This is a good point to further divide the purpose of MA's practice for some people.
TMA with hard contact and emphasis
Sport MA
MA done more as healthful exercise only. No desire or intent for hard contact or competition.
The last one gets tough to translate sometimes. I suppose it is in the same category as kid students keeping the doors open. Don't misunderstand the message. Every practitioner should get the same training and exposure. It is just a fact of life that some people can/will be able to go harder than others. Where/when/how you decide each person has satisfied the curriculum requirements is subjective. The 35 year old engineer with 4 kids and a wife, mortgage and other debt will look at things differently from the 24 year old unmarried engineer. Always.
@drop bear , this has to be factored into the SM.
Everybody spars in our classes. Hard rule. We have some adults that will never be competitive. They go light in sparring and that is understood. I take the time to have clear concise conversations about the effects. I always try to offset the loss of sparring effects with hard contact drills.
Somehow, somewhere every person learning a martial art must experience the sensation of being rocked and how to not freeze up and overcome it. I know of no other way to experience this than to have it repeatedly happen. If anyone else has found ways to minimize the risk I would love to hear them.
There has been some very good references about the effects of stress. Stress comes in two primary forms; mental stress and physical stress. Interestingly, each can affect the other and the variables are almost endless.
A mildly fit, sedentary worker with a laser focus and strong mental acuity can overcome more physical exertion than a body builder or defensive lineman in some situations. Naturally, the inverse can also be true.
Interestingly, there is quite a lot of recorded evidence of people of apparently average strength doing super human feats for extended periods. It is thought to be a Placebo effect whereas since the body has never felt stress at such a level it does not register it as a negative thus the mind does not tell the body to shut down. Pretty cool stuff to me and exactly the 'indominable spirit' that many martial arts talk about.
I think the greatest variable in this discussion is at what point does the stress of a situation start to adversely affect the person?
Some people come in our classes and are effectively stressed before they ever walk in the door. Others come in with quite a lot of capacity. I have seen a similar occurrence in siblings of close age a number of times. Regardless of where the stress trigger starts for a given person the goal is to move the trigger farther out as they continue to practice. Learning how to move the scale for each individual is a challenge the instructor/teacher has to figure out.
All this said, I feel some people will always have a greater capacity for stress than others.