Time-resolved 3D-PC MRI measurements of the upper leg muscles during dynamic knee flexion: the effect of the fatigue threshold

Motivation: Dynamic phase-contrast (PC) MRI is used to characterize muscle contractions using a small FOV across various percentages of maximal contractile-force (MCF). However, whole muscle evaluations requires multiple motion cycles, increasing the risk of fatigue, especially at high MCF. Goal(s): The goal of this study is to investigate the impact of exercising above and below the fatigue threshold (FT) on the whole-muscle 3D PC-MRI velocity data. Approach: Two dynamic 3D PC-MRI data acquisitions were performed at 90% FT and 110% FT. Results: FT was at 30% of the MCF. Magnitude and temporal patterns of the FH velocity were not different between conditions and muscles. Impact: Exercising slightly above the fatigue threshold does not impact 3D PC-MRI derived FH velocity data for the hamstring muscles compared to below-threshold levels, suggesting that muscle fatigue may have limited effect. However, further analysis of strain-rate and strain are required.