After Netilas Yadayim in the morning, one says Asher Yatzar as part of Birchas Hashachar. Avudram writes that one should say it even if he didn’t use the bathroom.
The Beis Yosef asks, since the bracha was instituted to be said after relieving oneself, why should one say the bracha even if he didn’t use the bathroom?
The Vilna Gaon explains that besides thanking Hashem for returning our soul (Modeh Ani), Asher Yatzar expresses gratitude for rejuvenating our body after sleep. Therefore, in the same way that Hashem returns our soul to serve him, we are also obligated to use our “new” physical body to fulfill Hashems with excitement and enthusiasm. And this is what Rav Yehudah ben Teima means when he says:
“Be strong as a leopard, swift as an eagle, fast as a gazelle, and brave as a lion to do the will of your Father who is in heaven.”
(Beis Yosef 6, Darkei Moshe, Vilna Gaon; Mishnah Avot 5:20; Kitzur Shulchan Aruch 1)