Correlation of lactate and pH in human skeletal muscle after exercise by 1 H NMR

We have made in vivo 1 H NMR measurements of the time course of pH and lactate in human skeletal muscle after exercise. Spectra were obtained in a 4.7‐T 30 cm bore Bruker Biospec spectrometer with a 2.5‐cm diameter single surface coil. pH was determined from the shift of the endogenous carnosine H‐C 2 peak while lactate concentrations were determined by comparison with endogenous total creatine, taken to be 28.5 m M / kg wet wt. Fitting the data shows that the exponential decay of lactate (‐0.094 ± 0.014 min ‐1 , t 1/2 = 10.6 min) is slower than that of pH (‐0.147 ± 0.015 min ‐1 , t 1/2 = 4.7 min), n = 7 with two different volunteers. These values are significantly different with P < 0.0005. Relaxation times of lactate and creatine were also measured for lactate quantitation: creatine Tl. 1.23 ± 12 s. T2, 136.2 ± 26.4 ms (both in resting human muscle); lactate Tl (in postmortem rabbit muscle), 1.0 ± 11 s and T2, 80 ms (in postexercise human muscle). At the end of intense exercise, the lactate level reached was 25.3 ± 4.0 m M and the average pH drop was 1.0 pH unit. We discuss the implicaions of these measurements in conjunction with existing data on other sources of H + flux, phosphocreatine resynthesis, H + transport, and contribution of inorganic phosphate to buffering. © 1991 Academic Press, Inc.