Maternal exercise during pregnancy affects the rat musculoskeletal system and indices of energy metabolism : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Science at Massey University, Manawatū, New Zealand
The developmental origins of health and disease hypothesis postulates that
environmental cues perceived by the developing organism during early life program long-term health
outcomes. A series of studies were undertaken to examine the developmental programming effects of
maternal exercise during pregnancy on offspring musculoskeletal health and energy metabolism using
a rat model. Firstly, an exercise
that did not cause a potentially confounding stress response in the exercising animal was
identified. Secondly, pregnant dams then performed this exercise and its effects on fetal growth
and the maternal stress response were quantified. Finally, the offspring of dams that exercised
throughout pregnancy were allowed to grow to maturity, and the effects
of maternal exercise on their musculoskeletal health and energy metabolism were assessed.
Throughout these experiments, body composition was assessed by dual- energy X-ray absorptiometry,
and tibial parameters were measured using peripheral quantitative computed tomography. Maternal
stress was quantified by measurement of faecal corticoid metabolites. Serum concentrations of the
fully and undercarboxylated forms of the bone-derived hormone osteocalcin, and expression of genes
related to osteocalcin carboxylation, were measured to explore their role in the response of
offspring bone and energy metabolism to maternal exercise.
Two exercise types, rising to an erect bipedal stance and tower climbing, were initially tested in
non-pregnant rats. Both rapidly caused changes in the tibias of exercised animals without inducing
stress. In pregnant rats, both exercises increased fetal growth relative to controls, and neither
caused a physiological stress response in
the dams. Since rising to an erect bipedal stance had the greater effect on fetal growth, it was
selected for use in the final study in which the offspring were grown to maturity. Maternal
exercise throughout pregnancy was associated with sex-dependent changes in
the bone and body composition of the mature offspring. Male offspring of exercised dams had
increased adiposity and serum undercarboxylated osteocalcin concentrations, while offspring of both
genders had lower volumetric bone mineral density at the tibial diaphysis, relative to controls.
These results suggest that maternal exercise has long- term effects on the musculoskeletal system
and energy metabolism, and that undercarboxylated osteocalcin may play a role in these effects.