The influence of age and exercise modality on growth hormone bioactivity in women.
OBJECTIVE
Prior research has indicated that the loss of skeletal muscle mass and bone mineral density observed with aging is related to the prominent age-related decline in the concentration of serum growth hormone (GH). However, there is limited data on the effects of aging on GH responses to acute bouts of heavy resistance exercise (HRE) and aerobic exercise (AE).


METHODS
The present investigation examined the effects of a HRE protocol and an AE protocol on immunoreactive GH (IGH) and bioactive GH (BGH) in active young and old women.


RESULTS
Older women had a diminished serum IGH response to both the HRE and AE protocols compared to the younger women, however a similar response was not observed in serum BGH. Additionally, the HRE protocol elicited a greater BGH response than the AE protocol exclusively in the younger group.


CONCLUSIONS
Regardless of exercise mode, aging induces an increase in growth hormone polymerization that specifically results in a loss of serum growth hormone immunoreactivity without a concurrent loss of serum growth hormone bioactivity. The greater BGH response to the HRE protocol found in the younger group can be attributed to an unknown serum factor of molecular weight between 30 and 55kD that either potentiated growth hormone bioactivity in response to HRE or inhibited growth hormone bioactivity in response to AE.
Department of Kinesiology, The University of North Carolina at Charlotte, Charlotte, NC 28223, USA.
Scott E
SE
Gordon
Human Performance Laboratory, Department of Kinesiology, University of Connecticut, Storrs, CT 06269, USA; Department of Physiology and Neurobiology, University of Connecticut, Storrs, CT 06269, USA. Electronic address: William.Kraemer@uconn.edu.
William J
WJ
Kraemer
Human Performance Laboratory, Department of Kinesiology, University of Connecticut, Storrs, CT 06269, USA.
David P
DP
Looney
Human Performance Laboratory, Department of Kinesiology, University of Connecticut, Storrs, CT 06269, USA.
Shawn D
SD
Flanagan
Human Performance Laboratory, Department of Kinesiology, University of Connecticut, Storrs, CT 06269, USA.
Brett A
BA
Comstock
Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802, USA.
Wesley C
WC
Hymer
D000328:Adult; D000367:Age Factors; D000375:Aging / Q000502:physiology*; D018592:Cross-Over Studies; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005260:Female; D019382:Human Growth Hormone / Q000378:metabolism*; D006801:Humans; D008875:Middle Aged; D020127:Recovery of Function / Q000502:physiology; D055070:Resistance Training; D014891:Weight Lifting / Q000502:physiology; D055815:Young Adult
D019382:Human Growth Hormone
Aging; Bioassay; Immunoreactivity assays; Rat tibial line assay; Resistance exercise