Jørn W. Helge

Normal mitochondrial function and increased fat oxidation capacity in leg and arm muscles in obese humans

Aim/hypothesis:The aim of this study was to investigate mitochondrial function, fibre-type distribution and substrate oxidation during exercise in arm and leg muscles in male postobese (PO), obese (O) and age- and body mass index (BMI)-matched control (C) subjects. The hypothesis of the study was that fat oxidation during exercise might be differentially preserved in leg and arm muscles after weight loss.Methods:Indirect calorimetry was used to calculate fat and carbohydrate oxidation during both progressive arm-cranking and leg-cycling exercises. Muscle biopsy samples were obtained from musculus deltoideus (m. deltoideus) and m. vastus lateralis muscles. Fibre-type composition, enzyme activity and O2 flux capacity of saponin-permeabilized muscle fibres were measured, the latter by high-resolution respirometry.Results:During the graded exercise tests, peak fat oxidation during leg cycling and the relative workload at which it occurred (FatMax) were higher in PO and O than in C. During arm cranking, peak fat oxidation was higher in O than in C, and FatMax was higher in O than in PO and C. Similar fibre-type composition was found between groups. Plasma adiponectin was higher in PO than in C and O, and plasma leptin was higher in O than in PO and C.Conclusions:In O subjects, maximal fat oxidation during exercise and the eliciting relative exercise intensity are increased. This is associated with higher intramuscular triglyceride levels and higher resting non esterified fatty acid (NEFA) concentrations, but not with differences in fibre-type composition, mitochondrial function or muscle enzyme levels compared with Cs. In PO subjects, the changes in fat oxidation are preserved during leg, but not during arm, exercise.

Three‐dimensional reconstruction of the human skeletal muscle mitochondrial network as a tool to assess mitochondrial content and structural organization

Mitochondria undergo continuous changes in shape as result of complex fusion and fission processes. The physiological relevance of mitochondrial dynamics is still unclear. In the field of mitochondria bioenergetics, there is a need of tools to assess cell mitochondrial content. To develop a method to visualize mitochondrial networks in high resolution and assess mitochondrial volume.

Muscle metabolism during graded quadriceps exercise in man

The aim of the study was to examine local muscle metabolism in response to graded exercise when the involved muscle mass is too small to elicit marked hormonal changes and local blood flow restriction. Nine healthy overnight fasted male subjects performed knee extension exercise with both thighs kicking at 25% of maximal power (Wmax) for 45 min (23 ± 1% of pulmonary ) followed by 35 min of kicking with one thigh at 65% and the other at 85%Wmax (40 ± 1%). Primed constant infusion of [U‐13C] palmitate and [2H5]glycerol was carried out. Blood was sampled from a femoral artery and both femoral veins, and thigh blood flow was determined by thermodilution. Muscle biopsies were obtained from m. vastus lateralis of both thighs. From rest through exercise at 25, 65 and 85%Wmax the thigh blood flow (0.3 ± 0.1, 2.5 ± 0.2, 3.5 ± 0.2, 4.1 ± 0.3 l min−1) and oxygen uptake (0.02 ± 0.01, 0.27 ± 0.03, 0.48 ± 0.04, 0.55 ± 0.05 l min−1) increased (P < 0.05). The plasma fatty acids oxidized in the thigh (5 ± 1, 114 ± 15, 162 ± 30, 180 ± 31 μmol min−1) increased (P < 0.05) with exercise intensity, whereas the total thigh fat oxidation (19 ± 6, 312 ± 64, 356 ± 93, 323 ± 120 μmol min−1) increased (P < 0.05) from rest, but remained unchanged through exercise. The thigh glycerol uptake (1 ± 1, 16 ± 4, 24 ± 10, 39 ± 8 μmol min−1) increased significantly from rest through exercise at 25–65 and 85%Wmax, respectively. Glucose uptake and glycogen breakdown always increased with exercise intensity. In conclusion, in the presence of a high blood flow and oxygen supply and only small hormonal changes, total fat oxidation in muscle increases from rest to light exercise, but then remains constant with exercise intensity up to heavy exercise. However, with increasing exercise intensity, oxidation of plasma free fatty acids increases and accordingly oxidation of other fat sources decreases. These findings are in contrast to whole body measurements performed during graded exercise involving a large muscle mass during which fat oxidation peaks at around 60% of .