Am I weak? Trouble doing pull ups...

[vojdancov]

I'm not sure what this is called, but what you do is pull a chair up to the bar, then put your chin over the bar, let yourself hang off the chair, and slowly go down (ie do the reverse of a pull up- start from the top then slowly go back down to the starting position).

Those are called negatives

 

[JTM]

I'll be honest I haven't been doing any leg work as I do a lot of cycling and football. But i will start adding some squats and leg extensions into my workout then. I guess the more muscle i gain the more it will help burn fat no matter where it is i.e. legs.

Sounds like you really need to overhaul your routine. Cycling and football isnt enough to call "leg work". Make sure you are including squats, lunges, step-ups and deadlifts into your workout.

If you want bigger biceps, put the dumbbells down and do some chin-ups.