Endocrine Responses To Repeated Exercise Bouts With Varied Macronutrient Ingestion During Recovery
James A. Betts1, Keith A. Stokes1, Rebecca J. Toone1, Clyde Williams
Appropriate nutrition is a central component of effective exercise performance and adaptations to physical training, partly due to the mediating influence of various nutrients on
endocrine responses to exercise.
PURPOSE: To examine selected endocrine responses to repeated bouts of exercise with ingestion of carbohydrate alone or a mixture of carbohydrate and protein during an
intervening 4 h recovery.
METHODS: Six healthy men participated in 3 trials, each separated by 7 days and involving a 90 min treadmill run at 70% max (R1) followed by a 4 h recovery, before a
second exhaustive treadmill run at 70% max (R2). At 30 min intervals during recovery, participants ingested a solution containing either 0.8 g sucrose·kg-1·h-1 with 0.3 g·kg-1·h-1
of whey protein isolate (CHO-PRO), 0.8 g sucrose·kg-1·h-1 (CHO) or 1.1 g sucrose·kg-1·h-1 (CHO-CHO). The latter 2 solutions therefore matched the former for carbohydrate
and for available energy, respectively.
RESULTS: Serum concentrations of growth hormone increased from 1.7 ± 0.9 μg·l-1 at baseline to 16.7 ± 7.8 μg·l-1 after R1 across all three treatments (means ± standard
deviations; P 0.01). Similar concentrations were apparent immediately following R2 irrespective of whether CHO or CHO-CHO had been ingested (19.3 ± 3.9 μg·l-1 and 19.2
± 5.4 μg·l-1, respectively), while ingestion of CHO-PRO resulted in significantly higher concentrations than CHO or CHO-CHO at this time-point (30.8 ± 4.0 μg·l-1; P 0.05).
Growth hormone binding protein concentrations were unaffected by R1 but increased significantly across all three treatments during R2 from 414 ± 202 pmol·l-1 to 577 ± 167
pmol·l-1 (P 0.01), with no treatment differences. Analysis of variance revealed an effect of treatment in relation to 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) relative to either CHO (796 ± 278 nmol·l-1) or CHO-CHO (838 ± 134
nmol·l-1). Plasma testosterone concentrations increased during R2 from 9.3 ± 3.3 nmol·l-1 to 14.7 ± 4.6 nmol·l-1 across all three treatments (P 0.01), with no treatment
differences.
CONCLUSION: Ingesting carbohydrate with added whey protein isolate during post-exercise recovery appears to modulate the growth hormone and cortisol responses to a
repeated exercise bout.
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