Both have local and systemic effects. LR3 raises systemic levels more because of its longer half life while DES is cleared faster once it spills over out of the local area.
They've demonstrated localized, focused muscle growth in animals, and no real reason to believe it doesn't work the same in humans. It's just the simple mechanics of the compound hitting the receptors in the area it's injected.
Regular use of these actually raises acromegaly risks more than rHGH or the IGF-1 levels would suggest, because they are mostly immune to IGF binding protein, and especially LR3, stays highly active
for a long time. Usually IGFBP locks
up 99% of IGF, so only 1% is active, but not DES or LR3. You'd have to get free IGF levels tested (instead of just total) to get an accurate picture of IGF levels.