The Science of Endurance

Today we’ll be talking about endurance and the science that we know about so far. Now you don’t have to run marathons or do triathlons for this to apply to you. On some level starting at the 800m mark endurance starts to play a factor. I doubt you’ll find a runner out there that could run a mile or a lot less when they first started. Fast forward a few years and that runner could be doing a marathon. Isn’t that crazy? But how does that work exactly? How does the body change and what is the best way of going about building it? Other than few basic biology things (fast twitch vs slow twitch) I don’t know a lot about how endurance works really. Even though I ask my body to tackle at least one endurance event every year lately. I figured if it’s something that is interesting to me it might be interesting to you too. So let’s find out together!

What exactly is endurance

As usual we will start off with a definition. It turns out that we use certain words interchangeable with endurance even though strictly speaking we shouldn’t. Stamina is how long you can stress a muscle for at or near maximum contraction. So how long can you hold a plank. Endurance however is how long you can ask the same muscles to sustain the same movement probably a significant amount under maximum capacity. Or how long you can run for. That’s what we’re talking about today. Even though I’ll probably default to running this applies to all endurance type events.

The biology of endurance

I knew that endurance runners had more of those slow twitch (type 1) versus fast twitch (type 2) muscle fibers and that you can change your relative abundance of both with training. Type 2 muscle fibers contract faster, with greater strength and are wider than type 1 fibers and are involved in things like sprinting and lifting but they tire out pretty fast. The actual muscle fibers (actin and myosin) in fast twitch muscles are thicker meaning that they can deliver more power, faster. However, since they don’t have as many mitochondria surrounding them they burn through their energy supplies pretty fast.

Type 1 fibers are thinner, contract slower and tire out much more slowly than their fast twitch cousins. When they do tire type 2 fibers are recruited and that means you won’t be able to keep going for very long after that happens. Type one muscle fibers have more mitochondria and capillaries surrounding them meaning they have a better supply of long term energy and the means to deliver that energy to those thinner muscle fibers keeping you going longer. Non-trained individuals have a close to 50/50 balance of these types of fibers but with a high degree of training either way you can swing the ratio to about 75/25. Genetics also play a role in this ratio and how efficient you will be in building each sort of muscle fiber. However studies show that in general people are able to train effectively and work on this ratio either way (Bouchard and Lortie, 2012).

Cardiovascular fitness also plays a large role in endurance performance. Many new athletes will report that their legs (or arms) felt fine but that they had to stop because they got out of breath, dizzy or their chest was on fire. Those are all benchmarks of poor cardiovascular fitness. It was also what made me pull back when I started running. It’s not instant but the time you can exercise increases pretty fast once you start because of modifications in your cardio-pulmonary system. A decrease in heart rate, increased heart stroke volume, increased blood plasma volume without changes in the number of red blood cells leads to reduced blood viscosity and increased cardiac output are all changes that come with endurance training. That’s pretty cool but what does it mean? It means that to accomplish the same movement your body and your heart has to work way less hard. It also means that your risks for things like heart attacks and strokes are greatly reduced. Plus you get to keep all those benefits even during the hours you’re not training!

Early mornings are pretty much a given in endurance training!

How to build it

Long and slow but also ‘short’ and fast has been a tried and true method for endurance training for years and it does work. Most running training plans incorporate a long run and a speed run every week for this reason including mine. The faster run or speed workout ever week is all about moving your lactate threshold back. That’s the point at which you start to accumulate lactic acid in your blood faster than you can remove it. Training hard moves that point backward week after week. If you want to know tons more about the science of speed work I wrote all about it here so we won’t dive too deep into it again.

The other quintessential run (or something else) in the schedule each week is the long one. Typically these are long, long slow plods where we’re told not to focus on time but rather just covering the distance. Why are we doing that one? Usually these runs make up 20-25% of your weekly volume. These runs serve quite a few functions really so sit tight. The first one is just getting you used to time on your feet in a non-complicated way. That can mean different things for different athletes. I could be toughening your feet, helping you to choose the right gear, getting used to fueling your workouts and hydrating along the way. Even though it isn’t sexy it’s important but it happens in the background so don’t worry about it. The second thing is that it physiologically prepares you for the race. As those long runs get longer and the distances greater you really do start to believe you can do it. Now let’s get into the biology! Endurance events generally rely on the aerobic system rather than the anaerobic system. Long runs serve to stress the aerobic system so it works more efficiently at longer and longer distances. Part of that is the muscles of the body getting better at burning more fat for energy rather than just carbs. When that switch happens athletes often report the feeling of ‘hitting the wall’. So we practice it over and over again very, very slowly so we don’t crash on race day. These long runs also ramp those cardiovascular changes into hyperdrive. How long is a long run, well whatever feels long to you is totally a long run but… Lots of those biology changes really get going at the 90 minute mark. At this point the muscles, joints and even the bones of the body start adapting to the harder training and become stronger which can go a long way in preventing injury.

These sort of plans work very well for getting you to that distance AND working on your speed at the same time. Which is to say they do work and have worked well for years. But there is new evidence emerging that there is more that you can do. Or put another way there are options that endurance athletes have long overlooked. You certainly don’t have to incorporate these things into your training but you might want to for a variety of reasons like injury, fun or weather certain times of the year. All of these changes in your muscles and your cardiovascular system do something beyond just make your be able to do the same thing for a really, really long time. It actually improves your running (or whatever) economy. That means it takes you less energy to cover the same distance, it’s pretty easy to see how that would be hugely beneficial in tackling a new endurance challenge. But it turns out there are more options than just long workouts and doing the same thing a bit faster.

One thing that has been gaining traction in endurance circles as of late is strength training. I’ve always heard that I should be doing it to prevent injury but it turns out it really helps with endurance training too! There has been lots of research as of late that points out that incorporating things like High intensity interval training (HITT) outside your sport and heavy strength training helps build your endurance in your main sport rather than hurting it. That myth comes because the reverse is not true! If your goal is to build those fast twitch fibers for feats of strength doing endurance training actually works against you and lowers your sprinting performance. Like I said many studies show now that athletes do get an endurance benefit from strength training but lets mostly highlight one. (The others are below too.) In elite endurance runners who ran more than 30 miles a week incorporating explosive and heavy weight resistance training actually lead to an increase in running endurance and economy compared with the control group that did not do any strength training (Yamamoto et al., 2007). So well beyond just injury prevention we should all be incorporating strength training and counting it towards our goal!

There are also a lot of things that claim to help with endurance but just don’t. Realistically since we’re working on those slow twitch fibers and any help they can get from their fast twitch friends endurance really gets built by time on your feet. You could make a case that certain things that help with recovery maybe, could help by getting you back out there doing quality work faster but beware of other claims. Things like supplements, beetroot juice or caffeine are just fads and probably someone trying to sell you something no matter where they place in the google results, sorry.

Ice bath, nope just fun but that river is known to be pretty cold!

Side benefits

Building endurance for a particular fitness challenge like a marathon has all sorts of side benefits in your life. Though running and exercise in general isn’t the number one way to control body weight, what you eat is, but once you start spending a long, long time on your feet it certainly helps. That’s the thing about exercise we generally just don’t do it long enough to add up to a whole lot of pounds lost. Running one km doesn’t add up to a whole lot of calories burned, somewhere between 50 and 80 calories or about one apple. Start running 10 or 20 km at a time 5 times a week and that adds up to well over 4000 calories or a pound or two a week.

Training for endurance events lowers your blood pressure in a way some other forms of exercise just don’t. When regular runners start doing endurance work they all of a sudden see their blood pressure go down. Even in 4 weeks of training the results can be significant!

Many athletes will report that training for endurance events actually seems to give them more energy! But how can that be? How can spending hours and hours more every week working out make you less tiered overall? Well, endurance athletes actually produce more mitochondria (the powerhouse organelles of the cell) in general to meet those energy needs. Sure training does zap some of your energy some weeks but that increase in endurance can make you feel super-charged in your day to day life!

Well that was a long one wasn’t it? So we’ll wrap it up kinda quick. Isn’t it cool how the body can adapt in so many meaningful ways to help us accomplish something we couldn’t do just a few months ago. I think it’s crazy how my body makes these changes year after year when I decide to do something big … again! What part of endurance training just blows your mind? What are you training for this year?

Read what I read:

Bouchard and Lortie, 2012. Heredity and Endurance Performance. Journal of sports medicince.

Cornelissen et al., 2013. Endurance exercise beneficially affects ambulatory blood pressure: a systematic review and meta-analysis. Journal of hypertension.

Domínguez et al., 2017. Effects of Beetroot Juice Supplementation on Cardiorespiratory Endurance in Athletes. A Systematic Review. Nutrients.

Leveritt et al., 1999. Concurrent Strength and Endurance Training A Review. Journal of sports medicine.

Ronnestad and Mujika. 2014. Optimizing strength training for running and cycling endurance performance: A review. Scandinacian journal of medicine and science in sports.

Yamamoto et al., 2007. The Effects of Resistance Training on Endurance Distance Running Performance Among Highly Trained Runners: A Systematic Review. Journal of strength and conditioning research.

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