Setting: Earth, no more than a century in the future.
Premise: Certain US soldiers volunteer to receive genetic modifications that grant increased strength, endurance, and healing capabilities. Most of these capabilities are only technically superhuman--they are slightly above what a normal human can achieve. They can't lift cars or punch holes in steel bulkheads.
The greatest advancement is their endurance: an engineered soldier can theoretically run at a full sprint indefinitely, given a constant supply of calories and water.
Problem 1: The soldiers tend to push themselves beyond their new physical limitations, as they no longer experience the fatigue of a baseline human during exertion, and they do not have evolved instincts for their new capabilities. As a result, an engineered soldier can accidentally raise their heart rate and blood pressure to the point where they'll suffer instant death due to cascading burst blood vessels in their brain.
Solution: The engineered features include a pea-sized gland within the soldier's brain, which will create phantom physical sensations to warn the soldier when they begin to approach their limit.
If they ignore these sensations (like a buzzing cell-phone over their heart) and get too close to the fatal limit, the gland will instantly render the soldier unconscious, and gradually slow their heart.
Question: What are the potential flaws in the warning/killswitch gland? More specifically, what are the potential flaws in a safety feature which will instantly knock a soldier unconscious in a situation where they would otherwise have a very good chance of dying (>90%)?
Are there any obvious ways that an enemy force could exploit this killswitch to their advantage?
[Edit]Problem 2: Why not use the gland to mimic the fatigue sensation? The genetic engineering technology is still relatively new, and geneticists are able to create very straightforward sensations (ie, a given patch of skin, of a given diameter, will feel like it's buzzing). More abstract sensations, like fatigue, vary wildly from person to person (in terms of brain chemistry), so they've not yet developed a safe catch-all.
A second issue with mimicking the fatigue sensation is that soldiers are all trained to push past it as part of basic training (not just in this future setting, but in reality). The difference is that non-engineered--but otherwise healthy and fit--soldiers will typically reach muscle-failure before hitting any fatal heart rate or blood pressure.