Any board may provide by the resolution authorizing the issuance of the bonds or in the trust indenture hereinafter referred to, that additional bonds may thereafter be authorized and issued at one time, or from time to time, under such limitations and restrictions as may be set forth in said resolution or trust indenture, for the purpose of extending or improving such athletic establishments when deemed necessary in the public interest, such additional bonds to be secured and be payable from the revenues of the athletic establishment, as provided in section eight of this article.