There is a point in a workout where your body is calm in the knowledge of the hard work you are doing. A blissful state where trouble and doubt fade away, leaving only your harsh breath, the beat beat beat of your heart and the thud thud thud of your feet as you move.
This state is described as the runner's high. Though it is not exclusive to running as the form of exertion. (The thud thud of you pounding the road could be replaced with the rattle clink rattle as you attempt to kick the heavy bag through the wall). Many think that it is the holy grail of cardio states and you know you've worked hard if you experience it. And you have.
However, there is a deeper level than this.
When you go beyond this meditative state, the body does not take as kindly to your efforts.
It takes a lot to achieve the runners high state but going beyond it requires a reckless abandon of your biologically programmed 'conservation' approach to the workout. This must be exchanged for the attitude of being ready to die.
Indeed, the state of exertion past runners high is painful. It is stressful, and characterised by tears and a grimace, and cries and grunts, and snarls. It is an ugly state and reduces one to something not quite human. Something more base, primal. All that matters is the pace, the work. You are unintelligible in this state. All you care about is breathing. The body is in a state of panic and begs for conservation of energy. For recovery. For a few seconds to greedily gulp air. But your grit and pure will must overpower the programming. At this point, performance is almost 100% mental. And the question is not how fit you are, it's how fit you believe yourself to be. Or even simply, how badly you want to a achieve your goal. You vocally snarl through each shot you hit the bag with. Each rep. Each tuck jump. Each press up. And along with this torrent of animalistic growls comes frothy spit not unlike that of a savage ferrel dog ready to devour the next animal it sees. In short you are not only ready to die in such a state, you are quite ready to kill as well.
It is as the dust settles down after such an experience that you reach a knowing calm. Because you know you reached another level. A new depth to your gas tank that has previously remained untapped.
The dreadful pain haunts your thoughts now and then. As you recuperate. But you are more than willing to go through it because you know your opponent is not. Every time you wonder... 'how hard is he working?'
Over the following days the body aches and groans at the abuse you have put it through. But you inevitably recover. And not only do you recover but you grow stronger, physically and mentally. Finally you wake up a week later ready to go to war again.
This is not an experience had by hobbyists. You can get very fit by tracking performance and incrementally improving. But can never develop an unwavering, enemy-slaying willpower.
And such an attribute is arguably essential to those of a violent, martial inclination.