DIFFERENCES IN MUSCLE CONTRACTILE CHARACTERISTICS AMONG BODYBUILDERS,ENDURANCE TRAINERS AND CONTROL SUBJECTS

The purpose of this investigation was to compare the myosin heavy chai n (MHC) isoform expression of the triceps brachii muscle and isoinerti al, isometric and isokinetic strength indices in competitive bodybuild ers (CB, n = 5), recreational resistance trainers (RT, n = 5): enduran ce-trained rowers (ER, n = 5) and control (C, n = 5) subjects. Muscle tissue samples were analysed for MHC isoform content using 6% sodium d odecyl sulphate-polyacrylamide gel electrophoresis. The CB possessed s ignificantly smaller (P < 0.05) percentage of MHC type IIb proteins [1 2.92 (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 = 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 = RT > ER = 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)%] g roups. The CB [31.32 (SD 2.67)%] presented significantly more type I M HC isoforms only in comparison with RT. However, when changes in the p ercentage of MHC type I isoforms were converted to effect sizes (ES), it appeared that low statistical power rather than the absence of an e ffect accounted for the nonsignificant differences between CB and othe r groups (i.e. CB > RT = ER = C). Significant differences existed in i soinertial strength among the trained athletes (i.e. CB > RT > ER = C) , while isometric and isokinetic strength were not significantly diffe rent among any of the trained groups. However, the ES transformation o f data demonstrated that large differences existed between resistance- trained groups and ER for isometric and isokinetic: strength (i.e. CB approximate to RT > ER approximate to C). A statistically significant negative correlation (P < 0.001) was found between MHC type IIb isofor ms and isoinertial strength index (r = -0.68). The MHC type IIa protei ns were positively related to all the strength measures considered (r = 0.51 -0.61; P < 0.001). These data demonstrated different patterns o f MHC isoform expression among the different groups of athletes and it is suggested that these differences on occasion may affect the expres sion of strength.