The Anti-G Straining Manoeuvre (AGSM) is a countermeasure employed by fighter pilots in order to combat the decline in head-level blood pressure instigated by high +Gz-loading during tactical flight. The AGSM is a 4-second cycle of forced inhalation, isometric contraction of the arms, legs and trunk muscles together with a Valsalva Manoeuvre, followed by forced exhalation. The repeated tensing between forced breaths acts to increase intrathoracic pressure and venous return, augmenting head-level blood pressure. A pilot's ability to maintain an effective AGSM decreases over prolonged +Gz-exposure due to breathlessness and fatigue that is proposed to originate in the respiratory musculature. Thus, the present study implemented respiratory muscle training (RMT), a modality shown to increase respiratory muscle strength and endurance, as a possible intervention to help decrease AGSM-induced fatigue.Participants (n = 14: 26.9 +/- 5.3 yrs) trained with a commercially available respiratory muscle trainer (PowerlungRTM ) for 6-weeks, 4-times per week, 20 minutes per session. Every two-weeks, respiratory muscle (RM) strength and endurance were measured through Pulmonary Function Tests while performance was evaluated through measures of peak respiratory pressure, peak blood pressure and tidal volumes achieved during a loaded, AGSM breathing test. Training significantly improved RM strength measured in maximal expiratory and inspiratory pressures (+10.1%, p < 0.001 and -9.3%, p < 0.05, respectively) compared to control values, although the only improved performance measure was peak expiratory pressure (+8.1%, p < 0.01). Without evidence for improved respiratory endurance or the translation of RM strength gains to the performance of the AGSM (particularly in peak blood pressure), the benefits of using RMT to ameliorate AGSM fatigue in the G-environment appear limited.