Discernible means noticeable. If your extra hours training are having no discernible influence on your basketball game, it means your game has not changed.
You can use discernible in two senses. First, you can use it to describe something you physically see: Because the sky was so clear, the ship was discernible from miles off. You can also use it to describe something you sense or understand: When your younger brother told he was sorry he broke your baseball bat, the truth was discernible in his voice.