Blood pressure status and post-exercise hypotension: an example of a spurious correlation in hypertension research?

A single bout of exercise lowers blood pressure (BP) for up to 24 h afterwards. The magnitude of this post-exercise hypotension (PEH) has been reported to be correlated most strongly to pre-exercise BP, and this apparent relationship has influenced position statements about the value of exercise in arterial hypertension. Nevertheless, this correlation could be adversely affected by mathematical coupling and regression-to-the-mean artefacts. Therefore, we aimed to examine the degree to which BP status moderates PEH while, for the first time, controlling for these statistical artefacts. A total of 32 participants, with pre-exercise mean arterial pressures of 65-110 mm Hg, cycled for 30 min at 70% peak oxygen uptake. Systolic BP and diastolic BP were measured (Portapres) before exercise and for 20 min after exercise. Changes in BP were regressed against pre-exercise values, and against the mean of pre- and post-exercise BP, among other indices that are also known not to be prone to artefacts. Correlations between pre-exercise BP and the exercise-mediated reductions were typical of those previously reported (r=0.37-0.62, P<0.05), but not large enough to rule out spuriousness (P>0.05). Artefact-free indices of BP status (pre- and post-exercise mean as well as an earlier independent measurement) did not correlate with reductions in BP (P>0.05), which were moderated more by peak oxygen uptake and time of day (P<0.05). These data indicate that, if statistical artefacts are not controlled for, the influence of BP status on the degree of PEH can be spuriously exaggerated to the extent that other more important moderators of BP change are masked.