The relationship between relaxation time and muscle fiber composition was investigated in 16 males.
A highly positive correlation was found between muscle fiber composition and relaxation time. In addition, higher proportions of fast-twitch fibers were associated with longer relaxation times, indicating that the fast-twitch fiber has a longer relaxation time than the slow-twitch fiber.
Multiple regression analysis, which was conducted to investigate the suitability of relaxation time as a model for estimating muscle fiber composition, revealed that the T 1 and T 2 were significantly related to muscle fiber composition.
Therefore, the results of the present study indicate that relaxation time obtained by MRI can be used to estimate muscle fiber composition.

To evaluate the changes in muscle energetics following NaHCO₃ intake, we measured the phosphorus-31 nuclear magnetic resonance (³¹P NMR) spectra of human muscle in vivo during exercise. Seven male subjects performed two trials, a NaHCO₃ (Alka, Tr.) and a NaCI trial (Cont. Tr.), on two occasions. ³¹P NMR spectra were obtained serially during leg-elevating exercises. Before and during exercise, the intracellular phosphocreatine (PCr), inorganic phosphate (Pi) and pH were determined from the NMR spectra. The decrease of intracellular pH during exercise showed a tendency to be inhibited by NaHCO₃ intake, and the intracellular pH at the end of the exercise was 6.69 for Alka. Tr, and 6.51 for Cont. Tr. The decline of the PCr/ (PCr+Pi) ratio during exercise was not influenced by NaHCO₃ intake. The PCr/ (PCr+Pi) ratio was related exponentially to the intracellular pH. A remarkable decline of PCr/ (PCr+Pi) ratio occurred until the intracellular pH fell to about 6.7, but did not decrease below that. It was suggested that the intake of NaHCO₃ could decrease the rate of fall in the intracellular pH during exercise, and that the PCr store could be influenced by the intracellular pH when the pH was above 6.7, but not below that level.

A study was conducted to investigate using ³¹P NMR the relationship between the total excess volume of CO₂ output (CO₂ excess) due to bicarbonate buffering of lactic acid produced in exercise and the decrease of intracellular pH during incremental exercise. Five sprinters and 5 joggers performed incremental exercise to exhaustion on an bicycle ergometer. The values of CO₂ excess and CO₂ excess per body weight (CO₂ excess/W) were not different between the sprinters (2388±659ml, 36.7±8.5 ml·kg^-1) and the joggers (2275±278ml, 40.0±6, 3ml·kg^-1) . Below the ventilatory threshold (VT), from VT to the respiratory compensation point (RCP), and above RCP, the V_od2-V_co2 slopes were not different between the sprinters and the joggers, respectively (0.95±0.05 vs 0.95±0.06, 1.21±0.11 vs 1.30±0.14, 1.69±0.24 vs 1.76±0.18) . However, the joggers showed significantly higher CO₂ excess/W per blood lactate accumulation (ΔLa) in exercise (CO₂ excess/W/ΔLa, 5.34±0.32ml·kg^-1·mmol^-1·l^-1) than the sprinters (4.50±0.14ml·kg^-1·mmol^-1·l^-1) . The decrement of intracellular pH during incremental exercise showed a tendency to be smaller in joggers (0.63±0.18 pH unit) than in sprinters (0.83±0.10 pH unit), although there was no significant difference between the two groups. The values of CO₂ excess/W/ΔLa were correlated with the decrease of intracellular pH (r=-0.792, p<0.01) . It is suggested that CO₂ excess/W/ΔLa reflects the efficiency of the bicarbonate buffering system, and could be an important factor influencing the decrease of intracellular pH due to lactate production.

This study was aimed to explore the value of quantitative proton MR spectroscopy (1H-MRS) in the differentiation of benign and malignant meningioma. 23 cases, including 19 benign (grade I) and 4 malignant (grade II-III) meningiomas, underwent single voxel 1H-MRS (TR/TE = 2000 ms/68, 136, 272 ms). T2 relaxation time of tissue water and choline were estimated by an exponential decay model. Choline concentration was calculated using tissue water as the internal reference, and corrected according to intra-voxel cystic/necrotic parts. Tissue water T2 of benign and malignant meningiomas were (105 +/- 41) ms and (151 +/- 42) ms, respectively. The difference was statistically significant (P = 0.033). While Choline T2 of benign and malignant meningiomas were (242 +/- 73) ms and (316 +/- 102) ms respectively, the difference was not significant (P = 0.105). Choline concentration was (2.86 +/- 0.86) mmol/ kg wet weight in benign meningiomas and (3.53 +/- 0.60) mmol/kg wet weight in malignant ones; after correction they increased to (2.98 +/- 0.93)mmol/kg wet weight and (4.58 +/- 1.22) mmol/kg wet weight, respectively, and the difference was significant (P = 0.019). In conclusion, quantitative 1H-MRS is useful for the differentiation of benign and malignant meningioma by T2 relaxation time and absolute choline concentration.
Adult ; Aged ; Choline ; metabolism ; Diagnosis, Differential ; Female ; Humans ; Magnetic Resonance Spectroscopy ; methods ; Male ; Meningeal Neoplasms ; diagnosis ; metabolism ; pathology ; Meningioma ; diagnosis ; metabolism ; pathology ; Middle Aged ; Protons ; Young Adult