## 4 Discussion
### Asymmetry  
There was less upper limb symmetry for the CES test, which involves an asynchronous movement. The method involved comparing the left and right average cycles at each degree, which may have led to a higher measurement of asymmetry. Additionally, during cranking, the subject activates the rotator muscles in their trunk, which may contribute to the motion. Therefore, the asymmetry measured on the cranks is the result of the force generated by the upper limb coupled with trunk rotation, as well as the asymmetry of the subject's supports at the seat and footrest, which may allow for effective force transmission previously observed by [PERSON] et al., in 2008 [36]. In their study, [PERSON] et al. found greater upper limb asymmetry during asynchronous arm cranking compared to synchronous arm cranking in able-bodied participants. It would be interesting to extend these findings to wheelchair users and compare the upper limb asymmetry between different arm cranking configurations. Specifically, examining the upper limb asymmetry in wheelchair users during synchronous arm cranking could provide insights into whether the _ISI_ values align more closely with those observed during the HBP and SP tests. Conversely, the asymmetry on the field (SP) was lower than in other tests. One explanation for this limitation is that, in the absence of a force sensor, we used the data from the right and left wheel speeds to measure asymmetry at the start, middle, and end of the sprint. These variables may potentially be less representative than force data for expressing asymmetry during propulsion. The second way to explain this lower asymmetry on the field is the athlete's maneuverability. Indeed, the athlete seeks to move in a straight line and compensates for potential asymmetry with their technique to avoid any steering movements, which is accentuated by the large camber angle of sports wheelchairs. It would be interesting to test propulsion asymmetry on the field without trajectory management. Therefore, we can assume that upper limb asymmetry is better represented by the ballistic ergometer test (HBP), while the functional asymmetry measured on the crank ergometer represents differences between the upper limbs and the trunk's rotator muscles. The asymmetry measured on the field demonstrates the athlete's ability to avoid parasitic movements to optimize their straight-line movement.  
The instantaneous Symmetry Index was measured at different resistance levels. For the HBP, the load moved during the push varied in mass between trials. For CES, the electromagnetic resistance of the ergometer's motor varied between trials. For SP, the force generated during propulsion was at its maximum at the start and decreased throughout the sprint as the speed increased. Therefore, it was interesting to observe whether symmetry evolved with the different resistances. No significant decrease in symmetry with an increase in resistance was observed for HBP and SP, and conversely for CES with a significant difference between the trial with less resistance and the trial with the maximum resistance. However, the trend of less symmetry for the SP test during start-up, with maximum resistance, was reported according to the result of the study of [PERSON] et al. in 2015, which observed a decrease in symmetry under more strenuous conditions [37].  
In addition to the different orders of magnitude of asymmetries and variations between resistances that were not the same across the three tests, the authors observed no correlation between the asymmetries of the different tools. Therefore, the functional asymmetry of the upper limbs during wheelchair propulsion cannot be studied using a crank ergometer or a ballistic ergometer. The specific gestures imposed by CES, HBP, and SP may have an impact on the differences in functional asymmetry.