For those of you who hate reading: It's always safer to use a palms-down grip.
Pulling with a mixed grip in which one palm faces down and the other faces up puts way too much stress on the biceps of the palm-up hand, and it greatly increases your risk for injury. It's not uncommon to see biceps that have torn away from the elbow and crawled back up to the shoulder as a result of overloading the arm with a mixed-grip deadlift. The sholulder is also in a dangerous position when you're lifting with a mixed grip. It's at a mechanical disadvantage when your palm is up, and that's bad if you're trying to lift hundreds of pounds off the floor. If the risk of the injury weren't bad enough, the mixed grip can also lead to muscle imbalances, especially in the trapezius, which can end up bigger on one side than on the other. So much for that attempt to be proportionate!
The bottom line is only use the mixed grip if you're training for a competition in which you need every advantage to lift heavier. Otherwise, hold the bar with your palms down and wear lifting straps if your grip is weak.
Pulling with a mixed grip in which one palm faces down and the other faces up puts way too much stress on the biceps of the palm-up hand, and it greatly increases your risk for injury. It's not uncommon to see biceps that have torn away from the elbow and crawled back up to the shoulder as a result of overloading the arm with a mixed-grip deadlift. The sholulder is also in a dangerous position when you're lifting with a mixed grip. It's at a mechanical disadvantage when your palm is up, and that's bad if you're trying to lift hundreds of pounds off the floor. If the risk of the injury weren't bad enough, the mixed grip can also lead to muscle imbalances, especially in the trapezius, which can end up bigger on one side than on the other. So much for that attempt to be proportionate!
The bottom line is only use the mixed grip if you're training for a competition in which you need every advantage to lift heavier. Otherwise, hold the bar with your palms down and wear lifting straps if your grip is weak.