The Curious Problem of Arm Pump in Motocross Racing (Part I)

APU
5 min readMar 29, 2021
Deel arm pump motocross racing part 1
Image courtesy of the author.

By Dr. Gary L. Deel
Faculty Director, Wallace E. Boston School of Business, American Public University

This is the first article in a two-part series on the challenge of arm pump in motocross and how it can be mitigated.

In a recent episode of my podcast Intellectible, I welcomed professional motocross/supercross racer AJ Catanzaro to the channel, and we spoke at length about the ins and outs of the sport we both love. AJ and I covered a wide spectrum of topics, including tracks, bikes, trends and issues. But one of the topics we touched upon that I felt was deserving of a bit more discussion was the major challenge of arm pump for racers.

What Is Arm Pump in Motocross Racing?

Arm pump is a phenomenon where the forearms basically fill with blood from prolonged, intense use and, as a consequence, hand and wrist muscles are no longer able to function properly. Doctors call it compartment syndrome. But let’s break the mechanics down a bit further.

Inside your forearms are the muscles and major tendons that control the flexing of your wrists, the curling of your fingers, and the closing of your fists. If you turn your right palm face up, grab your right forearm firmly with your left hand, and begin opening and closing your right fist, you should be able to clearly feel these muscles moving on the inside of your arm — contracting and relaxing.

These muscles serve a critical purpose in motocross racing. They allow a rider to hang on to the bike, to work the controls, and to steer and move it as necessary to navigate the tracks we ride.

Motocross bikes have very high power-to-weight ratios, so riding one at a high speed is a lot like riding a mechanical bull. The acceleration is intense, requiring significant effort just to stay on the bike under power.

Then there are the G-forces associated with braking and the ups and downs of bumps, jumps, and obstacles throughout the tracks. It’s sufficient to say that motocross racing is a workout, especially at the pro level where AJ races.

Deel motocross jump 1
Making a challenging jump. Image courtesy of the author.

Forearm Muscles Have a Limited Amount of Endurance

Anyone can hang on to a motocross bike for the first few minutes. The problem lies in the fact that the ability of these muscles to endure is finite.

When those muscles eventually falter or fail during a race, the situation becomes very dangerous for the rider, who can no longer feel his hands or hang on to the bike at all. But the reason for the limitation in forearm muscle endurance is relatively unique.

Forearm muscles are actually encased in a kind of sleeve called a fascia. Think of it like a thick wrapping of cellophane around the body of the muscle.

But unlike cellophane, this fascia doesn’t stretch to allow the muscle to expand. There is some room, but once the muscle grows to fill the fascia — as it does when it fills with blood under intense use — the fascia constricts the muscle from expanding any further.

When this constriction happens, oxygenated blood can no longer flow into the muscle, nor can deoxygenated blood flow out of it. The muscle is essentially paralyzed under the constriction. That’s not to mention the hand and fingers downstream of the forearm muscle, which also cannot receive and exchange blood during such a scenario.

If you’re not a motocross racer but are curious to know what this physical effect feels like, you can simulate it at home. Simply grab hold of something sturdy overhead and allow yourself to hang from it. A pull-up bar will work nicely, but anything that will support your body weight — such as a thick tree limb in your backyard — will suffice.

It doesn’t matter how long you are or are not able to hang on before letting go. The experience for this purpose will be the same. Unless you have bad shoulders or some other point of failure that would cause you to let go first, your forearms will probably be the limiting factor.

As you hang from the overhead object, notice the feeling in your wrists, hands and fingers. You will probably feel a strain, but if you hang long enough — to your forearm muscles’ limits — you may actually feel your hands and forearms start to go numb. You want to hang on longer, but you can’t feel your fingers anymore. So despite your willpower, you can’t help but begin to let go and eventually fall.

Motocross Riders Need the Ability to Hang on to Handlebars for Safety

Motocross riders let go and fall also. But when they do fall off a bike, it’s not often onto their feet. It’s usually in a cringe-worthy end-over-end crash that can break bones and cause severe injury.

Suffice to say the ability to hang on to a bike’s handlebars is critical. So what can motocross racers do about this problem?

A common intuition here is just that a motocross rider should simply work on strengthening the forearms. It’s an understandable way of thinking.

After all, with most other muscles in the body, you train your muscles if you want to improve their overall power or endurance. If you want to run faster or farther, you need to build up your leg muscles. If you’re looking to increase your bench press numbers, either in terms of max weight or max reps, then you strengthen your chest muscles.

But arm pump cannot be fixed through training. In fact, working and strengthening your forearm muscles makes arm pump worse.

Why? Because, again, the volume inside the fascia in the forearms is finite. If you work out a muscle, the muscle builds up scar tissue and gets bigger. If forearm muscles get bigger, these leaves even less room in the fascia for expansion as blood engorges the muscle under rigorous use.

Incidentally, this is why, if you look at the physique of professional motocross or supercross racers, they are not, generally speaking, particularly muscular in any dimension. This is not to say they aren’t fit. They’re usually very lean with extremely high cardiovascular stamina. But unnecessary and counterproductive muscle mass is just dead weight in competition, so racers don’t usually pursue it.

But if training isn’t the answer to resolving arm pump, what is? In the next part, we’ll look at some other remedies — both practical and extreme — for this endurance problem in professional motocross racing.

About the Author

Dr. Gary Deel is a Faculty Director with the School of Business at American Public University. He holds a J.D. in Law and a Ph.D. in Hospitality/Business Management. Gary teaches human resources and employment law classes for American Public University, the University of Central Florida, Colorado State University and others.

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