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More on identifying your threshold power

In a previous post I identified ways you can use a histogram to find your threshold power. However, sometimes you may want to confirm the results of the histogram analysis, or you may not have suitable files for this type or analysis, or you may not have a power meter. In these cases there are several other methods for identifying your threshold power/heart rate.

  • Lactate Testing
  • Maximal Aerobic Power and Heart Rate Test
  • Time Trial
  • Power Profile Testing

This post provides some information on these options.

 

Lactate Testing

A lactate test is usually conducted on a special trainer that can control the resistance , and therefore power, being generated at any time. The test starts at a low intensity but increases by 30-50 watts every 3-5 minutes. Towards the end of each stage a small sample of blood (finger prick) is tested to determine the amount of lactate in the blood (in mmol). The lactate values are then plotted against the power output and heart rate for each stage. Some funky calculations are then made on the data to determine the threshold heart rate and power.

As this test involves analysing an individual riders blood lactate profile, the training zones created are highly accurate to the individual. The lactate profile itself can also provide an insight into a athletes physiology, including fat vs carbohydrate oxidation at rest and while riding at different intensities. These points alone make the lactate test extremely important as they enable the creation of a customised training plan for that person.

One important thing to note about lactate tests are that there are a number of methods used to determine training zones and threshold points. Each coach/assessor will generally stick with one method but it’s worth knowing the details in case you get a test done by someone else who uses a different method.

(Note: The protocol used by Argonaut Cycle Coaching for lactate testing is the same as the Australian Institute of Sport testing protocol, which includes calculation of five training zones based around two threshold points, known as LT1 and LT2.)

In general a lactate test is a great test to complete at the start of the season or at the beginning of the base training phase. This is because it helps identify the most effective intensities for endurance training (E1 and E2). Most training zone structures only calculate these as a percentage of threshold but this can be quite inaccurate.

 

Maximal Aerobic Power/Heart Rate Testing (aka Ramp test)

This test is more commonly referred to as a ramp test or MAP test. It is very similar to a lactate test, however the stage durations are much shorter and the ramp rate (increase in power per stage) is also less. This test can also be done on a standard trainer in your own home.

A normal ramp test starts at 100 watts for 1 minute and then increases by either 15 watts every 30 seconds or 30 watts per minute. As with the lactate test, the rider continues until they can no longer sustain the required power (staying seated the entire time). For a trainer or bike without power, this same test can be completed by simply shifting through the gears to obtain a 2-3kmh speed increase every 1 minute.

Unlike the lactate test, the primary output of this test is the riders maximum aerobic power output and heart rate. Percentages of this value are then used to great a general training zone scheme. These zone systems have been developed following years of research and are ‘good for the masses’.

My experience with using the zones from this test are mixed. However, it all depends on what zone system you use. Trying to apply a threshold based zone system to maximal data is fraught with problems, whereas using one based on a percentage of max is better. It wouldn’t surprise you then that I opt for the later when calculating zones based off this test.

One way that you can use this test is to try and validate a histogram assessment of your threshold. I have previously done this, albeit using a slightly different protocol.  For my test I used my Lemond Revolution trainer and a 50 watts per 3 minute ramp rate, starting at 100 watts. This is the same protocol I would use in a lactate test and I use it for three reasons, i) it keeps all of my test sessions the same, ii) I find the 3 minute ramp allows the heart rate to settle more and therefore provides a more accurate assessment of my heart rate at a certain power output, & iii) it exhausts my anaerobic stores more quickly after exceeding threshold and therefore helps replicate what my peak power would be during a hard effort on the road.

For the record, my previous test session was conducted on my Tacx trainer with the power controlled by the trainer. This test was completed on 28 February and I achieved a peak aerobic power of 327 watts at a max HR of 173 bpm (quite low power and HR by my usual standards – but that’s what happens when you’re coming back off a long illness). The second test session (in May) resulted in a peak power of 345 watts with max HR of 183 bpm. (nb: this power was taken as the complete avg power for the 350 watt stage – which I only just completed).

Using these numbers I can then do the following (very rough) estimates:

  • Threshold heart rate = 183 × 91.6% = 167 bpm, then
  • Find where I reach that heart rate during the test (1min 58sec into the 300w stage).
  • Deduct 30 seconds from this time to account for lag in heart rate response (1min 28sec = 88sec).
  • 88 sec / 180 sec per stage = .488 percent of stage completed
  • .488 × 50 watts stage = 24.4 watts
  • 250 watts (previous stage power) + 24.4 watts = 274.4 watts

And that’s pretty darn close to the 270-276 watt histogram assessment in my previous post!

(Note: While you can use a similar method to this to determine your threshold I prefer to use it as a second confirmation rather than rely on it solely.)

Time Trial

One of the most commonly used methods to determine threshold power or heart rate is to complete a time trial on the road. The duration of the effort generally varies anywhere from 20 minutes to 1 hour – although doing a 1 hour time trial just to determine the threshold is not usually recommended.

The problem with this method is that the heart rate and power for these efforts usually needs to undergo some ‘scaling’ to determine the threshold value. The problem is that an unfit rider can probably only hold their threshold power for 20 minutes whereas a fit rider can hold it anywhere between 40 – 60 minutes. As you don’t know what your threshold duration is, it makes this method the most ‘flaky’ of options.  It’s better than nothing and it does provide a good starting point, but if you’re really serious about your training then you should look to follow it up with one of the other options.

It’s also worth mentioning that doing a time trial on a hill or a time trial bike can alter the power and heart rate for the effort, thereby making the zones less applicable to normal riding on a road bike.  Finally, pacing these time trial efforts are also important.  Starting too hard can elevate the heart rate above threshold and as you keep pushing it stays high and therefore overestimates your threshold.

 

Power Profile Testing

This is a relatively new concept in testing but I have found the calculated threshold values closely match those derived from lactate testing conducted at the the same time (i.e. same fitness level).

As the name suggests, a power profile test requires the use of a power meter, with the test actually consisting of six separate efforts (6 sec, 15 sec, 30 sec, 1 min, 4 min & 10 min). Each of these efforts is completed at maximal intensity – although the 1, 4 and 10 minute efforts require some pacing.

The power numbers for each of these efforts then provide a snapshot of the riders abilities for the different energy systems. Additionally, the power numbers can be used to calculate a riders Anaerobic Work Capacity (AWC) and Critical Power (CP), and its the latter of these (CP) that closely matches the threshold power from a lactate test. Additionally the average power from the 4 minute test effort closely matched the peak aerobic power from either a lactate or ramp test. Together, this information can then used to set power targets (zones) for both aerobic and anaerobic intervals.

It’s worth noting that a power profile test can be completed on an indoor trainer, however it does need to provide power data. It’s also beneficial if the trainer has a good ‘road feel’ so the results more closely match the power capabilities when training on the road. The Tacx system I use, along with the Lemond Revolution, both provide an excellent road feel.  However, you do need to ensure they are properly calibrated before the test.

 

Training Zones

While knowing the threshold point is interesting, it’s greatest value comes from helping define the training zones to be used in everyday training.     There are various schema used to define the training zones, some are based on percentages of maximal heart rate or power, while others consider heart rate reserve, aerobic threshold (LT1) and lactate threshold (LT2).    It’s important when setting zones you use the correct system for the type of test you completed, for example don’t use a threshold based system when completing a maximal aerobic power test.

 

Argonaut Cycle Coaching’s Testing Services
Argonaut Cycle Coaching offers a number of performance testing services, including Lactate and MAP/RAMP testing, to help you identify your current fitness levels and to set accurate training zones.  Details of these tests can be found on the testing page of the website.

 

Jason Mahoney Thursday 24 October 2013 at 09:46 am | | Tips




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