Simultaneous Assessment of Skeletal Muscle Energetics and Blood Flow During Dynamic Exercise by Interleaved...

To simultaneously measure skeletal muscle energetics and blood flow (BF) before, during, and after dynamic plantar flexion exercise (PFE).

Non-localized pulse-acquire phosphorus-31 magnetic resonance spectroscopy (³¹P MRS) and phase contrast flow magnetic resonance imaging (¹H MRI) using golden-angle rotated spiral readouts were acquired in an interleaved fashion. Data were collected at rest, during PFE to volitional fatigue, and post-exercise recovery in 10 healthy adults. Interleaved popliteal artery BF was validated against conventional cine phase-contrast measures at rest and post-exercise recovery, while calf muscle energetics were validated by comparing to conventional ³¹P MRS-only measures at rest. To minimize motion artifacts during dynamic PFE, flow data were resolved in 3 dimensions (cardiac phase, pedal position, and exercise stage).

Resting phosphocreatine (PCr) and inorganic phosphate concentrations were similar between both techniques (both p > 0.05). During PFE, PCr declined to 46% ± 10% of rest. PCr recovery time was 43 ± 15 s. Resting BF was 132 ± 43 mL/min and increased up to four-fold during PFE depending on exercise stage and pedal position. Notably, there was excellent agreement between the interleaved and conventional BF measures (r² = 0.95, slope = 0.977, p < 0.0001) with minimal bias (12.62 mL/min) over a wide range of physiologically relevant BF values (from ∼60 to 600 mL/min).

The feasibility of simultaneous assessment of skeletal muscle energetics and BF during dynamic exercise by interleaved ³¹P MRS/¹H flow MRI was demonstrated along with good agreement between interleaved and conventional techniques during rest and recovery. One can now simultaneously quantify critical BF-metabolism relationships and use this to probe disease-related adaptations.