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OB-Rb mediated phosphorylation of STAT3 is required for leptin regulation of energy balance and body weight. In lean, but not in obese human skeletal muscle, leptin is able to stimulate fatty acid oxidation, suggesting triglyceride accumulation and lipotoxicity in obesity could be caused by changes in the leptin signaling cascade. Leptin may down-regulate leptin signaling in the target tissues by inducing the protein suppressor of cytokine signaling 3 (SOCS3), which blunts JAK2/STAT3-dependent leptin signaling and causes leptin resistance in the skeletal muscle. Protein-tyrosine phosphatase 1B (PTP1B) is a negative modulator of leptin and insulin signaling because is able to dephosphorylate JAK2 and the insulin receptor and may explain leptin and insulin resistance in peripheral tissues. Exercise partially prevents muscle leptin resistance in rodents. Therefore, the aim of this study was to study if sprint exercise could be a leptin signalling mimetic in human skeletal muscle.

Methods. Tyr1007/1008-JAK2 and Tyr705-STAT3 phosphorylation level and SOCS3/PTP1B protein expression were determined by western blot in fifteen young healthy men in response to a 30 s sprint exercise (Wingate test). Subjects were randomly distributed into two groups.

One group exercised under fasting conditions (n=7, C), and the other ingested 75g of glucose (G) one hour before exercising (n=8).

Results. Tyr1007/1008-JAK2 phosphorylation was unaffected in the control Wingate test (all P0.05 versus rest). In contrast, compared to pre-exercise levels, Tyr1007/1008-JAK2 phosphorylation was increased 120 min after the Wingate test performed following glucose ingestion (P0.05). Compared to pre-exercise conditions, Tyr705-STAT3 phosphorylation was increased 30 min after the sprint exercise (P0.05). Glucose ingestion blunted the increase in Tyr705-STAT3 phosphorylation detected 30 min after the Wingate test. In the glucose group, 2 hours (P0.05) and 4h (P0.05) after the Wingate test Tyr705-STAT3 phosphorylation was increased compared to pre-exercise levels. Compared to pre-exercise conditions, SOCS3 protein expression was increased 120 min after the sprint exercise (P0.05 versus resting). Glucose ingestion blunted SOCS3 protein expression increase 120 min after the Wingate test. The level of PTP1B protein expression was not affected by either glucose ingestion or exercise (all P0.05).

Conclusions. STAT3 phosphorylation level and SOCS3 protein expression is markedly increased 30 and 120 min respectively, after sprint exercise. These responses were blunted by oral glucose ingestion. Our results suggest that sprint exercise performed in fasting conditions is a leptin signalling mimetic in human skeletal muscle.

Granted by the Ministerio de Educación y Ciencia (BFU2006-13784 and FEDER).

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13:00 - 14:00 Poster presentations PP-PH05 Physiology 5





Introduction: It is generally considered that performance in long duration events is mainly determined by maximal oxygen consumption (VO2 max), the energy cost of locomotion and the fractional utilization of VO2 max (also called aerobic endurance). It has been proposed that the amplitude of the slow component of the VO2 kinetics during severe intensity exercise should be added to this model. Since this variable shares many underlying mechanisms with aerobic endurance, we wanted to determine whether these two physiological parameters were independent one to each other.

Methods: Thirty moderately-trained male endurance athletes gave their written informed consent to participate in this study. They completed a maximal continuous graded exercise test (session 1), followed by two randomly ordered constant power tests (sessions 2 and 3), and a constant duration test (session 4). All tests were performed on a bicycle ergometer, Constant power tests were performed at an intensity corresponding to 90 and 100% of peak power output (PPO) measured during session 1. The slope of the relationship between intensity of exercise and the natural logarithm of time to exhaustion was considered as the index of aerobic endurance (IE, unitless), and used afterwards as the criterion measure for aerobic endurance. The slope of the relationship between work and time was considered as the critical power (CP, in W), and used afterwards for intensity determination during session 4. Constant duration test consisted in two bouts of 6 minutes of exercise at an intensity corresponding to 30% of the difference between CP and PPO. Sixty minutes of passive recovery were given between the two bouts of exercise. Oxygen uptake was determined continuously on a breath-by-breath basis during session 4. The signals from both tests were resampled to second by second and ensemble-averaged to produce an average response. A classical bi-exponential model was used to fit this new signal and estimate the amplitude of the slow component.

Results: Once the study completed, participants were ranked according to their IE. The median-third was excluded. The higher third formed the high aerobic endurance group (HEG) and the lower third formed the low aerobic endurance group (LEG). There was no overlap in IE between groups. Mean VO2 peak and IE for HEG and LEG were 4122 ± 511 vs 3911 ± 825 ml.min-1 (NS) and -21.7 ± 3.4 vs -13.9 ± 0.7 (p 0.001), respectively. The amplitude of the VO2 slow component was not different between groups (626 ± 96 vs 536 ± 168 ml, corresponding to 26 ± 3 vs 24 ± 7 % of end exercise VO2, respectively; NS) and was not associated with IE (r = 0.14, NS).

Conclusion: Contrarily to our hypothesis, the amplitude of the VO2 slow component was not associated with aerobic endurance. It can therefore be considered as a possible independent predictor of performance in long duration events. Future studies should assess its relative weight when compared with the classical determinants.




Introduction: Mathematical models in the form of a nonlinear dynamical system have recently been developed both for heart rate (Stirling et al, 2008a) and oxygen uptake kinetics (Stirling et al, 2008b, 2005). The point of maximum curvature has been proposed by Stirling and Zakynthinaki, (2008) as a marker for physiological time series. This marker defines the point after which the heart rate no longer continues to rapidly rise and instead follows either a steady state or slow rise (i.e. the slow component). The aim of this study is to apply these methods of analysis and models to examine the way the point of maximum curvature changes with improved fitness resulting from training.

Methods: Beat to beat heart rate data were obtained from an athlete who performed a series of bouts of exercise at different constant intensities. The optimal fit of the heart rate model to the basic response pattern (Zakynthinaki et al, 2007) of the raw un averaged data was obtained used a stochastic optimization algorithm (Zakynthinaki and Stirling, 2007; 2008). The point of maximum curvature was then calculated using the method described in Stirling and Zakynthinaki (2008). The same point is calculated for the same exercise intensity following a period of training which has resulted in speeded kinetics.

Results: It was observed that by calculating the point of maximum curvature, the time and the value of the heart rate at which the heart rate time series changes from a rapidly rising function to either a steady state or slow component was easily detected. The point of maximum curvature was also found to change with speeded kinetics following a period of training.

Discussion: A method based on obtaining the point of maximum curvature was used for determining the time and heart rate (or oxygen uptake) after which a plateau or a slow component in the heart rate (or oxygen uptake) kinetics is achieved. This method was shown to be of much use for understanding the heart rate kinetics in response to constant intensity short duration exercise. We concluded that the point of maximum curvature is a useful tool for understanding speeded heart rate kinetics following training. This method also has many applications in similar problems in oxygen uptake kinetics.

References Stirling JR and Zakynthinaki MS, (2008) J Nonlin Math Phys 15(sup3), 396-403..

Stirling JR, Zakynthinaki MS, Sampedro J and Refoyo I (2008a) J Nonlin Math Phys. 15(sup3), 426-436.

Stirling JR, Zakynthinaki MS and Billat VL, (2008b) Bul. Math. Biol, 70(5):1348-1370.

Stirling JR, Zakynthinaki MS, Saltin B, (2005) Bul. Math. Biol. 67(5), 989-1015.

Zakynthinaki MS, Stirling JR, (2008). Comp Phys Comm, 179(12), 888-894.

Zakynthinaki MS, Stirling JR, Sillero M, Sampedro J, Refoyo I, Materials Matematics, UAB (2007).

Zakynthinaki MS, Stirling JR, (2007) Comp. Phys. Commun. 176(2), 98-108.

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Background Fire-fighting is physically very demanding. Testing of firefighters’ physical ability is needed, but there is no close agreement between performance on standard laboratory tests and results of simulated rescue operations [1]. This suggests that tests should be carried out on fire-fighting-related activities, which may include tasks in the heat. The Metamax II (Mmx) is a portable metabolic analyzer that allows field testing [2]. This instrument like all electronic instruments does not tolerate heat. Moreover, the Mmx’ software requires that both inspired and expired air is passed thru its triple V flow transducer to work properly. When firefighters work at the scene of fire, they are dressed up for smoke diving, inspiring from bottles with pressurised air led to the face mask thru a solid tube. Expired air is released to the surroundings. Consequently, during smoke diving only expired air is available for analysis by the Mmx. Therefore, to measure the oxygen uptake of firefighters during smoke diving by the Mmx, we had to modify the instrument. We here describe our approach.

Principle of operation The Triple V flow transducer is a turbine-type flow-meter a light-weight fan rotates in proportion to the flow. Two sets of diodes and photocells (flow 1 and flow 2) record each rotation, and the sequence 1–2 or 2–1 distinguishes between inspiration and expiration. Only data for expirations are used for further calculations, but the software requires an inspiration signal between two expirations to work properly.

Methods: An extension to the cable connecting the Triple V to the main unit was cut. The individual wires of the cut ends were mounted on a small circuit board with a Pic 16F 628/20 microprocessor, programmed to pass all signals thru during expiration. After a complete expiration the microprocessor produced an artificial inspiration signal. Noise was removed. The signal in each wire during use was read on an oscilloscope.

Connections to fit the Triple V to the outlet of the Interspiro face mask were made, thus allowing expired air to pass from the mask thru the Triple V. The Mmx II was placed in a dedicated heat-protected box mounted out the subject’s back, and tubes as well as the Triple V were heat protected by isolating materials.

Results: With no inspiration signal the software did not work properly, reporting a lung ventilation at least 30% too low. The microprocessor reproduced the square-wave signals even during maximal expirations. During exercise lasting up to 8 min in a heat chamber (t 120 °C) the temperature in the heat protecting box stayed below 30 °C.

Conclusions By proper modifications the Mmx II may be used to measure the oxygen uptake of firefighters dressed up for smoke diving even in hot and polluted environments.


1. Heimburg, Rasmussen, Medbo. Ergonomics, 2006; 49: 111–126.

2. Medbø, Mamen, Welde, Heimburg, Stokke. Scand J Clin Lab Invest. 2002; 62: 585–598.




INTRODUCTION: The use of the walking poles has increased, however de literature still does not a consensus about their benefits. It as also been reported that the load carriage with poles use, spite of reducing the mechanical load of the lower limb may cause higher fatigue. The purpose of this study was to determine the effects of poles and load carriage on the walking velocity and on rate of perceived exertion (RPE). The velocity was examined for four walking condition: non-poles and non-load (W), with poles and non-load (WP), nonpoles and with load (WL), with poles and with load (WLP).


Twenty six healthy masculine volunteers walked at a self-selected pace during a pedestrian field track with 821 m long on level terrain (mean±SD, age 23,30 ± 2,69 years; body weight 76,96 ± 12,19 Kg; height 176,25 ± 5,70 cm; body fat percentage 14,69 ± 5,89%). The subjects completed each trail in a randomized order after return to the metabolic rest values between trails. The rest heart rate (HR) and oxygen consumption (VO2) were recorded by a portable telemetric system. Rating of perceived exertion (RPE) was measured at the end of each trial by the modified Borg scale (1-10)[1]. The weight carriage was 25% of the subject’s body mass, in a backpack with internal frame, sternum strap, hip belt and load lifters adjusted for each subject as well the telemetric poles.

RESULTS: Significantly differences were not found in RPE for comparisons M vs MP and ML vs MLP. Walking speed shows a significantly decrease ( = 0,05, IC 95% 0,01 to 0,1, P 0,05) between M vs MP.


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