How much can you improve – part 1

How Much Can You Improve?

Part 1

You just took up running and are excited about your new activity.  You’ve taken care of the necessary stuff – bought a good pair of running shoes, purchased running specific clothing, and scouted the best places to run in your town and neighborhood.  You’ve gotten over the initial aches and pains that cropped up when you first started running so that now your workouts are quite enjoyable.  Naturally, your thoughts then turn to wondering just how much you can improve; how fast you can get.  What are the odds that there is elite level talent lurking in your genetic structure?  Or above average talent?  Is there any way to determine this in advance?  That’s our topic today – just how much can you expect to improve and what are the odds that you will be a great runner?  Probably not surprising, scientists have wondered the same thing and have conducted research to answer this same question.  This research provides some reliable data for us to consider, data that may really surprise you, so let’s have a look at it.


One of the best research studies on this topic is the HERITAGE family study.  In this study, a consortium of 5 research universities in the United States and Canada teamed up to research the role genotype (i.e. genetics) plays in response to training.  They recruited more than 600 healthy, sedentary subjects and examined a wide variety of physical characteristics and responses to training – things like VO2max, heart rate, lactate threshold, and power output.  The result of this large research project was some very interesting data and a significant increase in our understanding of the range of human response to exercise (1).

To begin, the subjects were given a battery of physical tests to establish a baseline for each subject.  Then all the subjects were put on a standardized 3 days per week exercise program for 20 weeks.  The program started off with 30 minutes of cycling on a cycle ergometer at 55% of VO2max 3 days per week and was gradually increased to 50 minutes of cycling at 75% of VO2max 3 days per week.  This range of exercise intensity (55% – 75%) is considered to be an easy work load.  All exercise sessions were supervised with intensity and duration being monitored very closely for compliance by each subject.  After 20 weeks on this program the subjects were tested again to determine changes in fitness.


Of the more than 600 subjects who participated in this study, data from 481 was used to determine the range of response to the standardized exercise program.  Improvements in fitness were measured by changes in VO2max.  The average increase in VO2max was 400 ml/min, a 17% improvement.  However, this number conceals the wide range of response that was observed across all the subjects.  The range of response was -5% to 56%.  Some subjects actually experienced a decrease in fitness on this program of as much as -5% while others improved as much as 56% – an amazingly wide range of response to the exact same training program.  Table 1 summarizes the range of changes across the entire subject population.

Table 1: Heterogeneity in response to training*

Change in VO2max (ml/min)

% Change in VO2max

Number of Subjects

% of Subjects

-100 – 0

-5 – 0%



0 – 200

0 – 8%



200 – 400

8 – 17%



400 – 600

17 – 24%



600 – 800

24 – 33%



800 – 1000

33 – 42%







* Data is extrapolated from graphs in the research study. Exact figures not provided.

Tables 2 – 4 graphically displays the data from table 1.  Table 2 shows the distribution of changes in VO2max in absolute terms – i.e. the number of subjects falling within each category.  Table 3 displays the distribution of changes in VO2max in percentage terms – i.e. the percentage of subjects falling within each category.

Table 2:  Distribution of changes in VO2max  

Table 3: Distribution of changes in VO2max in percentage

Table 4 shows the distribution of changes in VO2max expressed in percentage, i.e. the number of subjects in each category of % change in VO2max.

Table 4: Distribution of % Improvement in VO2max

Are the results of the HERITAGE family study unique?  No, they are not.  Other studies have been done with similar results.  A study by Prud’homme et al found an average improvement in VO2max of 12% with a range from 0% to 41% (2).  Lortie et al reported gains in VO2max ranging from 0% to almost 100% (3).  Kohrt et al reported very similar numbers with an average improvement in VO2max of 24% and a range from 0% to 58% (4).


What does the HERITAGE family study teach us?  The first thing we learn is that knowing the average improvement from a particular program does not provide any data as to the response of any one individual.  It would be easy to assume that this program was a success since the average improvement for the subjects was 17%.  However, just providing the data on the average improvement doesn’t alert us to the vast range of responses measured in the study, nor does it cue us in to the fact that 2% of the subjects showed negative gains while another 16% showed no or very little gains.  The response of fully 18% of the subjects indicates that this program was not very successful in increasing their fitness levels.  On the other hand, the 17% average also doesn’t tell us about the outstanding results of 14% of subjects that improved from 24% to as high as 56%.  The bottom line is that while it’s nice to know the average improvement from a particular program, the underlying reality is that very few of the subjects improved exactly 17% – in fact most improved more or less than 17%.

A critical thing the HERITAGE family study provides is a vivid picture of just how much variability there is in human response to exercise and that the variability falls on a normal distribution curve (bell shaped curve).  The range of response in the HERITAGE family study is 61%.  As noted above, other studies have found very similar ranges of response.  Within that 61% range of response, note that a relatively few subjects are found out at the edges of the bell shaped curve (very poor response or very good response) while the majority of subjects fall in-between the two extremes (average response).  About 15% of subjects will respond in the low range, 15% in the high range and the remaining 70% in the average range.  What does this mean to you?  It means that the odds are that you are average, that the likelihood that you posses elite level genetics is not very high.  It also means that the likelihood that you will be a poor responder is also very low.

Another important point to be made is that just because one person’s performance improves by X% following a particular exercise program it does not follow that everyone else will respond the same way.  It is very easy for someone to say “I followed XYZ program and improved my marathon time by 20 minutes so it’s a great program”.  While that runner improved his/her marathon performance by 20 minutes on a particular program it doesn’t mean another person will improve the same amount.  Many others will improve more or less than this runner’s 20 minute improvement.  The data suggests that some will see their performance decline even while others are improving dramatically.

This raises another interesting question.  Does a person’s initial level of fitness provide any indication as to their potential?  In other words, if you are a beginner runner and you are very slow, does this mean that you will always be slow?  This question was addressed by the HERITAGE family study too and the researchers found “that age, sex, race, and initial fitness level had little influence on the response of VO2max…”  In other words, just because a person may start with a low initial level of fitness it does not mean they will be poor responders.  A sedentary person’s initial capacity does not indicate if that person will be a low, average, or high responder to an exercise program.  The only way to determine what your individual response to training will be is by actually working out – it can’t be predicted in advance.

Recall that the intensity range of the exercise program used in the HERITAGE study was 55% to 75% of VO2max.  In his book “Daniel’s Running Formula” author Jack Daniels, PhD, prescribes a workout intensity of 65-75% of VO2max for easy and recovery runs.  While Jack’s book is written for runners, the point is that the 75% VO2max intensity reached by the subjects in the HERITAGE study is not a highly intense workout.  Note that despite the relatively mild intensity level of the program, there were still subjects whose performance declined.  Approximately 10 subjects, 2% of the total, saw their performance decline.  What should we make of this?  Why did these subjects performance decline, especially when so many others improved performance on the exact same program?  The answer is not clear from the available data, but I suggest it is because as mild as this program was it was still too much effort for these particular subjects.  Typically, a decline is performance is due to a too high training load.  As difficult as it may be to accept that this very moderate training program of 3 workouts per week for less than an hour per workout and at a mild level of intensity was too high a training load for some of the subjects, the decline in performance experienced by 2% of the subjects indicates otherwise.

Considering the large range of response to the exercise program, what do you think the odds are that every runner should follow the exact same training program?  In my conversations with other runners I am often told that a particular program is best because it is used by elite runners.  The logic here is that since elites are the fastest runners on the planet that their training program is obviously the best.  However, is elite performance due to a superior training program or do elite level genetics play a major role in their performance?  Note the subjects in the HERITAGE  study who improved more than 42% all while training the same as all the other subjects who didn’t improve nearly this much.  Would you train the 18% of subjects in the HERITAGE who experienced very poor results exactly the same as the upper 14% that improved from 24% to 56%?  The evidence is that some will likely experience a decrease in performance on the exact same program that others used to improve a significant amount.  I suggest that the wide range of responses indicates that no one training program is right for every person.  I suggest that there is likely a range of optimal training load as wide as the response evidenced in HERITAGE and other studies.


The HERITAGE family study shows that there is a about a 60% range of response in humans to a standardized training program.  Following the exact same training program, the range of response in the HERITAGE family study includes negative responders (up to -5% decrease in performance), low responders, average responders, and high responders (up to 56% improvement).  The range of response falls into a normal distribution curve (bell shaped curve).  The data shows that knowing the average response from a training program is insufficient to provide any clue as to how any one individual will respond to that program, nor does it provide any evidence of just how wide a range of response will result.  The odds are good that you will be an average responder, with only about a 15% chance of being a low responder and a 15% chance of being a high responder.  Finally the wide range of response to a standardized training program implies that there is an equally wide range of optimal training loads and that standardized training for all, despite the clear fact that low, average, & high responders exist, is probably not optimal training for all.


1.  Bouchard C, An P, Rice T, Skinner J, et al  Familial aggregation of VO2max response to exercise training: results from the HERITAGE family study  J. Appl. Physiol.  87(3): 1003-1008, 1999

2.  Prud’homme D, Bouchard C, Leblanc C, Landry F, Fontaine E.  Sensitivity of maximal aerobic

power to training is genotype dependent  Med Sci Sports. 16:489-493, 1984

3.  Lortie G, Simoneau J, Hamel P, Boulay M, Landry F, Bouchard C.  Responses of maximal aerobic power and capacity to aerobic training  Int. J Sports Med.  5: 232-236, 1984

4.  Kohrt W, Malley M, Coggan A, et al  Effects of gender, age, and fitness level on response of VO2max to training in 60-71 year olds  J. Appl. Physiol.  71:2004-2011, 1991


How much can you improve – part 1 — 6 Comments

  1. Rich, It is so refreshing to find an open minded thinker – no ax-to-grind, just good stuff.

    Wish I’d found a source years ago. Would have been both a better runner and a better father.

    Thanks, Fred

  2. Rich, it surprises me that the HERITAGE study only examined the changes in VO2max to determine how much subjects improved by while on this training regimen. As you established in another article (Do Increases in VO2max cause performance to improve?) VO2max is, at best, loosely related to increases in performance. It seems to me that having the subjects undergo a time trial at the start and end of the program would be a better gauge of fitness (admittedly, the subjects would be able to plan a better pacing strategy the second time, since they could learn from and adjust their strategy from the previous time trial, but I still think it is a better alternative)

    Also, I think that one major uncontrolled variable, diet, could be largely responsible for the range of improvement seen in VO2max. Some subjects could over eat because they felt that after a 30 minute workout they were entitled to a large amount of food, therefore gaining weight and lowering VO2max (assuming VO2max was measured in ml/kg/min). On the other hand, some subjects could have lowered their calorie intake while simultaneously increasing their calorie output, resulting in a calorie deficit and those subjects losing weight and increasing VO2max.

    Finally, I’d like to thank you for all these articles. The ones I’ve read have been very informative- keep ’em coming!

    • Hi, Jake.

      The challenge is that the exercise physiology community a) finds it easier to test for VO2max than measure changes in performance via a time trial and b) have too often assumed that improvements in VO2max cause improved performance. More recently exercise scientists are actually taking the time to measure both changes in VO2max and performance, which is encouraging.

  3. Hi Rich,
    Interesting Read.

    Not sure if this factor was taken into consideration or if it was assumed, but regarding the 2% who presented a negative response to the training program and a decline in VO2 max were mentioned to have been too unfit to handle or respond to this level of training.

    “The answer is not clear from the available data, but I suggest it is because as mild as this program was it was still too much effort for these particular subjects. Typically, a decline is performance is due to a too high training load. As difficult as it may be to accept that this very moderate training program of 3 workouts per week for less than an hour per workout and at a mild level of intensity was too high a training load for some of the subjects, the decline in performance experienced by 2% of the subjects indicates otherwise.”

    Could it be that the subjects in this category were already fit and the training volume was less than they already maintain and resulting in a loss of fitness? Or was it examined that they were too unfit and they were over training.

    Might be a possibility.


  4. Because that possibility could change the whole outlook on success of the HERITAGE study and the hypothesis might be that an increase in training load leads to a relative improvement in VO2 max.

    Especially since the training load was so low. Overtraining is highly unlikely even considering the mere 2% who were in this “category”.

    I suppose the question is if they are infact too unfit, or the possibility they were too fit.

    • Grant,

      It has been several years since I read the HERITAGE study but as I recall none of the subjects in the study were currently regularly exercising or involved in training.


Leave a Reply

Your email address will not be published. Required fields are marked *