The stretch position of an exercise is one of the most productive positions you can put that target muscle in. It helps activate more muscle fibers by sending an emergency signal to the body and it can also help stretch out the fascia (the tough sheet of connective tissue surrounding the muscle that can restrict muscle growth), allowing more room for the muscles to grow (if you're familiar with Ironman Editor-in-Chief Steve Holman's "Positions of Flexion" training, then you'll already be well-versed in the multiple benefits of stretch-position training).
This fascial-stretching aspect is best done after you've already performed other bicep exercises and filled the biceps with blood...gives the fascia something to work against during the stretch (like squatting down in a pair of tight jeans, just out of the laundry).
The best stretch exercise for the biceps is the incline curl...and it's generally done with dumbells. THIS version, however, is going to use a barbell.
Now, you're probably wondering how you can use a barbell with the incline curl...won't the bar hit the bench? Absolutely it will...but we don't really care as much about what happens beyond that maximum stretch position. we're using only a very portion of the range of motion to target a very specific position to put the biceps in.
The other question would be, why use a barbell at all when you CAN get a full range of motion with dumbells.
And the answer is that for maximum stretch (even beyond what you can get with a dumbell), we actually WANT to lock the arms into position on the bar. With the arms locked in, it gives the muscles something to stretch against in addition to the stretch you get just with the incline position.
So by combining the position with the locked-in-ness of the barbell, you actually get a greater stretch on the biceps than is possible with dumbells in the exact same position.
And I'll tell you right up front...this degree of stretch is not comfortable. It won't injure you, but it's not comfortable. Also, if you DO have any bicep injuries or issues, you should skip this one because of the stretch-tension involved.
To do this one, you'll either need a partner or a rack (you may also be able to do this one with a flat bench, too). If you have partner, you can just have them hand the bar to you and take it from you when you're done the set.
I've got the rack setup here...I have an incline bench set with the high end in the rack. The barbell is set on the safety rails, which are just barely at arms-length when I get into position on the bench. If you want to try this with a flat bench, the bar will be resting on a bench set behind you.
Use a light weight for this...it's about the stretch, not how much weight you can load onto the bar. You don't need a whole lot of weight to get that stretch. I've only got 10 lbs on each side of the bar and that was plenty.
You'll also notice that I'm not sitting on the bench like a normal person ;)...I've got my feet on the seat and my upper back is over the end of the bench. During the exercise itself, I'm going to basically be laying back over that top end of the bench force the chest out and allow the shoulders to stretch back more, which puts even greater stretch on the biceps.
Lean down on one side and grasp the bar then lean down to the other side to get the other side. This is how you'll have to do it since you want to be sure those rack rails are not so high that you can just reach back and grab the bar, because that'll mean the bar will rest on the rails during the stretch part of the exercise itself. And that will basically defeat the whole purpose of this setup!
Once you've picked up the bar, lay back over the top end of the bench, letting the weight pull your shoulders and arms back and down. You'll instantly notice a MASSIVE stretch on the biceps. Hold that for at least 5 seconds.
Now curl up until the bar hits the back of the bench. You can either just touch the bench or you can do a static hold, pushing the bar against the bench for a few seconds.
Lower back into the stretch slowly and hold again, repeating the sequence.
Aim for 4 to 6 stretch reps on this one. That stretch position is basically the maximum anatomical stretch you can put on the biceps and it's going to be intense.
When you're done, because the rails should be set just below the bottom position, just unroll your grip on the bar and set it back down on the rails to finish. If you have a partner, they can just take the bar from you.
As I mentioned above, this is a great exercise to do AFTER you've already done another bicep exercise to fill the muscle with blood, giving you something to stretch the fascia against (POF style). Barbell or dumbells curls are a good example of this.