Intervals are always good. Any exercise is good, but you have to do it.
When I ran cross country, way back in 1978, the coach made us do a 2 x 440 sprint, then a 1 x 440 walk. And repeat it 5 times (15 x 440=3.75 miles). That's when we did not run the outside short lap of 6 miles, or the long lap of 8 miles...
It should be good.
FIRE no later than 7/5/2016
at 56 (done), securing '16 401K match (done), getting '15 401K match (done), LTI Bonus (done), Perf bonus (done), maxing out 401K (done), picking up 1,000 hours to get another year of pension (done), July 1st benefits (vacation day, healthcare) (done), July 4th holiday. 0 days left. (done) OFFICIALLY RETIRED 7/5/2016!!