1 example sentence using flexor.
Flexor used in a sentence
Flexor in a sentence as a noun
It is also simply not true what you are saying, just think about the main function of the hip flexors - pulling the knee up, and the function of the glutes - rotating the pelvis; then think which of those two actions is more common in cycling and to which degree.
Flexor definitions
noun
a skeletal muscle whose contraction bends a joint