I used Ostra (MK-2866) before. It helped retained muscle mass during PCT, but for me personally, I didn't seem to recover as well. Could have been the PCT drugs though because I did another cycle and had a hard time recovering during PCT without the Ostra.
This is before I decided to blast and cruise.
Im doing a log now started last week running Ostarine and GW. S4 ill run towards the end. GW is promising for endurance muscular and cardio. Definitely helps my run times and Rest between sets has shortened too.