## 4 Discussion
Although some of the error in the skinfold technique can be due to poor technical skill, this was not the case in the current data set, as the lead researcher was ISAK Level 3 with over 15 years of experience in completing skinfold measures. The larger measurements achieved with the skinfold technique are likely a result of skinfold measuring a slightly different aspect of surface anatomy to ultrasound and DEXA. When a skinfold is raised, it includes a double layer of the dermis, and may also include more than a single layer of adipose. Furthermore, using skinfold callipers to assess adipose tissue can present difficulties when examining the separation of muscle and fat [21]. Ultrasound, when used correctly, may give a more valid measure of the adipose tissue depth alone. [PERSON] et al. [22] outlined the importance of the adipose being uncompressed, with a significantly less-accurate measurement recorded when the ultrasound probe exerted any pressure on the skin. The previous authors also noted that due to the nature of the skinfold calliper measurement, compression of the adipose tissue cannot be avoided. The larger difference between the two techniques on the front thigh location may also be a result of slightly different body positions during the measurement. ISAK [17] stipulates that when a skinfold measurement is taken at the front thigh site, the participant should be seated with their back upright and leg straight. The quadricep muscles are relaxed to allow for easier pick up of the skinfold. In the present study, ultrasound images were taken with participant stood up with their feet shoulder-width apart. Although participants were instructed to relax, there is likely to be an element of error included in this comparison from the different body positions. Previous comparisons of skinfold and ultrasound techniques have used mixed-sex or female-only populations [21; 22; 27], and despite often demonstrating a strong linear relationship between the techniques have consistently shown skinfolds to be higher. However, acknowledgement of the difference in compressibility between male and female adipose tissue [23] indicates that the exact nature of the relationship between skinfolds and ultrasound measures needs to be established in a sex-specific manner. This study provides indication of this relationship for the untrained male population. In conclusion, skinfold and ultrasound measurement techniques demonstrate significant, strong correlations that indicate a linear relationship between the two measures. Caution should be exercised when assessing those with higher adipose deposits due to some discrepancy from the linear trend when measures are high. Despite this, skinfolds measure consistently higher than ultrasound and so the exact nature of the relationship should be established on a population basis before using either technique as a surrogate for the other. Conceptualization, H.R.-S., S.J., A.O. ; methodology, H.R.-S., A.O. ; software, H.R.-S., A.O. ; validation, H.R.-S., J.F., A.O., S.J. ; formal analysis, A.O., H.R.-S., E.P., J.F., S.J. ; investigation, H.R.-S., E.P. ; resources, H.R.-S., E.P. ; data curation, H.R.-S., A.O. ; writing--original draft preparation, H.R.-S. and A.O. ; writing--review and editing, J.F., E.P. and S.J. ; visualization, H.R.-S.; supervision, J.F. and S.J. ; project administration, H.R.-S. and E.P. All authors have read and agreed to the published version of the manuscript. This research received no external funding. The study was conducted according to the guidelines of the Declaration of Helsinki, and was approved by the Institutional Ethics Committee of University of Winchester (protocol code BLS/11/15 and 06/11/2015). Informed Consent Statement: Informed consent was obtained from all subjects involved in the study. The data presented in this study are available on request from the corresponding author. The data are not publicly available due to original ethical approval and con-sent not allowing for the sharing of data on a public repository.