Abstract
The purpose of this study was to examine the metabolic and physiological effects of running at three different percentages of body-weight (BW): 100, 75, & 50 on a lower body positive pressure treadmill (LBPPT). Twelve healthy college aged students, 6 male and 6 females, on a current training regimen and current/previous competitive experience participated in the study. The participants performed three graded exercise tests (GXT) using a custom protocol following a Latin Square design. Variables analyzed in the study included absolute VO2max (L/min), HRmax (bpm), maximal oxygen saturation (%), maximal RPE, test performance (minutes), O2 pulse, and VT1 & VT2. A 3 x 2 mixed-model RM-ANOVA was used to compare main effects of within-subject differences (BW-3) and between-subject differences (gender-2). No significant differences were seen in VO2max and VT1 & 2 (bpm) between the BW percentages (p>0.05). HRmax was significantly different between the 100-75 & 100-50 %BW comparisons. Average HRmax at 100%: 186±7.8, 75%: 183±7.5, & 50%: 182±7.7. Maximal RPE showed significance in the 100-50 & 75-50 comparisons. Maximal oxygen saturation showed significance in the 100-75 & 100-50 comparisons. Average SaO2 at 100%: 96±1.5, 75%: 97.7±1.2, & 50%: 97.9±0.9. Significant differences were also seen in performance between 100-75, 100-50, & 75-50 comparisons. Average performance at 100%: 11.4±1.5, 75%: 14.1±1.8, & 50%: 16.6±1.5. Based on the percent of their HRmax, VT1 was significant in 100-75 & 100-50 comparisons while VT2 was significant in men only at 100-50 comparison. Based on these results, it appears that training at a lower percentage of BW can lead to similar cardiopulmonary adaptations achieved at 100% BW, without the same level of stress applied, supporting the rationale behind conducting the study. Increased pressure from the LBPPT applied to the lower extremity may have acted as a mechanism in increasing venous return which in turn increased the stroke volume and caused the decreased HRmax in the participants. Lower HRmax and increased performance time may also indicate training at a lower percent of BW may allow individuals to sustain a prolonged steady-state at a similar intensity at 100% BW potentially allowing for an extended stimulus applied to the working musculature improving overall performance.