when you get older, your natural test and GH will go down(meaning older than 25!!!), making it harder to sustain lots of muscle on your frame, thats why people cycle steriods, PCT is good to keep your gains and restore natural test levels, but you cant change what God gave you, if you are natuarally skinny then probably your gains will go down after a while, if you want to get gains and keep your gains, then be natural, because all the gains you get your body got naturally so your body will most likly keep naturally granted you keep training and eating the same, i wouldnt think running Trenbolon for a year would be that safe might i add, best way to keep your gains is maybe 2smaller cycles a year, w/a good PCT, but like i said, eventually they will go down to whatever weight your body can naturally sustain, that depends on person really, hope tht helped