## 4 Discussion  
In this within-subject study design, we examined the effects of upper-limb exercise on experimental pain sensitivity in healthy individuals. We compared the changes in pain sensitivity between two different protocols to control for exercise intensity: one targeted HR (THR protocol), and the other was based on a subjective rating of perceived exertion (BORG protocol). We found that arm aerobic exercise at a moderate-high intensity of 60% \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Variables**} & \multicolumn{4}{c}{**THR Protocol**} & \multicolumn{4}{c}{**BORG Protocol**} \\ \cline{2-7}  & **Rest** & \multicolumn{2}{c}{**Exercise**} & \multicolumn{2}{c}{**Rest**} & \multicolumn{2}{c}{**Exercise**} \\ \cline{2-7}  & **BL** & **Pre** & **Post** & **BL** & **Pre** & **Post** \\  & **Mean** & **Mean** & **Mean** & **Mean** & **Mean** & **Mean** \\  & **(SD)** & **(SD)** & **(SD)** & **(SD)** & **(SD)** & **(SD)** \\ \hline
**PPT** & 369.85 & 363.58 & 371.95 & 372.75 & 362.83 & 374.77 \\
**(kPa)** & (126.56) & (128.63) & (134.09) & (112.23) & (115.31) & (121.58) \\ \hline
**HPT** & 47.21 & 46.98 & 46.94 & 47.47 & 47.36 & 47.23 \\
**(\({}^{\circ}\)C)** & (2.69) & (2.70) & (2.87) & (2.22) & (2.31) & (2.66) \\ \hline
**THP** & 55.22 & 55.05 & 52.81 & 56.83 & 57.10 & 52.99 \\
**(NPS)** & (23.29) & (24.60) & (24.58) & (18.9) & (21.71) & (23.08) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Pain sensitivity measures pre- and post-rest session and pre- and post-exercise in both control intensity protocols. Figure 1: HR, RPE, and Power during the 20 min of exercise for both protocols. HR (left panel), RPE (middle), and power (right panel) variables during the exercise as recorded every 5 min on THR (gray line) and BORG (black line) protocols. * indicated significant differences over time between the protocols \(p<\) 0.05.  
of reserve HR, or of 7 on the 1-10 Borg scale, did not lead to the expected hypoalgesic effects. Specifically, no changes in the PPT, HPT, and pain ratings of THP were identified compared to the resting condition in both protocols. A higher mean HR was found when the THR protocol was applied compared to the BORG protocol, while the RPE was the same. To the best of our knowledge, only a few previous studies have examined the effects of upper-limb aerobic exercise on pain sensitivity. In the study of [PERSON] et al. [13], healthy female participants and fibromyalgia patients performed arm aerobic exercise in two sessions with a 15 min pause between, at a constant power of 60 watt until fatigue. PPT increased in both groups following the exercise, indicating an EIH effect, yet no differences were found in the THP ratings. [PERSON] et al. [13] determined the exercise protocol based on the power, while HR was not monitored. This eliminates comparability to the current study results. However, the fact that the participants continued until exhaustion indicates that a higher effort for a short duration was achieved. This may explain the hypoalgesic effects identified in the [PERSON] study, but not in our study. Another study that examined the hypoalgesic effects of upper-limb aerobic exercise was carried out by [PERSON] et al. [12]. Specifically, they examined the effect of both lower and upper-limb aerobic exercise on toothache threshold induced by electrical stimulation. The 20 min exercise intensity was determined by a HR of 150 beats per minute for all participants. The results revealed that both lower-limb pedaling and arm cranking induced EIH, as expressed by an increase in pain threshold with no differences between the muscles involved. The study defined the pain threshold as an \"unpleasant but not painful sensation\". The different definition of pain threshold that was used in our study, where participants were asked to indicate the onset of pain sensation, may explain the different results between the [PERSON] et al. findings and our study. In addition, the mean HR in our study was 130 bpm, lower than that of the [PERSON] et al.