Sprint training has a greater effect on muscle glycolytic capacity. i.e improves your ability to disperse lactic acid build up thus tolerate longer high intensity intervals.
What if we could manage both at once? Well, we can.
Burgomaster et al (2007) discovered that high interval training was a time efficient way to increase skeletal muscle, oxidative capacity and create similar metabolic adaptions as endurance training.
Paavolainen et al, (1999) investigated the effects of simultaneous explosive-strength and endurance training on physical performance characteristics, 10 experimental (E) and 8 control (C) endurance athletes trained for 9 wk. The total training volume was kept the same in both groups, but 32% of training in E and 3% in C was replaced by explosive-type strength training. The simultaneous explosive-strength and endurance training improved the 5K time in well-trained endurance athletes without changes in their VO2 max. This improvement was due to improved neuromuscular characteristics that were transferred into improved running economy.
Nine fit male subjects performed a mean of 16 outdoor sprint running training sessions over 6 weeks. Distances sprinted were 30–80 m at 90–100% maximum speed and between 20 and 40 sprints were performed in each session. Endurance, sprint, sustained sprint and repeated sprint performance tests were performed before and after training. The results demonstrated that 6 weeks of short sprint training can improve endurance, sprint and repeated sprint ability in fit subjects. Increases in the proportion of type II muscle fibres are also possible with this type (Dawson et al, 1998)
Why do coaches ask endurance athletes to do sprint training? Because it’s a time effective way to build Vo2 max endurance while also improving effective lactic toleration / dispersal.
Put in simple terms over time, sprint training raises the threshold of what we can endure, thus helping us go faster, improves how fast our bodies disperse lactic acid – thus making space for more: aka ability to endure high intensity training for longer, whilst increasing muscle density and also improving VO2 max.
We get fitter!