an acquittance explains the following theory about exercise to me:

statement: just doing warm-up but not carrying on with the full aerobic workout causes more harm than not exercising at all

explanation:
each of us has a pre-determined lifetime heart beat capacity that varies between individual. Your heart fails as it approaches the limit. For example in theory: Bob with 70 beats per minute has a lifetime capacity of 2.5 billion beats (this number is made up for this example) will live: 2,500,000,000/(70*60minutes*24hrs*365days)=68 years before his heart naturally fails.

So the benefit of aerobic exercise is that it triggers the mechanism that lowers one’s resting HR over a long time. So Bob, after exercising over a long period of time, may have a resting HR of 60 beats which grants him in theory 11 years of additional life. The catch is that Bob has to “invest” by getting his HR way above his normal HR before he can reap the benefit. during workouts he is actually withdrawing from his lifetime capacity at a much faster rate (say at 160 bpm), but once he goes pass the trigger point (say, 60 minutes of exercising) the benefits comes in. And since Bob is only spending 1 hour “over-spending” and 23 hours enjoying the benefit of a lower HR, overall it’s a gain.

So the theory goes: if Bob only warms up or does a really short workout, he gets his HR up BUT does not hit the trigger point. He is actually just “over-spending” his HR reserve and not collecting the benefit. Therefore, his heart reaches the limit faster than if he does nothing. He heart fails earlier. He dies younger.

Honestly, I am perplexed when I hear this. But thinking about it, it seems to draw parallel from a lot of other things in life and it kind of makes sense in a way. So I am really curious, is this bull, or is there some truth to it?