How and why do very short (e.g., 1-2 second) breaks help in workouts?

[truthfullyspeaking]

Did 24.2 today and got 8+ rounds. Did the first 7 rounds of deadlifts 5/5. Tried to do the final round unbroken, but couldn't hold on to the bar and ended up doing 6/4 with a quick break between the 6 and 4.

Why does even a 2 second break between reps (on any movement, really) help? I get that you're "unloading" your body, but 1-2 seconds doesn't seem like a long time. Looking for a more technical answer here.

 

[buckswordbearer]

@truthfullyspeaking TLDR: Phosphocreatine (PCr)

During exercise, muscle fibers don't work continuously. They cycle on and off. This process delays fatigue. The amount of time in an off cycle is inversely proportional to the intensity of the activity. High intensity, short rest.

The off-cycle is when recovery occurs. Phosphocreatine is replenished, and byproducts diffuse away. It's a little bit misleading to think of phosphocreatine as an energy system. Phosphocreatine doesn't extract energy from food. Instead, it acts as a buffer for energy produced in the mitochondria and by glycolysis. In other words, phosphocreatine is “always working”; it is consumed and replenished during every muscle contraction and during the off-cycle between contractions.

Fatigue is complex, but one likely input is impaired release of calcium ions from the sarcoplasmic reticulum. Calcium ions help regulate muscle contraction. Accumulation of phosphate may play a role here; Phosphate is a byproduct of phosphocreatine breakdown.

So here we see phosphocreatine as an energy source, and its byproduct as a likely contributor to fatigue.

When you take a break, even a short break, it's an off cycle for all working muscles. Because you're in the middle of exercise, your heart rate is elevated and oxygen supply is increased. Phosphocreatine is replenished through oxidative phosphorylation, so the heightened oxygen supply means that there will be a relatively high rate of phosphocreatine replenishment even during that short break.

This process of replenishment means that the phosphate concentration decreases, which means that not only is there more energy available, but the muscle contractions will be more forceful.

8 Rounds is a heck of a score. If you have the patience for a re-test, fast singles on the deadlifts might be a good idea.

 

[abeck0486]

@buckswordbearer Did the fast singles because of another comment you wrote. Probably maximized my score because of that, so thanks.

 

[babydollalice]

@buckswordbearer Thank you for the detailed and technical, yet understandable reply.

 

[sonia5555]

@buckswordbearer Super interesting. Thanks for the detailed post.

What's the best way to train to improve how efficiently we replenish phosphocreatine and clear phosphate?

Because if I understand correctly, it would translate to a greater ability to perform at high intensity for longer, with stronger muscle contractions?

Or is it small potatoes comparatively and we should instead focus on improving the other/actual energy systems you mention in your post?

 

[buckswordbearer]

@sonia5555 TLDR: Build a big aerobic engine. Get really strong. Develop the ability to neutralize glycolytic by-products.

There are two considerations: Force and Energy. Force determines which muscle fibers are used, and energy determines the rate at which they can work. The challenge is synthesizing these two.

This is the Energy part:
PCr is replenished aerobically. More aerobic capacity means faster replenishment. But not all muscle cells are the same. Fast twitch fibers store more PCr than slow twitch. This is a big reason why elite sprinters can sprint so fast. Moreover, slow twitch fibers respond very well to aerobic conditioning, whereas fast twitch do not. This is why Zone 2 training is “necessary but not sufficient” for CrossFit conditioning. The amount available PCr and the rate of replenishment varies by fiber type. All muscle fibers are trainable / condition-able but to varying degrees.

This is the Force part:
The most effective way to preserve PCr is not to use muscle fibers. If your deadlift is 500, you’re using fewer muscle fibers to deadlift 185 than someone whose max is 315. The 500 deadlifter will fatigue less quickly because he is using fewer fibers and is able to have longer off-cycle phases between contractions. A 500 deadlifter in “decent shape” will outperform a 315 deadlifter in the deadlift part of the workout, even if the 315 deadlifter has 6 lungs, because the 500 deadlifter is using less muscle.

Strength creates capacity gaps that conditioning cannot bridge.

This is also the argument for fast singles. The benefit of the dropping the weight and not using any muscle fibers for one second per rep is greater than the time saved going touch and go. In a blazing fast workout like “Diane”, there’s not enough time to stop, but 24.2 is 10 times longer than an elite “Diane”. The energy preservation outweighs the time saved in 24.2

This is the curveball:
CrossFit is an intense training protocol, which means lots of fast twitch fibers and high contribution from the glycolytic system. Buildup of glycolytic by-products can impair oxidative ATP production because it lowers pH and messes up the function of creatine kinase, which is the enzyme that transfers energy to creatine (which turns it into phosphocreatine). So excessive glycolytic activity can slow down this PCr replenishment process.

Hope that helps a bit, although I think I just wrote a few words to say "CrossFit is hard". lol

If you want to read a lot more about this, I’ve got a bunch of papers linked at www.thegainslab.com/physinf

 

[sonia5555]

@buckswordbearer Very helpful. Thank you.

 

[momg]

@sonia5555 Try year of the engine. It works.

 

[truthfullyspeaking]

@buckswordbearer Thanks for this. Super interesting. Amazing that the body can essentially "replenish energy" in such a short amount of time.

 

[aaronemill12]

@truthfullyspeaking The thing that always blows my mind is how you'll be rolling on the floor dying after some WODs, but 15 seconds earlier you were actually doing the thing. I know there is often an element to sprinting when finishing a WOD, but the contrast is so stark. I often wonder, "Could I have kept going 1 more minute if my life actually depended on it?"

 

[jkhaemba]

@truthfullyspeaking You're dictating the breaks. You're in control. Can't do it with all movements but defo have to with some.