Endurance Training can often be referred to as Stamina Training)
Stamina (ability to suffer and resist) is the ability of an organism to exert itself and remain active for a long period of time, as well as its ability to resist, withstand, recover from, and have immunity to trauma, wounds, or fatigue.
A strong aerobic motor is developed during the initial build phase of a training plan. However in order to develop this aerobic motor it is necessary to introduce the specific ability of endurance or stamina. The initial aerobic training phase is usually carried out on principally flat terrain in order to maintain the heart rate in the correct zone. Endurance training on the other hand, which is more specific to trail or mountain races should be practiced on moderately rolling or even hilly terrain. Depending on the length of aerobic runs which have been performed in the initial aerobic building phase, but which have presumably been between 60 – 90 minutes, the endurance runs should progressively build from this initial volume to reach 180 to 240 minutes, or even longer for training in Ultra events.
Before looking at the various times of Endurance/Stamina runs that can be performed we can examine the physiological basis for this type of training.
Optimal Stamina training is considered to occur when the heart rate is between 80 and 90% of its maximum (below but approaching the Anaerobic Threshold). In this zone, breathing is fast but under control. The effort has been described as "comfortably hard". Research has shown that training in the Stamina zone helps push several critical thresholds (lactate, ventilatory and anaerobic) to faster paces. The result is faster performance before crossing these thresholds. The greater difference that we are able to construct between our heart rate in the aerobic state and our heart rate at the level of the Anaerobic Threshold the greater will be our elasticity and ability to vary pace within that zone and avoiding the creation of excessive fatigue.
The key muscular, organic and cardiorespiratory adaptations that result from Stamina training are related to the "Lactate Shuttle". It used to be thought that lactate simply started being produced and eventually accumulated to the point where fatigue sets in, modern research shows that lactate is always being formed, just at different rates. At rest and during light exercise, only small amounts are formed. During heavy exercise, large amounts are produced. Once formed, the body has mechanisms whereby the lactate is "shuttled" to other tissues to be used predominantly as fuel. This shuttling has a maximum capacity, however. Once this maximum capacity has been reached, the production of lactate outpaces its removal resulting in the accumulation of it in the blood. Thus, the lactate threshold is reached. It should be noted that lactate has a partner, a hydrogen ion. When the lactate and the hydrogen ion are together, they form lactic acid. However, lactic acid splits at a certain point into lactate and hydrogen ion as separate units. Like lactate, the hydrogen ion, which causes the working muscle cells to become more acidic and begin to fatigue, is controlled, up to a limit, by the body. This process is called the “Bicarbonate Buffering System”. This system captures the hydrogen ion thereby forestalling the rise in acidity in the muscles. Once this system is overwhelmed, however, the cells become more and more acidic and this interferes with energy production and leads directly to fatigue. Here on the right is a graphic illustration of how the lactate shuttle performs. Aren't you glad that you don't have to learn this stuff but just run and let the lactate shuttle do it's job?
Stamina/Endurance training helps to improve the efficiency of these two processes and over time, results in less lactate and hydrogen ions accumulating, effectively pushing the lactate threshold to a higher pace.
We can identify a number of basic variations of training within the endurance run.
Simple or Steady State – Just go out and run. Have fun and bring it on home. The heart rate will be held between 80 – 85% of maximum, following a sufficient period of warm up. These runs are moderately hard but do not tax the organism in an excessive manner. Recovery is short.
Fartlek – From the Swedish meaning “Speed Play”. During a Steady State run, and after a suitable warm up, periods of faster running can be inserted for times of between 1 to 5 minutes, interspersed with suitable intervals of slower running. No formal structure should be attached to this and both speed and timing should be dictated by feel. In a group it can be fun to take turns in deciding when the faster running takes place and how long it lasts – the others try to hang on. The heart rate will be at 80 – 85% of maximum for most of the run but will climb to 90 – 93% of maximum during the faster periods.
Tempo Run - Tempo runs are slightly more intense than steady-state runs. As the name suggests the aim is to improve the running tempo or rhythm with these workouts. Tempo runs should be "comfortably hard". The heart rate should remain between 85 and 90% of maximum. Similar to the steady-state run, tempo runs are continuous efforts but must be preceded by a thorough warm-up. This kind of run will be shorter than the other sessions starting from about 40’ up to a maximum of 60’.
Cruise Intervals - The Cruise Interval workout was popularized by the running coach, Jack Daniels. They are specifically designed to increase lactate threshold pace. Cruise Intervals are short but intense tempo intervals. They last three to eight minutes followed by short recovery jogs (30 seconds to 2 minutes). The running should be fast and strong with a smooth rhythm. Heart rate will rise to 90 – 95% of maximum during the intervals but will be kept at 80 – 85% of maximum for the rest of the run.
Progressive – As it says, the pace starts off slow and builds through the run until the maximum sustainable pace has been reached. A suitable cool down period should be foreseen. This kind of training can be more structured by diving it into three equal pace periods within the total period – slow, medium and fast. For example the first third of the run should be done below 80% of maximum, the second third between 80 – 87% and the third period from 87 – 93%. This is a harder session than those described previously and requires a longer period of rest and recovery.
Fast Ascents – During the run every ascent is run at a faster pace than the rest of the run, while the descents and flat terrain are used for recovery. A similar but opposite strategy would be to run the descents hard and use the ascents and flat terrain for slower recovery running. As in the Steady State run the heart rate should be maintained within the 80 – 85% of maximum range for the majority of the run but build up to 90 – 95% of maximum during the hard running phase in ascent (it will be difficult to raise the heart rate this high during fast descents but in this case the main adaptation is at the muscular level rather than in any anaerobic improvement).
An additional advantage that can be gained from Endurance/Stamina runs is the possibility, particularly for athletes who are planning on participating in longer race events but is also applicable to medium length racers, is the excellent opportunity for experimenting with race equipment and nutrition. Wearing a pack, carrying some extra clothing, bringing your own water, trying out the nutrition you intend to utilise when racing.