Abstract: Let $L$ be a link in $S^3$. We say that $L$ is {\it strongly $n$-trivial} if it admits a diagram such that for some set $V$ of $n+1$ crossing points, changing the under/over information on every non-empty subset of $V$ yields a trivial link. A link is called a {\it boundary link} if the components bound mutually disjoint Seifert surfaces. It is known that strongly $n$-trivial links are boundary links. However this statement does not hold for spatial graphs. In this talk, we discuss surfaces bounded by cycles of spatial graphs and the notion of strong $n$-triviality of spatial graphs.