## 4 Discussion
### Comparison of the Multi-Segment Linear Regression Method with Stage Durations of 12 s and 60 s  
To date, the multi-segment linear regression method had only been tested during an incremental test with 12 s stage durations [6], and the applicability of this algorithm to incremental protocols with longer stage durations (one or two minutes) remained to be verified. Indeed, the 12 s stage test employed by [PERSON] et al. resembles a ramp-like protocol, in which muscular effort is continuously increased to cope with the quick increases in workload. Such test differs noticeably from the graded steady state protocol employed here, where subjects were asked to maintain a fixed power output for 1 min. Based on this, it was predicted that the development of fatigue, the pattern of motor unit recruitment, and/or the sensation of muscular effort may be different in protocols with 12 s and 60 s stage durations, and that this may result in differences in the detection of EMG thresholds and in the % of VO2 MAX at which the EMG thresholds are reached. Interestingly, we found that the two breakpoints encountered, EMGT1 and EMGT2, occurred at higher percentages of VO2 MAX (around 70%-80% and 90%-95% of VO2 MAX, respectively), as compared to those found during the 12-s stage protocol (around 60%-70% and 80-90% of VO2 MAX, respectively). One possible explanation for these differences may be that, during exercise periods of longer duration, adjustments in motor unit rate coding may \"delay\" the recruitment of a significant number of motor units to higher relative intensities of exercise. Specifically, it may be that, with longer stage durations, exercise intensity is maintained at the expense of changes in motor unit discharge rate and/or synchronization and less so due to recruitment of additional motor units [27]. Due to this, great recruitment of additional motor units would be \"delayed/postponed\" until higher relative intensities of effort are reached, which explains why EMG thresholds occur at higher percentages of VO2 MAX. Alternatively, it might be hypothesized that, with longer stage durations, the sensation of muscular effort appears at higher relative intensities, and thus the signal that triggers the increases in neural activity occurs at a higher percentage of VO2 MAX [26].  
It is also worth noting that, with the 60 s stage duration protocol, we detected the first EMG breakpoint in 75% of participants, whereas, with the 12-s stage duration protocol, the first breakpoint was identified in 90% of subjects by [PERSON] et al. [6]. This small discrepancy may be attributed to slight differences in the development of fatigue in these protocols. Indeed, it is possible that, with the 60 s stage test, the sensation of muscular effort/fatigue increased gradually at the beginning and middle of the exercise, but increased more steeply towards the end of the test. Such progression of fatigue would lead to a EMG time course in which the first breakpoint is not so well marked (for an example, see Figure 1 of [PERSON] et al. [28]). In contrast, it is likely that, with the 12 s stage test, fatigue increased more progressively, thus resulting in an EMG time course in which two breakpoints are more easily recognized.