ive always been led to believe that after your base miles the way toi bring on speed it interv als at max hr.everyone has their own theory re time/intervals.what worked for me one year was 1min on/4off x8.next session 2om,30ff,next session 3on 2 off,next session 4 on,1 off,with 8 reps each,20mins warm up and cool down,everyother day i did an easier rise of 2 hrs no real stress.im just finishing my base miles/endureance and will start intervals next month,at the moment im aiming for 21 hrs a week in the saddle,doing 10 mins on/off big chain ring for leg strength.
at the weekends i train with the lads as they tend to stretch me.i prob stay at 80% hr except days when im absolutely pooped,like monday av hr was 122.shows i was tired.keep a note of your resting hr.