Cardiopulmonary responses to combined rhythmic and isometric exercise in humans

A rhythmic (R) and an isometric (I) exercise were performed separately and in combination to assess their additive effects on arterial systolic (P(as)) and diastolic (P(ad)) blood pressures, heart rate (fc), and minute ventilation (VI). The isometric effort consisted of a 40% maximal voluntary handgrip contraction (MVC) performed for a duration of 80% of a previously determined 40% MVC fatiguing effort. The R effort consisted of a 13-min cycle effort at 75% maximum oxygen consumption (VO2max). For the combined efforts, I was performed starting simultaneously with or ending simultaneously with R. Data on nine subjects yield statistically significant evidence (P less than 0.05) that the effects of I and R are not additive for the following three cases: (1) P(as) when I and R are ended simultaneously (I alone = 4.9, SEM 0.5 kPa increase; R alone = no significant change from steady state; I + R = 1.2, SEM 0.4 kPa increase), (2) P(ad) when I and R are started simultaneously (I alone = 4.1, SEM 0.4 kPa increase; R alone = 0.7, SEM 0.3 kPa decrease; I + R = 1.9, SEM 0.4 kPa increase), and (3) P(ad) when I and R are ended simultaneously (I alone = 4.1, SEM 0.4 kPa increase; R alone = 0.3, SEM 0.5 kPa decrease; I + R = 0.8, SEM 0.3 kPa increase). For all other variables and cases, there is not sufficient evidence to conclude that the effects of I and R are not additive. We conclude that R and I exercises do not invariably produce strictly additive cardiopulmonary responses.(ABSTRACT TRUNCATED AT 250 WORDS)