Article: Arm Pump and Motocross

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Arm Pump and Motocross

Jondy L. Cohen, M.D.

Stanislaus Orthopaedic & Sports Medicine Clinic


Arm Pump:

Medicines Neglected Syndrome

A debilitating condition is limiting the performance of some of the world's top athletes. This condition affects competitors regardless of age, sex, or race, and varies in severity from slightly annoying to downright dangerous. "Chronic Exertional Compartment Syndrome of the Forearm", the most common cause of "arm pump", lacks large foundations and other sources of funding and therefore little research is conducted on the subject. Although the world's governments are not racing to cure arm pump, the editors of Motocross Action want to help you sort fact from fiction, opinion from knowledge, and quackery from cure. Motocross Action contacted me, a practicing Orthopaedic Surgeon in Northern California, to define the current status of arm pump.

Although you have probably heard of arm pump it is unlikely that your doctor has. I extensively reviewed the medical literature and found almost nothing on this subject. In the "American Journal of Sports Medicine" in 1998 one author even states that "Chronic compartment syndromes of the upper extremity are rare, and only a few cases have been reported in the literature." A casual sampling of my sports medicine colleagues revealed only one that was familiar with the disorder. Conversely, almost every rider over adolescence that I contacted was not only familiar with the condition, but also aware of the existence of a surgical treatment and usually several nonoperative treatments. The fact that several national level pros have recently undergone surgery for arm pump has heightened interest in this condition.

Justin Buckelew - Motocross Arm PumpRiders suffering from arm pump often look for an easy fix. These folks don't want to put much effort into understanding the problem and would prefer that I propose a quick operation, medication, or corrective therapy. This attitude is common in many of my patients, regardless of the diagnosis. We Americans have become used to easy, drive through, technologically advanced solutions to life's problems. It's not surprising that we expect a modern, once a day, HMO covered, FDA approved, arthroscopic, computer controlled and laser guided, medical solution to arm pump. Unfortunately, the best way for you to treat your arm pump is to understand the cause of arm pump. Just like questions concerning jetting and suspension, no simple one-sentence answer is adequate. If you're a successful competitor lacking a factory mechanic then you have likely read volumes about jetting and suspension. If arm pump sometimes slows you down read on.

Forearm pain that occurs while riding is not always due to arm pump. Riders with carpel tunnel syndrome, ganglion cysts, arthritis, neck abnormalities, tennis elbow, and fractures have all complained of forearm pain while riding. In the interest of brevity I will only discuss arm pain due to Chronic Exertional Compartment Syndrome of the Forearm (CECSF). Please remember, this article cannot substitute for a good physical exam by a physician. Since I am writing about a condition and I haven't examined you, then maybe this isn't your condition. Your physician should be able to help.


The Heartbreak of Arm Pump

Severe arm pump can ruin a great day. A talented racer may meticulously prepare his bike and his body, spending thousands of dollars and countless hours, for the last race of the Winter Solstice Shootout Amateur National. He knows that this is the most important race of his life and that none of his competition is as prepared as he. This is HIS year to shine. Ignoring his pre-gate jitters he takes the holeshot and leads for several laps before his forearm muscles painfully enlarge and harden. His hands become useless and finger movement just adds to the hurt. He may hang on pitifully while his pace drastically slows. Eventually, with competitors passing at will, he exits the track, the day having lost its allure.

Not all cases of arm pump are as severe as this example. Often patients complain that they can ride trails all day without arm pump on one week and then pump up quickly at the track the next week. Symptoms usually occur at the palm side (volar) of the forearm rather than the back side (dorsal side). Numbness or tingling in the forearm and hand can occur. Fortunately, the symptoms of arm pump are temporary and hand function quickly returns after a short rest.


Acute Compartment Syndrome is Not Arm Pump

Persistent or progressive symptoms despite resting are worrisome and may indicate the start of a rare condition called "Acute Compartment Syndrome". Unlike the chronic form (arm pump), symptoms of acute compartment syndrome increase even after resting. The acute form usually results from an injury, but may occur after strenuous exercise. Acute compartment syndrome is a true emergency and may lead to permanent muscle damage unless surgically treated in less than 6-8 hours. If you cannot move your fingers 15 minutes after you stop riding be concerned and perform the following test. Have a friend move your fingers for you in both directions (flexion and extension). If this maneuver results in severe pain, go to a doctor. If your pain continues or increases long after riding stops seek medical attention at once! If you have acute compartment syndrome don't assume it's just arm pump, unless you like the moniker Lefty (or Righty).


Muscles and Two Stroke Engines

Understanding arm pump begins with understanding muscles. Muscles, like two stroke engines, burn fuel and oxygen to produce horsepower, exhaust, and heat. But, the motor between your legs (I mean your bike, stud) differs in some important ways from the motor inside your legs (your leg muscles).

Engines use air to transport intake and exhaust; the air/fuel mixture is made in the carburetor and carried as gas through the intake and transfer ports to the cylinder. The signal to burn this mixture initiates in the ignition and is carried by the spark plug wire to the plug. The burning gas expands forcefully pushing the piston down. This energy then progresses through the transmission and chain, to the rear wheel. Exhaust is sent through the exhaust port and out the pipe.

Muscles use blood to transport intake and exhaust; the blood/oxygen/fuel mixture is made in the lungs, and carried by blood through arteries (intake ports) and capillaries (transfer ports) to every tiny fiber in the muscle. (Figure 1). The signal to burn this mixture initiates in the brain (the ignition) and is carried by nerves (the plug wire). The burning occurs at every muscle fiber (the cylinders), causing them to either shorten or resist lengthening, depending on the amount of force pulling against it. Energy then progresses from muscle to tendon to bone. Exhaust leaves each muscle fiber by entering the bloodstream in capillaries that empty into veins. Motocross Arm PumpVeins bring exhaust filled blood back to the heart that pumps it to the lungs. In the lungs blood releases carbon dioxide and binds oxygen. (A more complete but longer explanation of this process is provided in the sidebar titled "More About Muscles".)

Muscles are often found together in "fascial compartments". Fascial compartments contain muscle wrapped in a layer of "fascia". Fascia, a tough but thin white gristle, envelops the compartment like a casing wraps a sausage. Fascia helps to both anchor muscles and to 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 big pressure increases within the compartment.

Forearm Design

The forearm has two sides, the palm side (called the "volar" side), and the backside (called the "dorsal side"). The muscles on the palm side of the forearm bend (flex) the fingers and wrist. The muscles on the backside of the forearm straighten (extend) the fingers and wrist. When you grab your bars notice how the muscles on both sides of the forearm tighten. The palm muscles are bending your fingers to grip the bars and the backside muscles are holding your wrist stable. Figure 2 shows the volar (palm) side and the dorsal (back) side of a forearm. Notice the muscle fibers (red) turning into tendons (white) before crossing either the elbow or wrist. Also notice that the fascia is removed in these photos in order to better see the muscles.


Figure 2: The palm side (left) and the back side (right) of a forearm. Notice the muscle fibers (red) turning into tendons (white) before crossing either the elbow or wrist. (Fascia has been removed.)

Figure 3 shows a crosscut section of forearm. The forearm has four fascial compartments that I have colored: 1.In pink are the muscles of the superficial volar compartment, 2. In orange are the muscles of the deep volar compartment, 3. In red are the muscles of the dorsal compartment, and 4. In yellow are the muscles of the mobile wad compartment. Usually only the two compartments on the palm side of the forearm, purple and orange (the superficial and deep volar compartments) pump up.

Arm Pump Details
Figure 2 Cross section of a forearm. Palm up.


How Arm Pump Happens

During vigorous exercise muscles require a tremendous amount of oxygen rich blood and commonly increase in volume by up to 20%. The engorged muscle inside the inelastic fascia results in increasing pressure within the compartment. Although gases and solids are compressible, fluids are not. The incompressible fluid within the inelastic facia makes the forearm feel hard as bone. (A similar mechanism is used elsewhere in the body to create a rigid structure out of soft tissue.) 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. This restricted outflow further increases the compartment pressures. If the compartment pressure rise higher than the pressure in the capillaries (the "capillary pressure") or even the arteries (the "arterial pressure") then these vessels may collapse and result in "muscle ischemia" - a painful condition of oxygen deprivation. Muscle ischemia leads to even higher compartment pressures via pathways we won't discuss here. This cycle of increasing pressure is depicted in Figure 3.

The scenario described above is a well-documented condition that occurs occasionally in the lower legs of distance runners. A few cases have been described in the hands, feet, thigh, elbow, and forearm. The condition is called various names including chronic compartment syndrome, effort-related compartment syndrome, exercise-induced compartment syndrome, and chronic exertional compartment syndrome. When it occurs in the forearm I refer to this condition as "chronic compartment syndrome of the forearm". (CCSF) All of these names seek to differentiate this condition from the much more dangerous syndrome of "acute compartment syndrome". (See Acute Compartment Syndrome above.)

Despite what the medical literature says, we all know that chronic compartment syndrome of the forearm in motocrossers is common. It is probably more common than chronic compartment syndrome of the leg in runners. The higher incidence in motocross is related to the fact that forearm muscles only get blood flow during relaxation. NASA performed a good study of forearm muscle blood flow in 1996. While studying normal volunteers they found "a significant reduction in muscle oxygenation even at levels as low as 10% maximal contraction." This explains why we pump up less when we relax, move our fingers and unclench our hands.

We pump up more on race day because forearm muscles only get blood flow when they are relaxed.


Nonoperative Solutions to Arm Pump

My research for this article included speaking to numerous riders and searching both the Internet and the medical literature. I found recommendations for arm pump ranging from scientifically accurate to downright bizarre. Since little true research about arm pump exists, very few of these remedies have been truly tested. Remember that if a single person says that after they did X then Y happened, it does not necessarily mean that Y was a result of X. This concept is how magic and superstition usually begin. On the other hand, the mind is a very poorly understood and powerful organ. True belief in a treatment often has remarkably good results, a well-documented phenomenon called the placebo effect.

I have broken nonoperative arm pump solutions into three groups based on the chance of success in reducing arm pump for a large population. My list does not mean that anything won't work for you as an individual (see preceding paragraph).

  1. High chance of reducing arm pump

    1. Frequent riding.
    2. Staying relaxed on the track, loosening the stranglehold on your grips, moving your fingers, and alternate between squeezing and relaxing your hands.
    3. Using more legs and less arms while riding.
  1. Medium chance of reducing arm pump

    1. Avoid heavy weights in arm workouts.
    2. Suspension set-up.
    3. Wrist curls with light weights and high repetitions.
    4. Forearm, wrist stretching.
    5. Using aspirin as a blood thinner. (The blood thinning attributes of aspirin work best at low dose. One pill a day is all you need.)
  2. Possible chance of reducing arm pump. Treatments that some riders believed helpful are sometimes diverse and contradictory:
    1. Taking nutritional supplements, vitamins, magnesium, potassium, calcium?
    2. Changing the bar type, composition, and position (some say up, some say down) .
    3. Lever position (some say up, some say down).
    4. Grip size and stiffness (some said smaller and stiffer grips helped, while others said a larger softer grip absorbs vibration and helped.)
    5. Steering Dampers.
    6. Gripper seat covers
    7. Acupuncture
    8. Magnets
    9. Voodoo


Operative Solutions to Arm Pump

Surgical release of the forearm fascia (fasciotomy) is easily performed by an Orthopaedic Surgeon. Fasciotomy is not a new or difficult procedure and is more commonly performed in the leg than the forearm. It is often performed in trauma patients to treat or prevent acute compartment syndrome. Fascia release consists of first incising (cutting) the skin and then either incising the fascia or actually removing a strip of fascia. The four fascial compartments in the forearm can be released through two incisions. A volar incision to release the superficial and deep volar compartments, and a dorsal incision to release the dorsal and mobile wad compartments.

The use of forearm fasciotomy for arm pump is very poorly documented in the medical literature. In the few studies that are written authors contradict one another on several points including what constitutes abnormal compartment pressures and which compartments should be released.

Some authors say that a resting compartment pressure over 20 mm Hg is diagnostic for this condition. Others maintain that an exertional pressure 30mm Hg below the diastolic blood pressure is important. While still others think resting pressures greater than 25mm Hg measured five minutes after exertion is diagnostic.

Similar disagreement exists on which compartments need releasing. Some authors recommend releasing all four fascia compartments while others only release those compartments with elevated pressures. Still others only release the volar compartments. Some of this confusion stems from the fact that in the leg fascial compartments have very little interconnection and therefore complete fascial release requires release of all compartments. In the forearm good evidence shows that compartments are often interconnected and effective release can be accomplished by releasing just the volar compartments.

No matter which compartments are released, the operation can be done as an out-patient procedure (no need for overnight stay). A cast isn't necessary and return to function rapidly occurs. Training can start about 2-3 weeks after surgery, and competition 4-6 weeks later.


The Bottom Line

My approach to arm pump is as follows. First try all the recommendations listed in the nonoperative section above. If you still have problems you should consider surgical release of your forearm fascia. Since not all patients improve with fascial release this step shouldn?t be taken lightly. I measure compartment pressures after riding to determine which compartments to release. I am currently seeking volunteers for a study to address the disagreements listed in the previous section. With further study and your help we may be able to eradicate arm pump in our lifetime.

Your Bike

Similar Functions Between Bike & Body

Your Body



Inflow & exhaust

Carried by




Fuel Mixes with Oxygen in


Intake Port

Fuel/air Mixture

Carried by


Transfer Port

Fuel/Oxygen Mix Sent to Final Area of Combustion by


Ignition (Initiates signals that are Carried by Spark Plug Wire)

Combustion Initiated or Controlled by

Brain (Initiates signals that are carried by Nerves)

Outflow Port

Exhaust Carried by


Exhaust Pipe

Exhaust Expelled by


Expansion (Gases push Piston down)

Burning Fuel Results in Forceful

Muscle Contraction (Shortening)

Chain to Rear Tire

Work Transferred Through

Tendons to Bone


What are Tendons?

Since all the muscle fibers in a muscle perform work, muscles are very bulky and require a constant flow of oxygen. These factors explain why muscles never cross a joint. If muscles did cross over joints, then bending the joint would squeeze the muscle reducing the needed blood flow. To avoid this problem muscle fibers transform into tendon fibers as they approach a joint. By the time the muscle crosses the joint the transformation is complete and it's the tendon that crosses.

Tendons are thin, strong, white, ropes that connect muscle to bone. Like muscle, tendons are made of protein rich fibers. The protein in tendons is a form of collagen that does not have the ability to contract. Tendons therefore require much less oxygen than muscles. Tendons, being thin and strong, are well suited to bending around a joint. Tendons are a great way to transfer the power of a muscle across a joint to the next bone. (Ligaments are a similar type of rope-like tissue but while tendons connect a muscle to a bone, ligaments connect one bone to another bone.) Muscles are anchored at both ends to bone, usually originating on one bone, attaching to a tendon, which then crosses a joint before inserting on another bone. The combination of a muscle and its tendon is often called a "musculotendonous unit". Some muscles, like the biceps muscle in the arm, cross a joint at both ends and thus have two tendons, one at each end. (See the arm muscle in figure 2)

Talk Like a Doctor; A Glossary of Buzzwords

Arterial Pressure

Pressure inside an artery.

"Arterial pressure is higher than venous pressure."

Capillary Pressure

Pressure inside capillaries.

"Capillary Pressure is less than arterial pressure but more than venous pressure."

Compartment Pressure

Pressure inside a muscle compartment.

"If compartment pressure rises higher than capillary pressure then muscles don't get enough oxygen."


Toward the back.

"My knuckles are on the dorsal side of my fingers."



"Extend your fingers and pull the clutch."


Tissue around the outside of a muscle.

"My fascia is tight."



"Flex your fingers around the grip."


Painful condition of oxygen deprivation.

"High compartment pressure can result in muscle ischemia."


Tissue death.

"Prolonged muscle ischemia can lead to muscle necrosis."


Rope like tissue that connects bone to bone.

"I tore a ligament in my knee."


Rope like tissue that connects muscles to bone.

"I can feel my tendons in my wrist."

Venous Pressure

Pressure inside a vein.

"Venous pressure is less than arterial pressure"


Toward the front of the body.

"My palms are on the volar side of my hand."

























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