Wednesday, 23 November 2011

Sprint Interval Training vs. Endurance Training

As some of you reading this article may know, I lead an interval running group out of Runners' Choice Waterloo.  All I keep telling this great group is that intervals are the most efficient use of your time- if you want to get fit and fast this is the most efficient way to go!! 

Then I started thinking to myself, "hmm, maybe I better check this out just to make sure I am 100% right."

In my search of the recent literature, I came across an article published in January 2011 out of the Journal of Medicine & Science in Sports & Exercise

This article proved exactly what I expected: sprint intervals (the awesome and fun workouts my group does), with a much lower time commitment, induced identical performance and physiological improvements compared to longer bouts of endurance training (long boring runs that regular people do not always have time for).

Study Design:

This is a breakdown of how the study was completed.  20 healthy subjects were divided into 2 groups.  Both groups would undergo 3 training sessions per week for 6 consecutive weeks.  This is what each group did:
  • Group 1: Endurance Training:
    • 30 minute runs (for first 2 weeks), 45 minute runs (weeks 3 and 4), and 60 minute runs (weeks 5 and 6).  All runs were done at 65% of their maximal effort.
  • Group 2: Sprint Interval Group:
    • 30 second maximal effort bouts with 4 minutes active recovery.  They would complete 4 sets in weeks 1 and 2 and up to 6 sets in weeks 5 and 6.
As you can see based on these numbers, the endurance group was working 30-60 minutes per session.  By contrast, the sprint interval group was only working a total of 18-27minutes (where most of that time was spent recovering). 


The improvements seen in both groups were measured in a number of ways (ranging from body fat percentage to 2000m Time Trial time).  Despite the sprint interval group spending less than half the amount of time running compared to the endurance group by the final weeks of the program, they still showed equivalent levels of improvement:

  • 2000m Time Trial: 
    • Both the endurance group and the sprint group showed about a 30s improvement throughout the 6 week program.  I was especially excited about this parameter because a ~2km TT is how we measure progress in the Runners' Choice group!
  • VO2 max:
    • This is the measure of the maximum amount of oxygen your body can consume per unit of time per kg of body weight.  Again, both groups showed similar levels of improvement (about 12% with each).
  •  Body Composition:
    • This one is interesting!  Both groups gained about 1.0% lean mass (muscle), which again is a positive sign for both groups.  However, the interval group lost 12.4% body fat, while the endurance group lost only 5.8% body fat.  While there is no significant difference in this study, these results are consistent with other studies on interval training.  Bottom line: you lose more fat in less time with intervals!
  • Cardiac Output:
    • This is the measure of how much blood your heart can pump throughout your body.  Interestingly, the endurance group showed a 9.5% increase, while the interval group showed none.  This shows that while interval training is extremely useful, it cannot 100% replace all forms of training. 
Bottom Line:

As you can see, interval training is an absolutely crucial component of training.  In approximately half of the total training time you can achieve:

  • The same improvements in your race times
  • The same improvements in your VO2 max
  • The same increases in lean body mass
  • Higher levels of fat loss
The only downside is that intervals are hard and painful!  So make sure you join a group or get together with some friends who can push you- otherwise your 100% maximal effort will quickly turn into 70% or less (or at least mine would).

A Few Additional Thoughts (after the fact):

Also, keep in mind that while you cannot replace long runs with intervals, by the same token you cannot eliminate the need for intervals with long runs.  Other parameters such as how your body produces and manages lactic acid were not measured in this study- something that interval training will have a more significant impact on compared to endurance runs.  

At the end of the day, best case scenario, doing both is ideal.  However, if you are limited by time, go with the interval workout.

Click here for the article


  1. Another benefit I've found from doing interval workouts or other hard efforts (i.e. hill training) are the hormonal changes that occur (increases in cortisol and testosterone). These act like a "pick me up" such that although I may be sore the day after a hard effort, my overall energy levels are higher and I feel more "alive".
    ...just some of my n=1 anecdotal support of interval training ;)

  2. Richard- good point!! Check out this review which shows your n=1 is actually much larger:

    It makes sense that testosterone and cortisol will have an impact on muscle growth/performance long term.

    However, this review shows that you can acutely modify testosterone and cortisol levels with interval/resistance training- which can acutely have an impact on your neuromuscular performance!

  3. Looks like an interesting review which the abstract provides just a taste of. Would be interesting to read the entire review. Not sure I'm willing to fork out $62.95 though :) Thanks for the link!

  4. Richard,
    WHAT? You don't want to spend $60 on an article?? Haha. I have a hard copy, but I can't seem to find a PDF on my computer to send to you. I'll let you know if it turns up.

    HOWEVER, for a good free source on the hormonal response to exercise, click on this link and download the pdf that is at the top of the search results. It is from 2000, so not the most up to date content, but still really good (and the price is right!)

  5. Thank you for giving us an additional information about endurance training.

    Irvine Endurance Training