This formula is based on the system before the 2009 engine update which allowed content developers to modify the rates (they made agility effect the drain rate).

    

/**

	 * Drains the player's run energy.

	 */

	public void drainRunEnergy() {

		double drainRate = 0.7D;

		double weightFactor = (weight > 1.371D ? (int) weight * 0.00729166D : 0.0D);

		// Truncated the weight factor to the nearest hundredth

		weightFactor = Math.round(weightFactor * 100.0D) / 100.0D;

		setRunEnergy(runEnergy - (drainRate + weightFactor));

	}



	/**

	 * Restores the player's run energy.

	 */

	public void restoreRunEnergy() {

		double restoreRate = 0.45D;

		double agilityFactor = (skills.getLevel(Skills.AGILITY) > 1 ? 0.001 * skills.getLevel(Skills.AGILITY) : 0.00D);

		setRunEnergy(runEnergy + (recoverRate + agilityFactor));

	}