If you’re trying to grow a big back, the lat pull-down is probably a go-to machine for you. Make sure you’re doing it right. Sports scientists at Pennsylvania State University conducted an experiment where they attached electrodes to the trapezius, latissimi dorsi, and the biceps of subjects as they performed a variety of lat pull-downs, and measured the amount of muscle activation that occurred. A pronated grip (palms over the top of the bar) recruited significantly more fibers in the lats than an underhanded grip. Width of the grip seemed to make little difference. This study builds upon earlier research that found that bringing the bar to your chest rather than your neck activated far more muscle fibers in both the lats and the biceps.