RESUMEN
Endurance athletes attribute performance not only to physiological factors, but also refer to psychological factors such as motivation. The goal of this study was to quantify the proportion of the variance in endurance performance that is explained by psychological factors in addition to the physiological factor VO2max. Twenty-five athletes of the U17 Swiss Cycling national team (7f, 18 m, 15.3 ± 0.5 years) were examined in a cross-sectional study with psychological factors and VO2max as independent variables and endurance performance in road cycling as dependent variable. Questionnaires were used to assess psychological factors (i.e. use of mental techniques, self-compassion, mental toughness, achievement motivation, and action vs. state orientation). VO2max was measured by a step incremental cycle ergometer test of exhaustion. Endurance performance was measured in a cycling mountain time trial (1,320 m long, incline of 546 meters). A multiple regression model was created by using forward selection of regression model predictors. Results showed that higher VO2max values (ß = .48), being male (ß = .26), and higher achievement motivation (i.e. perseverance, ß = .11) were associated with a better endurance performance. A more frequent use of one particular mental technique (i.e. relaxation techniques, ß = .03) was associated with a worse endurance performance. Our study shows that a physiological factor like VO2max explains endurance performance to a large extent but psychological factors account for additional variance. In particular, one aspect of achievement motivation, namely perseverance, was associated with a better endurance performance. HIGHLIGHTSEndurance performance is explained by physiological (e.g. VO2max) and psychological (e.g. perseverance) factorsVO2max explains young cyclists' endurance performance to a large extentPerseverance explained performance beyond the influence of VO2max.
Asunto(s)
Ciclismo , Resistencia Física , Humanos , Masculino , Femenino , Ciclismo/fisiología , Resistencia Física/fisiología , Estudios Transversales , Atletas , Estado Nutricional , Prueba de Esfuerzo , Consumo de Oxígeno/fisiologíaRESUMEN
Recently, a new automated carbon monoxide (CO) rebreathing method (aCO) to estimate haemoglobin mass (Hbmass) was introduced. The aCO method uses the same CO dilution principle as the widely used optimised CO rebreathing method (oCO). The two methods differ in terms of CO administration, body position, and rebreathing time. Whereas with aCO, CO is administered automatically by the system in a supine position of the subject, with oCO, CO is administered manually by an experienced operator with the subject sitting. Therefore, the aim of this study was to quantify possible differences in Hbmass estimated with the two methods. Hbmass was estimated in 18 subjects (9 females, 9 males) with oCO using capillary blood samples (oCOc) and aCO taking simultaneously venous blood samples (aCOv) and capillary blood samples (aCOc). Overall, Hbmass was different between the three measurement procedures (F = 57.55, p < .001). Hbmass was lower (p < .001) for oCOc (737 g ± 179 g) than for both aCOv (825 g ± 189 g, -9.3%) and aCOc (835 g ± 189 g, -10.6%). There was no difference in Hbmass estimated with aCOv and aCOc procedures (p = .12). Three factors can likely explain the 10% difference in Hbmass: differences in calculations (including a factor for myoglobin flux), body position (distribution of CO in blood circulation) during rebreathing, and time of blood sampling. Moreover, the determination of Hbmass with aCO is possible with capillary blood sampling instead of venous blood sampling.
Asunto(s)
Monóxido de Carbono , Mioglobina , Recolección de Muestras de Sangre , Femenino , Hemoglobinas/análisis , Humanos , Masculino , FlebotomíaRESUMEN
AIMS/HYPOTHESIS: The aim of this parallel-group, double-blinded (study personnel and participants), randomised clinical trial was to assess the interaction between metformin and exercise training on postprandial glucose in glucose-intolerant individuals. METHODS: Glucose-intolerant (2 h OGTT glucose of 7.8-11.0 mmol/l and/or HbA1c of 39-47 mmol/mol [5.7-6.5%] or glucose-lowering-medication naive type 2 diabetes), overweight/obese (BMI 25-42 kg/m2) individuals were randomly allocated to a placebo study group (PLA, n = 15) or a metformin study group (MET, n = 14), and underwent 3 experimental days: BASELINE (before randomisation), MEDICATION (after 3 weeks of metformin [2 g/day] or placebo treatment) and TRAINING (after 12 weeks of exercise training in combination with metformin/placebo treatment). Training consisted of supervised bicycle interval sessions with a mean intensity of 64% of Wattmax for 45 min, 4 times/week. The primary outcome was postprandial glucose (mean glucose concentration) during a mixed meal tolerance test (MMTT), which was assessed on each experimental day. For within-group differences, a group × time interaction was assessed using two-way repeated measures ANOVA. Between-group changes of the outcomes at different timepoints were compared using unpaired two-tailed Student's t tests. RESULTS: Postprandial glucose improved from BASELINE to TRAINING in both the PLA group and the MET group (∆PLA: -0.7 [95% CI -1.4, 0.0] mmol/l, p = 0.05 and ∆MET: -0.7 [-1.5, -0.0] mmol/l, p = 0.03), with no between-group difference (p = 0.92). In PLA, the entire reduction was seen from MEDICATION to TRAINING (-0.8 [-1.3, -0.1] mmol/l, p = 0.01). Conversely, in MET, the entire reduction was observed from BASELINE to MEDICATION (-0.9 [-1.6, -0.2] mmol/l, p = 0.01). The reductions in mean glucose concentration during the MMTT from BASELINE to TRAINING were dependent on differential time effects: in the PLA group, a decrease was observed at timepoint (t) = 120 min (p = 0.009), whereas in the MET group, a reduction occurred at t = 30 min (p < 0.001). VÌO2peak increased 15% (4.6 [3.3, 5.9] ml kg-1 min-1, p < 0.0001) from MEDICATION to TRAINING and body weight decreased (-4.0 [-5.2, -2.7] kg, p < 0.0001) from BASELINE to TRAINING, with no between-group differences (p = 0.7 and p = 0.5, respectively). CONCLUSIONS/INTERPRETATION: Metformin plus exercise training was not superior to exercise training alone in improving postprandial glucose. The differential time effects during the MMTT suggest an interaction between the two modalities. FUNDING: The Beckett foundation, A.P Møller Foundation, DDA, the Research Foundation of Rigshospitalet and Trygfonden. TRIAL REGISTRATION: ClinicalTrials.gov (NCT03316690). Graphical abstract.