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The aims of this study were to observe the behavior of carnosine peaks in human soleus (SOL) and gastrocnemius (GM) muscles following acute exercise, to determine the relaxation times and to assess the repeatability of carnosine quantification by 1H MRS at 7 T. Relaxation constants in GM and SOL were measured by a stimulated echo acquisition mode (STEAM) localization sequence. For T1 measurement, an inversion recovery sequence was used. The repeatability of the measurement and the absolute quantification of carnosine were determined in both muscles in five healthy volunteers. For absolute quantification, an internal water reference signal was used. The effect of acute exercise on carnosine levels and resonance lines was tested in eight recreational runners/cyclists. The defined carnosine measurement protocol was applied three times – before and twice after (approximately 20 and 40 min) a 1-h submaximal street run and additional toe-hopping. The measured T1 relaxation times for the C2-H carnosine peak at 7 T were 2002 ± 94 and 1997 ± 259 ms for GM and SOL, respectively, and the T2 times were 95.8 ± 9.4 and 81.0 ± 21.8 ms for GM and SOL, respectively. The coefficient of variation of the carnosine quantification measurement was 9.1% for GM and 6.3% for SOL, showing high repeatability, and the intraclass correlation coefficients (ICCs) of 0.93 for GM and 0.98 for SOL indicate the high reliability of the measurement. Acute exercise did not change the concentration of carnosine in the muscle, but affected the shape of the resonance lines, in terms of the shifting and splitting into doublets. Carnosine measurement by 1H MRS at 7 T in skeletal muscle exhibits high repeatability and reliability. The observed effects of acute exercise were more prominent in GM, probably as a result of the larger portion of glycolytic fibers in this muscle and the more pronounced exercise-induced change in pH. Our results support the application of the MRS-based assessment of carnosine for pH measurement in muscle compartments.

Defects in skeletal muscle energy metabolism are indicative of systemic disorders such as obesity or type 2 diabetes. Phosphorus magnetic resonance spectroscopy ((31)P-MRS), in particularly dynamic (31)P-MRS, provides a powerful tool for the non-invasive investigation of muscular oxidative metabolism. The increase in spectral and temporal resolution of (31)P-MRS at ultra high fields (i.e., 7T) uncovers new potential for previously implemented techniques, e.g., saturation transfer (ST) or highly resolved static spectra. In this study, we aimed to investigate the differences in muscle metabolism between overweight-to-obese sedentary (Ob/Sed) and lean active (L/Ac) individuals through dynamic, static, and ST (31)P-MRS at 7T. In addition, as the dynamic (31)P-MRS requires a complex setup and patient exercise, our aim was to identify an alternative technique that might provide a biomarker of oxidative metabolism. The Ob/Sed group exhibited lower mitochondrial capacity, and, in addition, static (31)P-MRS also revealed differences in the Pi-to-ATP exchange flux, the alkaline Pi-pool, and glycero-phosphocholine concentrations between the groups. In addition to these differences, we have identified correlations between dynamically measured oxidative flux and static concentrations of the alkaline Pi-pool and glycero-phosphocholine, suggesting the possibility of using high spectral resolution (31)P-MRS data, acquired at rest, as a marker of oxidative metabolism.

Carnosine is a performance-enhancing food supplement with a potential to modulate muscle energy metabolism and toxic metabolites disposal. In this study we explored interrelations between carnosine supplementation (2 g/day, 12 weeks) induced effects on carnosine muscle loading and parallel changes in (i) muscle energy metabolism, (ii) serum albumin glycation and (iii) reactive carbonyl species sequestering in twelve (M/F=10/2) sedentary, overweight-to-obese (BMI: 30.0±2.7 kg/m2) adults (40.1±6.2 years). Muscle carnosine concentration (Proton Magnetic Resonance Spectroscopy; 1H-MRS), dynamics of muscle energy metabolism (Phosphorus Magnetic Resonance Spectroscopy; 31P-MRS), body composition (Magnetic Resonance Imaging; MRI), resting energy expenditure (indirect calorimetry), glucose tolerance (oGTT), habitual physical activity (accelerometers), serum carnosine and carnosinase-1 content/activity (ELISA), albumin glycation, urinary carnosine and carnosine-propanal concentration (mass spectrometry) were measured. Supplementation-induced increase in muscle carnosine was paralleled by improved dynamics of muscle post-exercise phosphocreatine recovery, decreased serum albumin glycation and enhanced urinary carnosine-propanal excretion (all p