you better train twice a day for 6-7 days strait to gain the most effects.
Science IS behind those statements (actually more often training is even more beneficial)...
Look if building muscle was as easy as going couple days per week. MORE PEOPLE would be huge by now.
There is no science in hit/low volume approach.
Forde serious muscle gains (we arent bodyshapers) you need serious training. Few days per week just dont cut it.