Also see: What is Normalized Graded Pace (NGP)?

Previously we examined the concept of normalized graded pace (NGP), and the information it can provide regarding the relevant physiological response experienced by a runner on varied, open terrain. In other words, we established that during open field runs, due to changes in terrain, the “raw” pace reported by a GPS device will often not reflect the physiological cost of the effort, but NGP calculated from the raw GPS data and accounting for changes in terrain and relative intensity can be much more indicative of the actual effort.

Although the NGP is a valuable tool in and of itself, it is also a component of other more sophisticated tools that can help an athlete or coach to more clearly see their training progress and goals (the forest), despite often noisy and confusing individual training bouts (the trees). So, as the old adage goes, these tools will help the athlete or coach “see the forest for the trees.” One other important component of these more sophisticated tools is what is often referred to as the functional threshold, specifically in regard to running, the functional threshold pace (FTP).

The functional threshold pace (FTP) is a necessary parameter for the implementation of the more sophisticated tools that utilize NGP. That is, FTP is the criteria upon which relative fitness based calculations are performed. The sophisticated tools I am referring to are the training stress score for running (rTSS) and Performance Manager (PMC) modeling. We will come to these later, because first we need to establish what the FTP is and how it is determined.

So, what is the FTP? The FTP is the maximal running pace an individual can sustain for an effort of approximately 45 - 60 min in duration. What is the significance of the FTP you might ask? FTP enables further calculations regarding TSS and performance modeling relative to the individual’s fitness level. This is critical because, for optimal training and performance, pace based training metrics need to be expressed relative to a given athlete’s own ability, not the ability of some Olympic or professional athlete, or the athlete’s training partner, etc.

The FTP is analogous to a concept from the Exercise Science literature referred to as the Maximal Lactate Steady State velocity (MLSSv; (V. Billat, Bernard, Pinoteau, Petit, & Koralsztein, 1994; V. Billat, Sirvent, Lepretre, & Koralsztein, 2004), which is also closely associated with the lactate threshold (LT). As a little background, in the laboratory setting, the MLSSv is determined by performing a series of shorter efforts (e.g. ~ 20 min) and measuring blood lactate during the efforts at approximately 6 min into the effort and again near the end. As an example, an athlete might run four trials at 8, 9, 10 and 11 kilometers per hour (7:30, 6:40, 6:00 and 5:27 min/mi, respectively), and blood lactates are recorded at 6 and 15 min in each trial.

Table 1. Pace vs. blood lactate concentrations for 4 different constant speed trials. The pace highlighted in red is above (i.e. faster than) steady state lactate, hence, 6:00 min/mi (in blue) is MLSSv.

As you can see, the MLSSv is the fastest pace that can be maintained for this relatively short time without an observable accumulation of blood lactate. It so happens that MLSSv can typically be sustained for between 45 up to 70 min; or, around an hour. Further, the MLSSv is strongly influenced by the lactate threshold (LT) so that, as MLSSv increases (gets faster) so does LT, and vice versa (V. L. Billat, Sirvent, Py, Koralsztein, & Mercier, 2003). So, the MLSS is a proxy for the LT, and is in some respects more practical in that it uses a functional test to determine a sustainable pace. One can see how this is related to what is being called the FTP. One practical limitation to the determination of MLSSv is that it requires several test sessions. Additionally, it requires the drawing of blood and lactate determination. Fortunately, it really isn’t necessary to determine the FTP in this manner. Probably the most accurate (and practical) approach is simply to perform an effort in the one hour time frame. So, we can derive the FTP from a functional, practical test as opposed to performing a more laborious, impractical test. Again, credit should go to Dr. Andrew Coggan for popularizing this approach as applied to his NP/TSS system devised for cycling. For those of you who may have used this system, it may seem quite obvious to perform a one hour, or thereabouts, time trial to determine your FTP for running. For those of you who don’t come from a cycling background and aren’t familiar with the approach, it may not seem like a desirable approach to determine your FTP. In that case, there are more than a couple approaches to skin the proverbial cat and obtain a valid FTP.

It should be noted that there are several reasons we refer to this measure as the FTP as opposed to MLSSv; 1) we do not typically need to measure blood lactate to actually determine FTP 2) we can use “functional” or practical performances in lieu of formalized testing 3) to maintain continuity with the concept of FTP as it applies to NP/TSS system in cycling.

Practical approaches to determine a FTP:

1.       Actual performance from a recent race or hard training run of 10-15 km.

a.       If 10 km time was greater than 45 min, use 10 km

b.      If 10 km time was less than 45 min, use 15 km or half marathon

This is likely the most “valid” measure of the FTP because this is essentially the definition of FTP. For practical purposes, races will typically give us our best data compared to training sessions. Since 10 km is a common distance for running races, it’s a practical benchmark to use for FTP. Unfortunately, (or fortunately, depending on your perspective) some athletes can run a 10 km faster than 45 min, and since the MLSSv generally corresponds to efforts longer than 45 min, around an hour, if your 10 km time indicates a pace faster than MLSSv, then you need to use a longer effort (e.g. 15 km) as your benchmark. The 15 km is not nearly as common, so, in this case another option might simply be to use a hard training run that lasts 45-70 min in duration and use the average pace if on the flats, or NGP if on hills, for that effort. A key thing to note for all of these approaches is that, once you have established a baseline using one approach, it is desirable to stick with the same approach in successive attempts to establish FTP. This is because not only is FTP used to establish training intensities and TSS, it also serves as a measure of progress, and so, consistency is important when assessing progress. To determine if your training program is working, you want to compare apples to apples, and that means assessing your FTP under the most similar conditions possible in subsequent assessments. So, if using hard training runs, it would probably be best to stick with a standard duration (e.g. 60 min), or a standard course (e.g. 12 km) that takes approximately an hour to complete.

Alternatively, you can do essentially the same thing by choosing your best performances for a given time frame, say, 45 min.,that would correspond to a 10 km effort. In this case you can use the NGP calculated from open field runs as your testing benchmarks, and use these efforts to establish FTP on a frequent basis. In Figure 1a, you can see a Periodic chart of Mean Maximal 45 min NGP for all running efforts recorded in the data base. In this case, they are being plotted in mph to facilitate easier identification of the fastest efforts for this duration (high values). Highlighted in the circles, best efforts can be seen that are identified by arrows. In Figure 1b, the same data has been plotted in min/mi pace units, and with the connecting lines removed that can confuse identification when working with min/mi plots since the lower values are faster. In this figure, the lower horizontal line corresponds to a 7:20 min/mi pace, with the upper horizontal line corresponds to a 7:48 min/mi pace. So, the fastest efforts for this duration all lie within this range, except for one value labeled “outlier”.

It should be noted that no single value, especially when drastically different than other common measured values, should be given great weight. Due to the nature of GPS devices, interference, and altitude and/or speed measurement error, pace values may occasionally be inflated. Regardless, if an athlete has a one-off exceptional performance; it is generally not advisable to base training loads, and progress assessment on such unrealistic results. The athlete is being set up for failure. That being said, that particular “outlier” is likely a real performance (I.e. not an anomaly due to measurement error) based on PMC modeling which we will discuss in a later installment.

Figure 1a. WKO+ Chart of Mean Max 45 min NGP plotted in mph so fastest paces are easily identifiable.

Figure 1b. WKO+ Chart of Mean Max 45 min NGP plotted in min/mi. Lowest values are fastest.

Of course, FTP determination should be more exact than simply saying “somewhere between 7:20 and 7:48 min/mi pace”, that range is simply too large. Within the highlighted areas though, the five fastest paces for 45 min based on the NGP calculation were,

So, it can be seen that at no point was FTP faster than 7:30, but if based on 45 min effort, FTP could have been established as 7:34 min/mi or slower in July and 7:38 min/mi or slower in September. (These are with the exception of the “outlier”). For this particular runner, there aren’t many consistent effort runs of 60 min duration that can be used for FTP determination, so, in this case, 45 min is a practical duration to consistently use to assess and establish FTP. So, if hard training runs of 45 – 60 min are a regular staple of one’s training program, NGP values from these runs can be used to establish the FTP without formalized testing.

2.       Calculated 10 km or 15 km pace from shorter distance efforts. In particular, a 5 km performance used in conjunction with Daniels’ tables to determine pace for an effort of 50-65 min.

a.       Because all efforts longer than a few minutes are strongly influenced by the LT, it is possible to use the velocity vs. duration relationship established by Daniels for running to estimate FTP based on much shorter efforts. One should bear in mind that the shorter the duration of the effort (e.g. 1500 m), the greater the influence of anaerobic metabolism/capacity, and the greater likelihood of error. Events such as the 5 km for example should provide good estimates of FTP, since, for durations longer than 15-20 min, the anaerobic contribution will be much smaller. There is still the potential for some error though.

As an example, let’s say an individual just completed a 5 km race and this is the longest distance they have good data for. They completed the race in 18:22 min, at a pace of 5:55 min/mi. The individual could use the pace for the 5 km and Jack Daniel’s tables to determine that their vDot is 55, and they could likely run a 15 km in 58:33. This time for a 15 km effort would result in a 6:17 min/mi pace for FTP. There will likely be more error in this calculation than actually using a 10-15 km effort, but the error will be repeatable. So, if using this approach, as 5 km pace improves, FTP will also improve, and this can be used to re-establish FTP on a regular basis.

3.       Performance of a MLSSv determination

a.       Because MLSSv and FTP are essentially synonymous, determination of the MLSSv should provide a good estimate of FTP.

4.       From the results of a lactate threshold test

a.       Since the MLSS and the FTP both occur very close to the LT, and all three parameters should move in concert as a result of training adaptations (in other words, if one goes up, all three go up, and vice versa), LT determination should provide an athlete with a good estimate of FTP.

From the above approaches for the determination of FTP, methods 1 and 2 are most desirable, and practical. Methods 3 and 4, are rather laborious, can be costly, and not as practical to perform on a regular basis. For the purposes of fitness assessment, it is of value to obtain frequent benchmarks of fitness, so, more practical approaches (methods 1 and 2) will likely be most effective. On that note, although the determination of FTP is important for the establishment of training levels, as well as determination of rTSS and performance modeling, it is also an effective means of assessing training plan effectiveness. Since FTP is really an indirect measure of performance related to the lactate threshold (LT), it provides insight with regard to the effectiveness of a training program for the development of LT.

References

Billat, V., Bernard, O., Pinoteau, J., Petit, B., & Koralsztein, J. P. (1994). Time to exhaustion at VO2max and lactate steady state velocity in sub elite long-distance runners. Arch Int Physiol Biochim Biophys, 102(3), 215-219.

Billat, V., Sirvent, P., Lepretre, P. M., & Koralsztein, J. P. (2004). Training effect on performance, substrate balance and blood lactate concentration at maximal lactate steady state in master endurance-runners. Pflugers Arch, 447(6), 875-883.

Billat, V. L., Sirvent, P., Py, G., Koralsztein, J. P., & Mercier, J. (2003). The concept of maximal lactate steady state: a bridge between biochemistry, physiology and sport science. Sports Med, 33(6), 407-426.