Sprinting for endurance?

Running, November 15, 2016

If you’re an endurance athlete clearly training your cardio-vascular system and working on those slow twitch fibres will make up the bulk of your training. But whether you’re an Ironman or 10km P.B hunter, make sure you work on those fast twitch fibres. They will reward you come race day!

My last article expounded the virtues of more moderately paced interval with much reduced rest periods. Quite rightly, this encouraged one of my athletes to ask ‘if intervals at race pace are so great, why the hell do I have to do these flat out 10x400m?’ Well as my old coach said to me “If your coach can’t explain why you’re doing it, it probably ain’t worth doing!” So here is brief explanation of why running very fast should stay part of your annual training plan!

A Little Physiology

Whilst my last article focused mainly on cardiovascular improvements, the role of speed training centres much more on improving the neuro-muscular complex. In other words, speed training develops the power of muscles and the efficiency with which they are used. Before expanding on this, it may be helpful to briefly describe the three muscle fibre types. There are three; slow twitch type (I), fast twitch (IIx )and fast twitch oxidative (IIa).

Type 1a fibres are slow twitch fibres, they contract slowly, require least energy and generate low forces. They are well suited to endurance running.

Type IIx are explosive and tend to be used in sprinting. They have no aerobic ability and so will fatigue very quickly.

Type IIa fibres are a blend of the features of both I and IIx. These function anaerobically or aerobically meaning they can be recruited to either endurance or explosive work.

Whilst the body will predominately recruit slow twitch fibres for endurance racing, even these well adapted fibres will fatigue. When this happens more fast twitch fibres, of both types, are recruited and you start to slow, badly! Even before fatigue sets in, some type IIa fibres will be recruited in distances races especially as you take on short hills or accelerate.

For these reasons, and others I’ll come onto, it is greatly beneficial for the endurance runner to develop these muscle fibre types. The trouble is fast twitch fibres tend to be lazy and tend work on an ‘only when needed’ basis. So, to train these stubborn so and so’s you must run fast, very fast.

How fast?

Well some of your speed work should be flat out. Think Usian Bolt style, all out efforts. For most runners 30-50m of sprinting should see you reach top speed. A session such as 8-10 x 30m sprint with 3-4min recovery would be typical but a set of very steep hill sprints would work as well.

These sessions encourage the body to recruit large numbers of fast twitch motor units simultaneously and requires them to contract at optimum velocities. This type of training develops power in each stride and improves the nuero-muscular co-ordination required to make the contractions and recruitment efficient and fast. This pays off in races because it will improve running economy, going faster whilst using the same amount of energy.

Building some sprint training into your annual training blocks needs to be done gradually and thoughtfully to avoid injuries and get the most benefit. Certainly, there is no need for more than 2 sessions a week and one is most likely enough. Typically, the efforts need only be 5-10s but the rest interval needs to be around 2-3 mins. Each rep should be done with maximal effort, so recovery needs to be almost complete. As the efforts are very intense and the amount of muscle damage high, it is wise to keep other weekly sessions at a low intensity to allow recovery and avoid injury. Most studies show that the adaptations to this type of training happen within 4-weeks and then the gains plateau, so a short block of this work in the off season and again in the pre-season would be ideal.

Not quite so fast is good too!

The more traditional speed work, such as 10 x 400m at 1km pace, would have many of the above benefits. However, as the effort is not maximal the body will recruit both slow twitch and oxidative fast twitch fibres. Because the efforts are more sustained, but at a high enough intensity to require significant anaerobic respiration, a large number of IIa fibres will be recruited and these will become more efficient in several respects. They will become better at using oxygen as an energy source, the motor units will become ‘primed’ meaning they will be more easily recruited in subsequent efforts and the body will become better at blending the recruitment of type I and type IIa fibres. This type of training has been shown to significantly improve running economy and muscular power, with the bonus that it will continue to develop aerobic capacity.

This type of speed work can be introduced to your annual training more regularly, particularly as it continues to develop aerobic capacity. Running 200-400m at between your 1km-1500m P.B pace would be an ideal pace to encourage fast twitch recruitment and neuro-muscular co-ordination developments. Obviously when running at these speeds rest period will need to be longer and total distance lower. Recovery periods of between 2-3mins should allow adequate recovery to repeat the efforts. The number of efforts undertaken depends on the athlete, but most athletes will manage about 3-5km worth.  However, once you can no longer maintain your target pace it is probably time to start the warm down. Again 4-5week blocks are probably adequate to make gains in this area.

If you’re an endurance athlete clearly training your cardio-vascular system and working on those slow twitch fibres will make up the bulk of your training. But whether you’re an Ironman or 10km P.B hunter, make sure you work on those fast twitch fibres. They will reward you come race day!

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