Critical difference applied to exercise-induced salivary testosterone and cortisol using enzyme-linked immunosorbent assay (ELISA): distinguishing biological from statistical change.
Due to its noninvasive, convenient, and practical nature, salivary testosterone (sal-T) and cortisol (sal-C) are frequently used in a clinical and applied setting. However, few studies report biological and analytical error and even fewer report the 'critical difference' which is the change required before a true biological difference can be claimed. It was hypothesized that (a) exercise would result in a statistically significant change in sal-C and sal-T and (b) the exercise-induced change would be within the critical difference for both salivary hormones. In study 1, we calculated the critical difference of sal-T and sal-C of 18 healthy adult males aged 23.2 ± 3.0 years every 60 min in a seated position over a 12-h period (08:00-20:00 hours [study 1]). As proof-of-concept, sal-C and sal-T was also obtained pre and at 5 and 60 min post a maximal exercise protocols in a separate group of 17 healthy males (aged 20.1 ± 2.8 years [study 2]). The critical difference of sal-T calculated as 90 %. For sal-C, the critical difference was 148 % (study 1). Maximal exercise was associated with a statistically significant (p < 0.05) changes in sal-T and sal-C. However, these changes were all within the critical difference range. Results from this investigation indicate that a large magnitude of change for sal-C and sal-T is required before a biologically significant mean change can be claimed. Studies utilizing sal-T and sal-C should appreciate the critical difference of these measures and assess the biological significance of any statistical changes.
Institute of Clinical Exercise and Health Science, University of the West of Scotland, Hamilton, UK, l.hayes@londonmet.ac.uk.
Lawrence D
LD
Hayes
Nicholas
N
Sculthorpe
John D
JD
Young
Julien S
JS
Baker
Fergal M
FM
Grace
D000293:Adolescent; D000328:Adult; D018592:Cross-Over Studies; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D006854:Hydrocortisone / Q000378:metabolism*; D008297:Male; D055070:Resistance Training; D012420:Running / Q000502:physiology*; D012463:Saliva / Q000378:metabolism*; D013739:Testosterone / Q000378:metabolism*; D055815:Young Adult
D013739:Testosterone; D006854:Hydrocortisone