The objective of this investigation was to measure and document the existence of any significant differences in physical performance under operational conditions between the Launch Entry Suit (LES) and the new Advanced Crew Escape Suit (ACES). The LES is a partial pressure suit currently worn by astronauts during the launch and entry phases of Shuttle missions. The ACES is a full pressure suit under consideration as a replacement for the LES. One prototype ACES has been fabricated and was used in this investigation.This report presents the results of three tests conducted with six subjects to allow a comparative evaluation of the two suits. The three tests included a reach envelope test, a strength test, and a treadmill test. The reach envelope test measured and compared the maximum hand displacements during horizontal and vertical reaches of both left and right arms in one-g conditions. The strength test used an isokinetic dynamometer to measure and compare the peak concentric torque exerted by the subjects in both flexion and extension about six isolated joints: the left and right elbows, left and right knees, and left and right shoulders. The treadmill test measured and compared heart and oxygen consumption rates while walking at 1.6 meters per second (3.5 miles per hour) at zero percent grade for five minutes.There were no significant differences found between the two suits in any of the tests performed. This study was unable to demonstrate one-g human performance differences between the ACES and the LES with regards to a reach envelope test, a strength test or a treadmill test.