Use anaerobic-threshold intervals to gain more power on the flats
If you want to ride better on the flats, you should increase your functional threshold power (FTP). You can do so by taking on medium to long steady-state anaerobic-threshold intervals at high cadences.
On flat roads, air resistance, not gravity, is the greatest force to overcome. Time triallists are specialists who excel at putting out high power continuously throughout moderate to long distances. They also use an aerodynamic position with specialized equipment to limit drag. They are like diesel engines that keep the power going. So, if you are a lean mountain goat who flies uphill, your advantage is lost on flats unless you output similar wattage to the big diesels pulling on the front of the paceline.
If you want to ride better on the flats, you should increase your functional threshold power (FTP). You can do so by taking on medium to long steady-state anaerobic-threshold intervals at high cadences. You will increase your sustainable pace. The work will also increase your metabolic efficiency as you will burn more fat at a higher intensity over time. The higher cadences of 90 to 100 r.p.m. will shift the effort to your heart and lungs instead of on just the legs, which is key to endurance sports. The intervals must be long enough to isolate and tax the aerobic system and short enough to work harder than your normal steadystate pace.
Anaerobic threshold intervals
Find a flat road or one with a slight but consistent grade. Try to maximize time spent pedalling and spread the workload evenly across interval. Your cadence should be in the 90-to-105-r.p.m. range and the pace should be close to better-than-usual cruising speed.
Start with 20 minutes of warm-up, and then repeat the following three to five times:
10 to 12 minutes at 90 to 105 r.p.m. 100 to 110 per cent FTP
5 to 6 minutes rest between intervals