In football, the most backbreaking and demoralizing moments for the defense are at the end of a 10+ play drive. The offense is in the red zone and you see linemen and linebackers, hands on hips, gasping for air. They are unable to play with the intensity that they did just minutes prior. Why is this the case? Yes, players are sprinting sideline to sideline or attempting to impose their will on a 300lb counterpart. But the average play in football only lasts about six seconds. When you factor in the play clock, timeouts, and penalties, shouldn’t these guys be able to handle even the longest drives?
Football is anaerobic in nature. It is performed at high intensities for short bursts of time. Think of how many other sports are performed in this manner. A striking exchange in MMA, a scramble in jiu jitsu, a backdoor cut in basketball, a counterattack in soccer, even a weightlifting or crossfit workout can resemble this style at times. Even with seemingly adequate rest between these bursts, eventually we still hit that proverbial wall. The reason is: if you perform an anaerobic activity repeatedly, it eventually becomes aerobic.
But what is the mechanism behind this? These guys are professional athletes, surely they are in phenomenal shape. What difference does it make if an activity slowly transitions from anaerobic to aerobic? It basically comes down to how your body creates energy, and this is often a misunderstood concept.
The body has three main substrates from which it creates energy; creatine, carbohydrates, and fats. Fear not, I will only give you the cliffnotes version of how this stuff works. Creatine fuels your highest intensity activities (anaerobic), while fats fuel the lower intensity activites (aerobic). Carbohydrates are an interesting mix. The initial phase of carbohydrate breakdown is anaerobic, and the complete breakdown ends up aerobic. In fact, the aerobic oxidation of carbs is much faster than the aerobic oxidation of fats. Fats provide a great deal of energy, but it takes longer to metabolize fats than it does carbs.
It would seem like carbohydrates are literally the perfect fuel source. Unlike any other substrate, they can be used BOTH anaerobically and aerobically. The problem (there’s always a problem) is that our bodies have a limited capacity to store carbohydrates. We can store a total of about 400-600 grams of carbohydrates in our muscle and liver. Eventually, we will have to turn to fat for our energy needs as these stored carbohydrates will run low.
As we referenced earlier, fat is not as favorable a fuel source because the process of converting fat to energy (ATP) is very slow. The need for oxygen to break down fats is what makes it aerobic. Fat utilization simply can’t keep up with the speed and demands of high intensity exercise. However, unlike carbs, our ability to store fat is basically limitless. I mean, think about how fat a person can get. Pretty damn fat, right? Due to the limited capacity of the body to store carbohydrates, it’s safe to say that at some point in a workout or competition we will have to utilize fats to a greater degree. Even though it isn’t the most favorable fuel source for our sport, it becomes a necessity. This brings up another issue, metabolic flexibility.
Metabolic flexibility is the ability for the body to seamlessly transition from using carbs for energy to using fats for energy and vice versa. This is something that most people… do not possess. Have you ever gone on a run, completely bonked, then experienced a “second wind” and start feeling good again? This is one example of the shift from using carbs as a primary fuel source to fats. In a sport, you don’t have time to bonk. We need something to make this transition much smoother.
L-Carnitine is a compound produced by the body that helps to get fat into something in the cell called the mitochondria. The mitochondria are the part of the cell that take in nutrients and create energy from it. In fact, the rate limiting step (slowest step) of using fat for fuel is this carnitine transporter. By addressing this carnitine issue directly through supplementation, we could make this limiting factor more efficient.
This is not simply theory, there are studies showing the efficacy of carnitine when it comes to exercise performance. One study showed increased fat utilization at low intensities, which spared carbohydrate use for higher intensities. This basically ensured that you would be using your nutrients optimally (i.e. not ‘wasting’ carbs on low intensity exercise). Carnitine supplementation has also shown improvements in anaerobic exercise performance in trained individuals, possibly for this same reason. This “trained” detail is an important one as many supplement studies are performed in untrained individuals. Training in general (especially in beginners) leads to a virtual guaranteed improvement in performance, and is an easy way to fudge the results of a study. In addition, carnitine supplementation has shown a reduction in ammonia, a byproduct of exercise that causes fatigue, and an increase in blood flow. It truly has a positive effect on nearly every aspect of exercise performance.
As you venture to the supplement store or interwebs, you’ll notice that there are many different types of carnitine. The studies referenced use all different types, so it doesn’t appear as if one is more efficacious than the others. However, different forms of carnitine require different dosing methods. L-Carnitine and Carnitine Tartrate require insulin for maximal uptake in muscle, therefore they must be taken with a meal containing carbohydrates. Acetyl L-Carnitine is not as insulin dependent and can be taken whenever you want. No matter what form you choose, I would take 2 grams every day, even on off days.
Due to its performance benefits in both aerobic and anaerobic activities, nearly every athlete can benefit from carnitine supplementation. Although it is available over the counter in any sports nutrition store, always check with your organization’s governing body before taking any supplement.