Training Zones

Contributed by Jeff Henderson 

Through the course of training for a marathon you have and probably will hear all sorts of terms tossed around. Many of which you probably haven’t heard before, particularly if you come to speed workouts.

So, let’s make like we’re in elementary school again, except these words are much larger, you won’t have to write them in cursive on a chalk board and we will not be holding a spelling test at the end of the week!  The following words of the day are brought to you by the letter A!


Aerobic Threshold – You aerobic threshold in simple terms in the high end of the spectrum with which you can run or walk comfortably while also being able to carry on a conversation. This is the zone that you should utilize for the bulk of your training. While training aerobically your body is burning oxygen with oxygen and creates a temporary energy source. The easiest way to determine your true aerobic threshold is to utilize heart rate training. Your aerobic threshold(also known as lactate threshold) is typically about 20 beats/minute slower than your lactate/anaerobic threshold, or about 65% of your max heart rate. As you develop your aerobic system your aerobic threshold will gradually rise.

Lactic Acid – Lactic acid is a derivative of exercise that is produced in the muscles during periods of high exertion. As you start to push the need past your aerobic threshold you slowly start to develop lactic acid. The concentration of lactic acid increases at higher levels of intensity as your body begins to produce more lactate(a by-product of carbohydrate metabolism) than your body tissue is able to remove. This point is known as your lactate/anaerobic threshold and is the purpose behind doing Lactate Threshold(LT) workouts. Tempo Runs, LT Intervals and LT hills are examples of workouts we have done that are designed to increase our lactate threshold. At the point of lactate threshold your body begins to tighten up, muscle soreness occurs, and you become physically unable to push any harder. Lactate threshold is the single most important element to faster performances in the marathon and half marathon.

Anaerobic Threshold – As mentioned above, once you drift out of your comfort zone and are not able to speak in complete sentences, comment on the birds flying above, etc. you have discovered your anaerobic training zone. If you discover this lovely zone on Saturdays during your long workout SLOW DOWN YOU ARE GOING TOO FAST! Once you have reached your anaerobic training zone your body is no longer producing energy by burning glucose with oxygen. If you keep pushing in the anaerobic phase your body quickly burns through the energy source created and lactic acid builds up forcing you to slow down. We are able to raise our anaerobic threshold through workouts designed to make our bodies develop and endure through the process of lactic acid production. Over time our bodies become more efficient at removing lactic acid at a rate equal to its production. Workouts such as last week’s workout definitely push that needle. Thus the reason many of you were still feeling its effects on Thursday and Friday.

Q - I am an MIT member training for my third marathon, and am very confused by what is meant by recover runs.  Do they make me faster or help me get rid of lactic acid so I can be better the next day?  Should I be doing this type of run or taking the day off completely after I run hard?
A - This is a question I know runners wonder about, as I get asked similar things quite a lot.  A recovery run is a relatively short, slow run typically done the next day following a hard interval session or the day after a tough tempo run.  Many runners assume the purpose of this light workout is to allow recovery from those intense efforts the day before.  I have frequently heard coaches and trainers discuss how recovery runs will increase blood flow to the legs, and that this will flush all the lactic acid out of the fatigued muscles.  The plain truth and physiological fact is that muscle and blood lactic acid levels return to normal within 60 minutes after even the most intense physical efforts.  Additionally, there is no evidence that the sort of light activity a recovery run requires enhances damaged muscle repair, the rebuilding of glycogen storage, or any other physiological response that is relevant to muscle recovery.

Although it may seem counterintuitive, recovery runs do not enhance recovery. That being said nearly all elite endurance athletes practice this sort of training, and they would not do this if they did not believe there was some important training benefit to be gained.  Recovery runs actually increase your fitness, and they are very important for experienced runners, as they challenge you to run (although very slowly) in a so called pre-fatigued state (that is, a condition where fatigue is still present from the effort the day before).

Remember that fitness is an adaptation to a stimulus, and often the optimal stimulus for runners is pushing yourself and performing your workouts beyond the point of initial fatigue.  These hard workouts are often called the key workouts of the week, and they are challenging in pace, and perhaps also duration, and they take your body much further past the point of initial fatigue.  Conversely, recovery runs are typically done entirely in a fatigued state, and as such also serve to enhance your fitness even though the efforts are much slower in pace and typically much shorter in distance.

Let me be clear, I believe that the sort of training program with built in recovery runs should only be practiced by those that are experienced runners.  First timers in a marathoner-in-training program or half-marathoner-in-training programs should allow for a day of rest after an intense, key workout.

If you do choose to utilize recovery runs, here are some guidelines:

•If you choose to run again within 24 hours of completing a key workout, the next run should typically be a recovery run.

•Recovery runs are really only necessary if you run four or more times a week.  If you are on a four day per week training program, your first three workouts should be key workouts and your fourth run of the week only needs to be a recovery run if it is done the day after a key workout, instead of the day after a rest day.  If you run five times a week, at least one run should be a recovery run, and if you run six or more times a week at least two runs should be recovery runs.

•The trick is to balance this sort of training appropriately.  To much fatigue leads to overuse injuries so it not advised to complete two consecutive hard workouts.  Similarly it is not advised or typically necessary for experienced runners to insert two recovery runs between hard efforts.  What you are aiming for is the optimal training stimulus to promote the best fitness adaptation; therefore some patience and experimentation will likely be required to find the best recovery run balance for you.

•The optimal length and pace of recovery runs is not fixed.  Your goal is to run in the pre-fatigued state not to negatively influence your training performance in your next key workout. Generally, your recovery runs should not be particularly long or fast or you will diminish your abilities in your next key workout.

•We know the champion runners from Kenya are notorious for running very slowly in their recovery runs, so do not be too proud to follow their lead.  Remember that even very slow running in the pre-fatigued state will yield improvements in your overall running fitness, which will ultimately enhance your performance in races.

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