1) press ctrl + b
2) release
3) press shift + 7
You may already know this, and the RSI concerns still stand (I'm not sure what all goes into RSI risks), but wanted to clarify if the concern is over pressing 4 keys at the same time that are all over the keyboard.
# remap prefix from 'C-b' to 'C-a
unbind C-b
set-option -g prefix C-a
bind-key C-a send-prefix
I've heard that he reason for ctrl + b is because screen uses ctrl + a, which just doesn't make any sense to me. You can nest both tmux and screen and to get to an inner layer you press (if ctrl + a has been mapped) ctrl + a + a - and now your command is sent to the inner tmux/screen.Defaults matter. It is not feasible to configure this on every machine you touch so one have to remember both the default one and the sane one...
But at least the defaults should be sensible.
C-b is terrible for your wrist, especially in conjunction with the following commands.
Choosing C-a isn't as much about preference as it is about not-terrible ergonomics. Now people are right to prefer anything other than C-a or C-b but C-a is objectively a much saner default than C-b.
[0] http://xahlee.info/kbd/keyboard_ctrl_vs_capslock_position.ht...
I always use the modifier key on the opposite side of the keyboard to avoid that issue. So for ctrl-b , I press the ctrl key on the right side of the keyboard worth my right pinky and press the b key with my left index finger.