Have been a masters swimmer for almost 3 years. I seem to have hit a plateau in improving my 100 free speed, which is not fast. I can't get below 1:29 in the 100; My fastest 50 is :42. I have increased by yardage to about 3500 per workout (from 2500) with more interval work five times per week. Also, I cycle and lift weights about three times a week.
I am 52, 6'3" and weigh 195; the main feedback I get from the masters coach is I need to minimize head movement during sprints.