## 3 Results  
The mean age of male players was 20.6 \(\pm\) 2.1 years for backs and 22.4 \(\pm\) 4.5 years for forwards, whereas for female rugby players it was 21.9 \(\pm\) 4.0 years for backs and 22.1 \(\pm\) 4.4 years for forwards. No differences were observed by sex (\(p\) = 0.661), position (\(p\) = 0.360) or sex-position (\(p\) = 0.442). However, we did detect sex-related differences for height, whereby male players were taller (1.80 \(\pm\) 0.01 vs. 1.64 \(\pm\) 0.01 m, \(p\) = 0.030), and position, whereby forwards were taller (1.76 \(\pm\) 0.10 vs. m, 1.71 \(\pm\) 0.10 \(p\) = 0.030). For weight, we found a statistically significant effect of sex whereby males were heavier than females (90.1 \(\pm\) 1.8 vs. 65.5 \(\pm\) 2.0 kg, \(p\) < 0.001), and this effect was observed in forwards and backs alike (\(p\) < 0.001) (see Table 1). We also observed an effect of position on weight, whereby forwards obtained a higher value than backs (90.0 \(\pm\) 17.0 vs. 69.8 \(\pm\) 13.7 kg, \(p\) < 0.001) in male and female players alike (\(p\) < 0.001). Regarding BMI, we found statistically significant differences according to sex (\(p\) < 0.001) and position (\(p\) < 0.001), whereby males had a higher BMI than female rugby players (27.8 \(\pm\) 0.6 vs. 24.2 \(\pm\) 0.7 kg\(\cdot\)m\({}^{-2}\)), an effect observed in forwards (\(p\) = 0.025) and backs (\(p\) = 0.002) alike, and forwards had a higher BMI than backs (28.9 \(\pm\) 4.3 vs. 23.7 \(\pm\) 3.2 kg\(\cdot\)m\({}^{-2}\), \(p\) < 0.001) in both male (\(p\) = 0.001) and female rugby players (\(p\) < 0.001). Body fat (%) was higher in forwards than in backs, as assessed by anthropometry (20.0 \(\pm\) 6.7 vs. 16.6 \(\pm\) 3.8%, \(p\) = 0.009) and BIA (22.6 \(\pm\) 9.7 vs. 17.3 \(\pm\) 7.3%, \(p\) = 0.019). However, anthropometry detected statistically significant differences according to position in females (\(p\) = 0.030), differences that were not identified by BIA in either male (\(p\) = 0.063) or female rugby players (\(p\) = 0.141) (see Table 2). By sex, no differences in body fat were identified by BIA (\(p\) = 0.203), but anthropometry detected higher values for female rugby players (21.1 \(\pm\) 1.1 vs. 16.3 \(\pm\) 0.9%, \(p\) = 0.001) in backs (\(p\) = 0.001) but not forwards (\(p\) = 0.098). Regarding lean body mass (%), no differences were observed when comparing forwards and backs by either anthropometry (\(p\) = 0.748) or BIA (\(p\) = 0.145). Anthropometry did not identify differences in lean body mass in either sex (\(p\) = 0.059), whereas BIA detected higher lean body mass in male players (46.8 \(\pm\) 1.7 vs. 37.3 \(\pm\) 1.9%, \(p\) < 0.001) in both forwards (\(p\) = 0.046) and backs (\(p\) = 0.001). Table 3 shows the results for skinfolds. In a comparison of players according to sex, we observed differences in triceps, abdominal, front thigh and medial calf skinfolds. Abdominal skinfold values were higher in male than female rugby players (\(p\) = 0.002), in forwards (\(p\) = 0.032) and backs (\(p\) = 0.023) alike. Females obtained higher tricipital skinfold values than male rugby players (18.4 \(\pm\) 1.3 vs. 14.6 \(\pm\) 1.1 mm, \(p\) = 0.029), with statistically significant differences (\(p\) = 0.002). The results of the experiments are summarized in Table 4.