Physical Fitness Stack Exchange is a question and answer site for physical fitness professionals, athletes, trainers, and those providing health-related needs. It only takes a minute to sign up.
Sign up to join this community
I've read and I've been told that using a thumbless grip, especially in pull-ups and pull-down:
It allows lessening the load on the forearm muscles and better targeting of the bigger back muscles – latissimus dorsi (lats).
It is suggested also in this video of Jeremy Ethier about lat pull-down.
But why it happens? I'd say that using a thumbless grip will release the thumb adductor, which is a hand muscle, not a forearm one.
That website's contention for why a thumbless grip lessens the load on the forearm muscles is that it prevents you from squeezing the bar:
in a thumbless grip, also known as a “false” or “suicide” grip, the thumb is held under or outside of the bar rather than around the bar. There is no squeezing involved.
However this absolutely would not apply to any kind of pulling exercise, where grip is essential to hold onto the bar. In those cases, removing the thumb would actually increase the load on the finger flexor muscles of the forearm.
This can easily be tested by doing a static hang from a chin-up bar with a regular grip and a thumbless grip. It is much harder to hang on with a thumbless grip.
