Reading research: Interrelationships between Muscle Structure, Muscle Strength, and Running Economy

Yesterday, I had a bit of a rant because I have a different opinion to many on how plyometrics affect the body.  When talking about the improvements in running economy that both resistance training and plyometrics cause, I think it is important to note that research shows that plyometric training does cause hypertrophy.  Some people (even some researchers) talk about plyometric training purely in terms of neuromuscular changes or they minimise the hypertrophy response.

I also noted that I differ from many in that I am not convinced that elastic energy is as trainable as people like to make out.  I have read more than one study that shows that plyometric training techniques do not cause any increased elastic energy storage.  Now I wouldn’t want to rule it out completely but I do think it is harder to train than many people think.

Since I like reading things I disagree with, let’s test that opinion today, by digging a bit deeper (literally) into the muscle fibres to see what is going on.

Gymnast with serious muscular development (photo by Sheilaz413)

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OK, muscles are cool.  What’s the study?

It’s called Interrelationships between muscle structure, muscle strength, and running economy,  by Komi et al., Medicine and Science in Sports & Exercise, 2003.

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So why are we looking at the muscles?

Well, some researchers think that the contractile and elastic structures of a tendomuscular system may affect running economy.

Specifically, our researchers in this study note that muscle fibre type might be important when it comes to how much oxygen a muscle uses for a given running speed.  Why is this relevant?  Well, when you’re thinking about running economy, you’re generally talking about oxygen usage for a given running speed.  So muscle fibre type could dictate running economy at different speeds.  Hopefully, that makes sense?

What else?  Well, researchers are also interested in the role of a large protein called titin, which has significant elastic characteristics and acts as an anchor between the Z-line and myosin within a single sarcomere.

You can read more about the role of the protein titin in Bret’s summary post on the subject but essentially the thing to remember is that titin is partly responsible for the elastic strength of a muscle and it has several isoforms, which are either more or less elastic than each other.  Different distributions of titin forms could therefore have an impact on running economy at any speed.

So what does the study set out to do?

The main purpose of the study was to investigate possible differences in running economy at different running speeds that might occur as a result of muscle structure, both in fibre type and in titin forms.

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So what did the researchers do?

The researchers took ten male national level middle-distance runners, using a variety of running tests, they measured their:

• VO2-max
• Maximal heart rate
• Peak blood lactate
• Maximal voluntary contraction strength of the knee extensors
• Speed in various running tests

In addition, approximately two hours after the running tests, needle biopsies were taken from the middle portion of the vastus lateralis muscle under local anasthetic.  The biopsies were treated and analysed (go and look at the study if you want to know more about this).

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So what did the researchers find?

The researchers found that muscle fibre distribution analysis revealed that type I fibres dominated in the subject group.

However, they also found that maximal voluntary contraction strength of the knee extensors was positively correlated with the area size of type II fibres and inversely correlated with the area size of type I fibres.  In other words, the stronger subjects had more type II fibres.  I suspect nobody was surprised by this result.

So what about running economy and muscle structure?

The researchers found that at the slowest running speeds, there were no significant correlations between running economy (i.e. oxygen uptake) and either muscle fiber distribution or fibre composition.  However, at the running speed of 7 m/s, the oxygen consumption and energy expenditure both correlated with type II fibre area and with Type IIb fibre distribution.  In other words, at the greater speed, the runners with larger amounts of type II fibres were more efficient.

The researchers also noted that the data confirm the very low distribution of type II fibres  in the muscles of endurance runners, suggesting that this fibre type is down-regulated by the type of activity.

And what about titin?

The researchers confirmed that in the present study, all ten subjects expressed the faster-mobility titin band.  Only one subject expressed the lower-mobility titin band as well and that subject was more economical than the others.

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What does it all mean?

Type two fibres are more efficient for faster speeds

The researchers noted that these results are in agreement with earlier findings a previous study, which found that endurance-trained runners were more economical than sprinters at lower speeds, whereas sprinters were more economical at faster speeds.  However, the interesting thing is that the economy seems to be related to fibre type.

The researchers also noted that previous studies have indicated that the speed a runner is able to maintain at their lactate threshold is the best physiological predictor of distance running performance.  This study suggests that the role of type II fibres may be key in achieving a high speed.

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Titin might be important for running economy

The researchers noted that this study may suggest that titin may play a significant role in running economy.  Since only one subject expressed the lower-mobility titin band and this subject was the most economical, this suggests the possible importance of the lower-mobility titin band as for an element increasing elasticity and therefore running economy.  However, the small number of subjects makes it difficult to tell what is going on.

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Conclusions

I guess this study shows that if you want to run long distances quickly you need some type II fibres.  That should upset a few people.

It also shows that there are definitely variations in running economy caused by titin forms.  However, it doesn’t yet show that these can be changed by training, so I don’t have to change my opinion about training elastic energy storage yet…