Basically, the old method of farming for Endurance/Strength, which would involve loading into a raid and sprinting to extract, is inefficient. After sprinting for one stamina bar worth of distance, your skill gain is cut all they way down to about 12%, depending on your Endurance Level of course. So that means that you spend a good 4 min sprinting to the extract with almost zero gain whatsoever. I have seen some people just choose to grenade themselves once they hit the limit, but that costs rubles. The method I found is much more efficient.
Here is the step by step process:
Step 1: load into a raid with only a Hatchet and drink Mayo. This will dehydrate you.
Step 2: Kill yourself.
Step 3: Do NOT use Therapists healing service.
Step 4: Heal any bleeds and broken limbs manually.
Step 5: Load into a raid and begin sprinting in any direction
By the time your point gain for the raid is maxed out, you will die from dehydration, sending you back to the raid menu to go again. This essentially cuts the time it takes to get to level 51 in half as it cuts out needing to run to extract.