What is the difference between someone lifting 50 lbs from the ground to overhead if it's for your job and the same activity for your fitness? Both might feel the same because they carry the same physical sensations. One is an obligation, and one is a choice, freely given.
Pain and suffering can be enjoyed and that enjoyment is determined by how we view it. The pain we choose might even be preferred to the comfort without an alternative.
There is some connection to character building and suffering. Educational theorists talk about a "skill transfer" that happens whenever participation in one activity transfers to an unrelated idea. When we subject ourself to something hard, we're trying to be braver; tougher. When we try to control our breath or pace when it's hard to, we're trying to be restrained and controlled. When we come up short and fail in the moment, we're trying to understand and embrace what it means to be humbled.
Suffering can help cultivate virtue.
We live in a world where aggressiveness is outlawed; we are told that to be liked we are to behave, have manners; be safe, be good. Yet, we can't deny that we feel that way, maybe often. The gym, then, is a haven for understanding ways that we feel that wouldn't fly in other environments. With exercise, we aren't denying those ugly feelings inside of us but giving it a place to thrive. On the track or in the gym, we can socialize them for our own good.
Why then is pain not just bearable, but at times, fun? How do we explain this to others, or even ourselves? It comes down to feelings.
Whenever we feel something there are two possible things going on. There is the sensation of what I'm physically experiencing. This, in the case of pain or suffering, is probably not pleasant regardless of the context. The other aspect though is what you feel "about" the suffering you are going thru. This, on the other hand, could be good; as you think back to the experience of pain, while unpleasant in the moment, could be fondness in retrospect. Being popped in the nose with a basketball when you are not looking makes you feel different than the pop on the nose from your sparring partner, despite the sensation being the same.
The answer is that pain is a complex of the brain. Unlike the notion that the body and mind are separate, amputees showed us that body and mind are indeed connected (i.e. phantom limb syndrome). In Melzack's theory of "gate control", he concluded that the pain mechanism is a 'multidimensional complex with numerous sensory, evaluative, and cognitive components'. In other words, there is great variation in pain based on mood, memory, and even attention. Thru the sequence of nerves and neurons, we determine if the stimuli result in pain.
What could determine the emotions around suffering? If we choose it.
We choose to exercise which means we choose to make ourselves feel a 'way'. This doesn't mean we are masochists nor that we want to hurt ourselves. On the contrary, we never go searching for pain; we try to navigate around it every time. Isn't that the point? With our experience, our skills, and virtue, we keep ourselves from serious harm.
We trust in ourselves that we will try and not quit. We trust in the programs we participate that they will bring out those virtues in us. Every time we choose to be there; it's never forced upon us & if you don't want to be there, you can leave.
Some cross the line. Some lose site of the balance needed to play the game long term. Instead of self-mandating the Hippocratic oath, they take instantaneous discomfort and turn it into long-term affliction with injuries. They confuse bravery with foolishness. There should be humility and caution when you choose something that has consequences and suffering.
In contrast to the work and domestic commitments of this life, we choose to exercise. We ordain our time with this focus over something else and that...is the point. Pain is a test of value; what are you willing to sacrifice in order to get something else in return?