Limitations
Several limitations may be associated with the present study. First, microneurography was not attempted during the first phase (bedrest), limiting the MSNA analysis. Second, sympathetic outflow included only efferent outflow to skeletal muscle, so these findings may not represent sympathetic outflow to other vascular beds. Third, cardiac output and thus systemic vascular resistance were not assessed, limiting our ability to interpret the hemodynamic results. Finally, instead of randomizing the order of stressors, a serialized order, employed in previously published studies [9, 42], was chosen to minimize the impact of any order effect on pre- and post-intervention comparisons. To minimize carryover effects, the schedule allowed sufficient recovery from the cold pressor to handgrip tests. The fact that baseline and recovery data were not different from one stressor to the next suggests that this strategy was appropriate.