Scientists investigated the effect of long-term endurance training on skeletal muscle fibres in humans. They compared biopsy samples from the vastus lateralis muscle of elite marathon runners (endurance-trained) with those of sedentary individuals (untrained control). The sections of muscle fibres were stained to show the activity of cytochrome c oxidase, an enzyme in the electron transport chain of aerobic respiration. Darker staining indicates higher enzyme activity.
Suggest one reason for the average difference in staining intensity between the muscle fibres of the endurance-trained runners and the sedentary individuals.
The endurance-trained runners were able to sustain prolonged high-intensity aerobic exercise for much longer than the sedentary group. Explain why.
The scientists determined the mean diameter of the muscle fibres using an optical microscope. The circular field of view had an area of 2.01 mm22.01\text{ mm}^22.01 mm2. The diameter of this circular area was equal to the width of 25 muscle fibres lined up side-by-side. Use Area=πr2\text{Area} = \pi r^2Area=πr2 to calculate the mean diameter of a muscle fibre in micrometres (μm\mu\text{m}μm). Show your working.
