Muscle

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Muscles play an obvious role in running, and understanding the different muscle types and recruitment patterns can help us optimize training techniques.

1 Muscle Fiber Types

Skeletal muscle fibers vary in their characteristics, and there are several different ways of categorizing them. While a simple categorization is appealing, in reality fibers tend to vary in multiple ways, so remember that while this is a useful model, All models are wrong. This is a little like classifying cars into different types. You can categorize cars based on the number of doors, how fast they are, what shape the back is, etc. The table below shows several classification systems and the characteristics of the fibers[1].

Categorization Characteristics
Contraction speed Myosin ATPase Myosin heavy chain Biochemical Motor Unit Classification Resistance to fatigue Force Generated
Slow Twitch Type I MHCI Slow Twitch Oxidative (SO) Slow Twitch Fatigue Resistant High Low
Fast Twitch Type IIa MHCIIa Fast Twitch Oxidative/Glycolytic (FOG) Fast Twitch Fatigue Resistant Medium Medium
Type IIb MHCIIx/d Fast Twitch Glycolytic (FG) Fast Twitch Fatigable Low High

1.1 Notes

  • There is a good correlation between type I and SO fibers, but the correlations between type IIA and FOG and type IIB and FG fibers are not so clear[2].
  • In addition to those shown in the table, mATPase also has IC, IIC, IIAC, IIAB types that are not shown[3].
  • The original Myosin heavy chain classification of MHCIIb in humans now appears to be the MHCIIx/MHCIId type found in small mammals[4], and humans do not actually have the MHCIIb form[5].
This is a picture visualizes some of the ways of categorizing muscle fibers.

1.2 Fiber Type Plasticity

There is overwhelming evidence that fibers can change type, with transitions between Type IIa and Type IIb being the most common[6]. Conversion between Type I and Type II has been shown to occur with severe deconditioning, such as spinal injury[7]. The only evidence of transitions from Type II to Type I with training is limited to studies of denervated muscles that were electrically stimulated for weeks[8]. In rats, the transformation occurred sequentially as type IIB/IIX to type IIA to type I, with the type IIB/IIX to type IIA occurring after 2 weeks and the type IIA to type I taking longer than 2 months[9].

2 Muscle Recruitment

We control our muscles so that we can lift a heavy weight or gently lift a cup of coffee. Our muscles are made up of many small fibers, and when we use less than our full strength we activate just some of those fibers[10]. So lifting the cup of coffee might only use a few of the fibers, but those fibers are fully activated. Each muscle fiber is either generating force or not; there is no in-between. Some muscle fiber types are more easily recruited, and the order is Type I, Type IIa, and finally Type IIb [11].This can be seen in the patterns of Glycogen depletion. Muscle recruitment has some important implications for training methods. To train all our muscle fibers we either have to generate the maximum force our muscles can produce or we have to exhaust some fibers so that others are activated in their place.

2.1 Endurance Training

Here's an analogy for muscle recruitment patterns while running long distances. Imagine each muscle fiber is a person and the long run is a war. Initially, the highly trained troops are the first to be deployed. When these highly trained troops become fatigued, then the reserve troops are called in to replace them. Eventually even the reserve troops become fatigued, and the draft calls in anyone who is able bodied. If things go on long enough, then the old men and children have to fight. In the same way we rely on a few well-trained muscle fibers early on in a run. As these muscle fibers become fatigued, we call on less well trained fibers. Thus as the training run progresses we work our way through the various muscle fibers. This is why a 15 mile training run does not provide 75% of the endurance benefit of a 20 mile run.

2.2 Maximum Strength Training

Lifting heavy weights requires engaging more of the muscle fibers. Maximum strength training has been shown to improve Running Economy without changing V̇O2max[12][13][14]. Improvements in endurance have also been seen with elite level cyclists undergoing maximum strength training (5-6 reps to failure)[15].

2.3 Plyometrics

Plyometrics use explosive exercises where the full strength of the muscles are engaged for a short period of time. Preceded a muscle contraction with muscle extension under load generates maximum muscle engagement. An example of this can be seen in box jumps, where you jump down from a box and then immediately jump back up. The jumping down extends the muscles under load (eccentric exercise) which then helps generate more force on the jump back up. Like Maximum strength training, plyometrics improve Running Economy and performance without changing V̇O2max[16][17][18][19]. Plyometrics have also been shown to improve neuromuscular control for running that follows cycling, such as occurs during triathlons[20].

3 References

  1. ↑ W. Scott, J. Stevens, SA. Binder-Macleod, Human skeletal muscle fiber type classifications., Phys Ther, volume 81, issue 11, pages 1810-6, Nov 2001, PMID 11694174
  2. ↑ N. Hämäläinen, D. Pette, Patterns of myosin isoforms in mammalian skeletal muscle fibres., Microsc Res Tech, volume 30, issue 5, pages 381-9, Apr 1995, doi 10.1002/jemt.1070300505, PMID 7787237
  3. ↑ RS. Staron, Human skeletal muscle fiber types: delineation, development, and distribution., Can J Appl Physiol, volume 22, issue 4, pages 307-27, Aug 1997, PMID 9263616
  4. ↑ K. Hilber, S. Galler, B. Gohlsch, D. Pette, Kinetic properties of myosin heavy chain isoforms in single fibers from human skeletal muscle., FEBS Lett, volume 455, issue 3, pages 267-70, Jul 1999, PMID 10437786
  5. ↑ D. Pette, H. Peuker, RS. Staron, The impact of biochemical methods for single muscle fibre analysis., Acta Physiol Scand, volume 166, issue 4, pages 261-77, Aug 1999, PMID 10468663
  6. ↑ Dirk Pette, Robert S. Staron, Mammalian Skeletal Muscle Fiber Type Transitions, volume 170, 1997, pages 143–223, ISSN 00747696, doi 10.1016/S0074-7696(08)61622-8
  7. ↑ RR. Roy, RJ. Talmadge, JA. Hodgson, Y. Oishi, KM. Baldwin, VR. Edgerton, Differential response of fast hindlimb extensor and flexor muscles to exercise in adult spinalized cats., Muscle Nerve, volume 22, issue 2, pages 230-41, Feb 1999, PMID 10024136
  8. ↑ T. Eken, K. Gundersen, Electrical stimulation resembling normal motor-unit activity: effects on denervated fast and slow rat muscles., J Physiol, volume 402, pages 651-69, Aug 1988, PMID 3236252
  9. ↑ A. Windisch, K. Gundersen, M. J. Szabolcs, H. Gruber, T. Lomo, Fast to slow transformation of denervated and electrically stimulated rat muscle, The Journal of Physiology, volume 510, issue 2, 1998, pages 623–632, ISSN 0022-3751, doi 10.1111/j.1469-7793.1998.623bk.x
  10. ↑ Brian R. MacIntosh, Phillip F. Gardiner, Alan J. McComas, Skeletal muscle : form and functio, date 2006, publisher Human Kinetics, location Champaign, IL, isbn 0736045171
  11. ↑ Brian R. MacIntosh !!author1!!, Phillip F. Gardiner !!author2!!, Alan J. McComas !!author3!!, Skeletal Muscle: Form And Function, Accessed on 13 April 2013, 2006, publisher Human Kinetics 1, isbn 978-0-7360-4517-9, pages 201–
  12. ↑ O. Støren, J. Helgerud, EM. Støa, J. Hoff, Maximal strength training improves running economy in distance runners., Med Sci Sports Exerc, volume 40, issue 6, pages 1087-92, Jun 2008, doi 10.1249/MSS.0b013e318168da2f, PMID 18460997
  13. ↑ Johnson, Ronald E., et al. "Strength training in female distance runners: impact on running economy." The Journal of Strength & Conditioning Research 11.4 (1997): 224-229.
  14. ↑ GP. Millet, B. Jaouen, F. Borrani, R. Candau, Effects of concurrent endurance and strength training on running economy and .VO(2) kinetics., Med Sci Sports Exerc, volume 34, issue 8, pages 1351-9, Aug 2002, PMID 12165692
  15. ↑ P. Aagaard, J. L. Andersen, Effects of strength training on endurance capacity in top-level endurance athletes, Scandinavian Journal of Medicine & Science in Sports, volume 20, 2010, pages 39–47, ISSN 09057188, doi 10.1111/j.1600-0838.2010.01197.x
  16. ↑ L. Paavolainen, K. Häkkinen, I. Hämäläinen, A. Nummela, H. Rusko, Explosive-strength training improves 5-km running time by improving running economy and muscle power., J Appl Physiol, volume 86, issue 5, pages 1527-33, May 1999, PMID 10233114
  17. ↑ AM. Turner, M. Owings, JA. Schwane, Improvement in running economy after 6 weeks of plyometric training., J Strength Cond Res, volume 17, issue 1, pages 60-7, Feb 2003, PMID 12580657
  18. ↑ Robert W. Spurrs, Aron J. Murphy, Mark L. Watsford, The effect of plyometric training on distance running performance, European Journal of Applied Physiology, volume 89, issue 1, 2003, pages 1–7, ISSN 1439-6319, doi 10.1007/s00421-002-0741-y
  19. ↑ Plyometric training improves distance running performance: A case study, Journal of Science and Medicine in Sport, volume 5, issue 4, 2002, pages 41, ISSN 14402440, doi 10.1016/S1440-2440(02)80117-7
  20. ↑ Jason Bonacci, Daniel Green, Philo U. Saunders, Melinda Franettovich, Peter Blanch, Bill Vicenzino, Plyometric training as an intervention to correct altered neuromotor control during running after cycling in triathletes: A preliminary randomised controlled trial, Physical Therapy in Sport, volume 12, issue 1, 2011, pages 15–21, ISSN 1466853X, doi 10.1016/j.ptsp.2010.10.005
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