The purpose of this study was to investigate the relationship between towing force during tethered swimming with different high-intensity interval training (HIIT) protocols using an elastic cord and front crawl swimming velocity, and to suggest the use of towing force parameters based on the results. Ten college male competitive swimmers participated in the experiments, which involved towing force measurements during front crawl swimming using 3 protocols of HIIT and time trials over 25m, 50m, 100m, and 200m. The 3 HIIT protocols were 8 sets of tethered 20s trials with 10s rest time intervals (“TABATA protocol”, 20―10s protocol), 8 sets of tethered 8s trials with 12s rest time intervals (8―12s protocol), and 2 sessions of 5 sets of tethered 5s trials with 10s rest time intervals (5―10s protocol). The swimmers were connected to a load cell using an elastic cord to measure the towing force during tethered swimming. The times taken for the 25m, 50m, 100m, and 200m distances were recorded by counting the number of frames in the video footages. The critical speed (CS) was calculated using a regression formula from the distances and the times required for the time trials. Simple linear regression analyses were performed to investigate the relationship between the towing force and mean velocity from the front crawl time-trials. The maximum towing force during all of the HIIT protocols was significantly correlated with the mean velocity for all distances and CS, and the regression formula was significant (p<0.05). Mean towing force during all of the HIIT protocols was significantly correlated with the mean velocity for 200m and CS, and the regression formula was significant (p<0.05). Logarithmic approximation of the time-force curves (peak and mean forces in each set) during HIIT was valid, and the y-intercept (towing force) of the approximation formula were significantly and negatively correlated with the mean velocity for all distances (25―200m and CS) and all HIIT protocols, the regression formula also being significant (p<0.05). From the viewpoint of feedback, the mean towing force during HIIT was useful for evaluating the workout effort during HIIT during tethered swimming using an elastic cord. The Y-intercept of the approximation formula from the maximal or mean forces during HIIT was best for evaluating the workout effort, although arithmetic processing of the logarithmic approximation will be required.