The Physiology of FIRST

Since 2003 two marathon running and ironman triathlete exercise physiolgists at Furman University have recommended a unique training program they call FIRST training.  The FIRST training method has received a lot of attention from the running community, including articles in Runners World and a book published by Rodale press.  The attention paid to the FIRST program is well deserved because the inventors of the FIRST method have research data showing that more than 70% of the experienced runners who participated in the three FIRST marathon training research studies set personal records or beat their most recent performance in the marathon.

Clearly, the FIRST training program has been very successful for a large majority of those who tried it.  What is the physiological explanation offered by the Furman team for the success of the the FIRST program?  Why does it work and why does it work better than other programs?  Let’s have a look at the FIRST method and see what we can discover.

Standard Physiological Explanation

The FIRST “3plus2” training program consists of three quality runs plus two cross-training workouts each week.  The Furman University athlete scientists preach that the three weekly runs – consisting of track repeats, a tempo run, and a long run – work together and improve performance by primarily improving endurance, lactate-threshold pace, and leg speed.  They further teach that the two weekly cross-training sessions contribute to improved run performance through several physiological mechanisms including allowing increased recovery time to muscle fibers stressed by running, increasing the muscles ability to utilize oxygen and fat as energy sources during exercise, and improved cardiovascular function.

As part of the FIRST research studies subjects completed a battery of fitness tests.  These tests revealed that, physiologically speaking, the every runner had measurably improved in at least one of the measured variables.  For example, the tests showed that:

  • VO2max increased more than 4% on average
  • Running speed at lactate threshold increased by 2.3 – 4.4%
  • Running speed at VO2max improved by 2.4 – 7.9%

The scientists suggest that the tested physiological changes explained the success of the FIRST program.  In other words, the FIRST physiologists offer the accepted physiological explanation for why FIRST works – improved cardiovascular and metabolic factors.

What About Other Programs?

The challenge with the physiological explanation for the FIRST results is that we know that many other training programs have documented equal or greater improvements in the same physiological variables.  For example, researchers reported in 2002 that elite marathoners running an average of 180 km/week (110 miles/week) significantly improved VO2max during eight weeks of pre-competition training.  Another study found a 8.9% increase in VO2max as a result of a seven week training program with experienced male runners.  These are just two examples – there are a number of others.

More than 70% of the experienced marathoners participating in FIRST either set a PR or beat their most recent performance – in other words they performed better with the FIRST program than with any other program they had used.  Yet, how can FIRST be physiologically better than other programs if those other programs are improving the same physiological variables to the same or greater extent?

The only answer suggested by the FIRST researchers is “training with a purpose”.  They write that most runners train haphazardly, have an incomplete training program, or both.  The challenge with the answer is that it fails to account for the results of those studies that have examined serious or elite runners following complete training programs or to account for the results of the more serious, dedicated marathoners that participated in the FIRST studies.  While it is true that an incomplete or random training program is unlikely to produce optimal results can one really make the case that the elite marathoners cited in the study above generally engaged in incomplete or haphazard training?  Or that all of the prior training of the serious, experienced marathoners in the FIRST study  was incomplete and/or random, despite their level of dedication and seriousness to running?

The physiology world has long focused on the cardiovascular system and energy metabolism as the most important factors explaining endurance performance.  However, as we have seen, these factors fail to account for differences in the success of competing programs.  The physiological explanation offered for the FIRST results does not adequately explain the FIRST results, nor why FIRST is more successful than other programs.  In short, we know FIRST works as well or better than other programs, but we don’t know why it works.  The standard physiological explanation for FIRST completely fails to distinguish it from other programs.

A New Explanation

Since standard physiological wisdom doesn’t explain the success of FIRST, what does?  I believe the answer is “specific muscle fiber training”.  Here’s what that means – FIRST works better than other programs because it better trains the specific muscle fibers involved in running.  As simple and obvious as that answer may seem, I suggest it fully explains the success of FIRST. (I also suggest that this answer is not as obvious as it may seem, but that is a different topic.)

I suggest that muscle – not the cardiovascular system – primarily determines endurance performance.  Specifically, the sum total of the contractile properties and capabilities of individual muscle fibers determines how well a person will perform.  If you better train the muscle fibers involved in the act of running your running performance will be better than if your training is less effective at causing the appropriate adaptation in those same fibers.

The three categories of muscle fibers

Physiologists classify muscle fibers into three broad categories – slow twitch, fast twitch type IIA, and fast twitch type IIB.  The reason fibers are classified into different types or categories is that each type of fiber possesses different contractile characteristics.  On average, slow twitch fibers are the slowest, weakest, but most enduring; type IIA fibers have intermediate speed, strength, and endurance; type IIB fibers are the strongest and fastest, but posses the least endurance.  It is the contractile differences and training adaptations of the different fibers that explains the success of the FIRST program over other programs.

Training a muscle fiber

In order to train and cause an adaptive response in a fiber that fiber must be active and it must be overloaded.  In order to overload a fiber that fiber must be both active and worked to the point of fatigue.  This is a really important point – if you don’t fatigue a fiber it won’t adapt. Simply activating a fiber is insufficient to train that fiber.

Recall that different fibers all have different levels of endurance.  Logically, it takes longer to fatigue a fiber with a high level of endurance than one with a low level of endurance.  It takes longer to fatigue, and, therefore, train a slow twitch fiber than a Type IIA.  And it takes longer to fatigue a Type IIA fiber than a Type IIB fiber.

Muscle fiber activation during running

Muscle fibers are selectively recruited based on the amount of force required to perform a selected activity, activated in order from weakest to strongest.  For our discussion the important thing to know is that slow twitch fibers are active any time you run, from the slowest of runs to the fastest of sprints.  The Type IIA fibers are involved in most runs – anytime your pace increases beyond a slow run you activate Type IIA fibers.  Only during faster runs, such as when running sprints or intervals, are your Fast IIB fibers activated.  So, your slow fibers are always working when you are running, your Fast A fibers are involved during most runs, and your Fast B fibers are worked only during fast running.

Why FIRST Works

Putting together all the facts above provides the explanation for why FIRST works.  Simply, FIRST specifically trains all three types of muscle fibers.  The long run in the FIRST program causes the slow twitch fibers to adapt maximally because only during longer runs are slow twitch fibers sufficiently fatigued.  The speed and time of the tempo runs in the FIRST program primarily overloads the Fast IIA fibers.  The track repeats primarily overload the Type IIB fibers.  Specifically training each of the three fiber types produces better results than not training all three or not training all three optimally.

Don’t the tempo and track repeats train the slow twitch fibers?  After all, aren’t slow twitch fibers active during all runs?  Yes, the slow fibers are active during tempo runs and track repeats, but remember slow twitch fibers posses lots of endurance.  They can contract for hours before they fatigue.  A 30 minute tempo run and or a 2 minute track repeat is simply not long enough of a period of time to fatigue slow twitch fibers.  So, while the slow fibers are active during faster runs, faster runs don’t last long enough to fatigue, or fully train, the slow twitch fibers.

The same thing applies to track repeats.  Type IIA fibers can contract for as long as an hour before they fatigue.  Type IIA fibers are active during track repeats, but the repeats are too short to fully fatigue the IIA fibers.  The IIA fibers do get some training during track repeats, but not enough to cause a maximal adaptation in these fibers.

Finally, slow runs don’t activate the Type IIA or IIB fibers.  Remember, no activation equals no adaptation, so slow runs don’t train the IIA or IIB fibers.

So we see that faster runs don’t last long enough to fully train the Slow Twitch fibers and long runs are too slow to activate the IIA or IIB fibers.  Only by including long distance/slow pace, medium distance/medium pace, and short distance/fast pace in our program can we specifically and adequately overload and train all three types of muscle fibers.

Why FIRST Works Better

Now we know why FIRST works – it specifically overloads and trains all three types of muscle fibers.  But we still don’t know why it works better than other programs because, after all, pretty much every running program on the planet includes long runs, tempo runs, and track repeats.  If all programs include long, tempo, and short runs, then these three runs don’t explain the success or failure of any of them.  Again, I suggest the answer is found in muscle fiber.  Specifically, the answer is in how muscle fibers adapt to training.

Train, Rest, Adapt

In order to train a muscle fiber, you have to overload that muscle fiber.  But, overloading the muscle fiber is not the sole answer.  Overloading a muscle fiber is only the stimulus – it stimulates the fiber to adapt.  The adaptive response within the muscle fiber is what causes the improvement in performance; the muscle fiber gets stronger, faster, more powerful, and/or more enduring.  The adaptive response occurs during rest, not during training.

The process is train, rest, adapt.  Train a muscle fiber and then allow it to rest.  While it is resting, it recovers and adapts.  If you don’t train the fiber it won’t adapt.  But, insufficiently resting a muscle fiber hinders or stops the adaptive response, it slows or stops the recover process and short-circuits the adaptive response.

To cause a fiber to fully and maximally adapt you must specifically and adequately overload that fiber and then, equally important, allow it sufficient time to recover and adapt.

Recovery time

How long does it take a muscle fiber to recover?  Days or weeks, depending on the nature of the overload.

Have you ever noticed that the vast majority of programs usually only include one speed workout per week, one tempo run per week, and one long run per week; i.e. one of each type of quality run each week?  Most programs include multiple easy runs each week but not more than one of each type of quality run.  The most common reason given for this is that it takes at least a week to recover each of the specific quality workouts.  If you were to regularly run more than one type of quality run each week you would likely overtrain in a short period of time.

Now we see why this is true.  Each type of quality run overloads a specific type of muscle fiber and those specific fibers take a week (or longer, in many cases) to recover.  Hence, running one of each type of quality run per week usually allows sufficient time for each specific fiber to recover and adapt.

What about the easy runs?

Now we are down to the heart of the matter.  The real training difference between the FIRST program and other programs is the inclusion/exclusion of easy runs.  FIRST eliminates the easy runs and substitutes cross-training.  Other programs include easy runs.

Therefore, logically, it is the presence or absence of easy runs that explains the difference in performance of the FIRST program versus programs that include the same three quality runs per week.  What is is about easy runs that causes those programs that include them to be less effective than the FIRST program which doesn’t include them?

Logic tells us that easy runs must somehow impede or slow the adaptive response of the muscle fibers.  If all the facts above are true – and any physiology textbook will confirm that they are true –  then there is only one logical conclusion.  Easy runs impede to some degree the adaptive response of the muscle fibers.  Impeding the rate and magnitude of the adaptive response negatively affects performance.  That’s why FIRST works better than other programs.  Ultimately, it allows more recovery time for the muscle fibers which allows for a greater magnitude of adaptation which results in better performance.


The FIRST training program is a very effective training program, producing personal records or best recent performance in more than 70% of the experienced marathoners who participated in the program.  However, the physiological explanation offered by the FIRST scientist does not explain why FIRST works better than other programs.  A logical examination of facts about muscle fiber activation, training, and adaptation provides an answer supported by accepted muscle physiology.  FIRST more adequately trains the three types of muscle fibers and allows more recovery time for those fibers, resulting in a better performance versus that produced by other programs

1.  A muscle fiber must be sufficiently overloaded in order to cause an adaptive response.

2.  After a fiber is overloaded, it recovers and adapts.

3.  Insufficient rest slows the rate and magnitude of the adaptive response.

4.  The main difference between FIRST and other programs is easy runs.  Other programs include easy runs while FIRST substitutes cross-training in place of easy runs.

5.  The logical conclusion is that easy runs impede, to some degree, the adaptive response of the muscle fibers ultimately resulting in a slower race performance.

6.  FIRST is more effective than other programs because it more efficient in the training, resting, and adaptation of individual muscle fibers.


The Physiology of FIRST — 3 Comments

  1. Pingback: The Physiology of FIRST | Training Science

  2. Great website! I stumbled on it accidentally and now I’m reading all of your articles with the great straight-forward information I was looking for.

    This article mentions cross training but doesn’t provide examples of what a cross training activity might be. Don’t other exercises use the same muscles so we are still at risk of not recovering completely? I am a triathlete so break up my activities between the three disciplines, so I understand that swimming likely is quite different from from the running and biking; however if I lift weights the day after a tempo run or go for a good ride doesn’t that hinder recovery in my legs? Does doing a different movement with the muscle make the difference and not the force exerted?

    I find it hard to know how much to do each activity in order to keep performance high while not getting into a constant state of muscle fatigue.

    Thanks for putting up a great website for all athletes.

    • Hi, Ingrid.

      Yes, cross training can interfere with recovery from your primary workouts. But the degree to which a cross training workout might interfere depends on the specifics of the workout – the exercise being performed, the intensity of the workout, the amount of time it takes, etc. Some cross training workouts will interfere a lot, others little to none. For example, upper body strength training as a cross training workout won’t interfere with your running or cycling but it could interfere with your swimming workouts.

      Any workouts that train the same muscle groups – legs, for example, are the primary muscle group used in both running and cycling – have the highest probability of causing interference. That being said, you reduce the chance of overtraining your legs by alternating running and cycling compared to a program of running only or cycling only. The reason being is that while both activities use the same primary muscle groups (legs) they don’t both uses the exact same muscle fibers in the legs. There is overlap – some of the same fibers are used for both running and cycling – but there are also different muscle fibers being used and being fired in different sequences.

      Ultimately it comes down to figuring out what works best for your body. Through experimentation you will have to figure out what cross training workouts work best for you, what gives you the most benefit and greatest improvement in fitness and performance while keeping muscle and body fatigue to a minimum.

      Any form of exercise can be cross training. Swimming, cycling, running, strength training, rowing, eliptical, yoga, etc can all be primary workouts or cross-training workouts. The point of a cross training workout is to provide additional fitness via a different form of exercise than your primary exercise while simultaneously reducing the chance of injury and overtraining.


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