FTP and LT, what are they and what’s the difference?

Monitoring your progress is an essential process if you are to improve as an athlete. For some, including me, sitting down after a hard workout and analysing the data is something to actually look forward to. It’s great to see your numbers improving but testing also allows you to gauge the effectiveness of a training programme and observe long-term trends.

One traditional method of assessing an athlete’s physiology is by taking small blood samples from the fingertip or ear lobe and measuring the amount of lactate in the sample. A graph is then created outlining the athlete’s lactate threshold (LT), expressed in watts or speed, with an equivalent heart rate. This data is then used to establish training zones and track progress across a training phase. Your lactate threshold represents the exercise intensity, whether that be power or speed for example, at which lactate begins to accumulate in the blood quicker than the body can clear it. The problem with measuring lactate is that it requires a special analyser and test strips to conduct the procedure. FTP, or functional threshold power, is another test often used by athletes, however, the test does not require a lactate meter, just a way of measuring power.  Essentially, both of these tests are a measure of your endurance capacity and are potent predictors of your endurance performance potential i.e. a higher relative power (W/kg) at your FTP or LT is a good indicator of your race performance.

You can have your lactate measured in a physiology lab or in the field, whilst FTP can be determined by either a dedicated FTP test or through accumulating power data during your workouts. If you use TrainingPeaks, a cycling computer or heart rate watch, you may have received an update following a workout that you have achieved a new threshold. The goal of your training program is to increase the amount of power you can hold at threshold.

FTP and LT both represent your threshold intensity, about the pace you can maintain for an hour, and whilst the two numbers are highly correlated, they are normally not the same. Instead, research and experience has shown me that power at LT is often below an athlete’s FTP, not by much, somewhere in the region of 5%. This value is then used to create your training zones, providing ranges in power and heart rate for you to target depending on the aim of the session. Personally, I prefer power when possible, as heart rate can drift between intervals and can take a bit of time to reach the target value, whereas increasing your power to a particular range can be done in a matter of seconds.

            This might leave you wondering why the need for invasive laboratory testing if you can complete an FTP test with the equipment you have. Some research has shown that FTP failed to reflect any improvements after a 7-month block of training, however, lactate measurements were able to detect an improvement.

A lactate threshold test in a lab will also give you your aerobic threshold (AT). This intensity is much less than your LT and corresponds to the point where your blood lactate rises 1mmol/L above resting. Your aerobic threshold is also highly correlated to your Fatmax – the intensity at which you are burning the highest amount of fat. As you begin to exercise, the amount of fat you use for fuel will firstly start to increase, before dropping as the intensity of exercise. Your Fatmax is highly individual and is an excellent value to know if you are targeting fat adaption or trying to improve your body composition. For example, if you were planning to do a short (30-60min) fasted training session, you could target your Fatmax threshold. Whilst we can determine an estimate of your Fatmax from lactate testing, using gas analysis allows us to plot your individual Fatmax curve, providing you with a range of intensity to target during your fat burning sessions. This is particularly useful if you are embarking on challenge which involves long periods of long, slow activity, such as an arctic expedition or ultra-running race.

FTP and LT are both common terms used in coaching and both represent your anaerobic threshold, about the pace you can maintain for an hour. Beyond this threshold, a multitude of physiological factors contribute to an increased rate of fatigue. Despite reflecting the same threshold an being highly correlated, FTP and LT don’t often equal, with watts at LT often being below FTP. However, whilst FTP is a reliable test which can be done with a minimal amount of equipment, it may not reflect improvements from your training. Furthermore, your FTP does not yet indicate your aerobic threshold or Fatmax, which are both important measures for an endurance athlete.

Inglis et al., (2019). Maximal Lactate Steady State Versus the 20 Minute Functional Threshold Power Test in Well-Trained Individuals: “Watts” the Big Deal? Int J Sports Physiol Perform. 4:1-7.

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