¹H and ³¹P MRS Interleaved With High Time Resolution Reveals Closely Matching Creatine CH₂ and PCr Dynamics During Exercise

The rate of intramuscular phosphocreatine (PCr) depletion and recovery in response to exercise estimated from 31 P MRS is an established measure for oxidative capacity. The creatine CH 2 resonance in 1 H MRS is known to exhibit a similar pattern. So far, repeating the exercise for consecutive 1 H and 31 P experiments posed limitations on the interpretation. Acquiring both datasets in a single time‐resolved experiment allows for direct quantitative comparison of creatine‐CH 2 and PCr kinetics. This can help answer to what extent creatine‐CH 2 mimics PCr dynamics and provide data on the visibility of myocellular creatine. Twenty‐seven volunteers, assigned to a group with lower BMI ( n = 16, BMI = 22.1 ± 3.2 kg/m 2 , age = 35.7 ± 9.3 years) or higher BMI ( n = 11, BMI = 34.1 ± 3.6 kg/m 2 , age = 35.0 ± 6.6 years) were measured on a 7 T MR system and MR‐compatible ergometer. Localized 1 H and 31 P MR spectra were acquired interleaved during a single 5‐min submaximal exercise effort and recovery, with 6 s time resolution. Exercise led to reduced creatine‐CH 2 signal, while the CH 3 resonance remained stable. Neither the recovery nor exercise‐on‐kinetics time constants were significantly different when quantified from 1 H or 31 P MR spectra in each group (recovery, lower BMI: τ PCr‐recovery = 35 ± 12 s vs. τ Cr–CH2‐recovery = 36 ± 11 s, higher BMI: τ PCrrecovery = 65 ± 30s vs. τ Cr–CH2‐recovery = 60 ± 11 s, and exercise‐on, lower BMI: τ PCr‐on‐kinetics = 39 ± 14 s vs. τ Cr–CH2‐on‐kinetics = 38 ± 15 s, higher BMI: τ PCr‐on‐kinetics = 77 ± 53 s vs. τ Cr–CH2‐on‐kinetics = 70 ± 53 s). Significantly different time constants between the groups distinguished by BMI were detected, likewise with 1 H and 31 P MRS. Interestingly, though, creatine‐CH 2 and PCr depletion differed, correlating positively. Closely matching Cr–CH₂ and PCr kinetics was confirmed for the first time in single time‐resolved experiments, using interleaved 1 H and 31 P MRS. The strong correlation between τ PCr and τ Cr–CH₂ and preserved intergroup differences suggests that quantifying Cr–CH₂ by 1 H MRS might, within limitations, serve as a surrogate for the estimation of oxidative capacity via PCr from 31 P MR spectra. The results contribute to the discussion on NMR visibility of myocellular creatine pools.