Sunday, July 24, 2022

Is High Mileage Necessary To Run Fast At Your Races?

Maroochydore, Queensland- great for long runs
My colleagues and I were discussing just how much mileage a runner can safely increase before running the risk of injury. It does seem like mileage is a tricky topic for many runners. Often many runners would ask other runners how far they are running each week. 

Most runners track it. Some believe it holds all the keys to being successful in running (more is good, less is bad).  

My first running coach in secondary school taught my teammates and I that consistency in running and intervals were necessary for fast race times (we did cross country - 4.8 km and track and field - 3000m longest event). My junior college running coach emphasized quality over quantity (no junk miles). So why do some coaches and elite runners swear by high mileage?

Running an easy kilometer is totally differerent from doing 5 x 200 m at 30 secs a rep (that's a 2:30 min  kilometer pace). Recovering from the 5 x 200 m will be different compared to running an easy kilometer at say 6:00 min per kilometer.

Perhaps we should consider training what muscle fibers we have in our bodies before deciding on mileage. We all have 3 main types of muscle fibers. Type I or slow twitch muscle fibers which are the smallest and produce the least amount of forces, but once trained can go all day long without fatiguing. They also help to hold and stabilize our posture. They are fueled by aerobic energy. 

Picture by Kurt Rawlins from Pinterest
Type II or fast twitch muscle fibers which are further divided into Type IIa and Type IIx (also known as IIb). These are larger muscle fibers and produce a greater and quicker force (than type I), but have less mitochondria, myoglobin and capillaries (compared to Type I) and are prone to fatigue quicker.

Type IIa (also known as intermediate muscle fibers) is a mixture of Type I and IIx fibers. They use both aerobic and anaerobic energy systems and fatigue slower than Type IIx. Proper training of Type IIa fibers will increase their ability to utilize aerobic energy, translating to greater endurance.

Type IIx are the largest muscle fibers and produces the most forces but are inefficient and fatigues quickly as it has low oxidative capacity and relies on anaerobic energy.

If you only do easy long slow runs, you utilize your slow twitch (Type I) fibers. If you run harder, your intermediate Type IIa fibers kick in to help. If you are required to do a hard 400m sprint or longer then all 3 types of fibers are used.

All the muscle fibers are fueled by 3 energy systems, one aerobic and 2 anaerobic. The Phosphagen energy system (or ATP-CP system) uses creatine phosphate to provide energy that can only last 10-15 seconds at high speed. This is what is used when you are sprinting all out.

The next anaerobic (glycolytic) system uses carbohydrates to provide another short source but fast acting energy. Medium to high intensity runs utilize this system. 

Lastly, the aerobic energy system which takes 30-40 seconds to start (since it takes time to deliver increased oxygen to your muscle fibers) and uses carbohydrates and fats to deliver long term, high volume energy for your muscles.

So, if you're training for a good timing in a 10 km race, that is at least 90 percent fueled by the aerobic system. However a fast 10 km will require help from your intermediate and fast twitch fibers. It will NOT be enough to do just low intensity, long, slow runs which targets your slow twitch fibers. You need to train your intermediate fibers as well with tempo runs (race pace you can hold), 1km intervals with short recovery, hill reps of 300-600 metres etc.

Runnning definitely damages the muscle fibers used in training and racing. The faster you run, the more fibers damaged. Your slow twitch muscle fibers starts to run out of fuel and fatigue after 60-90 minutes and you will be using intermediate fibers to compensate. That's why you recover easily when you do easy slow runs while faster and longer efforts require you to rest 2-3 days before your next demanding session.

Your bone and tendons require more time to adapt compared to muscles so do not ramp up volume and speed too quickly otherwise you could sustain a stress fracture.

As for your energy systems, your Phosphagen systems recuperates in about 3 minutes. Your aerobic system needs about a day to replenish its muscle glycogen stores. The glycolytic system requires at least 2-3 days to recover from a tough anaerobic workout.

If you are training for a marathon, you obviously have to run higher mileage compared to training for a 3000m track race or a 5 km run. 

Understand the demands of your race. Plan and schedule workouts to meet those demands. Then you can add up your mileage. So mileage is not a training plan. It's simply counting the total distance you ran for the week.

Moreover our fitness, age, physical make up and experience makes us unique or n = 1. Just because someone else in your running club is running 100 km a week does not mean you should. 

Ultimately, the mileage you're able to chalk up is limited by the recovery needed between your workouts, not so much by how far or fast you want to run.

Wouldn't it be better to identify the workouts that target the muscle fibers and energy systems required to meet your race goals than to focus on your mileage?


Baker JR, McCormick MC and Robergs RA (2010). Interaction Among Skeletal Muscle Metabolic Energy Systems During Intense Exercise. J Nutri Metab. DOI: 10.1155/2020/905612.

McArdleWD, Katch FI and Katch VL (2000). Essentials Of Exercise Physiology. 2nd Edition. Baltimore: LippincottWilliams and Williams.

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