when i was at high test and high tren is where i noticed short of breath. at lower test and even higher tren i don't get this, bp is more stable and lets face it, tren is more quality lbm per mg than test. it might not look like it while on, but lets face it, drop 700mg of test ew and pct and it looks like muscle dissappears, drop tren and might lose some veins and strength but what you've added is there. overtime with no anabolics everyone will lose slowly what shouldn't be naturally however, imo tren adds more quality muscle than tren.
people even say that of primo. i've yet to run it. plan on it soon, gonna pick up enough to hit 600mg ew for about 20 weeks. should be sweet.