Resumen de Growth-Hormone Responses to Consecutive Exercise Bouts With Ingestion of Carbohydrate Plus Protein

James A. Betts, Keith A. Stokes, Rebecca J. Toone, Clyde Williams

• Endocrine responses to repeated exercise have barely been investigated, and no data are available regarding the mediating influence of nutrition. On 3 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-hr recovery, participants ingested either 0.8 g sucrose · kg�1 · hr�1 with 0.3 g · kg�1 · hr�1 whey-protein isolate (CHO-PRO), 0.8 g sucrose · kg�1 · hr�1 (CHO), or 1.1 g sucrose · kg�1 · hr�1 (CHO-CHO). The latter 2 solutions therefore matched the former for carbohydrate or for available energy, respectively. Serum growth-hormone concentrations increased from 2 ± 1 µg/L to 17 ± 8 µg/L during R1 considered across all treatments (M ± SD; p = .01). Concentrations were similar immediately after R2 irrespective of whether CHO or CHO-CHO was ingested (19 ± 4 µg/L and 19 ± 5 µg/L, respectively), whereas ingestion of CHO-PRO produced an augmented response (31 ± 4 µg/L; p = .05). Growth-hormone-binding protein concentrations were unaffected by R1 but increased similarly across all treatments during R2 (from 414 ± 202 pmol/L to 577 ± 167 pmol/L; p = .01), as was the case for plasma total testosterone (from 9.3 ± 3.3 nmol/L to 14.7 ± 4.6 nmol/L; p = .01). There was an overall treatment effect for serum cortisol (p = .05), with no specific differences at any given time point but lower concentrations immediately after R2 with CHO-PRO (608 ± 133 nmol/L) than with CHO (796 ± 278 nmol/L) or CHO-CHO (838 ± 134 nmol/L). Ingesting carbohydrate with added whey-protein isolate during short-term recovery from 90 min of treadmill running increases the growth-hormone response to a second exhaustive exercise bout of similar duration.