The aerobic and anaerobic thresholds

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Grethe

What is the aerobic threshold?

In Chapter 7 we discussed the different ways that the body can convert stored energy into motion. The aerobic energy system uses oxygen, and burns carbohydrate, fats and proteins.  It is relatively slow at producing energy, and therefore cannot be used when a lot of energy is needed quickly.  It is, however, the main energy system used for long distance running. For more intense activity, the body uses anaerobic energy systems which don’t require oxygen, but which produce waste products (notably lactic acid and protons) which build up in the muscles, and use up limited stores of glycogen.

The aerobic threshold is the level of effort at which anaerobic energy pathways start to be a significant part of energy production. Runners want to increase their aerobic threshold because this will enable them to run faster for longer before they tip into anaerobic metabolism which cannot be sustained for as long.

The pace which corresponds to your aerobic threshold is generally around your marathon pace.  As we shall see later, this is about 70% of VO2 max, or about 75% of your working heart rate.

What is the anaerobic threshold?

The anaerobic threshold is defined as the level of exercise intensity at which lactic acid builds up in the body faster than it can be cleared away.  For this reason, it is also sometimes called the lactate threshold or lactate turnpoint (LT).

There is some controversy about whether there really is a level of exercise intensity at which lactic acid in the bloodstream begins to increase.  There is evidence that lactic acid levels increase smoothly as exercise becomes more intense, and there does not appear to be an identifiable discontinuity or kink in the curve. On this view, the anaerobic threshold is simply point at which the lactic acid accumulation becomes noticeable to the runner.

When you run at close to your anaerobic threshold, running should be hard but not uncomfortable. Some runners observe a change in their breathing rhythm at the anaerobic threshold, from one breath for every four steps to one breath for every two steps.  At this level of exercise you can continue to speak, but not in complete sentences.

For experienced runners, your anaerobic threshold is somewhere between your half marathon pace and your ten mile race pace.   It should be about 10–30 seconds a mile slower than your 10km race pace.

10 Responses to The aerobic and anaerobic thresholds

  • […] about 75% of your energy from carbohydrates and 25% from fatty acids. When you run at about your aerobic threshold – which in elite runners is very close to their marathon pace, so roughly the intensity of a […]

  • I continue to be confused by the discrepancies from varous sources about what does and does not constitute lactate and/or anaerobic threshold. My CPT training said that those two (synonymous) states correspond to VT2, but the more I read, the more I’m convinced that it’s VT1, rather than VT2 that they correspond to. It’s VT1 where breathing rate becomes more rapid, talking is possible, but becomes different, and the body begins to metabolize carbs rather than fats. That being the case, what does VT2 signify, then? Thanks.

    Peg Molter
    mmmolter@ftch.com

  • […] On the other hand, if you want to improve speed, you might choose to reduce quantity and frequency but increase quality. The workouts are harder because you are working close to your aerobic/anerobic threshold. […]

  • […] pictures. Too often i pick up the pace on my runs to the point where I’m no longer under my aerobic treshold, but not this time – it was (almost) by the book aeorbic […]

  • Niklas:

    Since I started running (10-14 Km) about four months ago (once a week on average, with other training sessions in between) my training sessions are always around an AVERAGE heart rate of 93% up to 98% of the theoretical maximum for my age (169 BPM = 220 minus age) over the duration of between 1 and 1 1/2 hours of constant trail running. According to everything I have read, this should not be possible. As soon as I go over 100% for more than a couple of minutes at a time I get pretty exhausted and need to slow down.

    I assume this is a matter of “rule of thumb” not applying to everybody, and that my actual maximum heart rate is somewhat higher. However, even when using other formulas for max heart rate for instance this one (If you are a man, subtract half of your age and 5 percent of your body weight from 210 and then add 4.) I still end up with average heart rates above 90%.

    I am wondering of this training intensity is unhealthy or if I should just go on, as long as I feel fine after the run? Any qualified and informed input is welcome.

  • […] cardio refers to any activity performed in the ‘aerobic zone’ or below the ‘aerobic threshold‘ for an extended period of time (i.e. greater than 30 minutes). For running, this is […]

  • […] know the speed you need to run on your slow runs (a.k.a., zone 1), you need to know where your aerobic threshold is – finding this out is a big reason to do the test! The aerobic threshold is the threshold […]

  • LilyB:

    According to the formula for max hr 220-age(39) my max hr should be 181. I run with a heart rate monitor, so I know mine is slightly higher – 185 on my most recent runs. Just did a 6km and my average hr for 6km were 172. Which means that my entire run is above 90% of max and my last 1km is at average 181 which is 97% of max. From everything that I have read I shouldn’t be able to sustain that for that long. This stuff definitely differs from person to person.

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