Given my economic circumstances at the time and my off season pursuits (swimming), I started wearing Lycra shorts of my own design and production in the 1975-76 time frame. Getting lycra, nylon, T-shirt type jersey knit poly-cotton blend at the local fabric store was far simpler than trying to locate a nice wool Sergal Jersey of a design that I liked.
Sergal shorts were available and were the standard short in my area. They were very nice new but they did stretch and sag, the chamois dried out and the waistband stretched out (I used them for 3-4 years). Lycra never stretched out and it was shiny, a characteristic I found very desirable riding on the artificially lit velodrome at night.
Sheila Young won her Olympic Speed Skating Medals in a home made lycra suit in 1976 as well.
I believe 1976 seems to be the tipping point for when it spread widely. It took several more years before the production and design kinks were worked out.
Todd Teachout
Hercules, CA