Warning: strong language.
Also warning: rant.
A mixed grip deadlift is when you hold onto the barbell with one hand in a supinated/underhand position (palm facing out) and the other in an overhand position (back of hand facing out).
It can make deadlifting feel lighter or easier on the hands by sandwiching the bar between the opposing fists.
I reckon everyone should stop doing it so fucking often, and here's a comprehensive list of reasons why:
It looks dumb
It is dumb.
An overhand grip with straight arms and good scapular retraction (shoulders back and down) will recruit the big, broad muscles of your lats to connect your arms, core and back to the lower-body powerhouse of the pull.
The underhand grip, on the other hand (lol), will force that shoulder into a more protracted position, resulting in more tension through glenohumeral joint of the shoulder, specifically the long head of the biceps.
The glenohumeral joint is sometimes referred to as the 'true shoulder' and is involved in all of your favourite arm-based activities. If you like doing stuff, this is a joint you'd probably like to keep intact.
Biceps tears can and do happen during heavy deadlifts, and are more prevalent in the supinated arm. Chronically speaking, biceps tendinopathies are not much more fun.
Basically your lats are a lot bigger and stronger than one half of your biceps* and so will do a better job of taking that load and keeping your shoulder safe.
*if this is not the case please do a shitload of lat pull-downs every week for the rest of your life, thank you.
Let's have a closer look at your lats. From the Latin words “latissumus” (broadest) and “dorsum” (of the back), they cover a lot of body, originating at the centre of the body from :
the spinous processes of T7-L5 vertebrae (ie: quite a few mid-low backbones)
the wide, super-strong sheet of fascia around the lower back
the top crest of the pelvis
the lowest 3-4 ribs
the bottom corner of the shoulder blade,
… and ending in a single tendon inserting into the top of the humerus at the other end.
We all know and love the lats for their 'pull up' actions (adduction of the arm, as well as shoulder extension and medial rotation), but aside from that they also contribute synergistically to rotation, lateral flexion and extension of the trunk. So when lats on both sides are contracting simultaneously they have a powerful stabilising effect on the spine, they keep the barbell close to your centre of gravity, and can help you keep your back from rounding. Conversely, having one shoulder more protracted and externally rotated than the other will mean one lat is in a stronger position than the other – which may lead to slight bending or rotating to that side. You don't need me to tell you that this is not ideal posture under load for the spine.
Injuries aside, constantly training one side differently to the other will OBVIOUSLY result in different muscle development on each side. The underhand side will get a gimpy lat. You don't want a gimpy lat.
The benefit of the mixed grip deadlift is that at heavy loads it will allow you to lift more. This is because squeezing the weight between the opposite-facing hands gives your grip strength a boost. Grip is often the weakest link when deadlifting and the mixed grip is a neat way around that – at heavy loads.
So if you are a competitive powerlifter : ignore me, get off the internet and listen to your coach.
Everyone else : the mixed grip is for competing, testing rep maxes, and for your heavy-ass working sets. It's a great tool to be able to whip out of your pocket when you really need it, but if it's constantly used in training it will actually limit strength gains. Leave it in the pocket when you're warming up or training light.
“But I can't hold on to the bar any other way, it keeps slipping out of my hands.”
If your grip strength is your limiting factor in the deadlift, here's an idea: train your grip.
Or try chalk, straps if you must, or hook grip (thumb around the barbell, fingers over thumbs.)
“But I don't like hook grip it's uncomfortable.”
Consider the possibility that you are a giant sooky lala. Call yourself a waaambulance.
“But I alternate which hand is which so it will even out.”
No, you don't. Unless you keep a training diary featuring sentences like “Working sets 1, 3 and 5 were in a left-hand supinated mixed grip setup, working sets 2 and 4 and back-off set were right-hand supinated,” I don't want to hear it. I also would rather peel my eyelids off than read that diary.
You may think you're alternating your grip but I call bullshit. You're probably overhanding your dominant side more often or at heavier loads than the other side. Just keep it simple, stupid : double overhand until you're working really hard.
“But we should be training the back to be strong and resilient pulling in a variety of positions and planes.”
Bravo, I couldn't agree more – that must be why I see you doing so many Jefferson deadlifts, hey? Or single leg deadies, single leg good mornings, single arm ring rows, landmine/torsonator stuff, Pallof stuff, renegade rows, KB windmills, TGUs ... IDGAF but if you want to train odd positions or rotation just train it properly – mixing grips at light weights is half arsing everything.
The most reliable way to ensure your training is balanced is to perform bilateral movements symmetrically (as often as sports-specificity allows), and use unilateral movements to detect and correct imbalances.
Mixing grip on a deadlift is a handy trick, but one that should be used sparingly - once you've perfected everything else about your deadie and it's time to get heavy.