Training protocols involving maximal eccentric contractions are established methods for improvement of muscle strength. Training of the muscle strength is based on two different adaptation processes: muscle fiber hypertrophy and neurological adaptation(3,12,13,29). Additionally, changes in the quality of protein without hypertrophy is one of the primary adaptation processes during the early phase of heavy-resistance muscle strength training(32).
Few studies exist on the question of the optimal training frequency(24) in the early phase of eccentric heavy-resistance training. Until now, only the efficiencies of specially designed training protocols were investigated(12,15,16,32). Most of these training protocols included a time period of 6-8 wk with 2-3 training tasks per week (15,16,32). Earlier investigations on force training showed that pure eccentric or a combination of eccentric and concentric exercise generate a high training stimulus which improves the rapid force development (16) as well as the individual strength (11,30) and was mostly quantified in previous studies as the maximal isometric voluntary contraction(MVC) force (35). It is well established that strenuous unaccustomed eccentric exercise may result in increases in muscle protein serum levels (i.e., creatine kinase (CK), myosin heavy chain fragments (MHC), muscle soreness and stiffness, prolonged strength loss, and morphological changes (7,22,26) reflecting exercise-induced muscle damage. This eccentric exercise-induced skeletal muscle damage induces repair or regeneration processes(31) that result in a temporary muscular adaptation. On the other hand, during this time period the ability to generate muscle strength is reduced and prevents a successful training of technical abilities in performing sports-specific movements. Therefore, it is necessary to know the optimal frequency of training tasks in the early phase of eccentric strength training, which leads to an increase in MVC without extended regeneration periods.
The purpose of the present study was to investigate the effects of three different training frequencies during the early phase of eccentric strength training. We chose an eccentric exercise protocol involving the thigh muscles that is known to produce muscle damage at the beginning, and then subjects trained with it to evaluate its efficiency and muscular adaptation. The effects of the different training regimens were assessed by the improvement of MVC. Similar to earlier studies(4,7,22,23), the adaptation of the trained muscles was monitored by measuring plasma concentrations of muscle proteins and assessing muscle soreness.
MATERIALS AND METHODS
Subjects. Thirty healthy male volunteers (physical education teacher trainees) ranging in age from 21 to 25 yr were recruited from the Department of Sports Sciences (University of Innsbruck). All subjects had no physical limitations to exercise and were not involved in any unilateral leg training. The risks and benefits of the study were explained and written informed consent was obtained from each participant. The study was approved by the institutional review board of the local institution. Subjects were randomly assigned to one of three groups (see Table 1). All subjects were instructed to refrain from unaccustomed exercise during the course of the study starting 48 h before the first exercise session.
Training design. Exercise was conducted in a sitting body posture on an exercise rack specially designed to elicit the required eccentric action of the musculus quadriceps femoris (22,31). All subjects were tested for their maximal strength generation of the investigated leg with the knee held at an angle of 1.75 rad (3.14 rad correspond to full extension of the knee). Subjects then had to hold their knees at an angle of 2.62 rad, when a special trigger mechanism suddenly released 150% of the maximal voluntarily generated force. Subjects were instructed to straighten their knee against the pressure of this weight. But given the arrangement they could not help bending their knee, although they tried to resist. A pulley system allowed the researcher to bring the weight to the starting position without any loading concentric exercise of the investigated leg. After warming up each subject performed a single bout of eccentric exercise using only the nondominant leg. The training task consisted of seven sets of 10 eccentric contractions of the quadriceps femoris muscle group. Each contraction lasted 1-2 s, with 15 s of rest between contractions. The seven sets were each separated by 3 min of rest. To evaluate the training effects during the early phase of eccentric training, a training period of 6 wk was investigated. Under supervision and with adjustment to the increases in muscle strength, three groups (A, B, C; N = 30) performed the first training task at the beginning and the last training task after 7 wk at the end of the study period. Groups A (N = 10) and B (N = 10) additionally trained during the study period starting 1 wk after the first training task. Group A trained once a week for 5 wk and Group B (N = 10) twice a week for 2 wk and three times a week during the subsequent 3 wk.
Warm-up. The 10-min warm-up consisted of 5 min running because of the individual aerobic threshold, followed by 5 min of stretching the leg muscles, and finishing up with three series of eight knee bends.
Muscle soreness evaluation. Similar to earlier studies(7), muscle soreness and pain in all subjects were assessed by questionnaire before, and 1, 2, 3, 4, and 5 d after the first and last training task. On a scale of 0 (normal) to 10 (very sore) subjects rated the perceived soreness of the loaded quadriceps muscle.
Isometric muscle function test. The ability to generate MVC of the knee extensors was monitored before doing the first and the last eccentric exercise bout and 4 and 7 d after finishing, respectively. The procedure for investigating muscle function was adapted from a method described by Edwards et al. (8). After warm-up the subject was seated in an adjustable straight-backed chair, and a not extensible taut strap was passed around the ankle just above the level of the lateral malleolus. A seat belt was passed around the waist to firmly secure the pelvis. An 8-cm steel chain connected the strap with a load cell under the chair so that the knee angle was 1.57 rad. The load cell (Type V 2a, Hottinger-Baldwin, AT) was connected to a 2A/2D amplifier/transducer (DMC plus, Hottinger-Baldwin, AT) and the forces were recorded and displayed on the analog-to-digital data acquisition software package. Each subject performed three isometric MVCs of both quadriceps femoris, with a break of 1 min between each. The highest value achieved in the repetitions was used as the criterion score. The test-retest reliability was 0.92.
Blood analysis. Blood samples were drawn from a superficial vein of the forearm and collected in ethylenediaminetetraacetate (EDTA) coated tubes (Sarstedt, Nümbrecht, Germany) and immediately centrifuged. Samples were withdrawn immediately before performing the first and last eccentric training task and 4 and 7 d after finishing, respectively. Plasma CK activity was measured on the same day. Aliquots of plasma samples for MHC and cardiac troponin I measurements were subsequently frozen and stored at -20 °C until assayed. All measurements were done in duplicate.
CK activity. CK (molecular weight 88000) is a key enzyme of muscular metabolism that exists predominantly as a soluble sarcoplasmic protein in muscle fibers. CK is found in all types of skeletal muscle fibers in similar concentrations. Its half-live time in the general circulation is approximately 15.5 h (18). CK activities were measured at a temperature of 25 ° Celsius by means of a N-acetylcysteine activated, optimized UV test obtained from Merck (Darmstadt, Germany). For men the upper limit of the reference interval of CK is 80 U·L-1. The intra- and interassay coefficients of variation (CV) were 8.2% and 10.6%, respectively.
Myosin heavy chain. Myosin is a hexameric structurally bound contractile protein containing 4 light and 2 heavy chains (molecular weight 230000). MHC can be cleaved into its subfragments by enzymes. The rod portion can be further degraded to form light meromyosin and subfragment 2 (molecular weight 51000; 33). Concentrations of MHC fragments were measured by an immunoradiometric assay (E.R.I.A. Diagnostics Pasteur, Marnes la Coquette, France). This sandwich assay uses a pair of monoclonal antibodies primarily raised against two different epitopes on subfragment 2 in the rod of human ventricular beta-type heavy meromyosin. The antibodies used have been described in detail elsewhere (20,21). Briefly, owing to the strong structural similarity of beta-type cardiac MHC and MHC of slow-twitch skeletal muscle fibers (5,36), both antibodies react strongly with human slow skeletal MHC. The affinities of the antibodies to slow skeletal muscle myosin were identical to those to beta-type cardiac MHC (20). By contrast, the antibodies do not significantly react with cardiac alpha-type MHC, nor with MHC of human fast-twitch skeletal muscle fibers or of any human smooth muscle. Thus, the assay recognizes very well MHC fragments of human beta-type and slow muscle MHC. The monoclonal antibodies of the assay recognize MHC subfragment 2 in the whole molecule and as proteolyzed fragments. The upper limit of the reference interval of MHC in plasma is 300 μU·L-1. The detection limit of the assay is 10 μU·L-1. The intra- and interassay CVs were 3.8% and 7.2%, respectively. One μU/L corresponds to 1μg·L-1(20).
Cardiac troponin I assay. Troponin I (TnI) is a contractile protein of thin filaments in striated muscle fibers. It is part of the troponin-tropomyosin complex and exists in three different isoforms, one for slow-twitch skeletal muscle, one for fast-twitch skeletal muscle, and one for cardiac muscle fibers (34). A highly specific immunoenzymometric assay (E.R.I.A. Diagnostics Pasteur) developed by Larue et al. (19) was used to detect circulating cardiac TnI(molecular weight 24000 Da) in plasma. This assay does not cross-react with TnI of human skeletal muscle. No cardiac TnI (<0.1 μg·L-1) could be detected in the plasma of healthy volunteers or blood donors.
Statistics. The BMDP statistical software package was used for data analysis. The influence of training on responses to exercise were tested by ANOVA and ANCOVA with repeated measures and Greenhouse-Geisser adjustment of the P-value. Differences between groups were assessed by one-way ANOVA with a Newman-Keuls post hoc analysis. The paired Studentt- test was used for within group comparison. Mean, median, SD, and percentiles were calculated to describe continuous variables. AP- value of ≤ 0.05 was considered significant.
Subjects of all three groups were comparable, baseline MVCs of the legs, and baseline muscle protein plasma concentrations did not differ significantly between groups before the first training task. ANOVA and ANCOVA with repeated measures with one grouping and two within factors showed a significant influence of the additional training regimens on the time courses of CK, MHC, and MVC. Criterion measures differed significantly between the three training groups in response to the last training task. Although the subjects of group A and B performed a high-force eccentric training, no significant differences between the baseline plasma CK and MHC values before the first (base I) and last (base 2) training task were found. Cardiac TnI could not be detected in any sample taken, which excluded a protein release from the heart (cardiac beta-type MHC) and provides evidence for an injury of slow-twitch skeletal muscle fibers.
Responses to the Initial Training Task
Muscle soreness. Before exercise, all 30 subjects reported no perceived muscle soreness (rating 0 in all) of the quadriceps muscles. Soreness and pain assessed by questionnaire were maximal 24-48 h after eccentric exercise and declined on the subsequent days (mean ratings seeFig. 1).
MVC. Baseline MVC values of the exercised leg of all three groups did not differ significantly before the first eccentric exercise bout, and one-way ANOVA showed no significant between-group difference in the observed amount of decrease in MVC after this first training task as well (seeTable 2).
Muscle protein release. In all subjects baseline CK and MHC concentrations measured before the first training task were within the reference interval. CK and MHC increased significantly in response to exercise in all three groups without a significant between group difference (seeTables 3 and 4).
Responses to the Last Training Task
Muscle soreness. Before the last training task, all 30 subjects reported no perceived muscle soreness (rating 0 in all) of the quadriceps muscles. The last training task caused muscle soreness (mean rating 3.9) in most subjects of group C which was not significantly different from the response after the initial training task. Group A and B subjects, by contrast, did not complain of any muscle soreness in response to the last training task(see Fig. 1).
MVC. MVC values before the last training task of group B were significantly higher compared with baseline values before the first training task (base 1). Both other groups showed no significant increase in MVC. Moreover, MVC values before the last training task of group B were significantly higher compared with both other groups. After the last (second) training task subjects of group C again sustained a significant decrease in muscle force generation (see Table 2). This decrement in the MVC of the loaded leg was not significantly smaller than that after the first exercise bout. In both other training groups the last training task did not lead to significant changes in the loaded leg's MVC (seeTable 2).
Muscle protein release. In all subjects baseline CK and MHC concentrations measured before the last training task did not differ significantly from baseline values before the first training task (base 1). The last training task did not cause a significant increase in plasma CK and MHC in subjects of group A and B (see Tables 3 and 4, respectively). The subjects of group C again showed a significant increase in CK and MHC (see Tables 3 and 4, respectively). The magnitude of increase in both muscle proteins did not differ significantly from that after the first training task.
We investigated muscular adaptation and strength increase during the early phase of eccentric heavy-resistance training. The new approach in the present study was to compare the influence of the frequency of specific standardized training tasks on muscle injury and adaptation. Maximum isometric voluntary contraction (MVC) force, muscle soreness, and plasma concentrations of muscle proteins were used as indictors of muscle injury and adaptation before and after a period of 7 wk. One training regimen (Group A) included a low training frequency, a second (Group B) included a higher training frequency, and a third (Group C) no additional training tasks. In all training groups the first bout of heavy eccentric exercise resulted in a significant temporary loss of the exercised muscles capacity for force production, muscle soreness, and a significant delayed increase in muscle proteins (CK, MHC). MHC increase indicates a leakage of the muscle cell membrane and a dissociation or degradation of the contractile apparatus (6). In the absence of an increase in cTnI, the MHC increases indicate severe damage to some slow-twitch skeletal muscle fibers. This confirms prior observations(22,31).
Despite repeated high-force eccentric training in groups A and B, muscle protein plasma concentrations returned to reference ranges and muscle soreness vanished. In all groups there was no significant difference between CK, MHC, and muscle soreness baseline values before the first and last training task. After the training period, there was no significant difference in the response to the last training task of group A and group B. There were no significant increases in plasma levels of muscle proteins, no muscle soreness, and no temporary loss of MVC in both groups, which indicates a complete adaptation of the exercised muscles. Armstrong et al. (1) suggested that the first bout of eccentric exercise damages the most vulnerable fibers which are then replaced by more stress resistant fibers. However, Newham(25) suggested that the repeated-bout effect may result from changes in the property and amount of the connective tissue making the fibers more resistant to subsequent injury. Kuipers (17) postulated that the adaptation is probably attributed to a change in recruitment and to an increase in connective tissue as well. The lack of a significant increase in muscle protein plasma concentrations after the last training task in groups A and B is consistent with all these different hypotheses.
Only in group B did MVC significantly increase during the training period. The MVC of group B was also significantly higher compared with both other groups after 6 wk from the onset of training. This shows that a higher training frequency is necessary to improve MVC, whereas a low frequency is sufficient to maintain muscle adaptation. One explanation may be that the initial increase in strength during the early phase of eccentric training is accounted for by a neuronal adaptation(10,14,28). However, Staron et al.(32) showed that within the first several weeks of heavy-resistance training changes in the quality of protein without hypertrophy is the primary adaptation reaction. Whether these increases in strength result from training induced adaptations of the neuromuscular system or from other factors such as the quality of muscle proteins cannot be ascertained from our data. It seems unilikely that during the early phase of eccentric training only a single mechanism is responsible for the observed increase in strength. Concerning the adaptation process triggered by low frequency of training tasks, there is only one comparable study, from Balnave and Thompson (2). This study included an eccentric training once a week for a period of 8 wk with a 40-min walk down with a 25% gradient on a motor-driven treadmill at 6.4 km·h-1. Similar to our observations, the reactions to the first and last training tasks were assessed. Balnave and Thompson (2) showed that eccentric training reduces muscle soreness, the serum muscle protein response, and muscle function impairment. However, the progressively reduced CK responses still showed a significant rise after the second exercise test in the training group. This is in contrast to our data and may be caused by the differences in training regimens as well as the intensities of eccentric exercise.
Muscular adaptation in our study was exclusively found in groups A and B but not in group C. This is in contrast to other investigations which used maximal eccentric contractions of the forearm flexors as an exercise protocol(4) and to the reaction of the control group in the study of Balnave and Thompson (2). For the control group Balnave and Thompson postulated a long-lasting adaptation effect based on the fact that recovery in fatigue index response was more rapid after the second walk. Otherwise there was no significant difference between increases in serum CK, no significant difference in the fatigue index response, and only serum myoglobin values increased to a lesser extent after the second down-hill walk. Clarkson et al. (4) performed one bout of eccentric exercise using the forearm flexor muscles. This produced a period of adaptation between 6 and 10 wk such that muscle was more resistant to damage from a subsequent bout of exercise and a reduction in CK response after 6 months (4). All subjects of group C of our study experienced muscle soreness, showed a decrease in MVC, and had delayed increases in muscle protein plasma concentrations after the last (second) training task. There were no significant differences from the reactions after the first training task. In a previous study (23) with the same eccentric exercise protocol, we observed a rapid adaptation after 4 and 13 d such that the exercised muscle was more resistant to a subsequent bout of eccentric exercise. This adaptation was lost after 6 wk without specific eccentric training. The difference from prior observations of Balnave and Thompson (2) may be explained by the different eccentric exercise regimens. The main difference is that downhill walking excludes supramaximal eccentric muscle loads which were used in our study. If this is the reason for different adaptation periods, a connection between the level of eccentric muscle loading and the duration of adaptation must be postulated. Regarding long-lasting muscular adaptation after a single eccentric exercise bout, we could not confirm the results of Clarkson et al.(4). We and this group used comparable exercise regimens which, however, involved different muscle groups (m. quadriceps femoris and m. biceps brachii, respectively). M vastus lateralis and m. biceps brachii do not differ in muscle fiber type composition (50% slow-twitch and 50% fast-twitch muscle fibers) (9,27), which excludes a predominant influence of the muscle fiber type composition on the adaptation to eccentric exercise.
Study limitations. The intensity of eccentric maximal contractions used in the present study, in particular in the first session, was higher than those applied in earlier studies(2,12) or in the current typical training program used by athletes or others in the fitness community. However, we used this approach to be able to better study also the adaptation to the eccentric damage stress over the early phases of the training program. Furthermore, the use of a isometric strength testing protocol may be a possible limitation of the study design. Isometric strength testing was frequently used in previous studies on provoked neuromuscular adaptation and the efficacy of training regimens (2,11,32). According to more recent results (12), a specific eccentric strength testing could have been more appropriate because isometric force production underestimates the benefits of eccentric training and the eccentric force production ability (12).
In summary, our data indicate that during the early phase of eccentric muscle training a training task once a week is sufficient to maintain muscle adaptation, whereas training of at least 2 times a week is needed for strength increases to occur even with the use of supramaximal eccentric training. The gains during the early phase of training are greater with the higher frequency than with the low frequency training regimen without causing any additional muscle damage. The muscular adaptation after a single bout of high-force eccentric exercise of the thigh muscles was lost after 7 wk without training.
This study was supported in part by the contract 4982 from the Austrian Nationalbank Jubilee Fond.
Present address of S. Sorichter: Medizinische Universitätsklinik, Abteilung Pneumologie, Universitätsklinik Freiburg, Hugstetterstr. 55, D-79106 Freiburg, Germany.
Present address of J. Mair, P. Secnik and V. Parrak: Institut für Med. Chemie und Biochemie, Universität Innsbruck, Fritz-Pregl-Str. 3, A-6020 Innsbruck, Austria.
Present address of A. Kollor: Institut f¨r Sport- und Kreislaufmedizin, Universitätsklinik Innsbruck, Anichstr. 35, A-6020 Innsbruck, Austria.
Present address of Ch. Haid: Orthopädische Universitätskilinik, Universitätsklinik Innsbruck, Anichstr. 35, A-6020 Innsbruck, Austria.
Present address of E. Müller: Institut für Sportwissenschaften, Universität Salzburg, Akademiestr. 26, A-5020 Salzburg, Austria.
Address for correspondence: Prof. Dr. B. Puschendorf, Institut für Medizinische Chemie und Biochemie, Fritz-Pregl-Str. 3, A-6020 Innsbruck, Austria. E-mail: [email protected].
1. Armstrong, R. B., R. W. Ogilvie, and J. A. Schwane. Eccentric exercise-induced injury to rat skeletal muscle. J. Appl. Physiol.
2. Balnave, C. D. and M. W. Thompson. Effect of training on eccentric-induced muscle damage. J. Appl. Physiol.
3. Bührle, M. Power (Schnellkraft). Spectrum der Sportwissenschaften
4. Clarkson, P. M., K. Nosaka, and B. Braun. Muscle function after exercise-induced muscle damage and rapid adaptation. Med. Sci. Sports Exerc.
5. Diederich, K. W., I. Eisele, T. Ried, T. Jaenicke, P. Lichter, and H. P. Vosberg. Isolation and characterization of the complete human beta-myosin heavy chain gene. Hum. Genet.
6. Duncan, C. J. and M. J. Jackson. Different mechanisms mediate structural changes and intracellular enzyme efflux following damage to skeletal muscle. J. Cell Sci.
7. Ebbeling, C. B. and P. M. Clarkson. Muscle adaptation prior to recovery following eccentric exercise. Eur. J. Appl. Physiol.
8. Edwards, R. H. T., D. K. Hill, D. A. Jones, and P. A. Merton. Fatigue of long duration in human skeletal muscle after exercise.J. Physiol. (Lond.)
9. Gollnick, P. D., B. Sjödin, J. Karlsson, E. Jansson, and B. Saltin. Human soleus muscle: a comparison of fibre composition and enzyme activities with other leg muscles. Pflügers Arch.
10. Häkkinen, K. and K. L. Keskinen. Muscle cross-sectional area and voluntary force production characteristics in elite strength- and endurance-trained athletes and sprinters. Eur. J. Appl. Physiol.
11. Häkkinen, K. and P. V. Komi. Effects of different combined concentric and eccentric muscle work regimens on maximal strength development. J. Hum. Mov. Stud.
12. Hortobagyi, T., J. P. Hill, J. A. Houmard, D. D. Fraser, N. J. Lambert, and R. G. Israel. Adaptive responses to muscle lengthening and shortening in humans. J. Appl. Physiol.
13. Jones, D. A. Strength of skeletal muscle and the effects of training. Br. Med. Bull.
14. Komi, P. V. and E. R. Bushkirk. Effect of eccentric and concentric muscle conditioning on tension and electrically activity of human muscle. Ergonomics
15. Komi, P. V. Stretch-Shortening Cycle. In:Strength and Power in Sport
. P. V. Komi (Ed.). Oxford: Blackwell, 1993, pp. 169-179.
16. Komi, P. V. Training of muscle strength and power: interaction of neuromotoric, hypertrophic, and mechanical factors. Int. J. Sports Med.
17. Kuipers, H. Exercise-Induced Muscle Damage. Int. J. Sports Med.
18. Lang, H. Creatine Kinase isoenzymes
. Berlin, New York: Springer, 1981, pp. 1-9.
19. Larue, C., C. Calzolari, J. O. C. Leger, J. J. Leger, and B. Pau. Immunoradiometric assay of myosin heavy chain fragments in human plasma. Clin. Chem.
20. Larue, C., C. Calzolari, J. P. Bertinchant, F. Leclercq, R. Grolleau, and B. Pau. Cardiac-specific immunoenzymometric assay of troponin I in the early phase of acute myocardial infarction. Clin. Chem.
21. Leger, J. O. C., B. Bouvagnet, B. Pau, R. Roncucci, and J. J. Leger. Levels of ventricular myosin fragments in human sera after myocardial infarction, determined with monoclonal antibodies to myosin heavy chains. Eur. J. Clin. Inv.
22. Mair, J., A. Koller, E. Artner-Dworzak, et al. Effects of exercise on plasma myosin heavy chain fragments and MRI of skeletal muscle.J. Appl. Physiol.
23. Mair, J., M. Mayr, E. Müller, et al. Rapid adaptation to eccentric exercise-induced muscle damage. Int. J. Sports Med.
24. Moritani, T. Time course of adaptations during strength and power training. In: Strength and Power in Sport,
P. V. Komi(Ed.). Oxford, Blackwell, 1993, pp. 266-278.
25. Newham, D. J. The consequences of eccentric contractions and their relationship to delayed onset of muscle pain.Eur. J. Appl. Physiol.
26. Nosaka, K., P. M. Clarkson, M. E. McGuiggin, and J. M. Byrne. Time course of muscle adaptation after high eccentric exercise.Eur. J. Appl. Physiol.
27. Reichsmann, F., S. P. Scordilis, P. M. Clarkson, and W. J. Evans. Muscle protein changes following eccentric exercise in humans.Eur. J. Appl. Physiol.
28. Sale, D. G. Neuronal adaptation to strength training. In: Strength and Power in Sport,
P. V. Komi (Ed.). Oxford: Blackwell, 1993, pp. 249-265.
29. Schmidtbleicher, D. Maximal strength and speed of movements (Maximalkraft und Bewegungsschnelligkeit)
. Bad Homburg, Germany: Limpert, 1980.
30. Schmidtbleicher, D. Training for Power Events. In:Strength and Power in Sport
. P. V. Komi (Ed.). Oxford, Blackwell Science, 1993, pp. 381-395.
31. Sorichter, S., A. Koller, Ch. Haid, et al. Light concentric exercise and heavy eccentric muscle loading: effects on CK, MRI and markers of inflammation. Int. J. Sports. Med.
32. Staron, R. S., D. L. Karapondo, W. J. Kraemer et al. Skeletal muscle adaptations during early phase of heavy-resistance training in men and women. J. Appl. Physiol.
33. Warrick, H. M. and J. A. Spudich. Myosin structure and function in cell motility. Ann. Rev. Cell. Biol.
34. Wilkinson, J. M. and R. J. A. Grand. Comparison of amino acid sequence of troponin-I from different striated muscles.Nature
35. Wilson, G. J. and A. J. Murphy. Strength diagnosis: the use of test data to determine specific strength training. J. Sport Sci.
36. Yamauchi-Takihara, K., M. J. Sole, J. Liew, D. Ing, and C. C. Liew. Characterization of human cardiac myosin heavy chain genes.Proc. Natl. Acad. Sci.