In this study we have examined the relationship between the content of different isoforms of MyHC in the vastus lateralis m. quadricipitis femoris and the VO2 / power output relationship during incremental cycling exercise. Twenty-one male subjects: aged 24.0 ± 2.5 years, body mass 73.0 ± 7.2 kg, height 179 ± 5 cm, BMI 22.78 ± 1.84 kg . m-2 , VO2 max 3697 ± 390 ml . min-1 , 50.9 ± 5.2 ml . kg-1 . min-1 , participated in this experiment. The subjects performed an incremental exercise test until exhaustion. The exercise test started at power output of 30 W, followed by an increase amounting to 30 W every 3 minutes. The pedalling rate was maintained at 60 rev . min-1 . Gas exchange variables were measured continuously using breath-by- breath system Oxycon Jaeger. At the end of each step blood samples were taken for lactate concentration. Muscle biopsy samples taken from the vastus lateralis m. quadricipitis femoris, using the Bergstrom needle, were analysed for the content of different MyHC (I, IIa, IIx) using SDS-PAGE and Western blotting. The pre-exercise VO2, as a mean value of six-minute measurements, expressed both in ml . min-1 , and in ml . kg -1 . min-1 , was positively correlated with the content of MyHC II in the vastus lateralis (p < 0.01). We have also found that the pre-exercise values of VO2 in the group of subjects with a high proportion of MyHC II (59.9 ± 11.2 %) were significantly higher (p < 0.02, when VO2 was expressed in ml . min-1 , and p < 0.01 when VO2 was expressed in ml . kg-1 . min-1 ) than in the group with low content of MyHC II (27.5 ± 6.0 %) in the vastus lateralis. Moreover, we have found a significant negative correlation (r = -0.562, p < 0.01) between the slope in the VO2/PO relationship below the lactate threshold (LT) and the content of MyHC IIa in the vastus lateralis. The most interesting finding of our study was that the magnitude of the non-linear increase in the VO2 / power output relationship present above the LT was positively correlated ( r = 0.510, p < 0.02) with the content of MyHC II in the vastus lateralis. Our results show, that there is no simple relationship between the content of different types of MyHC in the vastus lateralis and the oxygen cost of work during incremental exercise test. Individuals with a high content of MyHC II in the vastus lateralis m. quadricipitis femoris consume more oxygen in the pre-exercise conditions than subjects with a low content of MyHC II in their muscles. Subjects with a high content of MyHC II require a smaller increase in VO2 for maintaining a linear increase in power output up to the lactate threshold (lower slope in this relationship), but after exceeding the LT, they consume more oxygen above that expected from the linear relationship below the LT, than the subjects with a low content of MyHC II in their muscles. Therefore, non-linear increase in the VO2 / power output relationship, present above the LT, is more pronounced in subjects with a higher content of MyHC II in the vastus lateralis m. quadricipitis femoris.
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