The article does not answer the question. (I don't believe there is a straightforward best answer but the article does not so much as make a conjecture beyond the most obvious prerequisites.)
Depression Four reviews42 44 57 58 presented analyses by weekly session duration (68 component RCTs, >5016 participants, online supplemental eFigure 12). The median SMD for ≤150 min/week and >150 min/week was –0.58 (IQR=–0.77 to –0.30) and –0.29 (IQR=–0.40 to –0.07), respectively.
Anxiety One review58 provided analyses by weekly session duration (17 component RCTs, online supplemental eFigure 13). The median SMDs for <150 min/week and ≥150 min/week were –1.23 and –0.99, respectively.
I definitely got the impression that this was working better than when I rode 15-25 hours a week, and there were definite diminishing returns with walking for distance. Not unlike how the first few bites of a candy bar are most of your experience and then at the end you’re mostly just finishing it. After the second or third bite it’s all downhill.
For me I find ~3 hours a week are what I need to feel good. As things ramp up (like they tend to in the summer) I tend to need those big rides, but if I do have to back off (say, winter) then as long as I don't go below an hour every other day, I'm good.
"Bicycle widows" is the term for spouses of cyclists who disappear at 7 am on weekends and don't reappear until after 1 pm, at which point they're stinky and exhausted, so they're useless until about 3 pm.
The thing with casual cyclists of a certain age (my club's demographic) is that they like to eat long lunches. So you might be making a respectable 16 mph for hours at a time and then a trip to a diner tanks your average mph. Club riders tend to go for distance, not speed. On a good day those guys would average 11+ mph door to door. Most days was closer to 10.
If you're prepping for a century, I believe the protocol we used for new cyclists was to ride more than 75% of the target distance on the previous Saturday and more than 65% miles on Sunday. And a lot of that is just ensuring your body can handle the amount of friction you're going to deal with in 100 miles. If it was just the serious members, it was more like 80/70. You're likely going to go slower on day 2, so however long it takes you to do 80 miles, it takes about that long to do 70 the next day.
I would not suggest anyone try to go much more than 100 miles (my longest day was 112, and my dad went out after to round up to 115). After I went to college my dad got into 24 hour challenges, which seemed properly nuts to me, and it turns out actually is. Ultra-endurance athletes can damage their heart, leading to atrial fibrillation, which he got. He's been living post-stroke for about 8 years now. He was volunteering some place and was fortunate the guy standing behind him when he went down was a retired EMT.
(For mental health.)
high intensity would be work you can do for only maybe a minute, not twenty, and as a result it won't keep your heart rate elevated very long.
so if they're basically saying 30 minutes 5 days a week, that's low intensity exercise.
Actually according to the article, high intensity can be done for twenty minutes. So what you’re calling “low intensity” is actually “high intensity.”
(Funny how this works both directions, isn’t it?)
Also, an exercise you can only keep up for 20 minutes at a time is pretty high intensity.