All Of Your Fitness Needs Under One Roof. Onslow Fitness is Jacksonville's only upscale 24/7 Adult Fitness Club committed to enriching your life. We are here to provide a comfortable atmosphere, personalized service and innovative programs. Our team of experienced fitness professionals are dedicated to helping you develop a work that is catered to your specific needs so you can find the best way to get in your best shape! Our services include the following: • Free Child Care • Fitness Coaching • Training Orientation • Personal Training • ActivTrax • Tanning Beds We are also proud to offer group fitness programs featuring Les Mills programs! Call us now and meet our dedicated staff and personal trainers. Let us help you reach your optimal health and fitness goals!