## 4 Discussion
### Effect of Individualization on the Perceived Realism of a Rowing Simulator (LIAC vs. IND)
#### 4.2.1 Rowing Cycle and Sub-Phases  
The individualization of the model parameters significantly improved the perceived realism of forces in drive, recovery, catch, release, and overall rowing cycle.  
For drive, individualization of \(G_{dl}\) was the key factor for the increased realism of resistive forces in the water. All participants except one were content with the magnitude of resistance, the peak force, and the change of forces in the water (\(\mu_{IND}^{Q5}=8.20\)). One participant reported that he felt constrained by the simulator when he tried to apply high propelling forces. This observation can be attributed to the fact that the rendering of the horizontal forces was also bounded with a safety limit of 450 N in the \(B_{y}\)-axis. For the experiment, rowers were instructed to row with 40-70% of maximum force application and within low to medium stroke rates to assess the general capability of the simulator. Since the participants were not explicitly informed about the safety limit, their expected force peak was not rendered for the rowers who applied higher propelling forces. Therefore, the simulator will be tested in future for a higher force rendering to account for higher propelling forces by the rowers.  
For recovery, individualization of rope tension forces significantly improved the perceived realism of forces (\(\mu_{IND}^{Q6}=8.00\)). Although a setting of 30 N rendered reduced recovery forces, some rowers preferred to experience the slight resistance, referring to the real rowing in a windy weather. Few rowers actually preferred to set even lower values than 30 N for \(\tau_{rec}^{min}\) stating that the residual resistance could still be perceived. However, due to design criteria of a tendon based parallel robot, the ropes must always be under tension to control the end-effector movement. Additionally, the selected value for \(\tau_{rec}^{min}\) should ensure a smooth transition from \(\tau_{rec}^{min}\) to \(\tau_{drive}^{min}\) without causing disruptive tension-force jumps on the ropes. Thus, for control and safety reasons the lowest limit of \(\tau_{rec}^{min}\) was set to 30 N. Nevertheless,the selected value was based on the initial trials on the simulator, and further experiments may yield a safe and less resistive \(\tau_{RC}^{min}\) tension forces on the ropes.  
Overall, individualization of \(\varphi_{bias}\), \(G_{dl}\), and \(C_{Bdrug}\) led to significant improvement in the ratings of catch and release (\(\mu_{IND}^{Q\mathcal{G}}=8.00\), \(\mu_{IND}^{Q\mathcal{G}}=7.80\)). A final setting of \(\varphi_{bias}=0^{\circ}\) was mainly reported to have rendered more realistic vertical forces during blade transition. In addition, four rowers who preferred a higher value of \(C_{Bdrug}\) judged that the increment encountered the previously criticized high decelerating drag forces at the initial and final blade contact with the water. However, other rowers who preferred the same or lower \(C_{Bdrug}\) values notified us that lower braking forces would be preferred. If the rendering of high braking forces at the water entry and exit had been reported in the pilot study, implementation of Froude number and turbulence effects to reduce the drag/lift coefficients might have been a more convenient approach than adjusting \(C_{Bdrug}\).