In reply to MischaHY:
Sure, a bit of extra protein cannot hurt if you want to build up muscle power, but that could be lentils, a steak, or whey hydrolysate. I know which of the three I would drop from my menu!
As for the collagen peptides, how would a fibrous tissue cell reassemble them into extracellular matrix fibers? I really do not see it. The collagen fibers will have to be made as full length proteins and then secreted by fibrous tissue cells, after which they can diffuse or be actively transported a certain range away from the cell before being incorporated into the meshwork of the ECM. Actually, if they were incorporated at all, short fragments could even weaken the network!
I presume the idea behind eating collagen to help your tendons is the same kind of naive marketing that suggests eating lots of sulfated proteoglycans to help regenerate cartilage in arthritic joints. This simply does not work either except giving you more gloriously smelly farts!
Creatine is a different situation, as supplementation will indeed measurably raise its levels throughout the body as it is a soluble small molecule, and it can be shown that this correlates with quicker recovery and thus allow more intense training schedules.
I can also confirm this anecdotally from my judo competition days 25 years ago, where I would take creatine while training multiple times most days (typically running or weights in the mornings, one or two judo sessions in the evenings). Below such training loads that run against the limit of recovery I doubt that it has much effect. You would be MUCH better off first increasing your training volume.
CB