Find Controle Not Displaying Values?

i used the textbox inside the panelbar i used the following codes the find the controle but the value i'm getting is null

foreach (RadPanelItem PanelItem in RadPanelBar1.GetAllItems())
{
RadTextBox txtAge = RadPanelBar1.FindControl("txtAge") as RadTextBox;
RadTextBox txtWeight = RadPanelBar1.FindControl("txtWeight") as RadTextBox;
health.Age = Convert.ToInt32(txtAge.Text);
health.weight = Convert.ToInt32(txtWeight.Text);
}

the value of txtAge and txtWeight is null. how to get the value of the textbox entred in run time.