## 4 Discussion  
The aim of this present study was to determine the relationship between skinfold measures of subcutaneous adipose tissue and ultrasound imaging techniques at three skinfold sites (biceps, triceps and front thigh). At all three skinfold sites, a significant, strong, positive correlation was observed. However, the mean difference between the two techniques differed significantly from zero for all three sites, with the skinfold technique producing higher values than the ultrasound images, and so caution needs to be exercised in directly comparing skinfold measures to ultrasound measures of adipose tissue. The significant, strong, positive correlations for all sites found in the current study are slightly lower than those found in various locations on the anterior thigh (r = 0.90-0.93) in mixed-sex healthy adults [21], and are similar to that for the front thigh (r = 0.86) in mixed-sex junior rowers [28], both with the knee flexed to 90\({}^{\circ}\). The addition of females into the population group and the use of non-ISAK specific measurement sites may account for the differences to the results from the current study. In fact, it has previously been suggested that ISAK measurement sites do not fulfil the criteria for noncompressed ultrasound measurements and so may result in inaccuracy in the ultrasound measurements in the current data set [26]. Appropriate technique is important to acknowledge, since previous technique comparison that failed to indicate standardization of technique has demonstrated inconsistent linear relationships on various sites in normal and overweight military personnel [29]. Nonetheless, the current research demonstrates a significant linear relationship between the two measurement techniques in a healthy, untrained, male population. Figure 1 indicates that as values of adipose tissue get larger, the relationship between skinfold and ultrasound measurement becomes less obvious (more points further away from the linear trendline). The occurrence of more outliers being associated with greater adipose tissue values was also observed in skinfold-ultrasound comparison studies looking at the triceps skinfold site (r = 0.72) by [PERSON] et al. [30] and various anterior thigh sites in mixed-sex healthy adults [21]. When measuring larger adipose tissue thicknesses, results may be limited by the skinfold exceeding the width of the calliper [31]. The calliper may just fit around the skinfold but with difficulty, altering the method of measurement. On larger skinfold measurements, the callipers may slip off the skinfold slightly, recording an inaccurate measurement [32]. When adipose tissue is thicker, the ultrasound waves lose more energy through absorption, reflection and scattering by attenuation [33]. In ultrasound studies involving adipose tissue (both visceral and subcutaneous), ultrasound wave beams were attenuated more in the thicker tissue due to the beam having to travel further [34]. Due to potential errors in measurement via both techniques, care should be taken when interpreting larger adipose tissue thickness from skinfolds and from ultrasound measures. Despite the significant, strong, positive correlations demonstrated in the current study, there was significant variance between skinfold and ultrasound measurement at all three sites. Specifically, the skinfold measurements were consistently larger than ultrasound measures at all three sites. The discrepancy between the two techniques appears to be further exacerbated when adipose tissue is larger, as shown by the bigger difference between skinfolds and ultrasound measures as the measures get larger in Table 1. This observation is consistent with previous research [21]. Comparison of both ultrasound and skinfold techniques to regional measures from dual-energy X-ray absorptiometry (DEXA) has indicated that ultrasound demonstrates a stronger relationship with DEXA than skinfolds [35].