The g thresholds at which these effects occur depend on the training, age and fitness of the individual. An untrained individual not used to the g-straining maneuver can black out between 4 and 6 g, particularly if this is pulled suddenly. Roller coasters typically do not expose the occupants to much more than about 3 g. A hard slap on the face may impose hundreds of g-s locally but may not produce any obvious damage; a constant 15 g-s for a minute, however, may be deadly. A trained, fit individual wearing a g suit and practising the straining maneuver can, with some difficulty, sustain up to 9 g without loss of consciousness.