Lower body positive pressure (LBPP) treadmill running is being used more frequently in clinical and athletic settings. A previous study in the Exercise Physiology Lab determined metabolic rate (VO2) on a LBPP and normal treadmill (NTM). Average (±SD) VO2at 5 and 6 mph on NTM was 2281.5±376.6 and 2609.5±427.4 ml O2∙min-1. Average LBPP at 60% body weight resulted in a VO2of 1714.1±374.6 and 1913.2±478.8 ml O2∙min-1at the two treadmill speeds. Interestingly, the percent difference in metabolic rate was not proportional to the decrease in weight (~30% vs. 40%). We predict the ~10% difference in VO2is attributed to upper body arm movement on the LBPP treadmill. PURPOSE: The purpose of the study was to measure metabolic rate running on an Alter G (LBPP) treadmill with and without upper body arm movement. METHODS: Thirteen active, non-obese, college age participants completed two exercise tests of walking and running at 60% body weight on an Alter G treadmill and 100% body weight on a normal treadmill. The tests were: (a) walking for 2 min at 0.894 m∙s-1(2 mph), (b) running for 3 min at 2.24 m∙s-1(5 mph) and (c) running for 3 min at 2.68 m∙s-1(6 mph). The volunteers were tested once with normal arm swing and once with arms stationary. Oxygen consumption was measured using open flow indirect calorimetryand last thirty-second averages were defined as steady state. RESULTS:Volunteers’ average (±SD) absolute VO2with arm use at 6 mph on the ATG with and without arms were 1866.0±550.5 and 1856.7±556.5 ml O2∙min-1 respectively. Volunteers’ average (±SD) absolute VO2at 6 mph on the NTM with and without arms were 2447.2±485.5 and 2517.3±575.5 respectively in ml O2∙min-1. CONCLUSION:As predicted, absolute VO2was significantly less running on ATG yet there was no difference in VO2on the ATG with and without arms. Running on the ATG is less efficient as shown by no change in VO2with or without arm movement. This could account for the ~10% less metabolic rate of our previous study comparing LBPP and NTM.