For all of the physical results, I'm going to skip mentioning them in great detail. Considering that both the HIIT and Moderate intensity exercise groups had the same caloric expenditure, other metrics are kind of irrelevant for this study. However, here are some graphs of measures they took. It's not suprising as you'd expect things like heart rate, V02 and Rate of perceived exertion to be much higher in the HIIT group (They all were).
However, I will talk about at least 2 of these graphs (below) which is the feeling Scale and RPE (rate of perceived exertion) scale, which are the crux of this whole review. These are both good measurements to get an understanding of how hard (mentally and physically) participants are working, and how that makes them feel.
As you can see with the RPE scale, each time the interval switched to the higher intensity, the RPE scale increased (not surprising) and decreased when changed to the lower intensity (also not surprising).
However, you can see that each time this change occurs, the rating on the feeling scale decreases. Meaning it's probably more and more difficult for participants to stay motivated and or continue.
What this all means
I can tell you from experience, HIIT training sucks. If you enjoy doing it, you're probably not doing enough, relative to your own ability.
I can also tell you that even with 11+ years of intense training under my belt, I often find it difficult to actually commit to using true HIIT training. So for an overweight and untrained, middle-aged women to feel similar, isn't really surprising to me.
What would be surprising if these women were willing to go and do this protocol on their own, consistently, with no one guiding them.... I'd imagine they won't.
See while HIIT may be time efficient and may or may not provide immense benefit above traditional cardio it's still really difficult to use it properly and effectively.
Now while that may sound like a cop out, try convincing an over weight middle aged women to work until the brink of throwing up (which is often how you feel after HIIT). Chances are you just can't do it.
Not to mention, for an individual of that nature, is doing true HIIT really even necessary? I'd say probably not and that the answer to that question is largely contextually based. While many people think HIIT is the best thing since creatine, chances are it's really only beneficial for a certain subset of individuals looking to get more shredded than they already are.
This doesn't mean that you shouldn't work hard. I'm a firm believer that you'll get out what you put in when it comes to training and nutrition. But in the context of a client, their ability and current body composition / athleticism, you'll need to keep in mind that if you use HIIT, often, they might hate you for it. And realistically, they might begin loathing the idea of working out.
How to use this information
To be brief, use context to determine how you should prescribe exercise. If the person severely over weight and untrained? If so, using HIIT probably isn't the best method.
You're old friend from high school asks how you got so shredded? Feel free to tell them that you did HIIT, but explain to them that it might not be the best idea for them (and then send them here ;).
While HIIT may be effective, it largely depends on the person,their ability, and motivation to make a change.
Why this should matter to you
First of all, it should matter because it reveals that using HIIT is largely dependent on the person you are prescribing it to.
While HIIT may or may not be efficient and a better option on paper, it won't be if the individual you are telling to do it hates it and never does it again. This is especially important for many older individuals who don't necessarily see the benefit of working out (because they are tired from working all day) or who have a seemingly have an insurmountable amount of weight to lose (this often causes people to give up shortly after starting).
Just keep in mind the next time you start telling people they need to use HIIT, it's based on context. Plus, using a lighter intensity and having the willingness to do it again is far more important than a single HIIT session that keeps people away from the gym forever.