Irisin Levels Are Lower in Young Amenorrheic Athletes Compared with Eumenorrheic Athletes and Non-Athletes and Are Associated with Bone Density and Strength Estimates

Irisin and FGF21 are novel hormones implicated in the “browning” of white fat, thermogenesis, and energy homeostasis. However, there are no data regarding these hormones in amenorrheic athletes (AA) (a chronic energy deficit state) compared with eumenorrheic athletes (EA) and non-athletes. We hypothesized that irisin and FGF21 would be low in AA, an adaptive response to low energy stores. Furthermore, because (i) brown fat has positive effects on bone, and (ii) irisin and FGF21 may directly impact bone, we hypothesized that bone density, structure and strength would be positively associated with these hormones in athletes and non-athletes. To test our hypotheses, we studied 85 females, 14–21 years [38 AA, 24 EA and 23 non-athletes (NA)]. Fasting serum irisin and FGF21 were measured. Body composition and bone density were assessed using dual energy X-ray absorptiometry, bone microarchitecture using high resolution peripheral quantitative CT, strength estimates using finite element analysis, resting energy expenditure (REE) using indirect calorimetry and time spent exercising/week by history. Subjects did not differ for pubertal stage. Fat mass was lowest in AA. AA had lower irisin and FGF21 than EA and NA, even after controlling for fat and lean mass. Across subjects, irisin was positively associated with REE and bone density Z-scores, volumetric bone mineral density (total and trabecular), stiffness and failure load. FGF21 was negatively associated with hours/week of exercise and cortical porosity, and positively with fat mass and cortical volumetric bone density. Associations of irisin (but not FGF21) with bone parameters persisted after controlling for potential confounders. In conclusion, irisin and FGF21 are low in AA, and irisin (but not FGF21) is independently associated with bone density and strength in athletes

Il tensore energia-impulso per un fluido perfetto in relatività ristretta e generale

Con questo lavoro si vuole discutere la connessione esistente tra l' equazione di continuità e l'equazione del moto di un fluido perfetto in Relatività Ristretta e Generale. Dapprima forniremo una breve introduzione sulle basi della Relatività Ristretta , introducendo il tensore energia-impulso ed analizzando in maniera specifica tale tensore per un fluido perfetto, ricavandone le equazioni del moto. Forniremo un secondo esempio di tensore Energia-Impulso per la materia incoerente. Conclusa questa argomentazione ci concentreremo sulla Relatività Generale, analizzandone i principi che sono alla base e privilegiando tra questi il Principio di Covarianza Generale come linea guida per le argomentazioni logiche. In maniera analoga a quanto fatto per la Relatività Ristretta riprenderemo la discussione per il tensore energia-impulso per un fluido perfetto dal punto di vista della Relatività Generale , soffermandoci nel caso di equilibrio idrostatico. Sempre nel contesto della Relatività Generale verrà in ultima analisi discusso il concetto di fluido incoerente e moto geodetico. L'ultimo capitolo è dedicato ad una appendice matematica nel quale vengono ricordati alcuni risultati dell'analisi tensoriali utili nel seguire i calcoli effettuati

Clinical characteristics of amenorrheic athletes (AA), eumenorrheic athletes (EA) and non-athletes (NA).

<p>Mean ± SD or Median (Interquartile Range); FGF21: fibroblast growth factor 21; AA: amenorrheic athletes; EA: eumenorrheic athletes; NA: non-athletes.</p>§<p>P values reported for log converted data.</p

Irisin and FGF21 levels in athletes and non-athletes.

<p>(A) Irisin and (B) FGF21 levels were lower in amenorrheic athletes (AA) compared to eumenorrheic athletes (EA) and non-athletes (NA) (ANOVA for three-group comparison for log converted values, followed by the Tukey Kramer test to compare any two groups). *, p<0.05 vs. EA and NA.</p