I've had a few people come out for our free trial classes, vanish for two weeks, then come back excitedly telling me about how they couldn't walk for three days afterwards and were sore for another week. They tell me this with enormous smiles on their faces and are then genuinely confused when I express concern.
Make no mistake, when it comes to physical activity pushing yourself in new ways will usually make you exhausted and sore at first. But being exhausted and sore shouldn't be your goal for every single training session. This is doubly important for any type of skill based discipline, like martial arts, parkour, etc. In grappling, this is the "time on the mat" principle: consistency is key for improvement. The more regular and frequent your training, the better you get. Far better to train moderately for 5 days than to go all out on one day and spend the next 4 days in bed recovering. I know because I've tried both.
As the article points out, we've been conditioned by the fitness industry to measure the worth of a program by how much we hurt during/after. I think this is the same phenomenon that makes us prefer body soaps that tingle because we can "feel them working." Let's say it plainly: grinding yourself into the dirt for every single workout does not make you tough. It makes you vulnerable. To injury, illness, indoctrination, etc. You don't want that.
Sometimes it's good to train really hard and be wrecked for a day. Overreaching will drive adaptation. But most days you should finish your training feeling good, not bad. The next day you should still feel good. Listen to your body and act accordingly. By means of for instance, today my right knee is bothering me a little - I'm not sure why and I'm not worried about it. But guess who is not going to be doing any jumping today.
You don't want the hardest, most extreme fitness program. You want the one that fits your goals. I don't market Fifth Ape as a belly buster/fat loss system because it's not. I also don't market it as the world's most intense workout, because that's relative. I'm much more interested in feedback like "That was fascinating!" or "I didn't know I could do that!" That's cool. That's people getting curious about how their bodies move.