Magnetic resonance follows how exercising muscles use fuel
Researchers followed changing chemical signals in the muscles of healthy men exercising inside a scanner. The small peer-reviewed study found differences associated with training history and exercise intensity. Combining two magnetic-resonance measurements captured fuel conversion and changes in cellular energy reserves, offering physiological information beyond measurements taken at rest.
Science··Midday
Eleven volunteers exercised inside the scanner
At the University of Nottingham in the UK, researchers observed muscle metabolism while healthy men worked an ankle pedal inside a magnetic-resonance scanner.[1], [2]
The study enrolled 11 men: four with endurance training and seven without it. Carbon measurements used data from ten after one participant was excluded because the labelled substance did not reach the muscle adequately. The small, male-only sample and existing differences in training history limit generalization; clinical diagnostic value was not established.[1]
Training history accompanies different fuel-conversion signals
Magnetic resonance spectroscopy distinguishes chemicals through their magnetic signals. The team followed carbon-labelled pyruvate, a molecule involved in fuel metabolism, as its label appeared in lactate, alanine and bicarbonate. At comparable relative effort, trained participants had stronger selected bicarbonate ratios and a lower lactate-to-pyruvate ratio. That pattern was consistent with more pyruvate being used by mitochondria, the cell’s energy-producing structures.[1]
Phosphorus measurements follow the muscle’s energy reserve
A second measurement, performed on a separate visit, tracked phosphorus signals. These revealed changes in phosphocreatine, an energy reserve, and in acidity inside muscle cells. More intense exercise in untrained men accompanied greater depletion of this reserve and a stronger fall in intracellular pH. Carbon and phosphorus measurements supplied complementary information about fuel conversion and energy balance during the same isolated muscle task.[1]
