This question already has an answer here:

- Totally Geodesic Submanifolds 3 answers

Also asked here: https://math.stackexchange.com/questions/1725787/when-are-the-minimizing-geodesics-of-a-totally-geodesic-submanifold-also-minimiz

A reference on totally geodesic submanifold (TGS):

http://www.map.mpim-bonn.mpg.de/Totally_geodesic_submanifold

Let "|" stand for restricted metric. Let $(S,g|)$ be a TGS of a complete Riemannian manifold $(M,g)$. In this case, is it OK to assume that $S$ should be defined to be complete as well? For example, we can think of $S=\mathbb{R}^2-{0}$, as a TGS of $\mathbb{R}^3$, but what's the point of not having that $\{0\}$? (I agree this is not exactly a question!)

**Now onto the question!**

Let $p,q\in S$ and let $c$ be a minimizing geodesic in $(S,g|)$ from $p$ to $q$. Now, since $S$ is TGS, $c$ lies fully in $M$, and a geodesic in $(M,g)$. But is $c$ a **minimizing geodesic** in $(M,g)$? if so, why? If not, what's a counterexample? Thanks in advance!