title: Growth Hormone Responses to Consecutive Exercise Bouts with Ingestion of Carbohydrate plus Protein.
abstract: Endocrine responses to repeated exercise have hardly been investigated and no data are available regarding the mediating influence of nutrition. On three occasions, participants ran for 90 min at 70% VO2max (R1) before a second exhaustive treadmill run at the same intensity (R2; 91.6 ± 17.9 min). During the intervening 4 h recovery, participants ingested either: (i) 0.8 g sucrose·kg-1·h-1 with 0.3 g·kg-1·h-1 whey protein isolate (CHO-PRO); (ii) 0.8 g sucrose·kg-1·h-1 (CHO) or; (iii) 1.1 g sucrose·kg-1·h-1 (CHO-CHO). The latter two solutions therefore matched the former for carbohydrate or for available energy, respectively. Serum growth hormone concentrations increased from 1.7±0.9 μg·l-1 to 16.7±7.8 μg·l-1 during R1 considered across all treatments (means±standard deviations; P≤0.01). Concentrations were similar immediately after R2 irrespective of whether CHO or CHO-CHO was ingested (19±4 μg·l-1 and 19±5μg·l-1, respectively), whereas ingestion of CHO-PRO produced an augmented response (31±4μg·l-1; P≤0.05). Growth hormone binding protein concentrations were unaffected by R1 but increased similarly across all treatments during R2 (414±202 pmol·l-1 to 577±167 pmol·l-1; P≤0.01), as was the case for plasma total testosterone (9.3±3.3 nmol·l-1 to 14.7±4.6 nmol·l-1; P≤0.01). There was an overall treatment effect for serum cortisol (P≤0.05), with no specific differences at any given time-point but lower concentrations immediately after R2 with CHO-PRO (608±133 nmol·l-1) than CHO (796±278 nmol·l-1) or CHO-CHO (838±134 nmol·l-1). Ingesting carbohydrate with added whey protein isolate during short-term recovery from 90 minutes of treadmill running increases the growth hormone response to a second exhaustive exercise bout of similar duration.
authors.affiliation: University of Bath, Human Physiology Research Group, Bath, Avon, U.K.
authors.forename: James A
authors.initials: JA
authors.lastname: Betts
authors.forename: Keith A
authors.initials: KA
authors.lastname: Stokes
authors.forename: Rebecca J
authors.initials: RJ
authors.lastname: Toone
authors.forename: Clyde
authors.initials: C
authors.lastname: Williams