。
I can't walk any further.
Literal
I [topic-は] this more walk-cannot [emphasis-よ].
これ以上 ('this much more, any further') is a fixed adverbial expression that almost always pairs with negatives — 'cannot do X any more.' 歩ける is the potential form of 歩く ('to walk'), so 歩けない = 'cannot walk.' The final よ asserts this as new information to the listener.