Ischaemic heart disease, skeletal muscle fibres and exercise capacity

Twenty-eight male patients with ischaemic heart disease (IHD)performed OBLA (onset of blood lactate accumulation) exercisestress tests and had muscle biopsies taken from their vastuslateralis muscle the day before coronary bypass grafting. All28 patients showed the same exercise performance pattern ascompared to healthy sedentary, age-matched, controls: a lowexercise intensity eliciting a blood lactate concentration of2.0 mmol x 1^–1 ( W_OBLA), W_OBLA corresponded to a highfraction (% W_OBLA) of W_SL (symptom limited or ‘maximal’capacity), and a low peak blood lactate concentration. The high% W_OBLA and low peak blood lactate indicated a reducedglycogenolyticcapacity (‘anaerobic’ performance). Muscle fibrecomposition disclosed a high mean value of fast twitch (FT),type II or ‘white’ muscle fibres, as compared tosedentary healthy controls. This indicated that this patientgroup constituted an extreme subgroup of the age-matched population.The distorted muscle fibre composition in IHD could refiectboth heredity as well as adaptation to physical inactivity,degenerative cytosolic properties, etc. Muscle and blood contentsof a mitochondrial electron trans-locator and nonspecific radicalscavenger, ubiquinone or coenzyme Q₁₀(CoQ₁₀), were low, whichcoincided with an elevated frequency of the fibre subgroup FT(c).The presence of the FT (c) fibre type is assumed to reflecthistological uma.