DIME Performance The Overshoot Phenomenon: Part 1

22 May, 2016

There are only a few papers to date showing the “overshoot phenomenon” [1, 2] and only one paper done using professional athletes within a season [3]. Explained very simply, an “overshoot” occurs when a taper or detraining from resistance training takes place. In other words, time off is taken from resistance (weight) training. The “overshoot phenomenon” is all about increasing the number of Type IIx muscle fibres. Why is this important?

Type IIx muscle fibres are your, fastest, most powerful muscle fibres.

Anecdotally I have heard the Great Britain cycling team, used this leading into the 2008 Beijing Olympics for their track cycling and cleaned up the gold medals. For now, let’s go into a little more detail.

TEAM GB IN THE MENS SPRINT AT THE 2008 OLYMPIC GAMES

There are 3 types of pure muscle fibres. Type I, Type IIa and Type IIx. Muscle fibres can also possess more than one type. Type I/IIa, IIA/IIx and I/IIa/IIx. These are known as hybrid muscle fibres. Type I are your slow twitch fibres contributing more to the endurance aspect of muscle contraction. Type IIa and IIx are your fast twitch fibres and contract much more rapidly than Type I. Among the normal healthy population, Type I and Type IIa are the predominant muscle fibre type. Pure Type IIx is generally less than 2% of muscle fibre composition [4]. Why is this important to know? Type IIx contract approximately twice as fast as Type IIa and about 5-10 times faster than Type I but fatigue very quickly [1]. Furthermore, IIx muscle fibre content has shown a strong positive linear relationship with sprinting speed among various mammalian species [4, 5].

A recent study by Trappe [4] examined the strength, speed and power of a muscle fibre from the vastus lateralis (outer quadricep) from a world champion sprint runner. Two muscle biopsy’s were taken (ouch!), one at rest and one after 4×7 maximal supine squats (like a leg press). Individual muscle fibres were analysed for their strength, speed and power characteristics.

What The Authors Found

329 muscle fibres were analysed from the biopsy. Of those, 24% represented Type IIx muscle fibres. While 34% represented Type IIa and 29% represented Type I muscle fibres. In this athlete, IIx fibres were twice as powerful as IIa fibres and 14x more powerful than Type I fibres. In addition to this, the authors reported the power output of this athletes Type IIa and IIx muscle fibres were higher than any human values reported to date. Furthermore, the genes involved with muscle growth were highly responsive to intense exercise and most pronounced in the Type IIx fibres. When hybrid IIa/IIx fibres were combined with the 24% pure IIx fibres, the IIx isoform represented 32% of the total muscle fibre distribution. Compare that with less than 2% from normal healthy individuals. The authors speculate that genetic traits in combination with years of specific training are the most likely explanations for these adaptations.

But what if you didn’t get to hand pick your parents and the particular genes at birth? Then the “overshoot phenomenon” may be something you can implement for your pure speed and power sport. In part 2, we will detail how an “overshoot” takes place and some of the research surrounding this topic.

References

Andersen, L., Andersen, J., Magnusson, S., Suetta, C., Madsen, J., Christensen, L., Aagaard, P., Changes in the human muscle force-velocty relationship in response to resistance training and subsequent detraining. Journal of Applied Physiology, 2005. 99: p. 87-94.
Andersen, J., Aagaard, P., Myosin heavy chain IIX overshoot in human skeletal muscle. Muscle Nerve, 2000. 23: p. 1095-1104.
de Lacey, J., Brughelli, M., McGuigan, M., Hansen, K., Samozino, P., Morin, J.B., The effects of tapering and power-force-velocity profiling and jump performance in professional rugby league players. Journal of Strength and Conditioning Research, 2014. 28(12): p. 3567-3570.
Trappe, S., Luden, N., Minchev, K., Raue, U., Jemiolo, B., Trappe, T., Skeletal muscle signature of a champion sprint runner. Journal of Applied Physiology, 2015. 118: p. 1460-1466.
Kohn, T., Curry, J., Noakes, T., Black wildebeast skeletal muscle exhibits high oxidative capactiy and a high proportion of type IIx fibres. Journal of Experimental Biology, 2011. 214: p. 4041-4047.