## 4 Discussion
### Force Velocity Profile Comparison  
In each of the tests, the measured force and velocity were found to be highly correlated (R\({}^{2}\) = 0.9-0.97), with an observable reduction in the force generated corresponding to an increase in the speed of movement, which is consistent with previously reported findings in the literature regarding the upper limb [16; 18; 33]. This result also means that the method for evaluating strength during a 20 m sprint, used in the present study, makes it possible to obtain an athlete's force-velocity relationship of the physical and technical capacity on the field with non-invasive on-board sensors.  
Figure 3: Box plot (median and quartiles) of Instantaneous Symmetry Index (_ISI_) of upper limb between the three tests (CES HBP and SP) and between the three levels of resistance (0, 50, and 100). The black diamonds represent the average of the variables. CES means crank ergometer sprints test, HBP means horizontal upper limb ballistic push-offs test, and SP means 20 m wheelchair sprint test. Resistance “0” is the minimum resistance imposed during the tests, “50” is the half of max resistance imposed during tests, and “100” is the maximum resistance imposed during tests. “558” represents significant differences (\(p\) < 0.001) between CES and SP test, “_EEE_” represents significant differences (\(p\) < 0.001) between CES and HBP test, “_EEE_” represents significant differences (\(p\) < 0.05) between HBP and SP, “_EEE_” represents significant differences (\(p\) < 0.01) between HBP and SP, and “_μ_” represents significant differences (\(p\) < 0.01) between _ISI_ at different levels of resistance in the same test.  
The maximal theoretical power outputs (P0) are higher for the HBP and CES tests compared to the SP test. This could be explained by the methodology and equipment used, which may underestimate the estimated power output. The sportsmen with their wheelchairs were on a smooth parquet floor which offered a low rolling resistance, which does not allow the athletes the time to develop a lot of force before reaching high velocity. During the SP test, only the power used for propulsion is quantified. Athletes likely produced more power, but this would be lost due to material deformation. Additionally, the athlete's position in their sports wheelchair is not optimal for generating maximum force with their upper limbs [34]. The estimation of resistance forces may also be underestimated. We had no tool to quantify air resistance, and rolling resistance was interpolated from the rolling resistance measured over 5 m at slow speeds [29].  
Force-velocity relationships were more force-oriented on the ballistic ergometer and more velocity-oriented on the field. The F0 of the CES test was between that of the HBP and SP tests. It is possible that the simplicity of the movement, such as athletes pushing in only one direction against a rigid and non-deformable structure, allows for maximum force development by recruiting the maximum number of muscles. The crank motion in the CES test also occurs against a rigid structure, with athletes strapped to their wheelchairs and the wheelchair strapped to the ground. In contrast, the motion involves pushing with one hand and pulling with the other, requiring a certain motor coordination to optimize force development. Athletes were not accustomed to this motion. The force and power developed by athletes may increase with a learning effect on this test.