INTRACELLULAR AND EXTRACELLULAR SKELETAL-MUSCLE TRIGLYCERIDE-METABOLISM DURING ALTERNATING INTENSITY EXERCISE IN HUMANS

1. The main purpose of this study was to evaluate non-invasively with magnetic resonance spectroscopy (H-1-MRS) changes in the concentration s of intracellular (IT) and extracellular (between muscle fibres) trig lycerides (ET) in skeletal muscles of trained males (age range: 24-38 years) during two standard exercise protocols of alternating velocitie s. 2. Protocol 1 consisted of locomotion in a shuttle manner between t wo lines 30 m apart at four different velocities (1, 2, 3 and 4 m s(-1 )) which were alternated every minute in a standard routine for 90 min , whereas Protocol 2 included locomotion between two lines 20 m apart at only three velocities (2, 2.7 and 4 m s(-1)) until volitional exhau stion. The heart rate during both protocols fluctuated between 140 and 200 beats min(-1). 3. Using pre-exercise muscle water to quantify ind ividual total creatine (TCr) that was utilized as an internal standard and assuming that TCr does not change during exercise, subjects' mean IT and ET concentrations in soleus (Sol) muscle before Protocol 1. (n = 8) were 45.8 +/- 4.8 mmol (kg dry weight)(-1) (mean +/- S.E.M.) and 93.1 +/- 14.1 mmol (kg dry weight)(-1), respectively. After the exerc ise, the concentrations of IT and ET were not significantly different from the values at rest. Before Protocol 2 (n = 4), IT concentrations in Sol, gastrocnemius (Gast) and tibialis (Tib) muscles were 46.4 +/- 13.6, 35.0 +/- 12.1 and 23.1 +/- 4.8 mol (kg dry weight)(-1), respecti vely, and were not affected by the exhaustive exercise. The ET concent rations in Sol, Gast and Tib were 136.4 +/- 38.1, 175.3 +/- 86.5 and 7 9.3 +/- 20.0 mmol (kg dry weight)(-1), respectively, and they did not change significantly after exhaustion. 4. The study showed that levels of IT and ET were not affected by alternating intensity exercise to f atigue. This suggests that IT and ET in human Sol, Gast and Tib muscle s do not contribute significantly to the energy turnover during this t ype of exercise. Energy for this type of muscle contraction may arise primarily from muscle phosphocreatine (PCr) and glycogen breakdown, ci rculating glucose and fatty acids from triglycerides other than those encountered within and between muscle cells.