Both are OK. The first is better because the subject of the second clause (it strengthens my muscles) is 'it', i.e. 'riding my bike'. So the cause and effect link is strong in this sentence. In your second sentence, the link between riding your bike and strong muscles is not as clear.

Las dos son correctas gramaticalmente, pero la primera tiene más sentido lógicamente, y vas a oír esta construcción con mucho más frecuencia. Eso dicho, puedes agregar un "afterwards" a la segunda y va a sonar bien: I like riding my bike because my muscles get stronger afterwards. Otros ejemplos: I really like watching comedy because it makes me laugh. I love going outside because I always feel great afterwards. I'm really into playing tennis. It's a crazy good workout. I'm a big fan of skateboarding. It's like so much fun as long as you don't crash.

2.

Hello can you help me? Could you plz tell me <she was a bad back> meaning?

Second sentence