It has been demonstrated that the oxygen cost of work is higher in individuals possessing greater proportion of type II muscle fibres (Coyle et al. 1992). In the present study, we examined the relationship between the content of MyHC II in muscle and the oxygen cost of incremental work in humans.

Twenty-one male subjects: aged 24.0 ± 2.5 years (mean ± S.D.), body mass 73.0 ± 7.2 kg, height 179 ± 5 cm,V_O2,max 3697 ± 390 ml min^-1, participated in this experiment. The exercise test started at a power output of 30 W, followed by an increase amounting to 30 W every 3 min, at 60 rev min^-1. Gas exchange variables were measured continuously using a breath-by-breath system (Oxycon-Champion 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 were analysed for the content of different MyHC (I, IIa, IIx) using SDS-PAGE and Western blotting.

The pre-exercise V_O2, as a mean value of 6 min measurements, expressed both in ml min^-1, and in ml kg^-1 min^-1, was positively correlated with the content of MyHC II (P < 0.01). We have also found that the pre-exercise values of V_O2 in the group of subjects with a high proportion of MyHC II (59.9 ± 11.2 %) were significantly higher (P < 0.02, when V_O2 was expressed in ml min^-1, and P < 0.01 when V_O2 was expressed in ml kg^-1 min^-1) than in the group with low content of MyHC II (27.5 ± 6.0 %). We, as others (Barstow et al. 2000), have also found a significant negative correlation (r = -0.562, P < 0.01) between the slope in the V_O2/power output relationship below the lactate threshold (LT) and the content of MyHC IIa. Moreover, the magnitude of the non-linear increase in the V_O2/power output relationship present above LT (see Zoladz et al. 1995) in our study was positively correlated (r = 0.510, P < 0.02) with the content of MyHC II, opposite to the findings by Barstow et al. (2002).

Our results show that individuals with high content of MyHC II consume more oxygen in the pre-exercise conditions and require a smaller increase in V_O2 for maintaining a linear increase in power output up to LT, but after exceeding the LT they consume more oxygen above that expected from the linear relationship below the LT than subjects with a low content of MyHC II.

This work was supported by the Polish State Committee for Scientific Research (KBN) grant 4PO5D05817.