The first being recovery, after a stress event, our muscles need to repair minor damage, refill with glycogen, eliminate waste etc quickly. This is an evolutionary smart thing to do as it gets us back online quickly ready to face stresses (lions) again. The time frame for this process could be from seconds to a few days depending on the severity of the stress.
Once we are "functional" again (ie recovered, feeling 100%, whatever) our bodies then go to work super compensating, this is the second process, new muscle tissue genesis happens here (incase the next lion is faster than the previous one). It is a long slow process taking many days in some cases ,depending on the severity of the stress faced.
Many lifters get back in the gym after the first process (ie they have recovered), Thus ruining their chances of building muscle with the second process. Initially in the noob stage any protocol works well because they can both recover and build muscle in the couple of days rest the protocol gives them. Not long tho as the stressors are increased the time taken to complete the two processes starts going over the protocols "allowed" rest period. Muscle building stops and stalls/ injuries ensue. But when pressed they are adamant they're not overtraining because they still feel 100%. they don't realise feeling 100% is not stronger than 100% of last week. you want to feel 102% you doofus's. That additional 2% takes as long or longer than getting back to the 100%.
The other point to note is that when the severity of any stress is increased there comes a point when cell or organism destruction ensues. The closer the stress comes to this threshold the more our body super compensates. So yes you can lift not heavy enough. The super compensation can also happen infrequently enough that any gains made will be lost again as the body prioritises survival (don't need to spend resources fuelling things we don't use).
What I advocate is neither of these. I lift big, I push close to cell destruction (injury, exhaustion) to get the biggest effect. Then I wait until my body has both recovered (process 1) and adapted (process 2) to this stress and maybe a few extra days for good measure, then I do it all again. This way is so close to optimal it isn't even funny, compared to the work every body else is doing in the gym.
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