1. Our aim was to determine whether the vasodilating substance nitric oxide (NO) contributes to the rise in forearm blood flow observed during mental stress in humans. We also determined whether the NO might be released as a result of cholinergic stimulation of the vascular endothelium. 2. Blood flow was measured in both forearms using plethysmography during several 3‐5 min bouts of a colour word test. In one forearm the nitric oxide synthase blocker NG‐monomethyl‐L‐arginine (L‐NMMA) and other drugs were infused via a brachial artery catheter. The contralateral forearm served as a control. 3. When L‐NMMA was given prior to mental stress it blunted the rise in blood flow in the treated forearm almost completely. The normal blood flow response returned during a second bout of stress conducted after a wash‐out period. During a third bout of mental stress, administration of more L‐NMMA again blunted the blood flow responses to mental stress. 4. When atropine was given prior to mental stress, the increases in blood flow were reduced in the treated forearm. Subsequent administration of both atropine and L‐NMMA caused a somewhat greater reduction in the blood flow responses than those observed with atropine alone. 5. These data demonstrate that NO plays a role in forearm vasodilatation during mental stress in humans. It is likely that most of the NO is released by cholinergic stimulation of the vascular endothelium.

All methods were sensitive to variation in both the rate of EE and the duration over which activity was monitored. Accelerometry and PAR are useful methods for categorizing EE in epidemiologic studies among pregnant women but absolute estimates are biased relative to HR.

A woman's HR, VO2, and the relationship between these two parameters are altered during pregnancy. Change in slope of HR/VO2 regression curves indicates less energy expenditure at a given HR as pregnancy progresses, compared with postpartum conditions. A woman's true energy expenditure would be overestimated at rest, and underestimated during physical activity, if these physiological changes are not taken into account.