Let oneself down while climbing, say, fib about underlying muscles (6)
I believe the answer is:
abseil
'let oneself down' is the definition.
(I've seen this before)
'fib about underlying muscles' is the wordplay.
'fib' becomes 'lie' (a fib is a lie).
'about' shows that the letters should be reversed in order.
'underlying' means one lot of letters go next to another (in a down clue, some letters lie under others).
'muscles' becomes 'abs' (short for abdominal muscles).
'lie' reversed gives 'eil'.
'eil' after 'abs' is 'ABSEIL'.
'while climbing say' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for abseil that I've seen before include "Climb down using a double rope" , "Descend rock face on rope" , "Use a rope to climb down a mountain" , "going down" , "Slide down on rope" .)