## 2 Materials and Methods and Results
### Phase 4: Live Trials
#### 2.3.1 Individual Scrum Test Procedures  
Participants were recruited from college and amateur men's and women's rugby clubs. The inclusion criteria were that athletes had to have played rugby for at least 3 months and performed structured resistance training for at least 3 months to help ensure general familiarity with the positions and actions required to perform the tests. Participants were excluded if they had suffered any upper- or lower-body injury that could have affected their performance on either test. Both backs and forwards were included, as the position of an individual scrum represents the same idealized body position all players would want to achieve during a ruck, maul, or tackle. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Comparison**} & **Mean of** & **SD of** & **95\% CI for** & **95\% LOA for** \\  & **Difference (Volts)** & **Difference** & **Mean Difference** & **Differences** \\ \hline Day 1 vs. day 0 & \(-\)0.002 & 0.010 & (\(-\)0.004, 0.000) & (\(-\)0.022, 0.017) \\ Day 7 vs. day 0 & \(-\)0.001 & 0.003 & (\(-\)0.002, \(-\)0.001) & (\(-\)0.006, 0.004) \\ Day 180 vs. day 0 & \(-\)0.001 & 0.004 & (\(-\)0.002, 0.000) & (\(-\)0.009, 0.008) \\ Day 7 vs. day 1 & 0.001 & 0.008 & (\(-\)0.001, 0.003) & (\(-\)0.015, 0.016) \\ Day 180 vs. day 1 & 0.001 & 0.007 & (\(-\)0.000, 0.003) & (\(-\)0.012, 0.015) \\ Day 180 vs. day 7 & 0.001 & 0.003 & (\(-\)0.000, 0.001) & (\(-\)0.005, 0.006) \\ \hline \hline \end{tabular} Notes: SD = standard deviation; CI = confidence interval.  
\end{table} 
Table 1: Bland–Altman analyses between all paired days among days 0, 1, 7, and 180. Figure 7: Bland–Altman plots of day-to-day reliability. We marked the 2 pads that were used throughout the experiment with lines to indicate heights from the floor (the bottom of the pad started at 42 cm from the floor and the top of the pad ended at 89 cm from the floor). The scrum machine was set on top of a section of artificial turf we purchased, and the back edge was placed against the wall so that it could not move. We loaded over 250 kg in weight plates near the front of the sled and had research assistants stand on the sled to keep the sled from tilting up while the participants pushed. Because of the less-than-ideal traction of the artificial turf at maximal exertion, we slid a wood 2 \(\times\) 4 under the turf to provide foot support for the participants' cleats. A pair of 45.45 kg dumbbells were set behind the 2 \(\times\) 4, over the turf, to hold it in place and keep it from sliding back. Assessments were conducted through the off- and pre-season, but not during the competitive season, to reduce the interference due to fatigue on the athletes during testing. All assessments were conducted in a single session. Athletes reported to the Exercise Physiology lab with their cleats and the shoes they normally perform resistance training in. After providing informed consent and pre-assessment screening for injuries and experience, athletes had their height measured barefoot using a Seca 213 stadiometer (Seca, Chino, CA, USA). Next, body mass was measured using a Tanita BF-350 Total Body Composition Analyzer (Tanita Corporation, Tokyo, Japan). Then, the athletes put their cleats on and had their height measured in cleats for use in setting their scrum position. We calculated 40% of their height in cleats and marked the pads of the scrum machine at this height [21]. Athletes were positioned so their shoulders were aligned at this height marking. They then assumed a scrum position with their feet placed far enough back so that their knees were at a 120 \(\pm\) 5-degree angle (confirmed by a goniometer) while keeping their spine visually parallel to the floor. This angle was chosen because it represents the body position for maximal force production in an individual scrum [21] and minimizes the forces that would be generated vertically against the pads (only forces aligned with the load-cell axis can be measured).