Reibun
。・・・、。

My, my. No matter that it's just a phys-ed class... if you don't approach it with the determination of a real match, it won't be useful when the time comes for actual combat, you know.

Literal

My-my. However physical-education [gen-の] class [although-といえど]... serious-match [gen-の] spirit [with-で] face-not-[conditional-なければ], actual-combat [quotative-という] time [to-に] useful not-become [polite-ませんよ].

おやおや is an interjection expressing mild surprise or concern. いかな...といえど is a literary concessive — いかな (classical for 'no matter how/what') + といえど 'even if one says.' 意気込み 'spirit / determination / zeal' is a vivid noun from 意気込む 'to be fired up.' 臨む 'to face / confront' is a formal verb for approaching challenges. The whole sentence has the tone of an elder mentor giving a stern lesson.