Impact of Varying Exercise Intensity on Oxygen Uptake and Cardiovascular Response during Body Weight Supported Treadmill Walking in Healthy Adults

Abstract

Background: Body Weight Supported Treadmill Training (BWSTT) is effectively used in locomotive training for patients with neurologic and musculoskeletal deficits. The impact of BWSTT on oxygen uptake (VO2) and cardiovascular (HR and BP) response in patients has been shown to be variable, possibly due to level of Body Weight Support (BWS) or exercise intensity. The purpose of this study was to compare and quantify VO2, HR, and BP response in healthy adults during BWSTT at 0% and 30% BWS for two exercise intensities (35% and 50% VO2max). Methods: Eleven subjects (6 female, 5 male; 41.9 ± 11.3 y; 177.3 ± 6.9 cm; 79.0 ± 17.5 kg; 24.9 ± 4.2 kg/m2) provided informed consent for participation. Each completed a 5-minute rest trial followed by four treadmill walking trials; 2 at 35% VO2max (0% and 30% BWS; trials 0035 and 3035) and 2 at 50% VO2max (0% and 30% BWS; trials 0050 and 3050). Subjects rested a minimum of 5 minutes between each trail. For each trial the following was measured: HR (electronic monitor), BP (auscultation), RPE (Borg ratio scale), VO2 (indirect calorimetry). Mean data from minutes 3-5 were analyzed for differences between levels of BWS and exercise intensity levels using repeated measures ANOVA and Bonferroni post-hoc testing. Results: Mean walking speeds and elevations were 86.7 m/min and 0.6% (35% VO2max) and 91.1 m/min and 3.7% (50% VO2max). All trials showed significant (p < 0.05) increases in HR, RPE, VO2, metabolic equivalents (MET), minute ventilation (VE), Respiratory Rate (RR) and tidal volume (TV) compared to rest. No significant differences were seen in any tested variables between 0035 and 3035. HR, VO2, METS, and VE were significantly decreased in 3050 vs. 0050. HR, RPE, VO2, METS, respiratory exchange ratio and TV were significantly reduced in 0035 and 3035 compared to 0050 but were not different compared to 3050. Conclusion: BWS of 30% did not induce significant changes in VO2, HR or BP response while walking at 35% VO2max but did show significant reductions in HR and VO2 walking at 50% VO2max. Further, 30% BWS while walking at 50% VO2 max elicited similar VO2 and HR responses to unweighted walking at 35% VO2 max. This suggests BWS may allow for higher intensity exercise in patients while yielding reduced patient responses in VO2 and HR.