The Keys to Increasing Your Aerobic Capacity

by Dick Vincent

There are many components to improving fitness for distance runners but none is more beneficial than improving Lactate Threshold (L.T.). I thought I would briefly go over what L.T. is, how lactate is metabolized in the cells, what happens when you exceed your L.T., and how you can improve it. To keep this from exceeding the number of pages as in Gone With Wind, I will be as brief as possible and try not to get too technical.

There are three energy systems that the human body uses to produce Adenosine Triphosphate (A.T.P.), which is the gasoline your body uses to do work. The CPr (creatine phosphate) system, the glycolytic system and the aerobic system. Sprinters are all about the CPr system but we distance runners generally don't depend on that system for work. Although it is the most powerful energy system, it is the easiest to exhaust (it begins to unwind after 6-8 seconds). We have the glycolytic system that works without oxygen. That is your glycogen driven system (carbs supply this) and although not as powerful as the CPr system, it is more powerful than the aerobic system, albeit not as enduring. Finally, we have the aerobic system, the bread and butter of distance running energy.

The aerobic system is the mainstay for distance runners. It produces the least immediate power of the three energy systems, but it is the most easily trained and it is by far the most enduring. The aerobic system will work for hours, even days, for the well trained runner.

The glycolytic system supplies more power than the aerobic system and it will supplement the aerobic system to the marathon and beyond. The shorter our race, the more we use it, the longer our race, the less energy it contributes to our race but it is still very important. At 800 meters the glycolytic system provides 55+ percent of the energy. At the marathon it may provide as little as 3% but trust me, you will know it when it runs dry (does the word BONK ring a bell?).

The Creatine Phosphate system, (CPr ) is where sprinters and field event athletes derive their energy and is mostly insignificant for endurance athletes. It is also the most difficult to train and it runs at its peak for only 6-8 seconds. Therefore I won't address it at this time.

The aerobic system does most of the work when we are running at 65% of our maximum heart rate or less. It's main fuel is oxygen and fat. The mitochondria in our slow twitch muscles oxidize this and makes ATP. The more developed our aerobic system, the faster we can run while staying below our “aerobic threshold” or approx 65% of maximum effort. Once we cross that aerobic threshold the demand for more power is needed and the glycolytic system begins to supply more fuel. The beauty of slow twitch muscle fiber is that it can utilize both oxygen/fat and glycogen as fuel. Fast twitch has little or no mitochondria so it cannot metabolize oxygen. Fast twitch is anaerobic. Fast twitch 2A has some mitochondria and therefore can utilize some oxygen but still fatigues faster than slow twitch. (How much of each type of fast/slow twitch fiber we have varies with each individual).

As our pace increases more and more, and our effort climbs above the aerobic threshold, more and more glycogen is needed. There is a complicated chemical process that it goes through but it goes to the cells as pyruvate and then changes to lactate acid then lactate in the mitochondria. Lactate is metabolized and used to produce energy along with the oxygen and fat (NOTE: lactate is not the enemy we once thought it to be. It is fuel!). The faster we run, the more the glycolytic system supplements the aerobic system, producing higher levels of lactate. Then there comes a point where more lactate is going into the mitochondria than can be processed. At that point lactate begins to spill out into the blood and you have REACHED YOUR LACTATE THRESHOLD! Lots of CO2 is produced and your breathing rate begins to climb exponentially ( your breathing rate is driven by a need to expel CO2. Heart rate goes up when you need more oxygen). An athlete running at L.T. can only run approximately 1 hour at this pace before they are reduced to a crawl. The faster we go, the more lactate climbs, and the sooner that athlete will crumble.

Obviously, if we can increase our L.T. we can run faster. The faster we can run below our L.T., the faster we can run a marathon as nobody can run a marathon at their lactate threshold.. As I pointed out earlier, for the average runner L.T. is approximately 1 hour race pace. (Another estimated measurement would be 5k race pace plus 20-25 seconds per mile).

So how do we improve our lactate threshold? There are numerous workouts and also a couple of other approaches. First off, you can improve your pace at L.T. without actually improving your L.T., if you improve your aerobic fitness. Let's say you currently run a 9 minute per mile pace at 65% effort (aerobic threshold) and 8:30 per mile pace at lactate threshold. If over a training cycle your aerobic fitness improves so that at 65% you are running 8:45 pace, then your L.T. pace will be approx. 8:15 pace without actually increasing your L.T.. You are starting at a higher base fitness and that benefit will be passed on to the faster paces in all the training zones. One key to increasing your aerobic capacity is to not run your easy runs too fast. Running your easy runs too fast produces higher levels of lactate and that interferes with aerobic development, not to mention they aren't really easy.

Of course by doing workouts that target L.T. development you may be able to increase your threshold from 78% to 85% or more. Workouts such as tempo runs (I define tempo runs as running a pace at or above L.T.) specifically target lactate threshold improvement. Research has also shown that alternating the pace around threshold helps for better development. That can be done with a progression, very much like tempo, but slowly increasing pace from below L.T. to above it.

Cruise intervals (a misleading name as intervals on track workouts technically refer to the recovery period), are common track workouts. Cruise intervals are run at a pace slightly faster than L.T. with shorter recovery jogs. It's best if the rep itself is longer in duration (1k or more), and the recovery jog shorter. The idea is that you go beyond L.T. pace so that lactate spills into the blood, then on the short recovery your body clears some of it before you go back at it again. This helps your system to improve at handling lactate and adaptation occurs.

My favorite workout for this is what I call 7-3s. I originally thought of this as 9 to 5s (a take off of the 9-5 work week) but the average runner should start with 7 to 3s. After a warm up the athlete will run 7 minutes at threshold pace broken up with a 60-90 second recovery jog. Then a 6 minute segment at L.T. pace followed by another 60-90 second recovery jog. The next 5 minute segment is slightly faster than L.T. (approx 5 seconds per mile), then another recovery jog, followed by 4 minutes with a 10 second per mile pace increase. And finally the final 3 minutes at 15 seconds per mile pace increase. This gives an athlete 25 minutes at intensity pace. 8-4's provide 30 minutes at intensity and the 9-5's provide 35 minutes at intensity. Training at this intensity more than 35-40 minutes is closer to race effort and therefore requires too much time/days to recover.

Keep in mind you don't want to go significantly faster than L.T. pace. You want your body to adapt to utilizing and clearing lactate as well as getting as many minutes of training in as possible, without tiring yourself so much that you need too many days to recover. There is some lactate threshold development at faster paces but that tires the athlete significantly quicker and there isn't as much time spent at intensity. Running too fast raises the level of lactate in the blood so high that adaptation is hindered, along with taking far too much time for levels to drop. You want to get on with the show and not spend a lot of time recovering between reps. How much time you spend training over the course of the month is more important than how much effort you put into one individual workout. Train hard, recover fast, and train again.

There are many other workouts to improve L.T., these are just a few examples to get you on your way. Lactate threshold development may be the most important component to improvement, but it is not the only component to fitness. Leave room in your training cycle for other components. Many coaches and athletes have a macro cycle of 4-6 weeks dedicated specifically to lactate threshold improvement, but make sure your training cycle has a well balanced approach.

I look forward to putting this pandemic behind us and seeing you at the races.

Dick Vincent:

USATF Level 3 Certified Endurance Coach
I.A.A.F. Level 5 Certified Endurance Coach.

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