The physiological mechanism behind endurance and speed development is different and often conflicting due to hormonal responses — anabolic (speed) versus catabolic (endurance). Speed development involves high-force output (vertical and horizontal ground reaction forces), greater stride frequency and predominantly anaerobic respiration (small amounts of ATP/energy supply). So longer rest periods will be required after speed work. Endurance development, on the other hand, utilises the aerobic respiration (a large amount of ATP/ energy supply) with lower force output and stride frequency. So the recovery is much faster. Depending on the events, that is, short (middle distance) and long, both speed and endurance are vital aspects of overall running performance.
However, it is important to assess an individual’s requirement before prescribing speed and endurance training. If a runner lacks speed but has a good foundation in endurance, then focussing a block (six to eight weeks) of training on speed development, such as intervals at varying intensity, can be useful. But care must be taken with speed training, for it can be very demanding, particularly for novice runners. The volume should be gradually increased (10-20 per cent) weekly. A runner can also maintain speed and endurance by alternating training methods within the week.
For example, day one can focus on speed (intervals at various speed), and day two can focus on endurance work (steady, low-intensity runs). If an individual intends to train speed and endurance on the same day (less ideal due to the conflicting hormonal response), then speed work should be done first as the quality of speed deteriorates after a high volume of endurance work.