Serum IL-15 and IL-15Rα levels are decreased in lean and obese physically active humans.

Circulating IL-15 presence is required to stimulate anti-adipogenic effects of the IL-15/IL-15Rα axis in adipose tissue. Although exercise increases blood IL-15 expression post-exercise, it remains inconclusive whether physical activity can alter the baseline concentrations of this cytokine. The aim of this study was to determine whether physical activity regulates circulating IL-15 and IL-15Rα in lean and obese individuals. Two hundred and seventy-six participants were divided into five groups according to physical activity (PA), body mass and type 2 diabetes mellitus (T2DM) diagnosis: (a) lean PA (N = 25); (b) lean non-PA (N = 28); (c) obese PA (N = 64); (d) obese non-PA (N = 79); and (e) obese non-PA with T2DM (N = 80). Serum IL-15 and IL-15Rα, blood glucose/lipid profile and body composition were measured. Serum IL-15 and IL-15Rα decreased in PA participants compared to non-PA (P < .05), while IL-15 and IL-15Rα increased in obese with T2DM compared to obese without T2DM (P < .05). No differences were observed between lean non-PA and obese PA. Serum IL-15Rα was associated with fasting glucose (R2 = .063), insulin (R2 = .082), HbA1c (R2 = .108), and HOMA (R2 = .057) in obese participants. Circulating IL-15 and IL-15Rα are reduced in lean and obese participants who perform physical activity regularly (≥180 min/week), suggesting a regulative role of physical activity on the circulating concentrations of IL-15 and IL-15Rα at baseline. Moreover, the relationship observed between IL-15Rα and glucose profile may indicate a role of the alpha receptor in glucose metabolism.

Skeletal muscle IL-15/IL-15Rα and myofibrillar protein synthesis after resistance exercise.

In vitro and in vivo studies described the myokine IL-15 and its receptor IL-15Rα as anabolic/anti-atrophy agents, however, the protein expression of IL-15Rα has not been measured in human skeletal muscle and data regarding IL-15 expression remain inconclusive. The purpose of the study was to determine serum and skeletal muscle IL-15 and IL-15Rα responses to resistance exercise session and to analyze their association with myofibrillar protein synthesis (MPS). Fourteen participants performed a bilateral leg resistance exercise composed of four sets of leg press and four sets of knee extension at 75% 1RM to task failure. Muscle biopsies were obtained at rest, 0, 4 and 24 hours post-exercise and blood samples at rest, mid-exercise, 0, 0.3, 1, 2, 4 and 24 hours post-exercise. Serum IL-15 was increased by ~5.3-fold immediately post-exercise, while serum IL-15Rα decreased ~75% over 1 hour post-exercise (P<.001). Skeletal muscle IL-15Rα mRNA and protein expression were increased at 4 hours post-exercise by ~2-fold (P<.001) and ~1.3-fold above rest (P=.020), respectively. At 24 hours post-exercise, IL-15 (P=.003) and IL-15Rα mRNAs increased by ~2-fold (P=.002). Myofibrillar fractional synthetic rate between 0-4 hours was associated with IL-15Rα mRNA at rest (r=.662, P=.019), 4 hours (r=.612, P=.029), and 24 hours post-exercise (r=.627, P=.029). Finally, the muscle IL-15Rα protein up-regulation was related to Leg press 1RM (r=.688, P=.003) and total weight lifted (r=.628, P=.009). In conclusion, IL-15/IL-15Rα signaling pathway is activated in skeletal muscle in response to a session of resistance exercise.

Validity of the standing spike test as a monitoring protocol for female volleyball players.

THE PURPOSE OF THIS PAPER WAS: a) to provide reference values for the standing spike test for female volleyball players and b) to study whether the standing spike test is valid for assessing the theoretical differences between female volleyball players. The sample included 83 players from the first nine teams of the Spanish women's first volleyball division (52 Spanish players and 31 from other nationalities). The variables studied were the ball speed of the standing spike test, the age of the players, the player's role (outside hitter, opposite, middle-blocker, libero, or setter), height, and nationality of the players (Spanish or foreign). The results demonstrate the ranges for the standing spike among female performance volleyball players (70-82 km · h(-1)). The differences regarding nationality, player role, height, and age seem to indicate that the test is a valid instrument for monitoring the performance of female volleyball players.