A drill set up since regularly requiring oxygen (7)
I believe the answer is:
aerobic
'requiring oxygen' is the definition.
I can't judge whether this definition defines the answer.
'a drill set up since regularly' is the wordplay.
'drill' becomes 'bore' (synonyms).
'set up' says the letters should be written in reverse.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
The alternating letters of 'since' are 'ic'.
'bore' in reverse letter order is 'erob'.
'a'+'erob'+'ic'='AEROBIC'
Can you help me to learn more?
(Other definitions for aerobic that I've seen before include "Pavement edging" , "needing oxygen" , "Like exercise that aids the intake of oxygen" , "(Of exercises) related to increasing oxygen in blood" , "Type of exercise" .)