Intracellular and extracellular skeletal muscle triglyceride metabolism during alternating intensity exercise in humans

Abstract

The main purpose of this study was to evaluate non‐invasively with magnetic resonance spectroscopy (1H‐MRS) changes in the concentrations of intracellular (IT) and extracellular (between muscle fibres) triglycerides (ET) in skeletal muscles of trained males (age range: 24–38 years) during two standard exercise protocols of alternating velocities. Protocol 1 consisted of locomotion in a shuttle manner between two 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 exhaustion. The heart rate during both protocols fluctuated between 140 and 200 beats min−1. Using pre‐exercise muscle water to quantify individual 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 exercise, 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 mmol (kg dry weight)−1, respectively, and were not affected by the exhaustive exercise. The ET concentrations in Sol, Gast and Tib were 136.4 ± 38.1, 175.3 ± 86.5 and 79.3 ± 20.0 mmol (kg dry weight)−1, respectively, and they did not change significantly after exhaustion. The study showed that levels of IT and ET were not affected by alternating intensity exercise to fatigue. This suggests that IT and ET in human Sol, Gast and Tib muscles do not contribute significantly to the energy turnover during this type of exercise. Energy for this type of muscle contraction may arise primarily from muscle phosphocreatine (PCr) and glycogen breakdown, circulating glucose and fatty acids from triglycerides other than those encountered within and between muscle cells.

Relation of triglyceride stores in skeletal muscle cells to central obesity and insulin sensitivity in European and South Asian men

“…Peak areas for each signal were obtained and lipid resonances were quantified with reference to total creatine after correcting for T 1 and T 2 . The inter-examination coefficient of variation for IMCL with 1 H-NMR was 13 %, and the intra-examination reproducibility was 4 % [9].…”

“…Spectra were obtained using a PRESS (point resolved spectroscopy) sequence with TE/TR = 135/1500 ms and an 8 cm 3 voxel, using the creatine signal as an internal standard. The muscle spectra were analysed by VARPRO [9]. Peak areas for each signal were obtained and lipid resonances were quantified with reference to total creatine after correcting for T 1 and T 2 .…”

Fat distribution in men of different waist girth, fitness level and exercise habit

“…19 The coefficient of variation for these methods is B7% for IHCL 19 and 2% for IMCL. 20 Statistical methods Descriptive characteristics were compared using univariate general linear model analysis of variance with Bonferroni Fat distribution in the 'fat-fit' G O'Donovan et al post hoc tests. MR imaging and spectroscopy data were compared using general linear model analysis of covariance with Sidak post hoc tests.…”

Exercise training reduces fatty acid availability and improves the insulin sensitivity of glucose metabolism

“…IHCL and IMCL were measured by 1 H-MRS within 1 week of the metabolic study and prior to the start of the exercise programme [22,23] as detailed in ESM 1. Subjects were asked not to exercise for 72 h prior to the measurement.…”