SSJ muscle buff

During SSJ's first appearnce an increase in muscle mass was evident. After the Freeza arc this transformation effect is almost abscent.
Is due to artstyle change? Or our heroes got used to SSJ so they had better ki control and muscles were unnecessary?

I didn't really notice that in the manga. There might've been a few panels here and there where Goku looked bigger, but that's just inconsistent art.

It's just inconsistent art. Goku's muscle mass just gets drawn way bigger against Freeza around the tine he loses his shirt. When he freshly transformed, he was relatively the same size he was against Freeza earlier.