After a several months of constant effort but little improvement in capability, I've come to the conclusion that I could probably do with some interval work. Problem being that a google search will turn up a PILE of variations on actually doing intervals.

I'm 62, been biking about 20 months and my ride averages (20-40 miles, 600-800 feet climbing, 5 times a week) have been hovering right at the same 15.5-16.5 mph for months without change. I've got a Garmin and keep a spreadsheet of all the data on my rides and it is pretty obvious that my condition is static.

Comments? Links to interval descriptions that worked for you?