Correcting My Freestyle: Going from an S-Pull to an I-Pull

I'll ask a more basic question. What are S-pulls and I-pulls? An S pull is a freestyle pull where the hand enters in front as usual, then moves outward, then inward, before finishing straight back before exiting the water. The hand travels in an approximate S shape. An I pull (I suppose since I never heard this description before) is simple - hand enters and pulls essentially straight back. I think the S pull was specifically taught for many years, even decades because it was thought to be a more efficient/powerful technique. But Maglischo's book clearly states that modern research shows the straight pull is more efficient.

I'll ask a more basic question. What are S-pulls and I-pulls? An S pull is a freestyle pull where the hand enters in front as usual, then moves outward, then inward, before finishing straight back before exiting the water. The hand travels in an approximate S shape. An I pull (I suppose since I never heard this description before) is simple - hand enters and pulls essentially straight back. I think the S pull was specifically taught for many years, even decades because it was thought to be a more efficient/powerful technique. But Maglischo's book clearly states that modern research shows the straight pull is more efficient.