## 4 Discussion
For example, PDCI participants spent about 47% of their exercise session time at or above VT2 and 64% at or above 85% HRmax obtained from the CPET. PD non-CI participants spent 54.5% and 76% of their session time at or above these intensity levels, respectively. The HR at VT2 represented approximately 90% of participants' HRmax. [PERSON] et al. [9] used a similar protocol to our study, consisting of 4-minute intervals (45 s of exercise on a double-concentric resistance machine followed by 15 s of rest), interspersed with 3.5 min of recovery. They reported that their PD group (H&Y I-III) achieved high intensity (\(\geq\)85% of HRmax) during 67% to 84% of their repetitions. This result is comparable to our PD non-CI group (76%), but higher than the PDCI group (64%). [PERSON] et al. [9] found a significant improvement in VO2 peak following the intervention and concluded that HIIT is feasible for people with PD and promising for improving aerobic capacity in this population. In the current study, VO2 avg and %VO2 peak per round were significantly lower in both PD groups than in controls. While this difference can be partially explained by the presence of CI in the PDCI group, this does not expand to the PD non-CI group. Blunted HR in the PDCI group reduces cardiac output, which could significantly impact oxygen consumption [31; 32; 54; 59; 35]. Mitochondria dysfunction is another potential factor associated with reduced oxygen consumption in people with PD, which can reduce the arterio-venous oxygen difference by impairing the efficiency of oxygen extraction from the blood [6; 54; 60; 61]. Despite having a lower metabolic response per round, people with PD exercised at approximately 72% (PDCI) and 80% (PD non-CI) of their VO2 peak, which, although lower than the control group (92%), is still higher than amateur boxers, who achieved around 66% VO2 peak during pad work [4]. The difference in VO2 estimation methods, training protocols, participants' fitness levels, and training specificity may explain the variations in %VO2 peak observed between the two studies [4; 6; 58]. For example, our study collected metabolic data continuously throughout the boxing sessions, and combinations were not paced. In contrast, amateur boxers in the study by [PERSON] and [PERSON] (4) were paced at a cadence of 180 beats per minute, with metabolic data collected only after the cessation of the final round. The EE was significantly lower between the PDCI group and controls for session one, with a similar significant trend in session two. These findings suggest that PDCI participants may need to increase their training volume to meet the ACSM guideline of 1000 Kcal per week for health benefits and improvement in aerobic capacity [6]. Training volume adjustments may help compensate for the reduced energy expenditure of the PDCI participants, which was approximately 40 to 50 Kcal per session compared to the PD non-CI group and controls. Participants from our study exercised for approximately 18 min (4 rounds of 4 min 30 s each), in which the EE per session was approximately 200 Kcal in the PDCI group, 234 Kcal in the PD non-CI group, and 257 kcal in controls. To achieve the ACSM recommendation, people with PD with CI would need to exercise for 90 min per week (11.11 kcal/per min), while people with PD without CI would need 77 min per week (13 kcal/per min), and controls 70 min per week (14.27 kcal/per min). The EE of our participants was similar to that of young males and females (9.8 and 11.2 Kcal/min), punching for 2 min during a six rounds of boxing [62]. The PDCI group displayed a significantly higher RPE than the PD non-CI and control groups in the later rounds of session two. The mean RPE for the PDCI group in rounds 3 and 4 was 18.2 and 18.4, which coincided with the higher percentage of time spent above 85% of HRmax in these rounds 2 (Table 4). [PERSON] et al. (50) reported an RPE of around 13-16 during their 12-week boxing exercise program, which is lower than in our study.