Direct noninvasive quantification of lactate and high energy phosphates simultaneously in exercising human skeletal muscle by localized magnetic resonance spectroscopy

A novel method based on interleaved localized P-31- and H-1 MRS is presented, by which lactate accumulation and the accompanying changes in high energy phosphates in human skeletal muscle can be monitored simultaneously during exercise and recovery. Lactate is quantified using a localized double quantum filter suppressing the abundant lipid signals while taking into account orientation dependent signal modulations. Lactate concentration after ischemic exercise directly quantified by DQF H-1 spectroscopy was 24 +/- 3 mmol/L cell water, while 22 +/- 3 mmol/L was expected on the basis of P-31 MRS acquired simultaneously. Lactate concentration in a sample of porcine meat was estimated to be 40 +/- 7 mmol/L by means of DQF quantitation, versus 39 +/- 5 mmol/L by biochemical methods. Excellent agreement is shown between lactate concentrations measured noninvasively by H-1 MRS, measured biochemically ex vivo, and inferred indirectly in vivo from changes in pH, P;, and PCr as obtained from P-31 MRS data.