european college of sport science

Friday, June 26th, 2009
IMMUNOFLUORESCENCE MICROSCOPY TO INVESTIGATE THE LINK BETWEEN FAT METABOLISM AND INSULIN ACTION
SHAW, C.S.
UNIVERSITY OF BIRMINGHAM
Immunofluorescence microscopy has provided unique insights into skeletal muscle fat metabolism and its role in the development of
insulin resistance in skeletal muscle. Once transported across the sarcolemma, fatty acids can either cross the mitochondrial membrane
and undergo β-oxidation or enter intramuscular triglyceride (IMTG) synthesis. The IMTG content of type 1 muscle fibres is approximately
two-fold greater than type 2 fibres which appears to be related to a higher content of the IMTG synthesizing enzymes, namely
mitochondrial glycerol-3-phosphate acyltransferase (GPAT) and diacylglycerol acyltransferase (DGAT). IMTGs are stored within lipid droplets
(LD) which are preferentially located next to the mitochondrial network in trained individuals which enables the efficient oxidation of
fatty acids liberated during periods of elevated metabolic demand (endurance and resistance exercise). Recent advances in LD research
has shown that LDs contain a number of structural, enzymatic and membrane trafficking proteins and the protein composition of LDs
depends on the cell type and its lipolytic state.
The expanded adipose mass in obese individuals results in increased delivery of circulating fatty acids to skeletal muscle. When fatty acid
delivery exceeds fatty acid utilisation (oxidation or storage) the resultant accumulation of fatty acid metabolites, such as long chain acyl-
CoA and diacylgycerol, appears to inhibit insulin-stimulated GLUT4 translocation. The accumulation of IMTG in the skeletal muscle of
obese individuals does not appear to inhibit insulin action directly however IMTG metabolism plays an important role in determining the
concentration of intracellular fatty acid metabolites. Low rates of fatty acid oxidation in obese individuals, at least partially due to low
mitochondrial content, are likely to contribute to the accumulation of fatty acid metabolites. In addition, inadequate or incomplete IMTG
synthesis could also potentially explain why fatty acid metabolites accumulate in the skeletal muscle of obese individuals.
Over recent years the elevations in plasma fatty acids and inflammatory cytokines associated with obesity have been implicated in the
development of insulin resistance in the microvascular endothelium. Insulin-mediated synthesis of nitric oxide stimulates dilation of
arterioles and a redistribution of blood flow to skeletal muscle fibres prior to insulin stimulation of the muscle fibres. There is evidence that
microvascular dysfunction, typified by reduced NO-mediated vasodilation, occurs before impairments in insulin-mediated GLUT4 translocation.
Immunohistochemistry allows visualisation of microvascular endothelial cells and could potentially provide further insight into the
mechanisms behind obesity-related insulin resistance.
10:15 - 11:45
Oral presentations
OP-PH01 Physiology 1
DOES HAEMOGLOBIN MASS INCREASE WITH SEVERAL YEARS OF ENDURANCE TRAINING? - A CROSS-SECTIONAL
STUDY WITH U18, U23 AND ELITE NATIONAL TEAM CYCLISTS
WEHRLIN, J.P., CLÉNIN, G.E.
SECTION FOR ELITE SPORT
Introduction: It is unclear if haemoglobin mass (Hbmass) and red cell volume (RCV) increase with several years (ys) of training in endurance
athletes (Sawka et al., 2000, Heinicke et al., 2001, Prommer et al., 2008). Especially, little is known about changes between junior
and adult age. The aim of this study was to determine with a cross-sectional approach, whether national team endurance athletes in the
age-related teams ’under 18’ (U18), ’under 23’ (U23) and ’elite’ (>23 ys) are characterized by different Hbmass, RCV, plasma volume (PV)
and blood volume (BV).
Methods: Blood volume parameters (CO-rebreathing method) and other blood, iron, performance and training parameters were measured
in each a group of U18 (age = 16.9 ± 0.6ys; n = 15), U23 (age = 19.2 ± 1.2ys; n = 13) and elite (age = 27 ± 4.2ys; n = 14) male Swiss
national team cyclists (road, cross-country and track).
Results: There were no differences in either body weight related Hbmass (U18 = 14.4 ± 1.2g/kg; U23 = 14.0 ± 1.3g/kg; elite = 14.6 ±
1.0g/kg), RCV (40.4 ± 3.4; 39.2 ± 3.9; 40.8 ± 3.2 ml/kg), PV (63.6 ± 7.1; 64.6 ± 7.1; 64.6 ± 8.1 ml/kg) and BV (104.1 ± 8.6; 103.8 ± 9.8; 105.4
± 10.2 ml/kg) or absolute values. Absolute power at 4mmol/l blood lactate in the lactate threshold test was lower in the U18 than in the
elite group (p = 0.043) whereas differences in maximal absolute power output did not reach statistical significance (p = 0.102). Training
hours per week were lower (p = 0.032) in U18 than in the elite athletes.
Discussion: Our results indicate that several years of endurance training between the U18 and the elite age in national team cyclists do
not increase Hbmass, RCV, PV and BV, but power at 4mmol/l blood lactate concentration. Interestingly, in another recent cross-sectional
study with XC-skiers and triathletes (Steiner, Boutellier & Wehrlin, 2009), we found Hbmass to be lower at age 16 than at age 21 while it
was similar at age 21 and 28. Perhaps, Hbmass can increase with endurance training in athletes younger than 17ys? However, when
interpreting our results, one has to take into account, that although all our subjects where national team athletes, we used a crosssectional
design. This implies the risk of a possible selection bias. Studies with a longitudinal design are needed.
Conclusion: Hbmass can be similar in male U18, U23 and elite national team cyclists, what suggests, that Hbmass does not increase
with several years of endurance training in athletes from the U18, to the U23 and the elite national team.
References
Heinicke K, Wolfarth B, Winchenbach P, Biermann B, Schmid A, Huber G, Friedmann B, Schmidt W. (2001). Int J Sports Med, 22, 504-512.
Prommer N, Sottas P-E, Schoch C, Schuhmacher Y-O, Schmidt W. (2008). Med Sci Sports Exerc, 40, 2112- 2118.
Sawka MN, Convertino VA, Eichner ER, Schnieder SM, Young AJ. (2000). Med Sci Sports Exerc, 32, 332-348.
Steiner T, Boutellier U, Wehrlin JP. (2009). Book of Abstracts, ECSS Oslo.
OSLO/NORWAY, JUNE 24-27, 2009 341