AIM 1: To determine the acute effects of cold exposure and isometric exercise, on cardiovascular hemodynamics and autonomic regulation. The working hypothesis is that the combination of cold exposure with isometric hand grip (IHG) exercise would evoke a greater acute increase in arterial stiffness, wave reflection, arterial BP and sympathetic activity than cold exposure or IHG alone. In order to test this hypothesis, the investigators will use an environmental chamber at a temperature of 4oC to perform non-invasive measurements of arterial stiffness (carotid-femoral, femoral-ankle, and brachial-ankle pulse wave velocity [PWV]), pulse wave analysis (aortic BP and augmentation index [AIx]) using applanation tonometry of the radial artery. In addition, the investigators will use continuous beat-by-beat digital BP, power spectral analysis of heart rate variability and blood pressure variability, and spontaneous BRS to evaluate autonomic function during cold exposure.