What?I am going to present in this article is unlike any training system that I am aware of - it is in complete opposition to what our intuition tells and to what we have been conditioned to think about speed and strength training. If you wish to become faster, I am going to suggest you stop working your legs. If you wish to increase your bench press, I am going to suggest you stop working the chest, shoulders and triceps. I do not mean just for a week. I am talking about an extended length of time - on the order of 6-8 weeks. I believe the theory presented here could revolutionize the way athletes train, so please read on - temporarily forgetting old habits and dogmas - and let the science presented speak for itself.
Before I dive into theoretical speculation, we must look at the science of muscle fibers a bit.
There are three primary muscle fiber types in humans -- Type I, Type IIA, and Type IIB. Type I are referred to as "slow twitch oxidative", Type IIA are "fast twitch oxidative" and Type IIB are "fast twitch glycolytic" (1). And as their names suggest, each type has very different functional characteristics. Type one fibers are characterized by low force/power/speed production and high endurance, Type IIB by high force/power/speed production and low endurance, while Type IIA fall in between (2, 3, 4). The advantages of a certain fiber composition on performance in various sports is both obvious and well established - for example, marathon runners have 75% slow twitch fibers, while sprinters and weightlifters have 75% fast twitch (5, 6).
These characteristics are a result, primarily, of the fiber's Myosin Heavy Chain (MHC) composition, with MHC isoforms I, IIa and IIx corresponding with muscle fiber types I, IIA, and IIB, respectively (7) - A small % of hybrid fibers co-expressing two isoforms also exist (8). Myosin Light Chains have been found to exert an effect on some of these properties, but they are minor, and not as well characterized or understood (9), thus we will be dealing with only the MHC.
MHC IIx possess a shortening velocity 5-10 times that of MHC I and are also faster than MHC IIa (10, 11, 12). Power production, particularly at high velocities, is higher with IIx than either IIa or I as well (11, 13). Force (strength) production has generally been shown to be greater in MHC IIx than IIa (14, 15), though one study found the opposit (16). Both MHC II types have been consistently shown to be superior to MHC I in all three areas (10-16). So, clearly, it is favorable for speed and strength athletes to posses a high % of MHC II, particularly IIx.
MHC composition, and thus athletic potential, is thought to be determined to a great extent by genetics. However, various forms of mechanical and electrical stimulus (or lack thereof) have been shown to alter their expression, and it is this potential for manipulation that is the centerpiece of the system I am proposing. I will start with the two most interesting studies:
In the first study, subjects were put on a 3 month resistance training program, which was then followed by 3 months of detraining. Analysis of of the MHC composition of the vastus lateralis was done before training, after training, and following the detraining period (17).
Training resulted in a decrease in MHC IIx from 10% to 4% and an increase in MHC I from 49% to 51% - the opposite of what we want as a speed/strength athlete. This fast to slow conversion has been well characterized in the literature - both with bodybuilding type routines such as this, but also with routines typical of those used by power athletes. We will go into considerably more detail on this in a bit.
What is not as well characterized (and what is exciting) is what happened following the detraining period. At the end of the three months, MHC IIx had risen from 4% to 19%, while MHC I had dropped from 51% to 45%. Remember, MHC IIx started out at only 10% before training. This means a significant overshoot in MHC IIx occurred with detraining. Obviously, this is a speed/strength athletes dream.
In the second study (18), 15 women were divided into two groups -- the first group (T) had undergone a 20-week resistance training program followed by 32 weeks of detraining prior to the study. The second group (U) was totally untrained. Both groups were subsequently put on a 6-week training program. Fiber type % measurements for T were taken before and after the 20 weeks of training, after the the 32 weeks of detraining, and again after the 6 week training period. For U, measurements were taken before and after the 6 week training program.
The initial 20 week program for T caused a reduction in IIB from 16% to 1%. The detraining period caused an increase from 1% to 24% -- another instance of overshoot. And considering the length of the detraining period, it is possible that a greater overshoot occurred but that levels were returning to baseline by week 32 (17).
However, this is not the most interesting part, as we will see. Following the subsequent 6 week program, the IIB % of U dropped from 24.9% to 6.7%, but T only dropped from 24.2 to 12.9%. There reduction was far less than that of the untrained group. The differences in type I are just as dramatic. T showed no increase in type I while U increased from 37.5% to 50.5%. In addition to the slow to fast overshoots we have seen, this suggests that the on/off cycling might be causing a resistance to fast to slow transformations. Hopefully, at this point, you have put two and two together and are wondering what might happen if we put together multiple on/off cycles.
I should note that these studies did use untrained subjects and the training protocol was not typical of that used by power athletes, thus if this were the only these studies, they could perhaps be written off. However, a number of other studies argue for the possibility of this being much more than an isolated occurrence, as we will see.
We will first take a look at several studies showing fast to slow conversions which will help us to determine possible mechanisms, not only to allow us to develop training strategies to minimize them, but also to give us some insight as to how the slow to fast changes might be made to occur, so as to facilitate and optimize them.
Fast to Slow
Studies in both man and animal have consistently shown a fast to slow (FTS) MHC response to resistance training, with not only endurance and bodybuilding type routines, but even with with routines typical of speed/strength athletes. We will not concern ourselves with endurance studies, except to say that it causes a rapid slowing of the phenotype (IIx to IIa and IIa to I) without concomitant increases in strength, thus it should be entirely avoided by those wishing to maximize speed, strength, and power (5, 19, 20).
I will not do an exhaustive presentation of the fast to slow literature, as many of the studies use identical design with identical results -- I will focus instead on presenting the different protocols that have produced fast to slow adaptations.
Hortabagyi et al showed a 12% reduction in MHC IIx and 13% increase in MHC I after 12 weeks using high volume maximal effort isokinetic contractions, with eccentric only, concentric only, as well as with mixed training (21).
In another study, using a twice a week heavy (6-8RM), light (10-12RM) split, MHC IIx was reduced from 18% to 7.1% and 18.9% to 6.1% in just 7 weeks in both men and women (22a). Interestingly, between the 7th and 9th week, it leveled off in both groups and the % actually increased slightly in the women. A similar reversal of the STF occurred from week 7 to 9 in another study, using the same training protocol, but which looked at fiber type % (22b).
Twelve weeks of a typical bodybuilding routine caused a 25% MHC IIx reduction along with a slight MHC I increase (23).
It is probably not a big surprise to many that the above training methods caused FTS. However, a study using sprinters (24), employing their normal sprint preparation programs might be. Subjects were tested, following a three week training break, for MHC content, and sprinting speed. This was followed by a three month training period. Type IIx was found to have decreased by about 50%. And this is with a pre-contest sprint preparation protocol.
But, before you decide to just quit training altogether, it should be noted that sprint times still improved slightly (we mustn't forget about the neural and cross sectional area components of speed/strength/power), and type I decreased by 25%. Anderson et. al. and Esbjornsson et. al. have found a similar bi-directional shift (IIX to IIa and I to IIa) with sprint training (24, 25).
Another study, employing multiple 3 second cycle sprints did not observe this, but rather showed the decrease in MHC IIx and increase in MHC I observed in all of the other studies (26).
Slow to Fast
Slow to Fast transitions in the literature are also abundant, however not that many human studies deal with any sort of resistance training setting, thus we will have to dip a bit into other areas such as immobilization, reduced electrical activity, and reduced gravity, as well as animal studies.
Obviously, the studies most applicable to our purposes are those using detraining. We have previously mentioned 2 studies showing STF with extended detraining. Several detraining studies of shorter duration (2-4 weeks) have shown no STF transformation (27, 28). However, an analysis of MHC at the protein level have shown increases in MHC mRNA -- which is indicative of the early stages of IIa to IIb and I to IIa conversions -- in short term studies (21, 29). This makes sense given an MHC turnover time of 3-4 weeks (30). Thus, there is clearly evidence supporting STF given a detraining period of adequate length.
There is a lack of data on the effect of immobilization in humans, however, animal studies show STF transformations in as little as 2-7 days (31, 32).
Reduced loading situations such as space flight and its ground based counterpart, hindlimb unloading, result in rapid STF transitions. As little as 4 days of spaceflight in rats and 11 days in humans caused significant increases in MHC IIx and decreases in MHC I (33, 34). In another study, 17 days resulted in a doubling of the proportion of fast twitch fibers in the human soleus (35). While hindlimb unloading consistently shows STF is rats, it has been more mixed in humans (36).
Reduced neural activity, such as that which occurs in spinal cord injury or transection, rapidly and reliably show STF transformation in both slow-twitch and fast twitch muscles, beginning as early as five days and showing profound changes within 3 months (37, 38, 39, 40).
Obviously, some of the above situations are not exactly 100% analogous to the type of detraining that is practical to a power athlete. However, what they do show, is that given the proper stimulus (or lack thereof), MHC content displays a great deal of plasticity, and in a short enough time to be practical for implementation into a power athlete's off-season program.
Fast to Slow
The exact mechanisms behind the transformations observed is not conclusively known at this time. The most popular theory is that MHC IIx gene represents a default gene, which is switched under conditions of increased contractile activity (41, 42, 24). However, several studies have shown increased MHC IIx expression with certain types of training programs, most notably short duration sprinting (43), as well as with certain metabolic and hormonal conditions, including hyperthyroidism, hyperinsulinemia, leptin administration, and beta 2 adrenergic stimulation (44, 45, 46, 47). Thus, I think this view is flawed.
A more likely explanation is that the phenotype is adapted to its to meet the demands of its environment. Let's look at this from an evolutionary point of view -- in other words, what are the advantages of FTS vs. STF for the survival of the organism.
With resistance training, particularly employing strength training protocols, one would at first view the FTS as paradoxical in the face of mechanical overload. After all, that aspect, all else being equal, represents a weakening of the phenotype. However, on closer inspection, we find that it offers certain advantages, while still allowing the organism to adapt to the stimuli presented.
First, a FTS conversion would make the organism metabolically more efficient (48, 49), which is an obvious advantage in the times of scarcity in which we evolved. And, given that under non-training conditions, motor units associated with MHC IIx isoforms are only active 30-180 seconds per day, most current training programs are going to represent a significant increase in activity (50).
Second, the training stimulus with current protocols does not present a true maximal overload, particularly in regards to the eccentric component. This, along with the fact that some studies show MHC IIa fibers to produce equal or superior force at low velocities compared with MHC IIx (16), mean that a concentric/eccentric rep under typical strength training conditions (loads only as high as the concentric 1 RM and low velocities) could be adequately handled by a phenotype with a preferential IIa expression.
This makes it tempting to suggest loads equal to or greater than the ECCENTRIC 1 RM, however, speed of cross-bridging is less fiber type dependent (50b), thus it might overactivate and thus hypertrophy type I and IIa fibers. Therefore, we will leave this as an area for exploration at this point. The other method would be to employ only a concentric contraction at very high velocities (or perhaps at loads equal to the 1 RM).
Slow to Fast
The specific mechanisms responsible for STF at the micro level are not fully known. A couple of theories exist -- one involving the myogenic regulatory factor pathway and the other calcineurin:NF-AT pathway (36). However, these are very much speculative at present and are well beyond the scope of this today's article, thus we will not go into further detail, today.
At the macro level, we can once again turn to the advantage STF might produce for the organism. With the hormonal conditions mentioned above, it is fairly obvious. Beta 2 receptors are activated by epinephrine and norepinephrine, the so called "fight or flight" hormones. Clearly, a STF transformation of the phenotype would be advantageous for an organism that has to run away from a predator (or chase down its prey). This is likely what accounts for STF transformations that have occurred with short duration sprint training as well (51, 52).
As for hyperthyroidism, hyperinsulinemia, and leptin administration, what these all have in common is they are characteristic of the organism being in the "fed" state. Thus, the need for metabolic efficiency is done away with for the time being, leaving the organism free to assume a phenotype most conducive to the afore mentioned fight or flight situations.
With reduced mechanical loading and neural activity, the mechanism is likely the opposite of that which produces the FTS during training. In the face of reduced activity, thus reduced energy expenditure and need for muscular endurance, the afore mentioned metabolic efficiency would no longer be necessary for survival, thus the organism is free to once again assume the faster phenotype, which is clearly advantageous, all else being equal.
With detraining, it is likely that, from the body's vantage point, the abrupt withdrawal of stimulus following increased muscle activity with training is analogous to the near complete cessation of activity with immobilization/neural inactivation following normal activity (17). In other words, it "tricks" the body into thinking it can safely assume the metabolic inefficiencies that accompany the faster phenotype.
Muscle and Strength Losses
At this point, perhaps you are convinced of the possibility of slow to fast transformations but are concerned about the negative effects of the detraining period on muscle mass and strength. After all, spinal cord transection can accomplish STF, but it is not going to make anyone a great athlete. Fortunately, this is not a great concern. As I will show, both parameters rapidly return to normal levels (and above) when training is resumed.
The previously mentioned study by Staron et. al. (18) showed complete strength and power recovery after just 6 weeks of retraining following 20 weeks of detraining. Hortabagyi (21) and MacDougall (53) showed gains to beyond starting levels despite complete immobilization for extended periods. These are not surprising in light of data showing that majority of neural adaptation induced strength gains take place in the first 3-5 weeks of training (54). In addition, a couple studies have found that fiber areas of subjects trained for only a couple of months were equal to those of subjects trained for several years (54, 55). This has ramification that go far beyond what is presented today, but that is the subject of another article.
In next month's issue, we will discuss the practical implementation of the theories presented here for the speed, strength, and power athlete.
Questions and comments on this article can be sent to ParDeus@avantlabs.com
This article appears courtesy of www.mindandmuscle.net
1. Bee G, Solomon MB, Czerwinski SM, Long C, Pursel VG Correlation between histochemically assessed fiber type distribution and isomyosin and myosin heavy chain content in porcine skeletal muscles. J Anim Sci 1999 Aug;77(8):2104-11
2. Bottinelli R, Reggiani C Human skeletal muscle fibres: molecular and functional diversity Prog Biophys Mol Biol 2000;73(2-4):195-262
3. Thorstensson A, Grimby G, Karlsson J Force-velocity relations and fiber composition in human knee extensor muscles. J Appl Physiol 1976 Jan;40(1):12-6
4. Inbar O, Kaiser P, Tesch P Relationships between leg muscle fiber type distribution and leg exercise performance. Int J Sports Med 1981 Aug;2(3):154-9
5. Tesch PA, Wright JE, Vogel JA, Daniels WL, Sharp DS, Sjodin B The influence of muscle metabolic characteristics on physical performance. Eur J Appl Physiol Occup Physiol 1985;54(3):237-43
6. Gollnick PD, Armstrong RB, Saubert CW, Piehl K, Saltin B J Enzyme activity and fiber composition in skeletal muscle of untrained and trained men. Appl Physiol 1972 Sep;33(3):312-9
7. Schiaffino S, Reggiani C Physiol Rev Molecular diversity of myofibrillar proteins: gene regulation and functional significance. 1996 Apr;76(2):371-423
8. Andersen JL, Terzis G, Kryger A Increase in the degree of coexpression of myosin heavy chain isoforms in skeletal muscle fibers of the very old. Muscle Nerve 1999 Apr;22(4):449-54
9. Bottinelli R, Betto R, Schiaffino S, Reggiani C Maximum shortening velocity and coexistence of myosin heavy chain isoforms in single skinned fast fibres of rat skeletal muscle. J Muscle Res Cell Motil 1994 Aug;15(4):413-9
10. Harridge SD, Bottinelli R, Canepari M, Pellegrino MA, Reggiani C, Esbjornsson M, Saltin B Whole-muscle and single-fibre contractile properties and myosin heavy chain isoforms in humans. Pflugers Arch 1996 Sep;432(5):913-20
11. Bottinelli R, Canepari M, Pellegrino MA, Reggiani C Force-velocity properties of human skeletal muscle fibres: myosin heavy chain isoform and temperature dependence. J Physiol 1996 Sep 1;495 ( Pt 2):573-86
12. Larsson L, Moss RL Maximum velocity of shortening in relation to myosin isoform composition in single fibres from human skeletal muscles. J Physiol 1993 Dec;472:595-614
13. Widrick JJ, Trappe SW, Costill DL, Fitts RH Force-velocity and force-power properties of single muscle fibers from elite master runners and sedentary men. Am J Physiol 1996 Aug;271(2 Pt 1):C676-83
14. Eddinger TJ, Moss RL Am J Physiol 1987 Mechanical properties of skinned single fibers of identified types from rat diaphragm.Aug;253(2 Pt 1):C210-8
15. Bottinelli R, Schiaffino S, Reggiani C Force-velocity relations and myosin heavy chain isoform compositions of skinned fibres from rat skeletal muscle. J Physiol 1991 Jun;437:655-72
16. Morner SE, Canepari M, Bottinelli R, Cappelli V, Reggiani C Effects of Amrinone on shortening velocity, force development and ATPase activity of demembranated preparations of rat ventricular myocardium. Acta Physiol Scand 1992 Sep;146(1):21-30
17. Andersen JL, Aagaard P Myosin heavy chain IIX overshoot in human skeletal muscle. Muscle Nerve 2000 Jul;23(7):1095-104
18. Staron RS, Leonardi MJ, Karapondo DL, Malicky ES, Falkel JE, Hagerman FC, Hikida RS Strength and skeletal muscle adaptations in heavy-resistance-trained women after detraining and retraining. J Appl Physiol 1991 Feb;70(2):631-40
19. Fitzsimons DP, Diffee GM, Herrick RE, Baldwin KM Effects of endurance exercise on isomyosin patterns in fast- and slow-twitch skeletal muscles. J Appl Physiol 1990 May;68(5):1950-5
20. O'Neill DS, Zheng D, Anderson WK, Dohm GL, Houmard JA Effect of endurance exercise on myosin heavy chain gene regulation in human skeletal muscle. Am J Physiol 1999 Feb;276(2 Pt 2):R414-9
21. Hortobagyi T, Dempsey L, Fraser D, Zheng D, Hamilton G, Lambert J, Dohm L Changes in muscle strength, muscle fibre size and myofibrillar gene expression after immobilization and retraining in humans. J Physiol 2000 Apr 1;524 Pt 1:293-304
22a. Staron RS, Karapondo DL, Kraemer WJ, Fry AC, Gordon SE, Falkel JE, Hagerman FC, Hikida RS Skeletal muscle adaptations during early phase of heavy-resistance training in men and women. J Appl Physiol 1994 Mar;76(3):1247-55
22b. Fry AC, Allemeier CA, Staron RS Correlation between percentage fiber type area and myosin heavy chain content in human skeletal muscle. Eur J Appl Physiol Occup Physiol 1994;68(3):246-51
23. Jurimae J, Abernethy PJ, Blake K, McEniery MT Changes in the myosin heavy chain isoform profile of the triceps brachii muscle following 12 weeks of resistance training. Eur J Appl Physiol Occup Physiol 1996;74(3):287-92
24. Andersen JL, Klitgaard H, Saltin B Myosin heavy chain isoforms in single fibres from m. vastus lateralis of sprinters: influence of training. Acta Physiol Scand 1994 Jun;151(2):135-42
25. Esbjornsson M, Hellsten-Westing Y, Balsom PD, Sjodin B, Jansson E Muscle fibre type changes with sprint training: effect of training pattern.Acta Physiol Scand 1993 Oct;149(2):245-6
26. Harridge SD, Bottinelli R, Canepari M, Pellegrino M, Reggiani C, Esbjornsson M, Balsom PD, Saltin B Sprint training, in vitro and in vivo muscle function, and myosin heavy chain expression. J Appl Physiol 1998 Feb;84(2):442-9
27. Hather BM, Tesch PA, Buchanan P, Dudley GA Influence of eccentric actions on skeletal muscle adaptations to resistance training. Acta Physiol Scand 1991 Oct;143(2):177-85
28. Hortobagyi T, Houmard JA, Stevenson JR, Fraser DD, Johns RA, Israel RG The effects of detraining on power athletes. Med Sci Sports Exerc 1993 Aug;25(8):929-35
29. Andersen JL, Schiaffino S Mismatch between myosin heavy chain mRNA and protein distribution in human skeletal muscle fibers.Am J Physiol 1997 Jun;272(6 Pt 1):C1881-9
30. Bates PC, Grimble GK, Sparrow MP, Millward D Myofibrillar protein turnover. Synthesis of protein-bound 3-methylhistidine, actin, myosin heavy chain and aldolase in rat skeletal muscle in the fed and starved states. J Biochem J 1983 Aug 15;214(2):593-605
31. Loughna PT, Izumo S, Goldspink G, Nadal-Ginard B Disuse and passive stretch cause rapid alterations in expression of developmental and adult contractile protein genes in skeletal muscle. Development 1990 May;109(1):217-23
32. Jankala H, Harjola VP, Petersen NE, Harkonen M Myosin heavy chain mRNA transform to faster isoforms in immobilized skeletal muscle: a quantitative PCR study J Appl Physiol 1997 Mar;82(3):977-82
33. Jiang B, Roy RR, Navarro C, Edgerton VR Absence of a growth hormone effect on rat soleus atrophy during a 4-day spaceflight. J Appl Physiol 1993 Feb;74(2):527-31
34. Zhou MY, Klitgaard H, Saltin B, Roy RR, Edgerton VR, Gollnick PD J Appl Physiol Myosin heavy chain isoforms of human muscle after short-term spaceflight.1995 May;78(5):1740-4
35. Widrick JJ, Knuth ST, Norenberg KM, Romatowski JG, Bain JL, Riley DA, Karhanek M, Trappe SW, Trappe TA, Costill DL, Fitts RH Effect of a 17 day spaceflight on contractile properties of human soleus muscle fibres. J Physiol 1999 May 1;516 ( Pt 3):915-30
36. Talmadge RJ Muscle Nerve 2000 Myosin heavy chain isoform expression following reduced neuromuscular activity: potential regulatory mechanisms. May;23(5):661-79
37. Dupont-Versteegden EE, Houle JD, Gurley CM, Peterson CA Early changes in muscle fiber size and gene expression in response to spinal cord transection and exercise. Am J Physiol 1998 Oct;275(4 Pt 1):C1124-33
38. Castro MJ, Apple DF, Rogers S, Dudley GA Influence of complete spinal cord injury on skeletal muscle mechanics within the first 6 months of injury. Eur J Appl Physiol 2000 Jan;81(1-2):128-31
39.Talmadge RJ, Roy RR, Edgerton VR Myosin heavy chain profile of cat soleus following chronic reduced activity or inactivity. Muscle Nerve 1996 Aug;19(8):980-8
40. Talmadge RJ, Roy RR, Edgerton VR Persistence of hybrid fibers in rat soleus after spinal cord transection. Anat Rec 1999 Jun 1;255(2):188-201
41. Adams GR, Hather BM, Baldwin KM, Dudley GA Skeletal muscle myosin heavy chain composition and resistance training.J Appl Physiol 1993 Feb;74(2):911-5
42. Goldspink G, Scutt A, Martindale J, Jaenicke T, Turay L, Gerlach GF Biochem Soc Trans Stretch and force generation induce rapid hypertrophy and myosin isoform gene switching in adult skeletal muscle. 1991 Apr;19(2):368-73
43. Jansson E, Esbjornsson M, Holm I, Jacobs I Increase in the proportion of fast-twitch muscle fibres by sprint training in males. Acta Physiol Scand 1990 Nov;140(3):359-63
44. Houmard JA, O'Neill DS, Zheng D, Hickey MS, Dohm GL Impact of hyperinsulinemia on myosin heavy chain gene regulation. J Appl Physiol 1999 Jun;86(6):1828-32
45. Pette D, Staron RS Microsc Res Tech 2000 Myosin isoforms, muscle fiber types, and transitions Sep 15;50(6):500-9
46. Tankersley CG, O'Donnell C, Daood MJ, Watchko JF, Mitzner W, Schwartz A, Smith P Leptin attenuates respiratory complications associated with the obese phenotype. J Appl Physiol 1998 Dec;85(6):2261-9
47. Rajab P, Fox J, Riaz S, Tomlinson D, Ball D, Greenhaff PL Skeletal muscle myosin heavy chain isoforms and energy metabolism after clenbuterol treatment in the rat. Am J Physiol Regul Integr Comp Physiol 2000 Sep;279(3):R1076-81
48. Baldwin KM Effects of altered loading states on muscle plasticity: what have we learned from rodents? Med Sci Sports Exerc 1996 Oct;28(10 Suppl):S101-6
49. Baldwin KM, Herrick RE, McCue SA Substrate oxidation capacity in rodent skeletal muscle: effects of exposure to zero gravity. J Appl Physiol 1993 Dec;75(6):2466-70
50. Hennig R, Lomo T Firing patterns of motor units in normal rats. Nature 1985 Mar 14-20;314(6007):164-6
50b. Burton K J Myosin step size: estimates from motility assays and shortening muscle Muscle Res Cell Motil 1992 Dec;13(6):590-607
51. Cheetham ME, Boobis LH, Brooks S, Williams C Human muscle metabolism during sprint running. J Appl Physiol 1986 Jul;61(1):54-60
52. Taguchi S, Hata Y, Itoh K Enzymatic responses and adaptations to swimming training and hypobaric hypoxia in postnatal rats. Jpn J Physiol 1985;35(6):1023-32
53. MacDougall JD, Sale DG, Elder GC, Sutton JR Muscle ultrastructural characteristics of elite powerlifters and bodybuilders .Eur J Appl Physiol Occup Physiol 1982;48(1):117-26
54. Moritani T, deVries HA Neural factors versus hypertrophy in the time course of muscle strength gain. Am J Phys Med 1979 Jun;58(3):115-30
55. Tesch PA, Larsson L Muscle hypertrophy in bodybuilders. Eur J Appl Physiol Occup Physiol 1982;49(3):301-6