In recent days there has been an interesting discussion on the Fetcheveryone ‘Polarised training’ thread about the value of the short intense hill sprints that Renato Canova and Brad Hudson recommend for distance runners.
Typically these take to form of 6 or more short (6-8 second) intense uphill sprints with adequate recovery between each sprint. They can be done at either the beginning or end of a training session. Canova recommends them up to twice a week. I have never done them more frequently than once per week. Although 6 hill sprints do not add greatly to the training load of a ‘serious’ athlete, I have always been concerned to avoid the risk of excessive stress. It is more important to maintain good form that promotes optimum muscle fibre recruitment
One of the immediate benefits is a feeling of speed in your legs that can make subsequent fast pace running feel relatively easy. Some athletes do intense hill sprints in the 24 hours before a race for this purpose. Although I have not habitually done this, I usually do ‘bounding’ drills during the taper for a target race to achieve a similar result. In fact hill sprints are probably safer than bounding drills as they present little risk of injury provided you warm up adequately.
I think that the feeling of ‘having speed in your legs’ is based largely on the sensation of recruiting fast twitch fibres. However, you might wonder why this is helpful for a long distance runner, since fast twitch fibres are poorly adapted for aerobic metabolism. I suspect the reason is that fast twitch fibres are good at capturing the energy of impact at footfall as elastic energy. Provided you have developed the ability to recycle lactate from fast-twitch fibres to slow twitch fibres that can use the lactate as fuel, the fast twitch contractions do not lead to increase in blood acidity.