The irony is the mistake in question is actually much more beneficial for your shoulder strength as long as you know how to position your arm. Here’s the key to properly execute bicep curlsand set you on a more efficient path to getting fit.
When you make mistakes on your curls, they make it difficult for the bicep to take the full weight and fully benefit from the exercise. The problem is that the front deltoid is often more stressed than the bicep.
If you find that you often let your deltoid do the majority of the lifting, you may be able to see that the elbow throws itself forward during the curl. Instead, ensure that you keep your elbow behind you at all times. If necessary, consider lowering the weight. This will allow your bicep to take all of the weight.
Before getting too miffed that you’re compromising your potential gains, remember it’s always better to perform more reps at a lower weight while maximizing the load on your bicep than to be spreading the weight and whipping your elbow back and forth.