My own experience is that using a straight bar is not good and can cause injuries over time - the ez-bar seems to offer a more natural angle for the wrists. Others say that you need a straight bar to fully engage the biceps. I'd rather have smaller biceps and be injury free. Dumbbells, of course, allow your arms to move through a range of motion that suits their geometry, so I would favour these.
Hammer CurlsYou can do these standing up or sitting down. This video talks about slowly lowering and strict form - I tend to just do these fast as part of a circuit and not worry about form too much.
Barbell CurlsIt's only practical to do these standing up. This guy does not have perfect form - but then I rarely do either - as I said above, for circuit work there's little point. I prefer to avoid burnout by cheating - it's a lot more convenient than running off to get a lighter bar. Note: there are some aspects of form that are important - such as a good stance and straight back - I am not advocating the abandonment of all aspects of good form!
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