Yesterday I noticed that the lat on my left side looks smaller than on my right side. So I thought maybe I'm lifting uneven when doing Lat Pulldowns. In training today I really focussed on activating both sides of the lats evenly and noticed that my left biceps feels sore significantly quicker than the right one, which, to me, means that on the left arm my biceps takes over a lot of work the lats would have done. So I'm in fact lifting unevenly what results in the smaller left lat.
What can I do about that problem, apart from focussing on activating the lats evenly/focussing on activating the left lat instead of the left biceps. Maybe some pre-activation would help?
I'm doing regular Lat Pulldowns with an Overhand Grip, 3 sets x 10-12 reps. Other than that, I also do Cable Rows for my upper back. I'm not able to do Lat Pulldowns "one armed", because in my gym there is no such machine that allowes that. Only a cable machine with one cable.