Bone Abstracts

Background: Mechanical stimulation is thought to be critical for bone anabolic activity. It is unclear how quickly the growing skeleton responds to additional externally-applied mechanical stimuli. We wished to determine the acute effect of a standardised mechanical stimulus to the growing skeleton.

Objectives: To determine the acute time course and magnitude of bone’s response to whole body vibration (WBV) in pre-pubertal boys.

Methodology: Healthy boys aged 9–12 years were recruited to stand on either the Juvent 1000 (low magnitude, high frequency) or Galileo Advanced (high magnitude, variable frequency) vibrating platforms for 1, 3 or 5 days for 10 min (n=36). A control group (n=15) stood on a non-vibrating platform. Pre- and 10 min post vibration blood samples were taken to measure changes in bone formation (P1NP, osteocalcin), bone resorption (CTx) and the bone derived factors osteoprotegerin and sclerostin. Samples were collected half hourly for 2 h in the control group.

Findings: In the immediate pre to post vibration period P1NP decreased by up to 7.9% and CTx by up to 8.8% in the Juvent and Control groups; no change was seen in the Galileo group. There was no difference in the response between groups across the pre- to post-vibration period. At 8 days, in boys exposed to 5 days of WBV on either platform, there was an increase from baseline in P1NP of 25.1% (P=0.005) and in CTx of 10.9% (P=0.009). There was no intergroup difference. There was no change in osteocalcin. Osteoprotegerin increased by 7.2% at day 8 (P=0.08) possibly explaining the smaller increase in resorption. No change was seen in sclerostin.

Conclusion: In the growing skeleton a short period of mechanical stimulation resulted in increased bone activity, with a greater response in the formation marker P1NP than the resorption marker CTx after 5 days WBV. The lack of change in osteocalcin may reflect the ‘early’ nature of the response measured by P1NP in the bone formation process. Increased formation was not due to repression of sclerostin, nor due solely to increased remodelling/resorption, suggesting that other pathways mediate the acute anabolic response seen here to WBV.

Declaration of funding: K Ward is funded by Medical Research Council Grant Code U105960371.