19 STRUCTURAL AND FUNCTIONAL CHARACTERISTICS OF THE ELBOW EXTENSORS IN RESISTANCE AND ENDURANCE TRAINERS STRUKTURNE IN FUNKCIONALNE ZNA^ILNOSTI IZTEGOVALK KOMOLCA PRI VADBI MO^I IN VZDR@LJIVOSTI Jaak Jürimäe Jürimäe, J. (2000). Structural and functional characteristics of the elbow extensors in resistance… KinSI 6(1–2), 19–22 Abstract 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 indi- ces in bodybuilders (B; n=5), competitive rowers (R; n=5) and untrained control (C; n=5) subjects. Muscle tissue samples were analysed for MHC isoform content using electrophore- sis. The B possessed significantly smaller (p<0.05) percentage of MHC type IIb proteins (12.9±7.1 %) than R (31.2±2.7 %) and C (38.2±3.0 %) groups (i.e., BR≈ C). Significant differences existed in isoinertial strength among B and R subjects (i.e., B>R≈C), while isometric and isokinetic strength were not significantly different among trai- ned groups. However, the ES transformation of data demon- strated that large differences existed between B and other groups for isometric and isokinetic strength (i.e., B>R≈C). A statistically significant negative correlation (p<0.05) 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<0.05). 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. Key words: MHC isoforms, resistance training, endurance trai- ning, strength indices Izvle~ek Namen {tudije je bil primerjati izoformne miozinske te`ke ve- rige (MHC) mi{ice triceps brachii ter izoinercijski, izometri~ni in izokineti~ni indeks mo~i bodybuilderjev (B; n=5), vesla~ev (V; n=5) in netreniranih subjektov – kontrolna skupina (K; n=5). V vzorcih mi{i~nega tkiva je bila izmerjena vsebnost MHC z uporabo elektroforeze. Skupina B je imela zna~ilno (p<0,05) manj{i odstotek MHC tip IIb beljakovin (12,9±7,1 %) kot V (31,2±2,7 %) in K (38,2±3,0 %), torej BV≈K). Zna~ilne razlike obstajajo v izokineti~ni mo- ~i med B in V (torej B>V≈K), medtem ko pri izoinercijski in izokineti~ni mo~i ni bilo zna~ilnih razlik med obema trenira- nima skupinama. »VU pretvorba« podatkov je pokazala tudi, da obstajajo velike razlike med B in drugima skupinama v izo- metri~ni in izokineti~ni mo~i (torej B>V≈K). Statisti~no zna~ilna (p<0,05) negativna korelacija je bila dob- ljena med MHC tip IIb izoformami in izoinercijskim indeksom mo~i (r=–0,68). Vsebnost MHC tip IIa beljakovin je bila pozitivno povezana z vsemi uporabljenimi indeksi mo~i (r=0,51–0,61; p<0,05). Izmerjeni podatki ka`ejo na razli~ne vzorce izra`anja MHC izoforme merjenih skupin {portnikov, menimo, da te razlike lahko v~asih vplivajo na izra`anje mo- ~i. Klju~ne besede: MHC izoforme, trening mo~i, trening vzdr`lji- vosti, indeksi mo~i (Received: 20. 01. 2000 – Accepted: 11. 05. 2000) Institute of Sport Pedagogy, University of Tartu, Tartu, Estonia Contact address Jaak JÜRIMÄE Institute of Sport Pedagogy, University of Tartu, 18. Ülikooli St., EE- 51014 Tartu, Estonia Tel: +372 7 375 372 Fax: + 372 7 375 373 E-mail: jaakj@ut.ee 20 Jürimäe, J. (2000). Structural and functional characteristics of the elbow extensors in resistance… KinSI 6(1–2), 19–22 Introduction Human skeletal muscle structure may differ largely between individuals (Abernethy, Jürimäe, Logan, Tay- lor and Thayer, 1994). For example, the muscle fibre content of elite endurance athletes may contain up to 90 % of slow-twitch muscle fibres (Saltin and Goll- nick, 1983). Myofibrillar ATPase histochemistry has also demonstrated that bodybuilders may possess a similar (Alway, MacDougall, Sale, Sutton and McCo- mas, 1988) or even lower (Bell and Jacobs, 1990) pro- portion of fast-twitch muscle fibres in the vastus late- ralis muscle than sedentary controls. Furthermore, Tesch and Larsson (1982) showed that bodybuilders’ fibre type distribution in the vastus lateralis muscle re- sembles the histochemical profile of skeletal muscles from endurance athletes. These cross-sectional data raise the question as to whether training has produ- ced this particular fibre type profile. Equally, however, these data may be the product of sampling and/or ge- netic differences. It has been suggested that myofibrillar ATPase histoc- hemistry can not give an adequate characterisation of muscle contractile properties in athletes (Abernethy, Jürimäe, Logan, Taylor and Thayer, 1994), since the histochemical reaction of a muscle fibre reveals only the dominant MHC isoform present in this particular fibre (Danieli-Betto, Zarbato and Betto, 1986). Thus, in this study, the more sensitive electrophoretic tech- nique was used to compare the contractile characte- ristics of skeletal muscle tissue from different athletes. There were two purposes in this investigation. First, MHC isoform composition of the triceps brachii muscle was compared among bodybuilders (B), ro- wers (R) and untrained controls (C). Second, correla- tions between MHC isoforms and various strength in- dices were computed to determine the possible relationships between these variables. Methods Five B with an average training history of 4.8±1.2 years (range 3–6 years), 5 R with an average training history of 4.0±2.2 years (range 2–8 years) and 5 C subjects who had not been involved in any systema- tic physical activity during the previous 2 years parti- cipated in this study. All testing procedures were ap- proved by the local ethics committee and subjects were aware of the purpose and potential benefits of the study as well as the possible risks and discomforts. Strength was assessed isoinertially, isometrically and isokinetically (Abernethy and Jürimäe, 1996). Maxi- mal isoinertial strength was measured using one repe- tition maximum (1RM) triceps extension. Maximal iso- metric strength was determined at an angle of 0.52 rad. from full extension and maximal isokinetic strength at the contractile speed of 5.20 rad.sec -1 ac- cording to Abernethy and Jürimäe (1996). Muscle biopsies were taken from the triceps brachii muscle and analysed for MHC isoform composition using 6 % sodium dodecyl sulfate-polyacrylamide gel elec- trophoresis as previously described (Jürimäe, Aber- nethy, Blake and McEniery, 1996). Descriptive statistics (mean, standard deviation [SD]) for each of the dependent variables were determi- ned. As the raw data were normally distributed, pa- rametric analysis was completed. Specifically, a one- way analysis of variance (ANOVA) was used to test the effect of group for each dependent variable. An alpha level of 0.05 was adopted. The Scheffe method was used for post hoc analysis when a significant F ra- tio was found. In addition, the ES transformations were used to compare differences in dependent va- riables among B, R and C groups. ESs approximating 0.2, 0.5 and 0.8 were categorised as small, modera- te and large differences, respectively (Cohen, 1969). The Pearson Product Moment Correlation analysis was used to determine the correlation among depen- dent variables. Results Maximal strength values are presented in Table 1. Sig- nificant differences existed in isoinertial strength among B and R subjects (i.e., B>R≈C), while isome- tric and isokinetic strength were not significantly dif- ferent among trained groups. However, the ES trans- formation of data demonstrated that large differences existed between B and other groups for isometric and isokinetic strength (i.e., B>R≈C). (Table 1). Table 1. Maximal isoinertial (one repetition maximum triceps extension in kg), isometric (extension in Nm) and isokinetic (extension at contractile speed of 5.20 rad.sec-1) strength for the bodybuilders, rowers and untrained control group. Strength index BodybuildersRowersControls Isoinertial 61.3±7.2 31.5±7.8* 32.3±8.8* Isometric 117.2±19.9 84.2±16.9 76.4±14.1* Isokinetic 79.4±13.1 62.6±5.0 50.6±6.4 * Significantly different from bodybuilders; p<0.05. 21 There were significant differences in the relative distri- bution of MHC isoforms among the different groups (Table 2). The B possessed significantly smaller (p<0.05) percentage of MHC type IIb proteins than R and C groups (i.e., BR≈C). The MHC type I protein content did not differ significantly among different groups (Table 2). However, when the results of MHC type proteins were converted to ES, it appeared that low statistical power rather than the absence of an effect accounted for the non-significant differences between B and other groups (i.e., B>R≈C). Correlational analysis revealed statistically significant negative correlations (p<0.05) between MHC type IIb proteins and maximal isoinertial strength index (Table 3). In contrast, MHC type IIa isoforms were po- sitively related (p<0.05) to all considered strength va- lues. However, no significant correlations were found between MHC type I proteins and the strength mea- sures (Table 3). Discussion The present investigation demonstrated different pat- terns of MHC isoform expression for the triceps brac- hii muscle of B, R and C groups. The main finding of this investigation was that B presented significantly less MHC type IIb isoforms than endurance-trained R subjects. Traditionally, it has been thought that chro- nic endurance activity requires more muscle fibres with higher oxidative capacity than chronic resistan- ce training (Saltin and Gollnick, 1983). However, in this experiment, bodybuilding type resistance training of B may have resulted in greater fast motor unit re- cruitment than the training protocol of R specified for endurance development. In agreement with this hypothesis, Kraemer et al. (1995) demonstrated that 12 weeks of novel resistance training decreased the histochemically typed fast-twitch glycolytic muscle fi- bres to a greater extent (19.1 to 1.9 %) than novel en- durance training over the same time span (19.2 to 8.8 %) in previously untrained vastus lateralis muscle. Thus, the MHC type IIb isoform data were consistent with the concept of a »reserve population« of fast, type IIb MHC isoforms. That is, once regularly recrui- ted, MHC type IIb isoforms start to transform towards type IIa MHC proteins (e.g., Adams, Hather, Baldwin and Dudley, 1993; Jürimäe, Abernethy, Blake and McEniery, 1996; Kraemer et al., 1995; Staron et al., 1994). Indeed, bodybuilding training should result a more complete recruitment of all the fast motor units, which muscle fibres mainly consist of MHC type IIb proteins. The statistically significant negative correla- tion between the amount of MHC type IIb isoforms and tested maximal isoinertial strength (Table 3) furt- her supports the theory of the possible »reserve popu- lation« of MHC type IIb isoforms. Thus, according to these results, it appears that a lower percentage of type IIb MHC isoforms in muscle may indicate better isoinertial strength. Correlational data (Table 3) demonstrated that type IIa MHC isoforms may play an important role in musc- le tissue functional characteristics. The positive inter- correlations between MHC type IIa protein amount and all measured strength indices were statistically sig- nificant (p<0.05). Similarly, Nygaard, Houston, Suzu- ki, Jorgensen and Saltin (1983) and Schantz, Randell- Fox, Hutchinson, Tyden and Astrand (1983) have previously reported significant correlations between Jürimäe, J. (2000). Structural and functional characteristics of the elbow extensors in resistance… KinSI 6(1–2), 19–22 Table 3. The inter-correlations between myosin heavy chain (MHC) isoforms and isoinertial, isometric and isokinetic strength indices. Strength index MHC IIb MHC IIa MHC I Isoinertial –0.68* 0.66* 0.35 Isometric –0.45 0.51* 0.06 Isokinetic –0.49 0.61* –0.07 * Statistically significant; p<0.05. Table 2. Relative type IIb, IIa and I myosin heavy chain (MHC) isoform content of the triceps brachii musc- le of bodybuilders, rowers and untrained control group. Subject groupsMHC IIb MHC IIa MHC I Bodybuilders12.9±7.1 55.8±5.3 31.3±2.7 Rowers31.2±2.7* 42.8±3.0* 25.4±1.7 Controls38.2±3.0* 34.7±1.6* 27.1±1.8 * Significantly different from bodybuilders; p<0.05. 22 the histochemically typed fast-twitch muscle fibres and various strength indices. However, this has not been observed in other studies (Clarkson, Droll and Melchionda, 1982; Frose and Houston, 1985). The inconsistency of these results may be due to the limi- tations associated with histochemical fibre type asses- sment and differential propositions of muscle fibres with different MHC isoform profiles to hypertrophy (Abernethy, Jürimäe, Logan, Taylor and Thayer, 1994). It should be noted that B, who possessed significantly higher percentage of MHC type IIa isoforms over R and C subjects, had also significantly higher maximal isoinertial strength value (Table 2). In the light of the results of our study, it could be argued that MHC type IIa proteins in muscle tissue are the most favourable for bodybuilding resistance training adaptations. In summary, the present study compared the MHC isoform composition of the triceps brachii muscle in resistance and endurance trainers. According to the results, it appears that B possess significantly less type IIb MHC isoforms than untrained C or even enduran- ce-trained R. 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