‘Arm pump’ is a compartment syndrome ‘overuse’ type injury. In that respect it is quite unusual in motorcycle racing, as the majority of injuries are traumatic in nature. It seems to be more commonplace in motocross, yet the list of elite riders who have suffered from this complaint includes:
Toni Elias, Sylvain Guintoli, Nicky Hayden, Chris Vermuelen, John Hopkins, Makoto Tamada, Marco Melandri, Kenny Roberts Jnr, Jorge Lorenzo and even Casey Stoner.
It exists due to the complex coordination necessary at the hands, wrists, elbows, shoulders and spine required to control a high powered motorcycle.
It must be differentiated from Acute compartment syndrome (where symptoms do not go away with rest), which is a normally caused by injury and is a true emergency. There may be permanent muscle damage in acute compartment syndrome unless surgically treated in less than six hours. It has been discovered when testing canine muscle that fewer than 5% of muscle cells were damaged after 4 hours of ischemia, while nearly 100% of muscle cells were damaged after 8 hours of ischemia.
CECS is not unique to motorcycle racing, it has also been reported in rock climbers (Schoeffl et al 2004), windsurfers (Segura et al 2005) and manual workers (Soderberg 1996).
CECS is prevalent in all racing classes, though barely in the 125gp class where there are riders as young as 13 years old, and the machines lighter. We conduct an audit of our service each year (fig 1 below), and it would appear that the more powerful and heavier the machine the greater the incidence of CECS.
Fig 1 Armpump distribution by class by round 2010
Muscles are held in fascial sheaths. Fascia is a tough, but thin, white gristle that envelops the compartment like a casing wraps a sausage. Fascia helps to anchor muscles and give them form. Fascia is very strong, but it is not very elastic. The inelasticity of fascia surrounding muscle means that even small increases in the volume of a fascial compartment can cause large pressure increases within the compartment. When subjected to continuous exercise muscle becomes engorged with blood and can increase its cross sectional area by up to 20%.
The engorged muscle is encased inside the inelastic fascia and, as it grows, the pressure within the fascia compartment increases. Although gases and solids are compressible, fluids are not. The incompressible fluid within the inelastic fascia makes the forearm feel hard as rock.
If the "compartment pressure" rises high enough, blood vessels can collapse, which restricts or stops the flow through that vessel. Veins, with their low pressure and thin walls, collapse earlier than high-pressure, thick-walled arteries. When venous flow reduces, arterial blood continues to enter the fascial compartment but is restricted from leaving (venous congestion). This restricted outflow further increases the pressure within the fascia compartment. If the compartment pressure rises higher than the pressure in the capillaries, or even the arteries, then these vessels may collapse, resulting in "muscle ischemia"-a painful condition of oxygen deprivation.
When the activity is stopped, the pressures gradually dissipate and the symptoms resolve, unlike as previously stated Acute Compartment Syndrome which does not.
Objective criteria for the diagnosis of chronic compartment syndrome are:
- resting compartment pressures of 15 mm Hg or higher
- 1-minute post-exercise pressures of 30 mm Hg or higher
- 5-minute post-exercise pressures of 20 mm Hg or higher
There is usually pain out of proportion to the injury, tenseness of the forearm, swelling, and pain with passive movement of the compartment musculature. The patient generally has good capillary refill* and a palpable radial pulse.
If the volar compartment is involved, there may be paresthesias and altered sensation over the palm and the volar aspect of the thumb and index, middle, and ring fingers. The small finger is usually less affected than the others, because the ulnar nerve is less dramatically affected than the median nerve. The thumb and fingers will often be held in the flexed position. Elbow flexion and extension are painful, but are better tolerated than finger or wrist movement.
When the dorsal compartment is involved, sensation to the hand and fingers is usually normal, because the posterior interosseous nerve has no sensory component. There often is weakness of thumb, finger, and wrist extension. The hand and wrist are generally held in extension. Flexing the fingers causes excruciating pain.
When compartment syndrome affects the mobile wad**, there can be altered sensation over the dorsum of the hand. There may also be weak wrist extension. Elbow and wrist motion flexion is very painful. Finger flexion is better tolerated than elbow or wrist movement.
*Capillary refill is the rate at which blood refills empty capillaries. It can be measured by pressing a fingernail until it turns white, and taking note of the time needed for color to return once the nail is released. Normal refill time is less than 2 seconds
**(Mobile WAD is a collective term for the lateral muscles brachioradialis, extensor carpi radialis brevis & extensor carpi radialis longus).
Proposed Mechanism of action
When you grip something in your hand there is co-contraction between the muscle groups on the back (dorsal) and front (volar) of the forearm. To necessitate a stronger grip the wrist is pulled into extension. This co-contraction results in an increase in compartment pressure.
Thus to simply grip a handlebar increases pressure. To grip the handlebar of a rapidly accelerating or decelerating motorcycle necessitates stronger grip levels. If you then add the throttle action, which uses the dorsal wrist extensors more than the volar wrist flexors, then the clutch and brake levers, which use the volar finger flexors, then the complex nature of this injury starts to appear
Thus the main issue is that the arms are placed under a continuous but diverse load. Certain circuits load these factors differently –such as Oulton Park with its crests and lack of straights. Interestingly we visit Oulton park twice a year, and there is a noticable reduction in the volume of CECS patients at the second visit – suggesting specific ‘on the bike fitness’ as a measurable factor.
Ergonomics are extremely important with this type of injury, hence handlebar and lever position are crucial. As are lever pressures (carbon discs = lower lever pressure for a given braking force), short travel throttles, quick-shifters and so on. These are not the total solution as arm-pump still affects motogp riders, in theory the cream of the crop.
There is an important divide between those people who have ‘pathological CECS’ which does not improve with rider fitness nor respond well to conservative management, and those riders who experience symptoms at the milder end of the spectrum which does improve with rider fitness, technique refinement and is responsive to conservative management. Those riders with true pathological CECS are the ones who benefit from surgical decompression, indeed after talking with a surgeon he observed that the tissue surrounding the compartments is tougher in those people with true pathological CECS.
We assisted in the production of a study investigating any correlation between grip strength and forearm compartmental pressures. The results were interesting in that it showed a decrease in post exercise grip strength, which suggests that as the riders suffer from CECS they have to try harder to maintain the same level of grip on their machine.
As a service we have continously refined how CECS is managed over the last 5 years. We have now arrived at an approach that utilizes :
- Compartmental Myofascial release – to alter the compliance of the fascia (Annan 2010, Myers 2010)
- Biomechanical assessment of whole body – especially after a recent crash.
- Questioning on riding style and prefered technique –some riders do not use the foot operated rear brake, others cannot ride without one.
- Advice on remedial training programmes – to minimise any training unwanted training adaptations – and facilitate appropriate physiology changes.
- K-Tape to enhance drainage of the affected compartments, and facilitate biomechanical efficiency .
- It is planned to undertake a study of CECS pressures and their response to the various conservative management strategies that we utilize.
Surgical Management of pathological CECS
Many of the riders have undergone decompression by fasciotomy. This can be done either open or endoscopically. There exists debate between various surgeons as to the most efficacious method as in other surgical fields. We have had experience of both, the endoscopically performed procedure is assocaited with shorter recovery times, with the riders typically able to race at 3 weeks postoperatively. The open procedures take far longer and sem to have an association with keloid type hypertrophic scarring – likely as with the compartment being opened there is more tension on the closure sutures in the skin.
We have developed close links with a Consultant upper limb surgeon, who prefers the endoscopic method of surgery. He was kind enough to supply the pictures below. Central to his decision to operate is accurate confirmation that CECS behaviour is observed during provocative testing. For this he uses a BTE work simulator (Fig 2), this is preceded and followed by compartment pressure measurement (fig 3)and finally decompressive surgery as dictated (fig 4).
Warm up before you go out on track. A quick jog, the use of a turbo trainer or other exercise to get your blood flowing prior to riding can only help.
Forgetting to breath while riding—as silly as it may sound—is among the most common causes of arm pump in beginner-level riders. Paying attention to your breathing will also help you relax. Breath holding can also speed the onset of symptoms.
Annan J (2010) An introduction to Myofascial release – part 2. Course notes
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Myers T.W. (2001) Anatomy Train: myofascial meridians for manual and movement therapists. Churchill Livingstone
Schoeffl V, Klee S, and Strecker W (2004) Evaluation of physiological standard pressures of the forearm flexor muscles during sport specific ergometry in sport climbers. Br J Sports Med 38:422-425
Segura J F, Doreste JL and Mir-Bulló X (2005) Chronic forearm compartment syndrome in professional athletes. Journal of Bone and Joint Surgery - British Volume, Vol 88-B, Issue SUPP_II, 324.
Soderberg T A (1996) Bilateral chronic compartment syndrome in the forearm and hand. J Bone Joint Surg [Br] 1996;78-B:780-2.
Tomida Y, Hirata H, Fukuda A, Tsujii M, Kato K, Fujisawa K, Uchida A (2007) Injuries in elite motorcycle racing in Japan.