The use of HRV serves as an objective measurement for
the study. It is an indirect measure of stress through
measuring changes to the autonomic nervous system and
the equilibrium of the sympathetic and parasympathetic
components of the autonomic nervous system [44]. One
understanding of the mechanisms of stress relates to the
neurological interaction of stimuli or stressors on the body
and the related interaction with the autonomic nervous
system [45], thereby causing abnormal autonomic and
cardiovascular responses [46]. Although it is established
there are correlations between stress and the autonomic
nervous system, the results are variable [34] and as such
HRV will only be included as a secondary outcome measure.