This study aims to measure skeletal muscle metabolism in vivo during exercise using the non-invasive Magnetic Resonance Spectroscopy (MRS) technique. Specifically, phosphocreatine (PCr) kinetic and Acetylcarnitine levels will be determined at resting, during exercise and during the recovery post exercise. The target population is adult healthy men, with a wide range of maximal physical capacity.

Skeletal muscle mitochondrial activation during the transition from resting metabolism to exercise may modulated by CrAT activity. Furthermore, dynamic changes in acetylcarnitine during the transition from exercise to resting metabolism (acetylcarnitine off-kinetic) may also reflect the action of CrAT protein. To date, the only possibility to get information on CrAT activity is by taking a muscle biopsy and perform enzyme activity assays ex vivo. By dynamic MRS scanning, it might be possible to deduce information that reflects CrAT activity, thereby making the biopsy sampling unnecessary.

Inclusion Criteria:

• Males, Generally healthy
• Age 18-40 years old
• BMI 18 - 25 kg/m2
• No medication use that interfere with the aims of the study
• Stable level of daily physical activity or training for at least 6 months

Exclusion Criteria:

• Females
• Regular smokers, drug abuse
• Participation in other studies
• Weight gain/loss > 3 kg in the last 6 months
• Contraindications for MRS scans:
• Vegetarian eating behavior

In this study, 13 healthy young males (BMI <25 kg/m2), aged 18-40yr with different maximal aerobic capacity will be included. Specifically, 4 volunteers with a VO2max <40 ml/kg/min, 5 volunteers with a VO2max between 41 and 50 ml/kg/min and 4 volunteers with a VO2max >50 ml/kg/min will be included.