How To Improve Muscle Endurance For Crossfit

It's often said that exercise science explains what coaches have already figured out in practice. The truth is not too far off. For decades, our knowledge of how to enhance physical performance has outpaced our understanding of human physiology during exercise. However, this is soon to change. 

In recent years we've seen an explosion of new technologies that allow coaches and athletes to monitor physiological function in real-world settings, allowing them to better understand the relationship between external work outputs (velocity, power, etc.) and internal physiological states.

These new technologies reach far beyond traditional measurements such as heart rate, volume of oxygen consumption (VO2), and blood lactate, which are systemic indicators of physical exertion. For example, it is now possible to measure changes in local muscle oxygenation (SmO2), which is a measure of oxygen supply in exercising muscles. 

However, until recently SmO2 measuring devices were largely limited to research settings and the few devices that were available to consumers were difficult to use, stifling widespread adoption. NNOXX changes all of this by combining real-time lab-grade measurements with an easy-to-use mobile app. In this article we’ll show you how Crossfit athletes and coaches can use NNOXX to address one of the most common exercise limitations in Crossfit. 

Local muscle fatigue is one of the most commonly cited exercise limiters among recreational and competitive Crossfit athletes. However, the cause of local muscle fatigue is poorly understood, and training interventions intended to improve local muscle endurance have mixed results. 

One of the leading causes of local muscle fatigue is a restriction of muscle blood flow due to high intramuscular mechanical pressure. Under ordinary circumstances, there are two ways that muscle blood flow can increase. First, we have active hyperemia, which regulates blood flow on a contraction-by-contraction basis. However, across many muscle contractions, a different process called auto-regulation, controls muscle blood flow. Auto-regulation means that blood flow increases in response to the oxygen level in a muscle decreasing. Interestingly, the NNOXX One wearable clues athletes into this process by monitoring muscle oxygenation (SmO2) and nitric oxide (NO), which regulates local muscle blood flow and oxygen delivery. 

The combined effects of active hyperemia and auto-regulation determine the total change in blood flow from moment to moment during exercise. When either process is impaired, muscle blood flow and oxygen availability to muscles decrease. For example, suppose a Crossfit athlete contracts their muscles with excessive force. In that case, they can impede their muscle flow, causing local muscle fatigue and an inability to sustain their power output. This phenomenon is especially prevalent in Crossfit metcons using heavy weights or those that contain very high volumes of a single gymnastic movement with little recovery time between work sets. 

Now you know the underlying cause of local muscle fatigue during Crossfit metcons. However, that still leaves the question of how you can improve your local muscle endurance and performance. 

NNOXX

We must identify the rate-limiting factor for increasing muscle blood flow to determine which protocol will be most effective for improving local muscle endurance. For example, one athlete may have poor intramuscular coordination, resulting in a blunted active hyperemic response. Another athlete may have poor breathing mechanics and mobility, which puts excess tension on the working muscles and impairs their muscle's blood flow. Finally, a third athlete may lack strength in a specific movement. As a result, they contract their muscles with such high force during metcons that they cut off blood flow to the working muscles. These three individuals must use different training methods to improve their local muscle endurance because their underlying limitations differ.

After identifying an athlete's limitation, I would track week-to-week performance improvements with the NNOXX One wearable to ensure they adapt to the new training stimulus. For example, say an athlete is limited by strength, and their heaviest front squat is 225lb. One the first week, I would have that athlete perform a set of 30 unbroken thrusters while observing their SmO2 (muscle oxygenation) and mVO2 (muscle oxygen consumption) levels in the quadriceps muscles. 

I'd repeat the assessment above as this athlete improves their front squat strength. Suppose they can perform the same number of thrusters, in the same amount of time, with a higher finishing muscle oxygenation level. In that case, they have lowered the metabolic cost of that movement. Additionally, if they can perform the same number of thrusters, in the same amount of time with a lower mVO2 level, it means they completed the same amount of work while using less energy, as is demonstrated in the image above.

At some point, additional gains in strength will not be accompanied by improved thruster performance. At that point, we'd look to identify a new rate limiting factor. This is crucial since an individual's limiter will change over time if their training effectively addresses their current limitation. As a result, the athlete and their coach can continue to track changes in the athlete's physiology using the NNOXX One Elite platform to ensure they are always training in the most effective and efficient manner possible.