A couple of months ago Coach Broder discussed pacing (you can see his post here), and with Murph right around the corner, I figured it was a good time to talk about pacing again in greater detail and with some Murph-specific examples. (To refresh your memory Murph consists of a 1-mile run, 100 pullups, 200 pushups, 300 squats, and a final 1-mile run.)
Every CrossFitter has felt it — the feeling that you’re unable to do one more push up, where you want to run faster but your legs are like lead and your brain is fried. Hopefully, it happens at the end of your set or workout, but sometimes it shows up smack-dab in the middle.
The primary reason you feel this way is muscle fatigue, and there are two different kinds, or rather two different explanations for the fatigue. The first is caused by the Central Nervous System (CNS), the second by a build-up of metabolites (the junk leftover from the process of contracting a muscle).
1. CNS Fatigue
When you decide to do a pushup a signal from your brain comes down through your chest, arms and everything else you are using to perform the movement. This signal relies on lots of tiny electrochemical reactions. For the reaction to happen there needs to be a specific set up of ions to set off the sequence. As you repeat the same action over and over, and using the same muscles, it becomes more challenging for the body to reset the stage, so to speak. The further you get into your set the more likely it is that the reaction is diminished and eventually your signal strength is not strong enough to overcome your body weight and you get to lie on the floor for an extended period of time.
How to avoid CNS fatigue
Do smaller sets! Break 200 push ups into mini-sets of anywhere from 2 to 5, depending on where you’re at. Ideally, you want to do the highest amount of reps you can, take a short rest and repeat until your workload is complete. I break 200 pushups down into small sets of 2-3 pushups (2 push ups every 10 seconds is 12 per minute). By not pushing myself to fatigue, and allowing my body the 5 or 6 seconds to rest after each set, my muscles stay alert and ready to fire.
2. Metabolic Fatigue
Welcome to the red line, the point at which your breath can longer keep pace with your workload and everything, including your will to live, starts heading south. Your body uses several energy systems to allow you to keep moving all day long, but for the sake of keeping things as simple as possible we will just break them down into the general headings of aerobic (in the presence of oxygen) and anaerobic (in the absence of oxygen). When your heart rate is low and you are breathing comfortably your body is using the aerobic system. However, as the duration and intensity of your effort increases so does the demand for energy, and the slower aerobic systems cannot keep up so your anaerobic systems make a greater contribution. The problem is that as this anaerobic system uses up fuel it creates metabolic junk (lactic acid) as a byproduct, which requires even more oxygen for it to be burned as useable fuel. As your body diverts more blood flow to try and keep up with increased oxygen demands that light-headed or sick-to-your-stomach feeling may start to kick in.
How to Avoid Metabolic Fatigue
Learn where your red line is and stay just below it for as long as possible, only jumping past it as you near the completion of your task. The longer you can rely on aerobic systems for energy the better you will feel in longer workouts. This will take some experience and your fair share of suffering, but as you learn more about your body you will learn how to identify the correct pace and stay in a happy place.
We have done several smaller practice runs of Murph already so hopefully you have got some experience under your belt and started to learn your pacing. November 11 will be the real deal and we are excited to see you all there!
Duncan McNeill is a coach and co-owner of Alchemy CrossFit.