As described in this blog post below: http://www.training4cyclists.com/threshold-power/ Example: 3 x (3+3min) at VO2max / recovery. If you use a heart rate monitor, your heart rate should be above 95% of maximum at the end of these intervals. If you use a power meter, your target power could be in the area of 120% of your functional threshold power or even better based on your 5min maximum power. - See more at: http://www.training4cyclists.com/threshold-power/#sthash.DbD9Dyf9.dpuf
Or would you use the intervals methods described in the blog below: ▼ 10 minute controlled warm up with bursts up to FTP ▼ 20 minutes @ 85% FTP ▼ 4 minutes recovery @ 150 watts maximum ▼ 20 minutes @ 85% FTP ▼ 6 minutes cool down spinning at 100 rpm http://www.flammerouge.je/factsheets/functhresh.htm
Or have I missed the point of either recommendation in the blog posts above and are these type of intervals dependant on the time of year?