The Effect of Upright Lower Body Negative Pressure on Muscle Activity and Hemodynamics during Exercise

Purpose: The aim of the study was to evaluate the changes that occur in parameters relating to muscle work and muscle hemodynamicsunder the influence of upright Lower Body Negative Pressure (LBNP) application during walking. Methods: 18 young females were included in this study. All 18 subjects participated in 2 trials of a 12-minute walking exercise on a treadmill equipped with a LBNP chamber, on a constant speed of 5 km/h. The first trial was executed under the application of a LBNP program (3 stages of -15, -25 and -30 mbar), while the second trial was similar, but without the activation of the negative pressure chamber. During both trials, the Vastus Lateralis (VL) muscle hemodynamic conditions were monitored continuously with a Functional Near-Infrared Spectroscopy (fNIRS) device and parallelly, VL activation was monitored via a Surface Electromyography (sEMG). Heart Rate (HR) values were recorded in the beginning and during the10th min of each trial, after which, the difference between the 2 values was calculated. Immediately after the conclusion of each trial, participants were asked to provide a score for perceived exertion using Borg CR-10 scale (10 for maximum exertion). Results: During the LBNP trial, Total Hemoglobin (tHb) and OxyHemoglobin (O2 Hb) concentrations in the Vastus Lateralis (VL), was significantly lower compared to the control (p=0.007, p=0.001), but with a significant increase rate in deoxy-hemoglobin (HHb) (p= 0.001). Tissue Saturation Index (TSI%) showed no significant alteration between trials (p= 0.668). All calculated parameters relating to work output showed a significant difference in the LBNP trial compared to control. HR was increased (p= 0.001), there were an increase in MPF and RMS amplitude in the VL (p=0.006, p < 0.001, respectively) and subjects reported higher rate of perceived exertion (p=0.001). Conclusions: The application of LBNP showed elevated work characteristics, mainly on the work output and less local muscle hemodynamics. This could be a time efficient training tool for stressing the musculoskeletal system, faster improve body composition and potentially enhancing cardio respiratory fitness.