Although this page is about shearers' back pain, it is just as applicable to farriers, carpenters, plumbers, bricklayers, floor tilers and gardeners - or anybody who works bent over double.
Hour for hour, shearing is the most taxing of all pastimes. A typical shearers' day involves four two hour shifts, where he (or she) is bent over for most of that time. They are paid for each sheep shorn and the shearing shed is a typically masculine environment where 'the gun' is revered for being the fastest. It usually takes between 2 to 2.5 minutes per sheep, although it takes longer to do the rams and wethers (the castrated male sheep) since they have a larger frame. A modern shearer gets through 40 sheep per hour in an 8 hour day. It is truly back breaking work.
After each sheep is shorn it is pushed down the chute to join the others below decks under the shearing shed. the next one is then selected from the pen behind and dragged out. The shearer positions the sheep between his legs on its back and makes his first grand shearing stroke ('blow') down the belly of the animal. The act of dragging the sheep out of the pen is a welcome respite for the back as he uses his back muscles strenuously in the upright posture to do this. This action partially counteracts the doubled-over forces of the shearing position.
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shearers' back pain is endemic to the shearing industry with 90% of shearers having trouble at some time. Mostly it stems from the sustained contraction of the hugely powerful back muscles (erector spinae). These long cable muscles either side of the spine compress the spinal segments - the vertebrae and the water filled gristle-pillows in between - the intervertebral discs. The compressive forces of the back muscles working around the convexity of the bent spine are much greater than gravity.
With shearing, the back muscles contract strongly around the curved spine to hold the body up
1. SUSTAINED CONTRACTION OF THE BACK MUSCLES
With shearing the back muscles work at a significant mechanical disadvantage, stretched around a hooped spine. The sustained clench of the muscles creates a stinging pain caused by the build-up of lactates in the muscle fibres. Although these chemicals are flushed away each time the shearer gets back upright when the muscles relax, with sheep after sheep the muscles get fatigued and don't switch off properly. This leads to problems with coordinated movement - first step towards back trouble - but it also makes the muscles themselves more achy and sore.
A deeper bend at the hips, literally 'hanging on the ligaments' (as shown by the shearer in the foreground in the pink shirt of the Tom Roberts painting above) puts less compression on the back. For freedom of hip bending however, the hamstrings need to be long. Trouble is, the hamstrings become less extensible and shorten at the first sign of back trouble, which explains why shearers often have sore, tight hamstrings making them restricted at the hips.
Usually, the rams are shorn last in the shed as they are heavier and larger-framed - harder to handle and tougher on the back
Once a back becomes irritated the back muscles stay switched on when the shearer stands upright after each sheep, giving him the typical chest-out-front-bottom-out-back appearance and the waddling gait of a back in trouble, or a problem brewing. Often this is associated with another pain in the middle-upper back from the bow-string action of the muscles pulling on the spine up higher.
Fitter shearers can offset spinal compression by stronger lower abdominal muscles. The lower abs work like an airbag inside the lower belly, helping the spine stay upright. You may like to read about back muscle anatomy for more information. You can also read a popular page here about best exercises for a lower abdominals.
All intervertebral discs lose fluid through the day but get most of it back at night when the spine is stretched out in sleep
2. PROLONGED BENDING DEHYDRATES THE LUMBAR INTERVERTEBRAL DISCS
Shearers bending double squeeze fluid from their intervertebral discs. Some of this is recouped when they stand up again after each sheep, as the spine pulls apart again and sucks fluid in. However, on balance they lose more than they gain during each session and their discs progressively dehydrate. At the end of the day all shearers' discs are flatter and they are considerably shorter in stature than when they started. Even we non-shearers lose about 20% of our discal fluid through the course of a normal day and go to bed some 2 cm shorter.
Excessive bending loads up the lumbar discs by 50% and squeezes more fluid out
3. PROLONGED BENDING SMOTHERS THE METABOLIC ACTIVITY OF DISCS
Intervertebral discs do not have a blood supply - indeed they are huge structures to get by without a blood supply! They are critically dependent upon rhythmic squash-and-suck pressure changes to circulate fluid to pull nutrient-laden fluids in and push waste products out.
Discs also need on-off spinal compression to keep metabolically healthy. Discs are naturally torpid and need the mechanical stimulation to keep their biological maintenance and repair processes in top working order. Sustained loading, caused by bending double, sends them to sleep. However, the good news for shearers is that sitting all day at a desk is much worse than shearing!
Because discs don't have a blood supply they're critically depended on the suck-and-squirt of spinal movement to circulate discal fluids
Although shearers are by no means static when they are bent forward, they nevertheless load up their lumbar discs and squeeze the life out of them. The choked down metabolic activity makes their back more brittle and vulnerable; impaired in its ability to throw off other incidental assaults common to all spines. Shearers' discs become extra-sluggish and wear out sooner, especially if they sit in a car and drive home after work. The sustained compression literally smothers the discs.
4. PROLONGED BENDING CAUSES ADAPTIVE SHORTENING OF THE HIP FLEXORS
Many shearers find it difficult to stand upright after each sheep. This is because their back muscles won't switch off properly, nor their hip flexors. They have to heave themselves up, almost with a hand in the bottom to winch themselves straight and when they get upright their back stays arched and their knees slightly bent.
The most dominant hip flexor - the psoas muscle - is so strong it adaptively shortens very quickly if it is put in a shortened position for too long. This pulls the belly forward and helps contribute to making the back bad. You will see in How to Fix Shearers' Bad Back that as well as decompressing the spine, using the BackBlock also gently eases out tight hip flexors.
Repetitive trunk twisting, in this case to the left, jams the lumbar facet joints on the right
5. TWISTING ONE-WAY ARM ACTION LOADS ONE SIDE OF THE BODY MORE
Shearing is a very one-way activity. With a right-handed shearer for example, the left hand controls the sheep but using the right arm, particularly with the long shearing strokes, involves a twisting action of the waist that rotates the lumbar vertebrae. There will be a closing-down action of all the facet joints down the right side of the low back, but particularly of the L5-S1 level at the base of the spine. At the same time, there is a push-off action with the right foot to help propel the right hand away. For this reason, most right-handed shearers have right-sided low back pain (conversely for left handers) involving this level.
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