## 4 Discussion  
To our knowledge, this is the first study to demonstrate that boxing is a high-intensity exercise for people with PD with and without CI, based on individualized physiological profiles. Our results showed that the threshold for high-intensity exercise was attained despite the effect of CI on HR and metabolic outcomes during two boxing sessions. CI did not significantly lower the amount of time spent exercising at and above high-intensity threshold zones between PD groups, even though PDCI participants perceived that they were exercising harder than controls and PD non-CI participants. The study results also highlight that age-predicted equations underestimate exercise intensity in PDCI participants and should be used with caution. When exercise intensity was calculated using [PERSON]'s equation to estimate HRmax [6], the PDCI group exercised at approximately 74% MA-PHR (moderate intensity) during boxing rounds. By comparison, PD non-CI participants trained at 93% and controls at 99% MA-PHR, respectively, representing a high-intensity training zone [55,56]. However, when the HRmax obtained from the CPET was used to calculate exercise intensity, all groups reached 90-105% of their individualized HRmax. These results highlight that age-predicted equations underestimate exercise intensity in the PDCI group and should be used with caution. Exercise intensity in our study was higher than that reported for elite male and female athletes who exercise at approximately 80 to 95% of their individualized HRmax when sparring, simulating boxing matches, or training on boxing bags or focus pads [4,7,57]. The higher %HRmax achieved in our study compared to professional boxers may be due to the format of rounds, participants' fitness levels, and training specificity [6,58]. From a clinical perspective, our findings show that boxing is a high-intensity activity for PD with and without CI. Most boxing interventions in people with PD provide little information on exercise intensity and only include boxing as a portion of their exercise intervention [1,3,15,16,18,19,20,21,55]. To the best of our knowledge, only one study has investigated HR responses during boxing in people with PD [50]. In a feasibility study, [PERSON] and colleagues included ten participants with PD in the early disease stage (H&Y I-II) during a 12-week boxing training program split into three training blocks of 4 weeks each [50]. Participants achieved the target exercise intensity of \(\geq\)80% of their MA-PHR, which was less than our PD non-CI participants (\(\pm\)93% MA-PHR). Figure 3: Mean (95% confidence intervals) rating of perceived exertion during the first and second boxing sessions. The reasons for this may include an unknown number of participants with CI in their study compared with ours (participants were not categorized according to CI so this cannot be verified), or differences in the boxing protocol. For example, boxing rounds in the [PERSON] et al. study had a duration of 2-3 min each and were increased from six to eleven rounds per session during the 12-week exercise program. The authors used a Fightmaster unit with numbered pads for the boxing protocol, which also involved short bursts of punches (typically uppercuts lasting 10-15 s performed with maximal effort), loud upbeat music, and additional exercises such as star jumps [50]. By contrast, the boxing intervention in our study used equipment (punching bags and pads) typically available in community settings. In our study, the combinations and number of rounds were consistent, and although participants were asked to punch as fast and hard as possible, the punch rate and speed were self-selected. From a practical viewpoint, our data show that self-paced boxing training and standard boxing equipment could be used as an intervention to elicit high-intensity physiological responses in people with PD with and without CI. The results from our study show that the percentage of time spent exercising at high intensity differed according to cutoffs.