Fiber Type Adaptations
1. Sprint training induces an increase in Type IIB fibers and a decrease in type I fibers. But, the IIB fibers show an increased expression of the MHC IIA isoform. The Type I fibers show a decreased expression of the MHC I isoform, with an increased expression of the MHC IIA isoform. Here, we are seeing an adaptation toward the middle of the glycolytic / oxidative continuum. We are seeing a shift from both SO fibers and FG fibers to the FOG spectrum. I like this quote: “This seems related to a bi-directional transformation from both MHC isoforms I and IIB towards MHC isoform IIA.”
Acta Physiol Scand 1994 Jun;151(2):135-42 . Myosin heavy chain isoforms in single fibres from m. vastus lateralis of sprinters: influence of training. Andersen JL, Klitgaard H, Saltin B.
These results are also similar to this study:
Acta Physiol Scand 1990 Nov;140(3):359-63. Increase in the proportion of fast-twitch muscle fibres by sprint training in males. Jansson E, Esbjornsson M, Holm I, Jacobs I.
2. Body builders have a higher percentage of type IIA fibers and a lower percentage of type IIB fibers as compared to sedentary individuals. However, if we look at the actual protein expression in those fibers, it shows an even greater propensity toward the fatigue resistant spectrum, with a greater percentage of fast twitch fibers possessing only the MHC type IIA isoform and a lower percentage of fibers expressing both MHC type IIA and IIB isoforms. Further, body builders contain almost no fibers possessing only the MHC type IIB isoform.
Acta Physiol Scand 1990 Oct;140(2):175-80. Myosin heavy chain composition of single fibres from m. biceps brachii of male body builders. Klitgaard H, Zhou M, Richter EA. August Krogh Institute, University of Copenhagen, Denmark.
Similar results can be found in these studies:
Eur J Appl Physiol Occup Physiol 1996;74(3):287-92. Changes in the myosin heavy chain isoform profile of the triceps brachii muscle following 12 weeks of resistance training. Jurimae J, Abernethy PJ, Blake K, McEniery MT.
Eur J Appl Physiol Occup Physiol 1997;75(4):357-62. Differences in muscle contractile characteristics among bodybuilders, endurance trainers and control subjects. Jurimae J, Abernethy PJ, Quigley BM, Blake K, McEniery MT.
J Histochem Cytochem 1984 Feb;32(2):146-52. Human skeletal muscle fiber type adaptability to various workloads. Staron RS, Hikida RS, Hagerman FC, Dudley GA, Murray TF.
3. Endurance athletes show a higher percentage of type I fibers. (Staron RS, Hikida RS, Hagerman FC, Dudley GA, Murray TF. 1984). Endurance training also shows an increase in intermediate fibers expressing both MHC type I and MHC type IIA isoforms. Obviously, the muscle is adapting even further toward the fatigue resistant end of the spectrum. (Klitgaard H, Bergman O, Betto R, Salviati G, Schiaffino S, Clausen T, Saltin B. 1990).
4. Sedentary individuals possess a greater number of type IIB fibers, a greater number of fibers expressing only the MHC IIB isoform, and more intermediate fibers expressing both MCH IIA and IIB isoforms. (Klitgaard H, Bergman O, Betto R, Salviati G, Schiaffino S, Clausen T, Saltin B. 1990). Inactivity seems to be the major factor influencing an increased expression of MHC IIB.
J Appl Physiol 1995 May;78(5):1740-4. Myosin heavy chain isoforms of human muscle after short-term spaceflight. Zhou MY, Klitgaard H, Saltin B, Roy RR, Edgerton VR, Gollnick PD.
I love this quote: “…inactivity rather than the lifting exercise contributes to a low volume-percent mitochondria and a high percentage of type IIB fibers.” This is consistent with denervation and immobilization models.
(Staron RS, Hikida RS, Hagerman FC, Dudley GA, Murray TF. 1984).
So… What are the conclusions?
Look at the following quote:
“ST and FT myofibers express unique sets of muscle-specific genes, and these distinctive programs of gene expression are controlled by variations in motor neuron activity… brief burst of neuronal activity, interspersed between long periods of neuronal quiescence, promote the acquisition of FT-glycolytic fiber characteristics. Conversely, extended periods of tonic motor nerve activity stimulate a shift to the ST-oxidative myofibers phenotype.”
Genes Dev 1998 Aug 15;12(16):2499-509
A calcineurin-dependent transcriptional pathway controls skeletal muscle fiber type. Chin ER, Olson EN, Richardson JA, Yang Q, Humphries C, Shelton JM, Wu H, Zhu W, Bassel-Duby R, Williams RS.
What about this quote:
“Mammalian skeletal muscle fibers display a great adaptive potential. This potential results from the ability of muscle fibers to adjust their molecular, functional, and metabolic properties in response to altered functional demands, such as changes in neuromuscular activity or mechanical loading. Adaptive changes in the expression of myofibrillar and other protein isoforms result in fiber type transitions. These transitions occur in a sequential order and encompass a spectrum of pure and hybrid fibers. Depending on the quality, intensity, and duration of the alterations in functional demand, muscle fibers may undergo functional transitions in the direction of slow or fast, as well as metabolic transitions in the direction of aerobic-oxidative or glycolytic. The maximum range of possible transitions in either direction depends on the fiber phenotype and is determined by its initial location in the fiber spectrum.”
Can J Appl Physiol 2002 Aug;27(4):423-48. The adaptive potential of skeletal muscle fibers. Pette D.
Ryan A. Hall
J Histochem Cytochem 1984 Feb;32(2):146-52
Human skeletal muscle fiber type adaptability to various workloads.
Staron RS, Hikida RS, Hagerman FC, Dudley GA, Murray TF.
Muscle biopsy specimens were removed from the vastus lateralis muscles of three groups of human subjects: controls, weight lifters, and distance runners. The runners proved to be a unique group with respect to the variables measured (low body weight and percentage body fat, and high VO2 max). Additionally, a histochemical analysis of the biopsy specimens revealed that the runners had a significantly higher percentage of fiber types I and IIC than either the controls or the weight lifters. Using a cryostatic retrieval method, each of the fibers identified histochemically was then analyzed morphometrically using electron microscopy. The results of volume-percent mitochondria demonstrated a strong relationship between the ATPase activity and oxidative potential of the fiber types for all three groups such that the oxidative activity would be ranked I greater than IIA greater than IIB. Irrespective of fiber type, there were significant differences between the groups with regard to muscle-fiber mitochondrial (runners greater than lifters greater than controls) and lipid content (runners greater than controls greater than lifters). The lifters had a significantly greater content of mitochondria than the controls, which may suggest that inactivity rather than the lifting exercise contributes to a low volume-percent mitochondria and a high percentage of type IIB fibers.
Acta Physiol Scand 1994 Jun;151(2):135-42
Myosin heavy chain isoforms in single fibres from m. vastus lateralis of sprinters: influence of training.
Andersen JL, Klitgaard H, Saltin B.
August Krogh Institute, University of Copenhagen, Denmark.
The myosin heavy chain (MHC) composition of single fibres from m. vastus lateralis of a group of male sprint athletes (n = 6) was analysed, before and after a three months period of intensive strength- and interval-training, using a sensitive gel electrophoretic technique. Significant improvements were observed after training in almost all of a series of performance tests. After training the sprinters revealed a decrease in fibres containing only MHC isoform I (52.0 +/- 3.0% vs. 41.2 +/- 4.7% (mean +/- SE) (P < 0.05)) and an increase in the amount of fibres containing only MHC isoform IIA (34.7 +/- 6.1% vs. 52.3 +/- 3.6% (P < 0.05)). Fibres showing co-existence of MHC isoforms IIA and IIB decreased with training (12.9 +/- 5.0% vs. 5.1 +/- 3.1% (P < 0.05)). Only one out of 1000 fibres analysed contained only MHC isoform IIB. In contrast, a higher amount of type IIB fibres (18.8 +/- 3.6% vs. 10.5 +/- 3.9%, (P < 0.05)) was observed with myofibrillar ATPase histochemistry. The majority of histochemically determined type IIB fibres of sprinters seems therefore to contain both MHC isoforms IIA and IIB. Sprint-training appears to induce an increased expression of MHC isoform IIA in skeletal muscles. This seems related to a bi-directional transformation from both MHC isoforms I and IIB towards MHC isoform IIA.
Eur J Appl Physiol Occup Physiol 1997;75(4):357-62
Differences in muscle contractile characteristics among bodybuilders, endurance trainers and control subjects.
Jurimae J, Abernethy PJ, Quigley BM, Blake K, McEniery MT.
Department of Human Movement Studies, University of Queensland, Australia.
The purpose of this investigation was to compare the myosin heavy chain (MHC) isoform expression of the triceps brachii muscle and isoinertial, isometric and isokinetic strength indices in competitive bodybuilders (CB, n = 5), recreational resistance trainers (RT, n = 5), endurance-trained rowers (ER, n = 5) and control (C, n = 5) subjects. Muscle tissue samples were analysed for MHC isoform content using 6% sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The CB possessed significantly smaller (P < 0.05) percentage of MHC type IIb proteins [12.92 (SD 7.08)%] than RT [30.08 (SD 6.58)%] ER [31.20 (SD 2.74)%] and C [38.22 (SD 2.95)%] groups (i.e. CB < RT approximately ER < C). While the content of MHC type IIa isoforms did not differ significantly between the two resistance-trained groups [CB = 55.76 (SD 5.38)%; RT = 45.72 (SD 7.8)%], CB presented significantly more type IIa MHC isoforms than ER [42.84 (SD 2.98)%] and C [34.72 (SD 1.57)%] subjects (i.e. CB approximately RT > ER approximately C). The MHC type I protein content did not differ significantly among RT [24.20 (SD 4.89)%] ER [25.38 (SD 1.67)%] and C [27.06 (SD 1.81)%] groups. The CB [31.32 (SD 2.67)%] presented significantly more type I MHC isoforms only in comparison with RT. However, when changes in the percentage of MHC type I isoforms were converted to effect sizes (ES), it appeared that low statistical power rather than the absence of an effect accounted for the nonsignificant differences between CB and other groups (i.e. CB > RT approximately ER approximately C). Significant differences existed in isoinertial strength among the trained athletes (i.e. CB > RT > ER approximately C), while isometric and isokinetic strength were not significantly different among any of the trained groups. However, the ES transformation of data demonstrated that large differences existed between resistance-trained groups and ER for isometric and isokinetic strength (i.e. CB approximately RT > ER approximately C). A statistically significant negative correlation (P < 0.001) was found between MHC type IIb isoforms and isoinertial strength index (r = -0.68). The MHC type IIa proteins were positively related to all the strength measures considered (r = 0.51 0.61; P < 0.001). These data demonstrated different patterns of MHC isoform expression among the different groups of athletes and it is suggested that these differences on occasion may affect the expression of strength.
J Appl Physiol 1995 May;78(5):1740-4
Myosin heavy chain isoforms of human muscle after short-term spaceflight.
Zhou MY, Klitgaard H, Saltin B, Roy RR, Edgerton VR, Gollnick PD.
Department of Human Physiology, August Krogh Institute, Copenhagen, Denmark.
The influence of microgravity on the myosin phenotype of skeletal muscle fibers in the vastus lateralis of eight crew members was studied before and after 5-day (n = 3) and 11-day (n = 5) spaceflights (space shuttle flights: STS-32, -33 and -34). Single-fiber electrophoresis analyses showed that the proportion of fibers expressing only slow (type I) myosin heavy chain (MHC) in the vastus lateralis was significantly lower after than before 11 days of spaceflight. Although the family of type II MHC isoforms was elevated post- compared with preflight, the distribution among the isoforms of type II MHC was not statistically different. Based on monoclonal and polyclonal antibodies specific for three adult MHC isoforms and single-fiber electrophoresis, approximately 3% of the fibers analyzed coexpressed all three adult MHC isoforms. The results from immunohistochemical staining with two different sets of antibodies indicate a reduction in the percentage of fibers expressing type I MHC as a result of spaceflight. The mean difference, however, was significant only when the fibers were categorized simply as type I or II. These changes appeared to be highly individualized among the astronauts. These results suggest that a rapid change in MHC isoform expression can occur in some muscle fibers after a relatively brief exposure to spaceflight.
Eur J Appl Physiol Occup Physiol 1996;74(3):287-92
Changes in the myosin heavy chain isoform profile of the triceps brachii muscle following 12 weeks of resistance training.
Jurimae J, Abernethy PJ, Blake K, McEniery MT.
Department of Human Movement Studies, University of Queensland, Brisbane, Australia.
The purpose of this investigation was to determine whether 12 weeks of resistance training, which increased arm girth (5%) and forearm extensor strength (39%), also altered the myosin heavy chain (MHC) characteristics of the triceps brachii muscle. Fifteen healthy, active men volunteered to participate under experimental (n = 11) or control (n = 4) conditions. The experimental group completed four sets of eight to 12 repetitions for each exercise (i.e. triceps pushdown, close grip bench press, triceps kickbacks and biceps curl) with loads of between 70-75% of one repetition maximum (1RM) three times a week. The inter-set and inter-exercise recovery period was only 90 s. Skeletal muscle tissue was removed from the triceps brachii muscle prior to (W0) and following 4 (W4), 8 (W8) and 12 (W12) weeks of the investigation. Samples were analysed for MHC isoform content using 6% sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). MHC isoform composition in the control group did not change significantly. However, the percentage of MHC type IIb isoform decreased significantly from W0 to W4 and again from W4 to W12 [W0: 39.7 (9.2); W12: 29.2 (8.2%)] in the experimental condition. The increments in MHC type IIa [W0: 34.0 (9.9); W12: 41.5 (10.4)] and type I [W0: 26.3 (7.9); W12: 29.3 (9.6)] isoforms were not significant for the experimental group. However, the effect size (ES) transformation of changes in types IIa MHC content was moderate (ES = 0.75). Changes in MHC isoform content were not significantly correlated with changes in 1RM strength for the triceps pushdown exercise. These data indicated that resistance training rapidly, and in an ongoing manner, changed the contractile protein profile of trained skeletal muscle. However, changes in MHC isoform composition in the first 12 weeks of training were not implicated in the development of 1RM triceps pushdown strength.
Acta Physiol Scand 1990 Nov;140(3):359-63
Increase in the proportion of fast-twitch muscle fibres by sprint training in males.
Jansson E, Esbjornsson M, Holm I, Jacobs I.
Department of Clinical Physiology, Karolinska Hospital, Stockholm, Sweden.
Fifteen male physical education students were studied. The subjects trained for 4-6 weeks, 2-3 days per week, on a mechanically braked bicycle ergometer. A training session consisted of repeated 30-s 'all-out' sprints on a Wingate bicycle ergometer, on which the brake band of the flywheel was loaded with 75 g kg-1 body wt, with rest periods of 15-20 min between consecutive sprints. Thigh muscle biopsies were taken before and after the training period and were analysed for fibre types using a myofibrillar ATPase stain. The proportion of type I fibres decreased from 57 to 48% (P less than 0.05) and type IIA fibres increased from 32 to 38% (P less than 0.05). This study indicates that it is possible to achieve a fibre type transformation with high-intensity training. The effect of two-legged 'sprint' training on muscle fibre type composition may be related to a changed pattern of muscle fibre activation (e.g. an increased stimulation frequency). A change in fibre activation frequency may induce an increased synthesis of type II fibre myosin (fast myosin). Hormonal influences such as enhanced adrenergic stimulation of the muscle fibres cannot be excluded as a contributing factor, however.
Pflugers Arch 1990 Jun;416(4):470-2
Co-existence of myosin heavy chain I and IIa isoforms in human skeletal muscle fibres with endurance training.
Klitgaard H, Bergman O, Betto R, Salviati G, Schiaffino S, Clausen T, Saltin B.
August Krogh Institute, University of Copenhagen, Denmark.
The myosin heavy chain (MHC) composition of single fibres from m. vastus lateralis was analysed by one-dimensional electrophoresis and immunoblotting in three groups of young men with distinct difference in physical activity patterns. No major co-existence of MHC isoforms was found in the group with some daily physical activity. In the very sedentary group, however, 19 +/- 5% (P less than 0.05) of the fibres exhibited coexistence of MHC type IIa and IIb. Further, in the endurance trained group co-existence of MHC type I and IIa was manifested in 36 +/- 4% (P less than 0.05) of the fibres. Disuse and extreme usage of muscle both give rise to an elevation in co-expression of MHC isoforms in single muscle fibres but of markedly different combination of isoforms.
Acta Physiol Scand 1990 Oct;140(2):175-80
Myosin heavy chain composition of single fibres from m. biceps brachii of male body builders.
Klitgaard H, Zhou M, Richter EA.
August Krogh Institute, University of Copenhagen, Denmark.
The myosin heavy chain (MHC) composition of single fibres from m. biceps brachii of young sedentary men (28 +/- 0.4 years, mean +/- SE, n = 4) and male body builders (25 +/- 2.0 years, n = 4) was analysed with a sensitive one-dimensional electrophoretic technique. Compared with sedentary men, the body builders had a higher proportion of fibres containing only MHC type IIa (36 +/- 4 vs 12 +/- 2%; P less than 0.05), but a lower proportion of fibres with a coexistence of MHC types IIa and IIb (16 +/- 3 vs 34 +/- 2%; P less than 0.05) and nearly no fibres containing only MHC type IIb (1 +/- 1 vs 12 +/- 1%; P less than 0.05). Myofibrillar ATPase histochemistry only demonstrated a trend towards a higher proportion of type IIa fibres (31 +/- 6 vs 25 +/- 6%) and a lower proportion of type IIb fibres (18 +/- 5 vs 26 +/- 6%) within the body builders. These results, therefore, suggest an altered expression of MHC isoforms within histochemical type II fibres of human skeletal muscle with body building. Furthermore, in human skeletal muscle differences in expression of MHC isoforms may not always be reflected in the traditional histochemical classification of types I, IIa, IIb and IIc fibres.
Genes Dev 1998 Aug 15;12(16):2499-509
A calcineurin-dependent transcriptional pathway controls skeletal muscle fiber type.
Chin ER, Olson EN, Richardson JA, Yang Q, Humphries C, Shelton JM, Wu H, Zhu W, Bassel-Duby R, Williams RS.
Departments of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas 75235, USA.
Slow- and fast-twitch myofibers of adult skeletal muscles express unique sets of muscle-specific genes, and these distinctive programs of gene expression are controlled by variations in motor neuron activity. It is well established that, as a consequence of more frequent neural stimulation, slow fibers maintain higher levels of intracellular free calcium than fast fibers, but the mechanisms by which calcium may function as a messenger linking nerve activity to changes in gene expression in skeletal muscle have been unknown. Here, fiber-type-specific gene expression in skeletal muscles is shown to be controlled by a signaling pathway that involves calcineurin, a cyclosporin-sensitive, calcium-regulated serine/threonine phosphatase. Activation of calcineurin in skeletal myocytes selectively up-regulates slow-fiber-specific gene promoters. Conversely, inhibition of calcineurin activity by administration of cyclosporin A to intact animals promotes slow-to-fast fiber transformation. Transcriptional activation of slow-fiber-specific transcription appears to be mediated by a combinatorial mechanism involving proteins of the NFAT and MEF2 families. These results identify a molecular mechanism by which different patterns of motor nerve activity promote selective changes in gene expression to establish the specialized characteristics of slow and fast myofibers.
Can J Appl Physiol 2002 Aug;27(4):423-48
The adaptive potential of skeletal muscle fibers.
Pette D.
Department of Biology, University of Konstanz, Germany.
Mammalian skeletal muscle fibers display a great adaptive potential. This potential results from the ability of muscle fibers to adjust their molecular, functional, and metabolic properties in response to altered functional demands, such as changes in neuromuscular activity or mechanical loading. Adaptive changes in the expression of myofibrillar and other protein isoforms result in fiber type transitions. These transitions occur in a sequential order and encompass a spectrum of pure and hybrid fibers. Depending on the quality, intensity, and duration of the alterations in functional demand, muscle fibers may undergo functional transitions in the direction of slow or fast, as well as metabolic transitions in the direction of aerobic-oxidative or glycolytic. The maximum range of possible transitions in either direction depends on the fiber phenotype and is determined by its initial location in the fiber spectrum.
Acta Physiol Scand 1994 Jun;151(2):135-42 . Myosin heavy chain isoforms in single fibres from m. vastus lateralis of sprinters: influence of training. Andersen JL, Klitgaard H, Saltin B.
These results are also similar to this study:
Acta Physiol Scand 1990 Nov;140(3):359-63. Increase in the proportion of fast-twitch muscle fibres by sprint training in males. Jansson E, Esbjornsson M, Holm I, Jacobs I.
2. Body builders have a higher percentage of type IIA fibers and a lower percentage of type IIB fibers as compared to sedentary individuals. However, if we look at the actual protein expression in those fibers, it shows an even greater propensity toward the fatigue resistant spectrum, with a greater percentage of fast twitch fibers possessing only the MHC type IIA isoform and a lower percentage of fibers expressing both MHC type IIA and IIB isoforms. Further, body builders contain almost no fibers possessing only the MHC type IIB isoform.
Acta Physiol Scand 1990 Oct;140(2):175-80. Myosin heavy chain composition of single fibres from m. biceps brachii of male body builders. Klitgaard H, Zhou M, Richter EA. August Krogh Institute, University of Copenhagen, Denmark.
Similar results can be found in these studies:
Eur J Appl Physiol Occup Physiol 1996;74(3):287-92. Changes in the myosin heavy chain isoform profile of the triceps brachii muscle following 12 weeks of resistance training. Jurimae J, Abernethy PJ, Blake K, McEniery MT.
Eur J Appl Physiol Occup Physiol 1997;75(4):357-62. Differences in muscle contractile characteristics among bodybuilders, endurance trainers and control subjects. Jurimae J, Abernethy PJ, Quigley BM, Blake K, McEniery MT.
J Histochem Cytochem 1984 Feb;32(2):146-52. Human skeletal muscle fiber type adaptability to various workloads. Staron RS, Hikida RS, Hagerman FC, Dudley GA, Murray TF.
3. Endurance athletes show a higher percentage of type I fibers. (Staron RS, Hikida RS, Hagerman FC, Dudley GA, Murray TF. 1984). Endurance training also shows an increase in intermediate fibers expressing both MHC type I and MHC type IIA isoforms. Obviously, the muscle is adapting even further toward the fatigue resistant end of the spectrum. (Klitgaard H, Bergman O, Betto R, Salviati G, Schiaffino S, Clausen T, Saltin B. 1990).
4. Sedentary individuals possess a greater number of type IIB fibers, a greater number of fibers expressing only the MHC IIB isoform, and more intermediate fibers expressing both MCH IIA and IIB isoforms. (Klitgaard H, Bergman O, Betto R, Salviati G, Schiaffino S, Clausen T, Saltin B. 1990). Inactivity seems to be the major factor influencing an increased expression of MHC IIB.
J Appl Physiol 1995 May;78(5):1740-4. Myosin heavy chain isoforms of human muscle after short-term spaceflight. Zhou MY, Klitgaard H, Saltin B, Roy RR, Edgerton VR, Gollnick PD.
I love this quote: “…inactivity rather than the lifting exercise contributes to a low volume-percent mitochondria and a high percentage of type IIB fibers.” This is consistent with denervation and immobilization models.
(Staron RS, Hikida RS, Hagerman FC, Dudley GA, Murray TF. 1984).
So… What are the conclusions?
Look at the following quote:
“ST and FT myofibers express unique sets of muscle-specific genes, and these distinctive programs of gene expression are controlled by variations in motor neuron activity… brief burst of neuronal activity, interspersed between long periods of neuronal quiescence, promote the acquisition of FT-glycolytic fiber characteristics. Conversely, extended periods of tonic motor nerve activity stimulate a shift to the ST-oxidative myofibers phenotype.”
Genes Dev 1998 Aug 15;12(16):2499-509
A calcineurin-dependent transcriptional pathway controls skeletal muscle fiber type. Chin ER, Olson EN, Richardson JA, Yang Q, Humphries C, Shelton JM, Wu H, Zhu W, Bassel-Duby R, Williams RS.
What about this quote:
“Mammalian skeletal muscle fibers display a great adaptive potential. This potential results from the ability of muscle fibers to adjust their molecular, functional, and metabolic properties in response to altered functional demands, such as changes in neuromuscular activity or mechanical loading. Adaptive changes in the expression of myofibrillar and other protein isoforms result in fiber type transitions. These transitions occur in a sequential order and encompass a spectrum of pure and hybrid fibers. Depending on the quality, intensity, and duration of the alterations in functional demand, muscle fibers may undergo functional transitions in the direction of slow or fast, as well as metabolic transitions in the direction of aerobic-oxidative or glycolytic. The maximum range of possible transitions in either direction depends on the fiber phenotype and is determined by its initial location in the fiber spectrum.”
Can J Appl Physiol 2002 Aug;27(4):423-48. The adaptive potential of skeletal muscle fibers. Pette D.
Ryan A. Hall
J Histochem Cytochem 1984 Feb;32(2):146-52
Human skeletal muscle fiber type adaptability to various workloads.
Staron RS, Hikida RS, Hagerman FC, Dudley GA, Murray TF.
Muscle biopsy specimens were removed from the vastus lateralis muscles of three groups of human subjects: controls, weight lifters, and distance runners. The runners proved to be a unique group with respect to the variables measured (low body weight and percentage body fat, and high VO2 max). Additionally, a histochemical analysis of the biopsy specimens revealed that the runners had a significantly higher percentage of fiber types I and IIC than either the controls or the weight lifters. Using a cryostatic retrieval method, each of the fibers identified histochemically was then analyzed morphometrically using electron microscopy. The results of volume-percent mitochondria demonstrated a strong relationship between the ATPase activity and oxidative potential of the fiber types for all three groups such that the oxidative activity would be ranked I greater than IIA greater than IIB. Irrespective of fiber type, there were significant differences between the groups with regard to muscle-fiber mitochondrial (runners greater than lifters greater than controls) and lipid content (runners greater than controls greater than lifters). The lifters had a significantly greater content of mitochondria than the controls, which may suggest that inactivity rather than the lifting exercise contributes to a low volume-percent mitochondria and a high percentage of type IIB fibers.
Acta Physiol Scand 1994 Jun;151(2):135-42
Myosin heavy chain isoforms in single fibres from m. vastus lateralis of sprinters: influence of training.
Andersen JL, Klitgaard H, Saltin B.
August Krogh Institute, University of Copenhagen, Denmark.
The myosin heavy chain (MHC) composition of single fibres from m. vastus lateralis of a group of male sprint athletes (n = 6) was analysed, before and after a three months period of intensive strength- and interval-training, using a sensitive gel electrophoretic technique. Significant improvements were observed after training in almost all of a series of performance tests. After training the sprinters revealed a decrease in fibres containing only MHC isoform I (52.0 +/- 3.0% vs. 41.2 +/- 4.7% (mean +/- SE) (P < 0.05)) and an increase in the amount of fibres containing only MHC isoform IIA (34.7 +/- 6.1% vs. 52.3 +/- 3.6% (P < 0.05)). Fibres showing co-existence of MHC isoforms IIA and IIB decreased with training (12.9 +/- 5.0% vs. 5.1 +/- 3.1% (P < 0.05)). Only one out of 1000 fibres analysed contained only MHC isoform IIB. In contrast, a higher amount of type IIB fibres (18.8 +/- 3.6% vs. 10.5 +/- 3.9%, (P < 0.05)) was observed with myofibrillar ATPase histochemistry. The majority of histochemically determined type IIB fibres of sprinters seems therefore to contain both MHC isoforms IIA and IIB. Sprint-training appears to induce an increased expression of MHC isoform IIA in skeletal muscles. This seems related to a bi-directional transformation from both MHC isoforms I and IIB towards MHC isoform IIA.
Eur J Appl Physiol Occup Physiol 1997;75(4):357-62
Differences in muscle contractile characteristics among bodybuilders, endurance trainers and control subjects.
Jurimae J, Abernethy PJ, Quigley BM, Blake K, McEniery MT.
Department of Human Movement Studies, University of Queensland, Australia.
The purpose of this investigation was to compare the myosin heavy chain (MHC) isoform expression of the triceps brachii muscle and isoinertial, isometric and isokinetic strength indices in competitive bodybuilders (CB, n = 5), recreational resistance trainers (RT, n = 5), endurance-trained rowers (ER, n = 5) and control (C, n = 5) subjects. Muscle tissue samples were analysed for MHC isoform content using 6% sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The CB possessed significantly smaller (P < 0.05) percentage of MHC type IIb proteins [12.92 (SD 7.08)%] than RT [30.08 (SD 6.58)%] ER [31.20 (SD 2.74)%] and C [38.22 (SD 2.95)%] groups (i.e. CB < RT approximately ER < C). While the content of MHC type IIa isoforms did not differ significantly between the two resistance-trained groups [CB = 55.76 (SD 5.38)%; RT = 45.72 (SD 7.8)%], CB presented significantly more type IIa MHC isoforms than ER [42.84 (SD 2.98)%] and C [34.72 (SD 1.57)%] subjects (i.e. CB approximately RT > ER approximately C). The MHC type I protein content did not differ significantly among RT [24.20 (SD 4.89)%] ER [25.38 (SD 1.67)%] and C [27.06 (SD 1.81)%] groups. The CB [31.32 (SD 2.67)%] presented significantly more type I MHC isoforms only in comparison with RT. However, when changes in the percentage of MHC type I isoforms were converted to effect sizes (ES), it appeared that low statistical power rather than the absence of an effect accounted for the nonsignificant differences between CB and other groups (i.e. CB > RT approximately ER approximately C). Significant differences existed in isoinertial strength among the trained athletes (i.e. CB > RT > ER approximately C), while isometric and isokinetic strength were not significantly different among any of the trained groups. However, the ES transformation of data demonstrated that large differences existed between resistance-trained groups and ER for isometric and isokinetic strength (i.e. CB approximately RT > ER approximately C). A statistically significant negative correlation (P < 0.001) was found between MHC type IIb isoforms and isoinertial strength index (r = -0.68). The MHC type IIa proteins were positively related to all the strength measures considered (r = 0.51 0.61; P < 0.001). These data demonstrated different patterns of MHC isoform expression among the different groups of athletes and it is suggested that these differences on occasion may affect the expression of strength.
J Appl Physiol 1995 May;78(5):1740-4
Myosin heavy chain isoforms of human muscle after short-term spaceflight.
Zhou MY, Klitgaard H, Saltin B, Roy RR, Edgerton VR, Gollnick PD.
Department of Human Physiology, August Krogh Institute, Copenhagen, Denmark.
The influence of microgravity on the myosin phenotype of skeletal muscle fibers in the vastus lateralis of eight crew members was studied before and after 5-day (n = 3) and 11-day (n = 5) spaceflights (space shuttle flights: STS-32, -33 and -34). Single-fiber electrophoresis analyses showed that the proportion of fibers expressing only slow (type I) myosin heavy chain (MHC) in the vastus lateralis was significantly lower after than before 11 days of spaceflight. Although the family of type II MHC isoforms was elevated post- compared with preflight, the distribution among the isoforms of type II MHC was not statistically different. Based on monoclonal and polyclonal antibodies specific for three adult MHC isoforms and single-fiber electrophoresis, approximately 3% of the fibers analyzed coexpressed all three adult MHC isoforms. The results from immunohistochemical staining with two different sets of antibodies indicate a reduction in the percentage of fibers expressing type I MHC as a result of spaceflight. The mean difference, however, was significant only when the fibers were categorized simply as type I or II. These changes appeared to be highly individualized among the astronauts. These results suggest that a rapid change in MHC isoform expression can occur in some muscle fibers after a relatively brief exposure to spaceflight.
Eur J Appl Physiol Occup Physiol 1996;74(3):287-92
Changes in the myosin heavy chain isoform profile of the triceps brachii muscle following 12 weeks of resistance training.
Jurimae J, Abernethy PJ, Blake K, McEniery MT.
Department of Human Movement Studies, University of Queensland, Brisbane, Australia.
The purpose of this investigation was to determine whether 12 weeks of resistance training, which increased arm girth (5%) and forearm extensor strength (39%), also altered the myosin heavy chain (MHC) characteristics of the triceps brachii muscle. Fifteen healthy, active men volunteered to participate under experimental (n = 11) or control (n = 4) conditions. The experimental group completed four sets of eight to 12 repetitions for each exercise (i.e. triceps pushdown, close grip bench press, triceps kickbacks and biceps curl) with loads of between 70-75% of one repetition maximum (1RM) three times a week. The inter-set and inter-exercise recovery period was only 90 s. Skeletal muscle tissue was removed from the triceps brachii muscle prior to (W0) and following 4 (W4), 8 (W8) and 12 (W12) weeks of the investigation. Samples were analysed for MHC isoform content using 6% sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). MHC isoform composition in the control group did not change significantly. However, the percentage of MHC type IIb isoform decreased significantly from W0 to W4 and again from W4 to W12 [W0: 39.7 (9.2); W12: 29.2 (8.2%)] in the experimental condition. The increments in MHC type IIa [W0: 34.0 (9.9); W12: 41.5 (10.4)] and type I [W0: 26.3 (7.9); W12: 29.3 (9.6)] isoforms were not significant for the experimental group. However, the effect size (ES) transformation of changes in types IIa MHC content was moderate (ES = 0.75). Changes in MHC isoform content were not significantly correlated with changes in 1RM strength for the triceps pushdown exercise. These data indicated that resistance training rapidly, and in an ongoing manner, changed the contractile protein profile of trained skeletal muscle. However, changes in MHC isoform composition in the first 12 weeks of training were not implicated in the development of 1RM triceps pushdown strength.
Acta Physiol Scand 1990 Nov;140(3):359-63
Increase in the proportion of fast-twitch muscle fibres by sprint training in males.
Jansson E, Esbjornsson M, Holm I, Jacobs I.
Department of Clinical Physiology, Karolinska Hospital, Stockholm, Sweden.
Fifteen male physical education students were studied. The subjects trained for 4-6 weeks, 2-3 days per week, on a mechanically braked bicycle ergometer. A training session consisted of repeated 30-s 'all-out' sprints on a Wingate bicycle ergometer, on which the brake band of the flywheel was loaded with 75 g kg-1 body wt, with rest periods of 15-20 min between consecutive sprints. Thigh muscle biopsies were taken before and after the training period and were analysed for fibre types using a myofibrillar ATPase stain. The proportion of type I fibres decreased from 57 to 48% (P less than 0.05) and type IIA fibres increased from 32 to 38% (P less than 0.05). This study indicates that it is possible to achieve a fibre type transformation with high-intensity training. The effect of two-legged 'sprint' training on muscle fibre type composition may be related to a changed pattern of muscle fibre activation (e.g. an increased stimulation frequency). A change in fibre activation frequency may induce an increased synthesis of type II fibre myosin (fast myosin). Hormonal influences such as enhanced adrenergic stimulation of the muscle fibres cannot be excluded as a contributing factor, however.
Pflugers Arch 1990 Jun;416(4):470-2
Co-existence of myosin heavy chain I and IIa isoforms in human skeletal muscle fibres with endurance training.
Klitgaard H, Bergman O, Betto R, Salviati G, Schiaffino S, Clausen T, Saltin B.
August Krogh Institute, University of Copenhagen, Denmark.
The myosin heavy chain (MHC) composition of single fibres from m. vastus lateralis was analysed by one-dimensional electrophoresis and immunoblotting in three groups of young men with distinct difference in physical activity patterns. No major co-existence of MHC isoforms was found in the group with some daily physical activity. In the very sedentary group, however, 19 +/- 5% (P less than 0.05) of the fibres exhibited coexistence of MHC type IIa and IIb. Further, in the endurance trained group co-existence of MHC type I and IIa was manifested in 36 +/- 4% (P less than 0.05) of the fibres. Disuse and extreme usage of muscle both give rise to an elevation in co-expression of MHC isoforms in single muscle fibres but of markedly different combination of isoforms.
Acta Physiol Scand 1990 Oct;140(2):175-80
Myosin heavy chain composition of single fibres from m. biceps brachii of male body builders.
Klitgaard H, Zhou M, Richter EA.
August Krogh Institute, University of Copenhagen, Denmark.
The myosin heavy chain (MHC) composition of single fibres from m. biceps brachii of young sedentary men (28 +/- 0.4 years, mean +/- SE, n = 4) and male body builders (25 +/- 2.0 years, n = 4) was analysed with a sensitive one-dimensional electrophoretic technique. Compared with sedentary men, the body builders had a higher proportion of fibres containing only MHC type IIa (36 +/- 4 vs 12 +/- 2%; P less than 0.05), but a lower proportion of fibres with a coexistence of MHC types IIa and IIb (16 +/- 3 vs 34 +/- 2%; P less than 0.05) and nearly no fibres containing only MHC type IIb (1 +/- 1 vs 12 +/- 1%; P less than 0.05). Myofibrillar ATPase histochemistry only demonstrated a trend towards a higher proportion of type IIa fibres (31 +/- 6 vs 25 +/- 6%) and a lower proportion of type IIb fibres (18 +/- 5 vs 26 +/- 6%) within the body builders. These results, therefore, suggest an altered expression of MHC isoforms within histochemical type II fibres of human skeletal muscle with body building. Furthermore, in human skeletal muscle differences in expression of MHC isoforms may not always be reflected in the traditional histochemical classification of types I, IIa, IIb and IIc fibres.
Genes Dev 1998 Aug 15;12(16):2499-509
A calcineurin-dependent transcriptional pathway controls skeletal muscle fiber type.
Chin ER, Olson EN, Richardson JA, Yang Q, Humphries C, Shelton JM, Wu H, Zhu W, Bassel-Duby R, Williams RS.
Departments of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas 75235, USA.
Slow- and fast-twitch myofibers of adult skeletal muscles express unique sets of muscle-specific genes, and these distinctive programs of gene expression are controlled by variations in motor neuron activity. It is well established that, as a consequence of more frequent neural stimulation, slow fibers maintain higher levels of intracellular free calcium than fast fibers, but the mechanisms by which calcium may function as a messenger linking nerve activity to changes in gene expression in skeletal muscle have been unknown. Here, fiber-type-specific gene expression in skeletal muscles is shown to be controlled by a signaling pathway that involves calcineurin, a cyclosporin-sensitive, calcium-regulated serine/threonine phosphatase. Activation of calcineurin in skeletal myocytes selectively up-regulates slow-fiber-specific gene promoters. Conversely, inhibition of calcineurin activity by administration of cyclosporin A to intact animals promotes slow-to-fast fiber transformation. Transcriptional activation of slow-fiber-specific transcription appears to be mediated by a combinatorial mechanism involving proteins of the NFAT and MEF2 families. These results identify a molecular mechanism by which different patterns of motor nerve activity promote selective changes in gene expression to establish the specialized characteristics of slow and fast myofibers.
Can J Appl Physiol 2002 Aug;27(4):423-48
The adaptive potential of skeletal muscle fibers.
Pette D.
Department of Biology, University of Konstanz, Germany.
Mammalian skeletal muscle fibers display a great adaptive potential. This potential results from the ability of muscle fibers to adjust their molecular, functional, and metabolic properties in response to altered functional demands, such as changes in neuromuscular activity or mechanical loading. Adaptive changes in the expression of myofibrillar and other protein isoforms result in fiber type transitions. These transitions occur in a sequential order and encompass a spectrum of pure and hybrid fibers. Depending on the quality, intensity, and duration of the alterations in functional demand, muscle fibers may undergo functional transitions in the direction of slow or fast, as well as metabolic transitions in the direction of aerobic-oxidative or glycolytic. The maximum range of possible transitions in either direction depends on the fiber phenotype and is determined by its initial location in the fiber spectrum.
