Influence Of Unweighting On Muscle Oxygenation And Vo2 During Running On A Lower-body Positive-pressure Treadmill

Abstract

The influence of unweighting using a lower body positive pressure treadmill (PPT) on oxygen consumption (VO2) has been previously explored. However, it is unknown how different body weight settings (BWSet) in a PPT influence muscle oxygen saturation. PURPOSE:To describe the relationship between tissue oxygenation and VO2 while running across multiple BWSet on a PPT. METHODS: Six experienced runners participated in this study. Tissue saturation index (TSI), oxygenated hemoglobin (O2Hb), and deoxygenated hemoglobin (HHb) levels were obtained using a near infrared spectroscopy (NIRS) unit secured on the right vastus lateralis. VO2 data were collected using a metabolic cart. Subjects ran at a self-reported “easy” training pace for 4 minutes at 40, 60, 80, and 100% BWSet (randomized order), followed by 4 minutes of rest. Preceding each stage, subjects walked at 3 mph for 1 minute at 100% BWSet. The NIRS data from the last 30 seconds of each running stage were averaged and data from the last 30 seconds of each walking stage were subtracted to serve as a reference measurement. Linear mixed effects models were used to determine whether BWSet influenced VO2 and NIRS parameters. For the first model, BWSet was analyzed as a categorical variable and pairwise comparisons were then used to determine differences between each BWSet. For the second model, all data were normalized to 100% BWSet and analyzed as a continuous variable to allow development of regression models for each parameter. Slopes of the regression equations were then compared using Z-score estimates. RESULTS: When the data were modeled using BWSet categorically, BWSet significantly influenced VO2, TSI, O2Hb, and HHb (p<0.005 for each), and pairwise comparisons revealed significant (p<0.05) differences between each BWSet. When normalized data were modeled using BWSet as a continuous variable, there was a significant linear relationship for each parameter (p<0.005), but the slope for all NIRS parameters (β range: 0.010-0.12) were significantly greater than that for VO2 (β = 0.006). CONCLUSIONS: The results show that VO2 and tissue oxygenation change at different rates for varying BWSet on a PPT. Further research is necessary to determine if altered tissue oxygenation achieved on PPT influences training response.