Most guys struggle to build their biceps. This is usually because...
- They have crappy form.
- They lack stability.
- They're ignoring one of the functions of the biceps.
Swinging the weights, leaning back, doing half-reps, and letting the shoulders take over are all common issues. Training like this might boost your ego, but it won't build your biceps.
The best solution is to create a stable base by strengthening your lower and mid-traps, rear delts, and rotator cuffs so that you're placing tension on the biceps and making them work to overcome the weight.
Want a more immediate fix? Artificially create a position of stability during your curls. Take a look:
You can see that I'm getting support from the leg pads of a lat pulldown machine. This will allow you to drive your triceps back into the pad and create a very stable platform to train the biceps. It also makes it harder to cheat your reps. Another problem solved.
This all adds up to more tension going where you want it – the biceps. More tension equals more growth.
You already know the biceps bend the elbow. But they also supinate the wrist. Taking an offset grip will cause the weight to shift to one side.
Place the thumb-side of your hand up against the end plate of the dumbbell. This means if the dumbbell is pulling you into pronation, your supinators (including the biceps) have to work hard to keep the dumbbell level. You end up working both elbow flexion and supination. This increases the activation of the biceps during each rep.
By making these small tweaks, every rep will stimulate the biceps more than the regular, sloppy curls you see in gyms all over the world. Work to develop strength in this exercise and your biceps will grow way more than they were when you were "curling" the 60s.
Oh, and if you ever progress to using the 60s for reps on offset supported curls, your arms will be colossal!