## 3 Discussion
However, to account for individual-cell differences in load cells that showed some variance, we conservatively decided on a 30 min warm-up period as sufficient for the whole machine during use in human trials. Among the human participants, we were surprised to not find evidence of a learning effect in the first two to three maximal-effort trials. It is possible that in the four warm-up trials given, the participants had sufficiently familiarized themselves with the machine. The participants in this study had to have played rugby for at least 3 months, and on average most had played 2 years, so between their general familiarity with the scrum position and pushing in a horizontal contact position as well as having performed the warm-up trials, any learning effect may have been minimal and/or not captured in the 100%-effort trials for data collection. We also did not detect any fatigue effect after five trials. Following a systematic review of the literature, we found that taking at least 1 min of rest would provide enough recovery to avoid fatigue across 5 trials [3]; thus, by giving the participants 2 min of rest, we may have avoided causing fatigue that would limit peak or average performance during individual scrummaging. Only one other study has reported on the calibration of a scrum ergometer [26]. Similarly to our study, that study used S-type load cells. However, [PERSON] and colleagues [26] constructed a frame that provided a square pad that the players put their heads through the middle of. [PERSON] and colleagues then placed one S-type load cell behind each corner of the square pad. Their design of their ergometer apparatus only allows for one player to be tested at a time, rather than the full team, as our design ultimately allows. In their deadweight calibration procedures, [PERSON] et al. [26] also found a 99.99% reliability in the load-voltage relationship. However, [PERSON] et al. [26] only provided two trials of human participants and did not report inter-trial reliability. Comparing our results against studies focused on fatigue during repeated scrum trials, we saw no evidence of fatigue across the five trials, whereas other studies found that players fatigued after three repetitions [11; 22]. However, most of the prior studies used only 15-40 s of rest between trials. One study performed pilot testing among international-level French players and found good reliability (ICC = 0.8) across 3 trials separated by 6 min rest [11]. Therefore, we can conclude that when 2 or more minutes of rest is given between trials, peak and average performance will remain reliable for 3 to 5 trials, whereas with 40 s or less of rest, reliability could decrease after 2 or 3 trials as a result of fatigue. What has not yet been demonstrated in any research is the reliability of full-pack scrummaging. Furthermore, research needs to determine reliability for different playing levels--it seems logical that more advanced players may have better reliability than novice and younger players. The strengths of this research include having multiple phases of testing, with the results of each stage directly informing the design and research questions of the next phase. Additionally, a strength was including both male and female rugby players in the human trials to make the results more generalizable across the sexes. There are three primary limitations to this set of studies. The first is the direction of loading in the deadweight calibration; load cells were calibrated with their compression axis pointed vertically in order to set the weight plates on top. However, for use on the scrum machine, the load cells will be mounted horizontally, and players can create shear forces, thus lessening the amount of force produced by the players that is captured by the load cells.