Exertion

In extended combat, fighters will inevitably get tired, and overexertion will begin to take its toll. Any given combatant can exert themselves for five rounds plus an additional five multiplied by their Energy attribute before becoming fatigued.

Acquiring Exertion
If any one of these conditions are met in a round, the character is considered to have exerted themselves, and thus acquires 1 point of Exertion; continuing to do this for too long will cause them to become fatigued.
 * Reaching or exceeding their full movement speed
 * Making a movement action and an attack action
 * Making a full attack action
 * Reaching or exceeding their normal amount of swift actions in a turn
 * Making a Shield check without the Armor Proficiency trait

Reducing Exertion
Exertion can be lowered simply by resting or holding back in combat. Any round in which the character only defends themselves, moves less than their full movement speed without attacking, or otherwise fails to meet the conditions to acquire a point of Exertion, will reduce that character's Exertion by 1 point.

Effects of Exertion
Reaching or exceeding a character's maximum Exertion causes them to become fatigued. As per the rules for fatigue, the character will receive a -3 penalty to Strength and Coordination and a -1 penalty to Power and Agility. Once fatigued, the character may attempt an Energy check once per round as a free action; an Exceptional Success on this check will grant the character a second wind-- their Exertion will be reduced to half of its maximum, and they will no longer be fatigued.

Alternately, rather than attempt this Energy check, the character can simply spend turns resting until their Exertion has been reduced to half of its maximum. At this point, the character will no longer be fatigued.