Why do your legs burn on the Assault Bike & How to Fix It

We’ve all been there.  You’re crushing an Assault Bike workout and then your legs turn to knots.  The burning sensation quickly turns to a throbbing that could easily be overwhelming if you let it. 

The Point of Failure

You finish the workout and -after rolling around on the floor for a few minutes- your coach asks, “What prevented you from going any faster?”

My legs were burning so bad!”

So there you have it.  Your legs are the issue.  It’s time to give you a bunch of protocols to improve your leg’s endurance so you overcome the burn, right?  Not so fast. 

Finding & Dealing with the Source of the Problem

Just because your legs are burning doesn’t mean your legs are the problem.  This is counterintuitive at first.  Let’s get a better understanding of your physiology and figure out what’s really going on “under the hood.”

When your quads start throbbing, it’s *likely* because the oxygen is being used at a faster rate than it is being replenished.  When consumption is greater than delivery, oxygen saturation drops in the muscle.  But rather than letting up, you keep hammering down on the bike, so your body has to find a way to keep producing energy at the same output.  This is where your body starts creating lactate, or what is traditionally thought of as the anaerobic system (glycolysis).

What does this mean?

It means that your legs are using energy really quickly.  In other words, your muscular power or local muscular endurance are actually quite good.

What’s the issue then?

The issue is you can’t supply the muscle with enough oxygen.  This means some link in the supply chain is the source of the problem.

So yes, your legs burning was the glaring issue when you failed, but it’s likely not the source of the problem that caused you to fail.

Notable Exceptions

There can be exceptions to this. Mainly, untrained and detrained athletes. New trainees might have a utilization limitation, meaning their tissues aren’t able to consume all the oxygen being delivered. In other words, the oxygen is in the muscle, it just isn’t able to be used fast enough. New or untrained populations don’t have the capillary or mitochondrial density built up yet to .

Also, detrained athletes (e.g. a Games athlete who takes a month off after the Games), might have a utilization limitation for 4-6 weeks upon restarting training, but typically will “grow” out of that rather quickly as they get back in shape.

This is one reason why I don’t recommend coaches do testing as soon as an athlete starts back up into training again. I would give them a month or so to get back into shape so their typical limiters are what is being accessed.

However, for most trained athletes. There will be two typical culprits.

Two Potential Culprits

There are two “links in the chain” prior to the muscle that realistically could be your issue.

First is Respiration.  

If you aren’t getting oxygen from your environment into your bloodstream and carbon dioxide out of the bloodstream into the environment, then the whole system will grind to a halt.

It’s a simple concept that gets very complicated in the Sport of Fitness because the demands for breathing differ in every workout based on the exercises, the movement pairings, the loading, time domain, etc.  In other words, your limiter could be different for each novel test of fitness.  It’s totally possible that you have a respiratory limiter in one workout but not another.  

Here’s just one potential example.  Let’s say in workouts with bodyweight and cyclical components you breathe effectively, but in workouts with hinging patterns above a given threshold (% of your 1RM) where the load requires you to increase IAP (intra-abdominal pressure) and create a brace, then you can’t effectively exchange gas.

Regardless of why the athlete can’t breathe effectively, it means that they can’t deliver oxygen at the rate the muscle uses it, so your muscle starts to burn.

For more on respiratory limitations read…
Breath Work for the Sport of Fitness.

Second is Cardiac Output.

Let’s just say you are adequately exchanging gas so respiration isn’t your limiting factor.  Good news, this means there’s oxygen in your bloodstream.  Ideally, your heart swiftly pumps your oxygenated blood through your arteries and into the capillary beds in your muscle where oxygen gets “sucked up” and used by your mitochondria.

But that’s in an ideal scenario.  Unfortunately, that doesn’t always happen.  This is because the heart is pumping against the tension created by the working muscles.  The harder the muscle works (contraction strength), the less likely it is that the heart will be able to push through the blockages.  It’s the equivalent of a kink in a garden hose.

If an athlete has a weak heart relative to their muscle’s contractile potential, they will block blood flow from entering and/or leaving the muscle.  This means that oxygen can’t get in and/or carbon dioxide can’t get out.  That’s a recipe for a muscle that is put in a position to fail.  The muscle isn’t able to buffer the hydrogen ions and it becomes acidic.  Too acidic and the muscle won’t fire (contract).  In layman’s terms, you’re suffocating it.

So regardless if the issue is with the respiratory system or the heart, it’s the reason why your legs are burning on the Assault Bike.

Read: Mastering the Assault Bike

Note: You will never “fix” this issue.  You will only raise the contraction threshold at which it will happen.  You want to block blood flow from exiting the muscle at 50%+ of your 1RM, not at 35% of less.

Protocols that Work

So if it’s the cardio-pulmonary system that is the actual reason for your burning legs, what can we do to improve those systems? 

Truthfully, that’s a very long and complicated answer, and it’s the process I go through with my 1-on-1 Coaching Clients.

Yet, there are some staple protocols that I frequently use for athletes who have this limiter that could be “blindly” applied with some degree of success.

Here is a screenshot from Cyclical Supremacy that is a great workout that can be applied to many different athletes because it accounts for individuality.

Ramps-Up Intervals of this nature prevent muscular tension from being too high right off the bat.

For example, in a workout like 5 Sets: 60s Work, 60s Rest, it is likely that the athlete will start at their highest wattage and bleed watts throughout the interval.  This is a good strategy to get your best score, but a poor way to improve your limiters.

This is because tension likely blocked blood flow to the muscle and therefore the heart isn’t being worked effectively.

The solution is to start at a lower intensity and slow build.  This helps overcome cardiac lag and stimulates the heart to increase it’s output progressively…improving your actual limiter.

And if your limiter is respiration, ventilation will progressively build as well, so it really is a catch-all for improving your limitations without in-depth physiological testing

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