HIIT (High Intensity Interval Training) works. The jury has come back on that ruling and there isn’t much debate about it anymore. You can improve aerobic fitness, strength, grow muscle, even turn on inactive genes. Over the past few years study after study has shown the benefits of HIIT. What is missing are some more conclusive answers to how different approaches to HIIT vary and which one you want to follow.
Doing repeated intervals on the bike or the treadmill is certainly different than using body weight exercises, which is again different then using external resistance like barbells and dumbbells. Add in the challenge of how do you even compare the different modalities. The variables you use to control the intensity on a piece of cardiovascular equipment (heart rate, time) may or may not translate to what you can control doing more traditional strength moves like squats, deadlifts and presses. It is one thing to compare the length of two different bike intervals but how do you control and compare the intensity of a bike interval to that of a strength exercise?
Let’s not forget the impact different populations and their objectives have. The average person looking for improved health doesn’t need the same program that someone looking to drop the maximum amount of body fat which is again different from what a runner/cyclist needs or what a strength athlete is looking for. Everyone needs a combination of both strength and cardiovascular benefits but the mix changes depending on the person’s activities and objectives.
Androulakis-Korakakis et at. (2018) started to answers the question of which type of interval is best by comparing aerobically based intervals to resistance based intervals in well trained strength athletes. The aerobic group performed 8 weeks of cycling intervals twice a week. Each interval was for 30 seconds at 85% of maximum heart rate followed by 90 seconds of recovery at 50-60% max heart rate. They performed 8 rounds. The strength group used squats one day a week and deadlifts for their second training day. They performed 8 rounds of the prescribed exercise with a weight equal to 60% of their 1 repetition maximum weight. Each set was conducted until the subject reported a level of exertion equaling 80-90%. This came to 8-15 repetitions over 16-30 seconds. This group rested for 90 seconds between sets. Both groups were allowed to continue doing their normal training the rest of the week.
If you guessed that after 8 weeks both groups saw improvements in their aerobic fitness then pat yourself on the back, you’re correct. If you guessed that the group that did their intervals on the bike saw a significantly greater increase in cardiovascular fitness then you’ve earned a cookie.
When it came to strength improvements if you said both groups saw an improvement in strength then you area 3 for 3. Now for a perfect score did was there a difference in strength improvements between the two groups? No there was not. Sorry to ruin your perfect record. Both groups saw similar improvements in strength. I know you had your money on the lifting group.
So what does all of this really mean? Well, if you are a well trained strength athlete and you want to improve your cardiovascular fitness you can use strength based exercises to build your intervals. The results won’t be as great as if you used aerobic exercises but they will be positive and meaningful. Now what if you aren’t a well trained strength athlete? I think you would be safe assuming the same general conclusion applies to you though the exact magnitude of the changes and the difference between the two different training approaches may be different, however they will probably both still improve your aerobic fitness and your strength.
I appreciate this study because it is one of the first to look at the practical question of what type of exercises we can use for our HIIT and how they differ. The reality is in the gym all sorts of different movements are used to create HIIT circuits and trainers have been assuming they can create similar effects using body weight or strength exercises as they can with traditionally aerobic movements. This study starts to provide some evidence to that question and clearly shows that the strength exercises will create improvement in cardiovascular measures, though not as great as if you use aerobic based intervals. As always, you have to ask what your objectives are.
There are still some serious shortcomings to this study that keep us from implying any overly broad conclusions. First, the study was done with trained strength athletes. Their experience in the gym and the training state of their bodies means that they will have different responses then untrained individuals. The subjects were also primarily in their early 20s and the reactions of middle aged and older exercisers could be different. The subjects were also allowed to continue doing their normal training in addition to the prescribed HIIT. Both groups showed similar improvements in strength and that could be the result of their other training and have nothing to do with the HIIT. The squat/deadlift group also had a rather long rest period, far longer than is usually used in the gym for HIIT and this could be impacting the results this group saw. I am also concerned about the testing choices used by the authors. While valid, they are not as rigorous as other common techniques.
So what do these concerns mean to how I interpret this study? I still like that they are examining the difference between different types of HIIT circuits. I think the difference they found in cardiovascular improvements between the groups is suggestive of a more meaningful difference. While only limited conclusions can be drawn this a good first step in helping us really figure out what works best for HIIT and what the differences are between different HIIT approaches.
If you are more concerned with aerobic improvements but still want some strength gains then you should be utilizing more traditional aerobic movements. Not necessarily to the exclusion of traditional strength moves but certainly they need to form the foundation. If you are more focused on strength and similar benefits this study would suggest it doesn’t matter what you use for your interval tough I think the subjects continuing their regular training hid potential strength advantages to the lifting centric approach.
Androulakis-Korakakis, P., Langdown, L., Lewis, A., Fisher, J., Gentil, P., Paoli, A. and Steele, J. (2018) Effects of Exercise Modality During Additional “High-Intensity Interval Training” on Aerobic Fitness and Strength in Powerlifting and Strongman Athletes. Journal of Strength & Conditioning Research. Feb:32(2):450-457.