1H-MAGNETIC RESONANCE SPECTROSCOPY TO EVALUATE GENDER DIFFERENCES OF INTRAMYOCELLULAR LIPIDS (IMCL):

Skeletal muscles cover their energy from circulating and intracellular supplies (FFA and blood glucose vs IMCL and glycogen). It is unclear if gender differences exist in the consumption of these sources and it is still a matter of debate to what extent IMCL is used. MRS offers a unique tool to follow depletion of the major intramuscular energy stores in the same examination. PURPOSE Determination of IMCL before and after an endurance exercise in males (M) and females (F) as well as total fat oxidation. METHODS 9 trained M and F cycled on an ergometer at 50% Wmax (maximal workload) for 3-h. IMCL measurements in the M.vastus intermedius were done by a 1.5 Tesla MR-system, a flexible, 1H-double-tuned coil. 1H-MRS: PRESS TE 20 ms, TR 3000 ms, 128 acquisitions, 12x11x18 mm3. VO2 and VCO2 were determined by an β-Oxycon. Fat oxidation was calculated by a formula of Péronnet and Massicotte (1991). RESULTS IMCL levels at rest showed a significant difference (p < 0.05) between M (7.2 ±2.9 mmol/kg ww) and F (4.7 ±1.7 mmol/kg ww). Both gender depleted their IMCL significantly (p < 0.001), M significantly more (p < 0.001; 4.2 ±1.6 mmol/kg ww) than F (1.8 ±0.6 mmol/kg ww). Relative power output [energy used/50% Wmax] 4.5 ±0.4 vs 4.7 ±0.3, heart rate [% heart ratemax/min] 71 ±7 vs 75 ±3, oxygen uptake [VO2max] 62 ±7 vs 65 ±5 and RQ [VCO2/VO2] 0.88 vs 0.86 as relative indicators of performance intensity were very similar between M and F. Also the amount of fat oxidation (0.56 ±0.16 vs 0.43 ±0.14 g/min) and its relative contribution to total energy used (37 ±9 vs 42 ±14) did not differ between M and F. CONCLUSION While all standardized parameters and the contribution of total fat were similar in M and F, IMCL level at rest and its depletion during exercise were significantly different. A gender-specific substrate selection or differences in the long-term diet and training habit could cause this. Supported by Swiss National Fund (3100-053788.98)