CORRELATION OF LACTATE AND PH IN HUMAN SKELETAL-MUSCLE AFTER EXERCISE BY H-1-NMR

We have made in vivo 1H 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‐C2 peak while lactate concentrations were determined by comparison with endogenous total creatine, taken to be 28.5 mM/ 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, t1/2 = 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. Copyright © 1991 Wiley‐Liss, Inc., A Wiley Company