The word ‘intensity’ has a specific meaning in the context of training, and it’s not a descriptor for how challenging something is. Intensity is a measure of magnitude relative to maximal output. Or in other words, how close an exercise or workout is to your absolute maximum. The easiest way to think of this is in terms of rep-maximum. The heaviest load that you can lift for one repetition is the highest intensity possible.
By definition, intensity is inversely proportional to volume. As the volume goes up, intensity goes down. So a three-rep maximum is lower intensity than a one-rep maximum. Less weight due to higher volume = lower intensity. Or you can think of a 60m sprint. That’s peak intensity because you’re running as fast as you possibly can. A 5K, by comparison is much lower intensity because of the higher volume and resulting slower pace.
When we’re speaking in the context of a training program, the word intensity doesn’t have anything to do with perceived difficulty or how sweaty it makes you. So if I describe a marathon as ‘low-intensity’, it’s because it is. Is a marathon pace equal to the absolute fastest you could run if you were being chased by a lion? Of course not - the pace is slower to account for the volume. So the next time I describe your favorite fitness endeavor as ‘low-intensity’, please don’t get all riled up. I’m not saying that what you do is easy or worse or that you’re lazy. The snatch is hard. A 10,000m run is hard. One is intense, the other is less so. They’re both in the Olympics. Intensity doesn’t pass judgement or assign value, it’s just a relative measurement.