Getting tired is not the goal of training.
Getting tired is just about the worst thing you can consistently do to yourself. Unless you are competing—and ideally getting paid large amounts of money to train with the express goal of getting tired, being exhausted, and lying panting on the ground—you shouldn’t be aiming for exhaustion.
You’re not getting stronger when you’re tired.
You’re not getting faster when you’re tired.
You’re not improving your skills when you’re tired.
You’re just tired. And when you’re tired and try to do complex movements, that’s when injuries happen. Your body tells you this because it knows disaster is imminent. Your tissues are at risk, dehydration sets in, and you’re far more likely to get hurt if you push through.
“But don’t you need to be conditioned to play a sport, run distance, or even go on a hike?”
Of course. But conditioning should be a byproduct of doing meaningful, purposeful movement. Conditioning through the joy of movement and skill development is far more effective than conditioning through pain and suffering. Training sensibly will get you conditioned as a byproduct.
Another objection might be: “What about Navy SEAL BUD/S camp? It’s all about misery and suffering and seeing who’s got what it takes.”
That’s not training camp. That’s a weeding-out camp. It’s designed to see who can handle the worst conditions and survive, not thrive. The ones who make it through typically lose fitness. They end up worse than when they started. And the ones who don’t make it usually drop out due to catastrophic injuries.
In-season training in the military isn’t anything like the hell camp. It’s far more relaxed. Selection courses use extreme conditioning as a filter to select those with the desired physical and mental attributes, but they aren’t training or developing those qualities.
Breaking people down, getting them tired, getting them exhausted— that’s not training, and it can be counterproductive to your goals.