Now is the time that I start to adjust training plans to build my athletes’ FTP/LT. My athletes have spent a lot of time focused on their top end speed and power, but now is the time to build the base for next season.
Besides, “why do I have to do these long intervals?”, One of the questions that I get asked is “What happens to my body when I increase my LT/FTP?” This is an interesting question because increasing your FTP (Functional Threshold Power) or LT (Lactate Threshold) takes a lot of focused training blocks to increase. Without going into too much detail, your power at LT is THE limiting factor in your racing performance. In order for you to increase your power at LT , you must stress your body through focused training around your LT. This means getting a lot of time riding long intervals (20-30min) around your FTP.
My FTP is around 309 based upon my recent 20 min test at 326. I have been doing intervals 3-6 intervals for 20-30 minutes with a target average power level 280- 310. 295 to 310 for the 20 minute intervals, 285 to 295 for the 25 min, and 280 to 285 for the 30 min. The first interval is usually not too hard, and is actually hard to not go too hard. The suffering happens on the last few intervals in the set, but this is where the body realizes the stress and eventually starts making physical adaptations in your body. These intervals are stressful but not nearly as stressful as the shorter interval for the aneorobic system.
So now on to the answer… There are few things going on over time as your body adapts to this type of training. First, your muscle cells increase the number and size of the mitochondria. Mitochondria are the key aerobic engines inside your muscles. Also, more capillaries develop around the muscles so you are able to get more blood where it is needed. Both of these factors increase your respiratory capacity because now you are able to get more oxygen to your muscles and more CO2 away from your muscles in your legs, and thus they can stay aerobic with higher power outs. One of the reasons it takes months and years to become a great endurance athlete is because these adaptation take time. Since the racing season is mostly done, now is the time to spend the next 4-6 months working on building your FTP.