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1. This study was performed to assess whether muscle contractile properties are related to the presence of specific myosin heavy chain (MHC) isoforms. 2. Force‐velocity relations and MHC isoform composition were determined in seventy‐four single skinned muscle fibres from rat soleus, extensor digitorum longus and plantaris muscles. 3. Four groups of fibres were identified according to their MHC isoform composition determined by monoclonal antibodies: type 1 (slow), and types 2A, 2B and 2X (fast). 4. With respect to maximum velocity of shortening (V0), the fibres formed a continuum between 0.35 and 2.84 L/s (muscle lengths per second) at 12 degrees C. V0 in type 1 fibres (slow fibres) was between 0.35 and 0.95 L/s (0.639 +/‐ 0.038 L/s; mean +/‐ S.E. of mean). V0 in type 2 fibres (fast fibres) was consistently higher than 0.91 L/s. Ranges of V0 in the three fast fibre types mostly overlapped. Type 2A and 2X …