Fetching details from the dictionary...

to concentrate; to focus on; to devote; to apply oneself
to stiffen; to become tense
暗闘の中で目を凝らして相手の動きを追った。
I strained my eyes in the darkness to follow the opponent's movements.
デザインに工夫を凝らしました。
I put ingenuity into the design.
耳を凝らすと遠くから微かな音が聞こえてきた。
When I strained my ears, I could hear a faint sound from afar.