I'm afraid that the nature of your relationship with Virgin is not that of employer/employee, but rather that of an independent contractor, based on the amount of freedom that you have to determine your own working conditions.
However, in case I am wrong, your claim for compensation would be against the Workman's Compensation Fund
of the Department of Labour and in terms of the Compensation for Occupational Injuries and Diseases Act. The claim will be based on injuries sustained while on duty. The claim needs to be submitted by the employer and supported by medical report forms completed by the medical practitioner that examined you and determined when you may return to work. If you have a claim against the WCF, then in terms of the Act, you claim against the employer is excluded.
If you are an independent contractor, which I believe you are, your claim would be based on public liability of the gym, similar to the liability it has to all its customers to provide a safe gym experience and equipment that is in a safe condition to use for the purpose it is intended. A word of warning, though, your contract with Virgin might contain an indemnity clause excluding liability for such incidents. If in doubt, please take your contract to a legal practitioner for advice.
In order to succeed with your claim for damages suffered as a result of using the faulty equipment (assuming you get past the indemnity, which can be done in certain instances), you will have to prove that the gym was negligent in providing the faulty equipment, that you were using the equipment for the purpose it was intended for, that you suffered damages (injuries, medical expenses, loss of income, etc) as a direct consequence of the faulty equipment and the amount of your damages. There are attorney firms that specialise in this type of claim. Some would even represent you on a "no win, no fee" basis. The following websites might be of use in finding such legal representation: www.attorneys.co.za