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Training IntensitiesThe chart below is useful for each athlete involved in long distance (marathon training, triathlon training) and other endurance training. Below is a training intensity chart, similar perhaps to many you have seen before. It is a closely patterned after the basic intensity classifications for endurance training used by XC skiers and trainers in Norway. When they denote training intensity, this is the language used. I have added another column, lactate concentration. These values are based on several sources including long term studies of elite rowers in Germany. I think rowing and XC are very similar because they are both quadripedal exercise modes.
** Explaining the Two Thresholds I need to write another separate article on this issue of blood lactate and exercise intensity. The basic lactate threshold (also called anaerobic threshold) concept is a useful tool but also over-simplistic.
The traditional way of viewing the lactate threshold is that it is the exercise intensity at which the working muscle becomes "anaerobic" and lactic acid production commences. This is wrong, but the idea persists in the popular literature because it is an easy concept to get across.
The reality is this. Even at rest we are producing lactic acid in small quantities. Blood concentrations stay low because this lactic acid that is being produced one place can be taken up and used by another tissue. At low exercise intensities, no or only a very small increase in blood lactate concentration occurs. In fact, we sometimes see blood lactate drop a little from resting values at low exercise intensities, depending on what the athlete just ate. However, if we increase the exercise intensity enough, but not too much, we see blood lactate concentration increase to a new stable concentration.
Now we are crossing the Low Intensity Threshold (LIT). At this intensity(s), the blood lactate is not out of control. Lactate removal or clearance can also increase so that a new steady state is achieved. The highest blood lactate concentration that can be maintained during a 30 minute exercise bout corresponds to what we call the Maximal Lactate Steady State or MLSS. This lactate concentration varies with the sport. It is higher in activities that have a smaller active muscle mass like speed skating and cycling (4-6 mM). It is lower in rowing and XC which employ more active muscle mass simultaneosly (3-4 mM). There are also inter-athlete differences, of course. The intensity at which it occurs varies with training status.
When the intensity climbs above the MLSS workload, then we have exceeded the High Intensity Threshold (HIT) on the chart. At these intensities, lactic acid concentration would continue to climb over time until the concentration becomes high enough to inhibit muscle contraction and causes fatigue. The rate of accumulation will depend on how high above this threshold the intensity is and how effective the body is at clearing blood lactate. We have growing evidence to indicate that the best endurance athletes have higher lactate clearance rates. They get rid of lactic acid faster. So LIT represents an intensity at which blood lactate begins to rise. Between LIT and FIT we are working in a range where the increased production is accommodated for by increased clearance by non-working muscles, the heart (a lactic acid lover), the liver etc. HIT is the traditional red line, the exercise intensity above which fatigue is just a matter of minutes! How much time can be the difference between winning and losing.