Depends.  What do you want to accomplish with your biceps?

Bicep curls isolate the biceps, targeting that one particular part of the muscular system.  In general, isolations are inefficient, since you'll need to spend a lot of time on several exercises instead of much less time on only a few compound movements that train several muscular groups all at the same time.  This is why you'll find many big, compound movements being touted here and on CF boards.

That's not to say that isolations don't have their place.  If you are looking to even out a muscular imbalance, i.e. if your triceps are massively stronger than your biceps, that may be one way to avoid any harm due to the imbalance.  However, it's extraordinarily hard to get a muscular imbalance in the biceps / triceps system.  You really need to work specifically at getting an imbalance to do so.  The only other time that comes to mind when isolation work could help is for rehabilitation.

From what I know (and I could be wrong on this one), biceps are one of the more cosmetic muscles.  That is, big biceps don't make you much more functionally strong or fast.

So it all comes down to this: what are your goals?

Yep yep. These guys just about got it. If you want to be big then bust out some bicep curls. But if your main focus is the functionality of your arms, then work on kipping pulls, muscle ups, rock climbing, etc.

And whats this about breaking parallel on squats? Was that a question?

You do this because it engages your hamstrings and glutes more at this range of motion.

Yup.

I read that you shouldn't worry about bicep curls until you can correctly complete ten pull-ups. A reason being that your bicep growth is also dependent on your back and shoulder development. Not sure if that's true or not.

Breaking the plane when you squat, I read that you need to be slow and controlled when going past this point. Again, not sure if that's true.

Another thing to note about isolations... specifically the bicep curl.

By itself, it is somewhat (but not completely) worthless. Although, If you do a set of bicep curls and immediately follow it up with a compound exercise using the biceps (such as a chin up), it will work it a lot harder. Other muscles assist it in doing the same motion. It's similar to doing a set to failure, lower the weight, then do more reps... except not the same thing. I forgot what this method of training was called... Does anyone remember?

Don't forget that muscular growth is primarily a hormonal activity.
You guys stated amazing reasons but you're forgetting to mention that compound movements stimulate a lot more of a hormonal response than isolations do.



Also, a common problem of doing deep squats: inflexible hamstrings will cause a posterior pelvic tilt or otherwise known as a butt tuck. This can compromise spinal integrity and put you at risk for injury, not to mention limit spinal stability and therefore make your squat less efficient, resulting in less weight being able to be used than could be (within safety), and therefore less results.

I have noticed a lot that many new lifters tend to allow their knees to knock, which is not only unsafe in and of itself, but can make it harder to achieve proper hip depth (below parallel) without having a tucking butt. You have to consciously push your knees outward/to the side very hard and keep them out for the entire movement. This will help ensure you're recruiting your adductors (inner thigh muscles) and help ensure you can keep your pelvis and spine in proper locked extension.


short story: shove your damn knees out, get below parallel, and don't let your ass dip.