> Another part of the answer is that fatigue is largely in our heads.
Not in our heads, but in our nervous system. Some types of fatigue are due to feedback into our central nervous system that reduces muscle activation signals from your brain in order to avoid damaging the muscle. But if you're untrained, your body doesn't actually know where this point really is.
Most strength and endurance gains when you first start training are neurological, where the effect of this feedback loop is pushed back as your body learns the true threshold for muscular damage.
The heart does get fatigued though. You can run a horse into dying from a heart attack, for instance. Most people simply aren't fit enough to push it that far, as their other muscles would give out first.
Not in our heads, but in our nervous system. Some types of fatigue are due to feedback into our central nervous system that reduces muscle activation signals from your brain in order to avoid damaging the muscle. But if you're untrained, your body doesn't actually know where this point really is.
Most strength and endurance gains when you first start training are neurological, where the effect of this feedback loop is pushed back as your body learns the true threshold for muscular damage.
The heart does get fatigued though. You can run a horse into dying from a heart attack, for instance. Most people simply aren't fit enough to push it that far, as their other muscles would give out first.