrain at high speeds. Damage from the constant jarring will cause them LBP in later life."

The survey of 20 junior, 20 intermediate, 20 senior and 20 open-class shearers identified that LBP was related to the cumulative spinal loads and trunk postures they had worked in over a 10-year period.

Improved shearing skill levels over the same period resulted in a 100% increase in productivity or daily tallies. The downside is that there was a gradual deterioration in flexibility (7.6%/yr) as a result of the considerable load on the spine from bending forward for long periods each day.

The average daily tally was 198 sheep for the junior shearers and 396 sheep for the open-class shearers.

The shearers who had experienced LBP before requiring treatment bent forward and applied the same amount of force to their spine as those without pain.

Milosavljevic says this implies the compressive load force on their spine was the same.

The study showed there was a difference between individual shearers in the style and technique they adopted when shearing their sheep. The shearers suffering from LBP tended to twist their spine from the pelvis more than the shearers without back pain. Another difference was that the shearers without pain adopted a more symmetrical shearing style and technique and used their legs more to move around the sheep.

Legs are better designed to generate the forces and energy required when shearing a sheep. This suggests skills-based training programmes which teach shearers to keep their spine symmetrical while shearing will help minimise the risk of injury. On the other hand, Milosavljevic says refining the traditional stooped shearing techniques and styles is unlikely to reduce the high level of back injury risk by any great margin

Using a back harness reduces the forces on a shearer's spine by a significant 25-30%.

Shearers could also change their habits when they are not working. The more time a shearer spends bending forward, the longer it takes to counter the compression effect on their spine. Lying on their stomach and arching their back, or walking, during rest periods is better than sitting. Eliminating the catch and drag process would also help.

Milosavljevic says preliminary studies of an upright posture shearing platform (UPSP) would suggest shearing tables are the Holy Grail for the shearing industry. UPSPs offer the greatest promise for a considerable reduction in back injury risk. They reduce the forces and stresses on a shearers back by a massive 60-70%.

However, the study also showed that using a UPSP also doubled the time to shear a sheep. The shearers involved in the study had no previous experience of working on a UPSP. However manufacturers of UPSPs say that after training, familiarisation and practice some shearers can increase their daily tallies by as much as 10%.

Perhaps the challenge for the future is to train shearers to rethink how they shear sheep on shearing tables.

Another issue to consider is whether there will be an increased risk of shoulder injuries from adopting the UPSP technology, Milosavljevic says.

There has been extensive research and investment in UPSP development. Various forms of UPSPs have been available in Australia and NZ for about 40 years. 

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