The purpose of this study was to determine (1) the relationship between the flexibility of the waist muscles to the ability to cut back surfing, (2) the relationship between the ability of leg muscle strength to the ability to cut back surfing, and (3) the joint relationship between the flexibility of the waist muscles and leg muscle strength on the ability to cut back surfing. This research is a multiple relationship research with test and measurement methods. The population was taken from the canggu surf community club, which amounted to 20 people. The data are the results of waist muscle flexibility, leg muscle strength and the ability to cut back. The data obtained were tested using the SPSS 16 computer program. The sample used was the "population study" technique, which used the entire population to be directly sampled. The instrument in this study was to use tests and measurements of waist muscle flexibility, leg muscle strength, and the ability to cut back surfing. The research data uses the product moment relationship and multiple relationships. The results of data analysis obtained (1) the magnitude of the relationship between the correlation of waist muscle flexibility to the ability to cut back surfing r count of 0.604 > r table 0.444, (2) the magnitude of the relationship between leg muscle strength and surfing cut back ability r count of 0.614 > the value of r table 0.444, and (3) The magnitude of the joint relationship between waist muscle flexibility and leg muscle strength on the ability to cut back surfing is 0.620 and the value of f change is 0.016 <0.05. So it can be concluded that: 1). There is a significant relationship between the flexibility of the waist muscles with the ability to cut back surfing, 2). There is a significant relationship between leg muscle strength and the ability to cut back surfing, 3). There is a relationship between the flexibility of the waist muscles and the strength of the leg muscles on the ability to cut back surfing.