Today’s flight helmet incorporates targeting and cueing systems enabling the pilot to accurately cue onboard weapons against enemy aircraft while performing high-G aircraft maneuvers. While these systems undoubtedly increase a pilot’s capabilities, one obvious drawback to putting all this equipment on the pilot’s helmet is the increase in helmet weight that shifts the combined head and helmet center of gravity (CG) forward, while increasing moments of inertia on the neck. Operational concerns associated with the heavier helmet may result in decreased performance from muscle fatigue and increase in neck injury during ejection. The objective of this study was to measure the human’s level of neck and upper torso fatigue while wearing United States Air Force helmets of varied mass properties (weight, CG, moments of inertia) for durations up to 8-hours. Results found that helmets with a forward CG shift were significantly more uncomfortable on the subject’s neck and back than the helmets with a normal CG shift. Significant increases in upper neck and upper and lower back discomfort were reported as early as hour 2 and continued throughout the 8-hour session. The 4.5 lb helmet with forward CG shift was significantly more uncomfortable on the subjects than the 6.0 lb helmet with nominal CG shift.