REHIT: The Most Efficient Cardio Workout – Better than HIIT?
I’m just starting out my fitness journey but I over-analyze the crap out of everything so naturally I got to reading. I have two young kids (one of them a covid baby, and no, I’m not talking about the covid-19+ lbs I put on during the pandemic) so I wanted to get back on track in the most efficient way. I was looking for the MOST benefit in the LEAST amount of time.
I already knew about HIIT, but in my travels through scholarly journals I ended up reading about Reduced Exertion HIIT (REHIT), which is a HIIT (or Sprint Interval Training/SIT) protocol that only consists of 2 x 20 second maximal intensity sprints (yes, literally 40 seconds total), but seems to provide similar benefits to traditional HIIT.
The REHIT protocol generally goes like this, completed 3 times/week:
- Total time: ~10 minutes
- Warm-up (3-5 mins)
- Maximal intensity sprint (20 secs)
- Complete rest (2-5 mins) – complete meaning that you rest enough to be able to do another MAX intensity sprint at the same performance as the first
- Second Maximal intensity sprint (20 secs)
Apparently this is all it takes for a nice, quick boost in cardiovascular fitness, which is appealing to the lazies and unmotivated, such as myself.
Here’s a demo of the REHIT workout:
In total I’m referencing 3 articles that back this up.
Article 1: Effects of High-Intensity Interval Training vs. Sprint Interval Training on Anthropometric Measures and Cardiorespiratory Fitness in Healthy Young Women: https://pubmed.ncbi.nlm.nih.gov/30568598/
This article compared the effects of 8 weeks (3 workouts/week) of HIIT (4 x 4min @ 90-95% HR max with 3 min active recovery) vs SIT (4 x 30sec all-out sprints with 4 min passive or light active recovery).
Increase in VO2Max:
- HIIT: 14.5 ± 22.9%
- SIT: 16.9 ± 23.4% (Winner)
Reduction in sum of skin folds (body fat measurement):
- HIIT: 15.8 ± 7.9
- SIT: 22.2 ± 6.4 (Winner)
Total effective training (i.e. actual exercise) time:
- HIIT: 16 mins
- SIT: 2 mins (Winner)
A win for SIT. The difference in total effective training time is absolutely ridiculous.
Article 2: High-intensity interval training for health benefits and care of cardiac diseases – The key to an efficient exercise protocol: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6763680/
This is actually the article where I first heard of both SIT and REHIT. It provides a good backgrounder looking into a number of different studies talking about the different HIIT, SIT and REHIT protocols.
Key takeaway for me here is the discussions of lower volume/shorter SIT. The classic SIT protocol was 4-6 30 second sprints (e.g. what was used in Article 1). It was found, however, that glycogenolysis is only activated during the first 15s of a sprint. Glycogenesis is the formation of glycogen, which is the fuel the muscles use during intense exercise. Activation of glycogenesis is also inhibited in subsequent repeated sprints.
What this means is that the classic SIT protocol may be unnecessarily strenuous. When tested, this appeared to be confirmed (discussed in article). The REHIT protocol was then constructed, which was a SIT protocol with the shortest duration and least amount of work. The REHIT protocol is: 10-min SIT sessions, 3 sessions/week, involving only 2 x 20 second max intensity sprints. A 10-13% increase in VO2Max was shown in the studies referenced when testing REHIT over the course of 6 weeks.
Article 3: Effect of Number of Sprints in an SIT Session on Change in V˙O2max: A Meta-analysis: https://pubmed.ncbi.nlm.nih.gov/28079707/
This article is referenced by Article 2, but requires a closer look. This was a meta-analysis of various SIT studies (total of 38 SIT trials from 34 studies) looking to see what effect the number of sprint repetitions had on improvements in VO2Max.
The statistical analysis from all the studies reviewed found that there was a modifying effect of −1.2% ± 0.8% decrease per two additional sprint repetitions. Soooooo… they found that there was actually a DECREASE in benefit from completing more than two sprints… which is absolutely strange, but cool nonetheless. This is the main unintuitive thing throughout all this. But also the finding that definitely supports the REHIT protocol.
- The studies generally use a cycle ergometer (e.g. fancy stationary bike). This goes for most HIIT/SIT/REHIT studies actually.
- Data could be limited and studies could be flawed (e.g. selection of participants, # of participants etc.). I’m not the scientist though.
- Could be generally difficult for some people to tap into a MAX intensity sprint without specialized equipment. I just sprint on a hill and it seems to do the trick.
So yeah, this is interesting isn’t it? I’m interested anyway, so at least there’s one guy… I’m super confused why I haven’t heard more about this.