Metabolic effects of training in humans: a 31P-MRS study J. A. KENT-BRAUN, K. K. McCULLY, AND B. CHANCE Department of Biochemistry and Biophysics, School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104 KENT-BRAUN, J. A., K. K. MCCULLY, AND B. CHANCE. Metabolic effects of training in humans: a 3’P-MRS study. J. Appl. Physiol. 69(3): 1165-1170, 1990.-The purpose of this study was to determine the feasibility of measuring with 31P nuclear magnetic resonance the effects of an endurance training program on the high-energy phosphate metabolism of exercis- ing human skeletal muscle. The system used included a 1.9-T 30-cm-bore Oxford Systems superconducting magnet, a PhosphoEnergetics spectrometer, and a modified Cybex isoki- netic ergometer. Seven healthy human volunteers exercised their wrist flexor muscles 20 min/day 5 days/wk for 8 wk. Testing before and after the training period consisted of a performance test to measure muscle functional capacity and a ramp test to measure the work-energy cost relationship of the exercising muscles. The results indicate that the subjects had a significant increase in their work output on the IO-min performance test after training. They also exhibited an increase in the work-energy cost relationship on the ramp test as indi- cated by a decrease in peak Pi-to-phosphocreatine ratio and an increase in pH at the same relative power output after training. These results indicate that I) the training program was suffi- cient to elicit a training effect and 2) this effect was observed with “‘P nu c 1 ear magnetic resonance as an increased potential for oxidative metabolism, particularly at the high exercise levels. skeletal muscle; nuclear magnetic resonance; exercise; fatigue SKELETAL MUSCLE mitochondrial metabolism has an important role in exercise performance. Endurance train- ing has been shown to increase skeletal muscle mito- chondrial capacity (2, 8, 10, 15, 17). Skeletal muscle metabolism under steady-state conditions where O2 is not limiting appears to be regulated by [ADP] (5, 6, 16). Under conditions where pH does not change, intracellu- lar ADP levels are reflected by changes in the Pi-to- phosphocreatine ratio (P;/PCr). Muscle metabolism is traditionally measured via biochemical analysis of tissue biopsies, which is a technique with significant limitations regarding repeatability and feasibility in the in vivo situation. “P magnetic resonance spectroscopy (MRS) provides the opportunity to noninvasively and repeatably measure Pi, PCr, and ATP levels and intracellular pH during exercise (3, 4, 9). The work-energy cost relation- ship of muscle is defined as the change in Pi/PCr in relation to exercise intensity measured as power output (5). The work-energy cost relationship gives an index of mitochondrial function, i.e., it gives an indication of the capacity of the mitochondria to produce ATP at a rate sufficient to keep pace with the increasing demands associated with increased power output, thereby main- taining the cell in a steady state of metabolism (5, 11). Thus far, differences between healthy and diseased and highly trained vs. untrained controls have been detected using the MRS technique (1, 3, 6, 13, 20, 24, 31). The purpose of this study was to measure changes in the work-energy cost relationship of the skeletal muscle of the subjects before and after training by using 31P- MRS. To accomplish this, control subjects performed an 8-wk endurance training program with the wrist flexor muscles. We hypothesized that adaptations to endurance training would be reflected by reduced fatigue on an endurance performance test and an improved work-en- ergy cost relationship measured as a steeper initial slope of the power-PJPCr relationship determined from a ramp exercise protocol. METHODS Subjects. Seven healthy human volunteers, five men and two women, were utilized for this study. They ranged in activity level from sedentary individuals to a highly trained runner. None was involved in any other type of arm training before or during the testing/training period of this study. This study was conducted in accordance with the University of Pennsylvania Policy for Human Studies. IMPS. A 1.9-T 3O-cm-bore Oxford Systems supercon- ducting magnet and PhosphoEnergetics spectrometer were used to collect the 31P-MRS data (30). The arm probe was placed on a platform with a built-in 3.5cm copper sending and receiving coil tuned to both proton (80.2 MHz) and phosphorus (32.5 MHz) frequencies. The sample volume was -3 cm3. The subject grasped a non- magnetic handle and linkage connected to a Cybex II isokinetic ergometer. A system of straps was used to secure the arm in place. For all tests, the subjects were positioned with the belly of the wrist flexor muscles over the coil and the ergometer handle placed at a comfortable position relative to the subject’s forearm length. The same handle position was used by each subject for all their tests. A strip chart recorder connected to the ergom- eter was used to provide feedback regarding force output to the subject. The duration of all contractions was 0.5 s, and the range of motion for the wrist flexion was -60”. After the subject was placed in the magnet, the mag- netic field was shimmed using the proton signal. The 31P-MRS data were collected using an optimal pulse (45 ps) at a pulse rate of one every 3 s for the performance test and one every 5 s for the ramp test. To improve the signal-to-noise ratio, the MRS data were averaged for 0161-7567/90 $1.50 Copyright 0 1990 the American Physiological Society 1165