Metabolism
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Selection of fuels for muscle contraction
Even at rest, skeletal muscle accounts for more than one-fifth of total energy expenditure; obviously this increases greatly with exercise.
Muscle can use a variety of fuels, depending on the intensity of work being
performed, the duration of the exercise and also whether the individual is in
the fed or fasting state:
plasma glucose
muscle glycogen
triacylglycerol from plasma lipoproteins
triacylglycerol from adipose tissue reserves within the muscle
plasma non-esterified fatty acids
plasma ketone bodies
Skeletal muscle contains two types of fibres:
Experiment 1: Is ATP used in muscle contraction?
Rats
were anaesthetised and the gastrocnemius muscle on one hind limb was exposed
and subjected to electrical stimulation for three minutes to cause contractions.
The animals were killed, and both hind limbs were immediately immersed in liquid
nitrogen. The gastrocnemius muscles from both limbs were dissected out, and
the concentrations of ATP, ADP, creatine phosphate and creatine were measured.
| µmol /g muscle | unstimulated (at rest) | after stimulation |
| ATP | 5 | 4.9 |
| ADP | 0.01 | 0.11 |
| creatine phosphate | 17 | 1.0 |
| creatine | 0.1 | 16.1 |
What conclusions can you draw from these results?