HIIT versus cardio part 5 how do intervals affect performance and body composition

HIIT versus cardio part 5 how do intervals affect performance and body composition

We have previously discussed in our series of articles comparing HIIT (also known as interval training) and steady cardio both the relative benefits and costs associated with each approach, a discussion on the relative impact of EPOC for HIIT, looked at why comparing sprinters with marathon runners is a misleading way to present HIIT training, and most recently looked at the effects of steady state cardio on performance and body composition by looking at both research and empirical evidence.

HIIT - Research On Effects On Performance And Body Composition

HIIT has been shown in some research including the famous one conducted by Tremblay to have a slight muscle building benefit but as was noted earlier, these studies were conducted on beginners for whom any high intensity activity may be liable to produce a muscle building effect. This is a long way from saying that it will have an effect on experienced athletes with a history of resistance training behind them.

Research on high intensity training has consistently shown that it is associated with an entirely different metabolic response to low intensity training with a relatively new study (1) showing that interval training led to significant increases in anabolic hormones including testosterone, growth hormone, and IGF-1 when performed by twelve elite handball players.

Studies such as this have been repeated by others and together they help paint a picture of interval training inducing a positive hormonal response which is beneficial for body composition benefits and building muscle. Despite this we have to be careful of extrapolating studies showing beneficial hormonal effects associated with interval training in non-weight training subjects and assume it means bodybuilders should employ intervals unilaterally. As we have already discussed in our series, for the purposes of generating a large caloric deficit for instance, steady state cardio is a superior tool albeit one with a negative relationship to weight training. Set against this other research shows that interval training can produce similar metabolic adaptations to steady state cardio (2) in a much shorter period of time which certainly makes intervals a useful strategy for athletes needing to rapidly improve their fitness in a short time frame.

The one major issue with all the research though is that it tends to look at isolated, short term studies in beginners or, if they use trained athletes, they tend to be ones whose primary training focus does not require the use of weight training. In addition, it should be noted that the types of intensities used in these studies are rarely used by elite athletes in any sport for longer than a few weeks due to the rapid habituation that occurs not to mention the risk of overtraining associated with a high volume of interval training.

Empirical Evidence for HIIT

While there is a good deal of anecdotal not to mention research supporting the usage of HIIT training for accelerating fat loss its usage at the top levels of sport is relatively low and, as discussed already, the way it is suggested HIIT is performed tends to be very dissimilar to how any athlete on the track trains. We have already mentioned that we should be wary of applying data from untrained, non-weight training subjects and uncritically applying them to strength athletes so will discuss this in greater detail now.

One of the biggest drawbacks with interval training is that it is both neurologically demanding causing a big drain on the central nervous system but can also cause profound soreness especially in the legs, something which is exacerbated when bodybuilders use sprint training to conduct HIIT. Among elite athletes who sequence interval training into their routines it is rare to see it performed more than twice a week although shorter distance sprint athletes will go up to three a week.

How Bodybuilders Perform Intervals Cannot be Compared to Athletes 

Even then, these athletes will as we covered in part 3, utilise much longer rest intervals compared to that seen by those practising HIIT training. In addition, to a man (or woman) they will be following a high carbohydrate diet which is essential both for fueling exercise performance but also enhancing recovery from training. Given this how is it that many bodybuilders who are using HIIT attempt to do so while following a calorie restricted, and often carb constricted diet, while at the same time using shorter rests than world class athletes while attempting to perform intervals more frequently than track athletes (some gurus suggest daily intervals!), and with a higher volume of work. In addition, unlike track athletes, for bodybuilders the prime motivation for their training is to build a large degree of muscle mass which means they will already be doing more weight training than athletes involved in other sports.

What does this spell out? Quite clearly, anyone who is using intervals indiscriminately is going to face serious recovery issues especially in their leg training which is going to have the consequence of impeding muscle and strength gains massively. Compared to performing steady state cardio 3-4 times a week, anyone performing even a fairly restricted HIIT program for that number of times is going to really struggle to avoid their performance in the gym, not to mention their muscle mass from dropping off. If we add to this the fact that unlike athletes, the vast majority of bodybuilders employing HIIT are not used to this type of training so more likely to get sore/injured, and more likely to be using it while dieting, then it is clear that using intervals while training simultaneously for bodybuilding can be very damaging to physiques.

Rather than accepting uncritically the argument that intervals are superior we need to look carefully at our goals when training, and, if building muscle mass or maintaining it is a concern, then the usage of intervals needs to be thought about much more carefully than most do currently. Next week, we will sum up this series of articles and provide some concrete recommendations for trainees as well in part 6 of this series on HIIT vs Cardio.


  1. Meckel Y et.al (2011): Hormonal and inflammatory responses to different types of sprint interval training.
  2. Gibala MJ et.al (2008): Metabolic adaptations to short-term high-intensity interval training: a little pain for a lot of gain?