Author(s): HUBY, M., STAVROPOULOS-KALINOGLOU, A., WILSON, O., BLACK, A., O'HARA, J., Institution: LEEDS BECKETT UNIVERSITY, Country: UNITED KINGDOM, Abstract-ID: 2384

INTRODUCTION:
Murine genetic knockout models support the existence of a peri-exercise muscle-bone axis consisting of a feed-forward regulatory loop, involving skeletal muscle-derived interleukin-6 (IL-6) and bone-derived osteocalcin (OCN). In mice this axis regulates exercise substrate use and is necessary for optimum exercise capacity. Though the IL-6 response to prolonged exercise is well-characterised in humans, the exercise-induced OCN response is ambiguous. Moreover, whether factors that modulate the metabolic response to exercise (e.g., nutrition) affect the muscle-bone axis is unclear, thus, the presence and influence of this axis warrant explication. The present study compared the temporal responses of IL-6 and OCN (in various degrees of carboxylation) to different exercise modes (cycling versus running) with and without exogenous carbohydrate (CHO) ingestion.
METHODS:
In a randomised, double-blind, placebo-controlled, crossover design, ten male trained triathletes (age 31 ± 3 y; body mass 78.8 ± 6.2 kg; stature 182.1 ± 7.8 cm; VO2peak 59.1 ± 6.1 ml/kg/min) completed four, energy-matched, 120 min exercise trials involving treadmill running or cycle ergometer exercise at 70% of running-specific VO2peak with ingestion of either a 12% CHO (2:1 glucose:fructose; 90 g/h) or placebo solution. Venous blood samples were obtained at rest and every 30 min during exercise. Plasma IL-6 and serum carboxylated and decarboxylated OCN concentrations were quantified using enzyme-linked immunosorbent assay (ELISA). The exercise-induced responses of IL-6 and OCN forms were summarised via incremental area under the curve (iAUC) and compared by two-way (mode x CHO) repeated measures ANOVA. Time series outcome data were compared by three-way (mode x CHO x time) repeated measures ANOVA. Statistical significance was accepted at P < 0.05. Data are expressed as mean ± SD.
RESULTS:
For plasma IL-6 concentrations, no mode x CHO x time interaction was detected (P = 0.84) although significant main effects of mode (P = 0.006), CHO (P = 0.014), and a mode x time interaction effect (P = 0.007), were observed. Plasma IL-6 iAUC displayed a significant main effect of mode (P = 0.009) and CHO (P = 0.023) but no mode x CHO interaction whereby the overall plasma IL-6 response was higher in running versus cycling and in placebo versus CHO conditions, respectively. No differences were observed in either the temporal or overall responses (iAUC) of serum carboxylated or uncarboxylated osteocalcin between exercise modes or with/without exogenous CHO ingestion .
CONCLUSION:
These data indicate that when matched for energy expenditure the plasma IL-6 response to running is increased relative to cycle ergometer exercise and that, irrespective of exercise mode, exogenous CHO versus placebo ingestion blunts the exercise-induced IL-6 response. Despite substantial elevations of IL-6, there was no effect of exercise on the circulating concentration of any form of OCN under the conditions of the present study.