As a bike racer, or even a recreational rider, lactate threshold, commonly called functional threshold power, or FTP, is something you have almost surely heard about. A rider’s FTP is the maximum number of watts he or she can hold steadily for roughly an hour. While not precisely the same in terms of physiological definition, LT and FTP are used interchangeably. Most simply, LT is the point above which your body can’t produce enough aerobic energy to maintain output consistently without using anaerobic energy stores. Thus, LT is a “functional” threshold above which power output contributors, primarily energy systems, change significantly. It’s a number often thrown around as the major determining physical factor in a race performance.
In time trials and mountain climbing, especially, FTP (when considered with weight) is generally one of the best predictors of performance. As such, it’s a valuable measurement to track overall fitness and improvement. In fact, most training plans in the modern era are designed around an athlete’s LT. Beyond simply expressing your one-hour power, FTP can be an incredibly useful tool for estimating your maximum power output for efforts of different lengths, and determining long and short term fatigue. So, with that in mind, here are some examples of how to figure out what your FTP is and how a coach can use that information.
FTP: Criterium Racing
Because of the difficulty of a one-hour all-out effort, it’s typically easiest to use a super hard one-hour criterium race effort or a shorter time trial effort to determine FTP rather than the one-hour TT. Using a one-hour criterium file, FTP can be determined by simply using an athlete’s best normalized power (NP) for an hour. In the power files below, one from the Joe Martin Stage Race criterium and another from a collegiate circuit race, the normalized powers line up very well with each other, indicating these are close to his best overall efforts for an hour. JMSR’s criterium resulted in a normalized power of 329w, while the collegiate circuit race ended up at 331w. Although the average power was different in each case, the normalized power indicates the performance ceiling for the time racing. In the circuit race, the athlete rode in the winning breakaway for 40 minutes. In light of each of these efforts, the athlete’s FTP would be set right around 330w.
FTP: Circuit Race
And here’s the same data for the circuit race. You can see the average here is higher and they’re quite different in terms of consistency of output, but the normalized power is comparable with only a 2w difference. With the athlete’s input, I know these are both near maximal efforts for an hour.
FTP: Short Time Trial
Next, we’ll look at what this athlete’s FTP would be estimated at using a shorter TT. Typically, it’s best to use an effort of 20 minutes or more, then subtract out around 5% of that power to get the one-hour power. In this example, the athlete rode a touch under 23 minutes for a time trial just over 10 miles in length. Subtracting out 5% from his average of 337w (338w NP, very consistent) results in an estimated FTP of 321w. This is still in line with the previously estimated 330w, so it’s a safe estimate. It’s also worth noting that this was done on a time trial bike, which the athlete had very little experience on, so the position could have resulted in a slightly lower power output than a maximal effort on his usual bike would have produced. FTP is set at a range, and both 320w and 330w fall inside the range, so we can be confident in a conservative FTP setting of 325w.
FTP: On the Attack!
Let’s take a look at some other information FTP can tell us. Again at the Joe Martin Stage Race in category 1/2, here’s an outtake from the stage 2 road race. About 70 miles into the race, there’s a climb of around 9 miles and 30 minutes. With team goals in mind, the athlete here felt it was time to test the field and perhaps escape in a breakaway to try and avoid the field sprint. Up to this point, the average power and normalized power (167w and 253w respectively) were relatively low. As a percentage of FTP, the normalized power is under 80% for this athlete, meaning a well trained cat 1 road racer such as this generally still has plenty left in the tank for the rest of the race. Back to the race, the athlete spent time attacking up the climb, attempting to get away with a group. Unfortunately, the move never materialized. However, we do get some good data from the process. Like in the criteriums before, this effort was not a TT effort at a steady output. It included several high power jumps in the attempt to get away. You can see 9 power spikes near the middle of the effort that top out over 600w, either in attacking or responding to attacks.
So while the average power is only 300w for 30 minutes, under FTP in this case, the normalized power is 330w. This is an indicator that he was riding at or near his maximal effort in order to get away, but without going so far that he was dropped as a result of an unsuccessful breakaway attempt. In this case, FTP is a valid predictor of the limits of the athlete’s fitness during racing. As an experienced cat 1, this athlete clearly knows how to feel what his body is capable of and assure that he has enough gas left to stay in the race when his efforts don’t pan out. Remember, this is 3 hours into a 4.5 hour race! While it’s not recommend to use strict numbers as a guide to racing tactics, it’s valuable to know what kind of efforts your FTP allows you to do and it’s interesting to see how important FTP can be even in repeated anaerobic efforts such attacking on a climb.
LT: In Training
In training, LT becomes even more valuable. Due to its nature as the point over which anaerobic energy becomes a larger factor, LT is used to determine training zones for short efforts. This works because the aerobic system (which LT is almost entirely dependent on) recharges the anaerobic energy systems, up to a point. Over lactate threshold output, the pH balance in muscle decreases, damaging muscles and causing training stress that leads to adaptation after proper recovery. Other physiological markers of fatigue increase similarly. The further above LT you go, the more stress you create in training and racing. In this way, even normalized power isn’t enough to determine the difficulty of a workout. It’s important to know LT because time above LT is an important metric for examining the overall intensity of a training plan over both long and short-term periods.
Careful monitoring of work done at different power output zones allows us to make sure athletes aren’t overly fatigued. It also allows us to determine the right amount of stress and recovery, which can vary heavily between athletes depending on numerous factors. You can see from the examples above that LT is not simply how hard you can ride for an hour. These are just a few examples of how LT can be used to pull information from a ride that may not be immediately apparent. With software like WKO, there is access to so much more insight into each athlete’s unique physiology that can lead to better performance through analysis and planning. A properly set LT can play a huge part in implementing a smart training and recovery plan to maximize time efficiency, training stress, and adaptation that ultimately improves performance. Source Endurance partners with several LT testing facilities around the United States. Learn more about those options here.
Coach Mitchell Sides will be hosting a more in-depth webinar on this topic coming up on August 8th. Be sure to sign up- it’s free! Sign up now.
Mitchell Sides recently graduated from the University of Texas at Austin with a BSEd in Exercise Science and is the newest addition to the team at Source Endurance. He’s transitioned from a self-proclaimed overweight couch resident into a member of Texas’s first UCI continental professional cycling team, Elevate Pro Cycling. He specializes in coaching road cycling and is inspired by the mentorship aspect of the sport. Learn more about Mitchell.