Strength

Strength represents the raw physical power and muscle mass of a creature. It is the primary factor in determining a creature's ability to move heavy objects, preforming athletic feats, wield massive weaponry, and manage the weight of their own equipment without suffering physical exhaustion.

Carrying Capacity and Size

A creature's base carrying capacity is calculated by multiplying their Strength stat by a multiplier tied to their size class. For a Medium creature, this multiplier is 15 lb. This calculation is modified if a creature has proficiency in the Lifting skill; in this case, the creature adds twice their proficiency bonus to their Strength stat before multiplying by their size class multiplier. This total represents the maximum amount of weight a creature can carry while maintaining full mobility and combat effectiveness.
Physical scale significantly impacts these limits. While a Medium creature uses a multiplier of 15, larger creatures like those in the Colossal class use a multiplier of 75, allowing them to carry immense loads. Smaller creatures, such as those in the Tiny class, have significantly lower thresholds.

Encumbrance

When the weight of carried equipment and items exceeds a creature's base carrying capacity, they begin to suffer from encumbrance. This state is divided into two tiers of severity based on the percentage of weight held relative to the base capacity.
Encumbered status occurs when a creature carries between 101% and 150% of their base capacity. In this state, the weight becomes a significant burden, reducing the creature's movement speed by 50%. While encumbered the creature can not perform attacks or skill checks.
Heavily Encumbered status occurs when the weight is between 151% and 200% of the base capacity. To move at all, the creature must succeed on a Strength check with a difficulty class equal to the current carried weight divided by a multiplier tied to their size class. A successful check allows the creature to move up to one quarter of their total movement for that turn.
If a creature attempts to carry weight exceeding 200% of their base capacity, they are considered Over Capacity. At this point, the weight is too great for the creature to support even while standing still. They must immediately drop the excess weight, as movement and basic posture become impossible.

Movement

Base movement speed is determined by species and Strength. Species base speeds assume a Strength of 10. Every 5 points of Strength above 10 adds 5 feet to movement, while every 5 points below 10 reduces movement by 5 feet. These adjustments only occur in full 5-point increments.
Athletics proficiency modifies this calculation by adding twice the proficiency bonus to the Strength stat to determine effective Strength for movement. For example, a creature with 12 Strength and a +3 Athletics proficiency has an effective Strength of 18, granting a 5-foot speed bonus.

Sprinting

Sprinting allows a creature to move at high speeds outside of combat by making an Athletics check. The distance covered per turn is equal to 8 feet multiplied by the value of the roll. Sprinting is only possible when a creature is unencumbered by equipment; wearing any form of armor, including light armor, or carrying an object prevents a creature from sprinting.
A sprint can be maintained for up to one minute. To continue beyond this point, the creature must succeed on a check at the end of each minute. The DC for this check starts at 10 and increases by 5 for every minute the sprint has already been sustained.

Jumping

Your Strength determines how far you can jump.
Long Jump. When you make a long jump, you cover a number of feet up to your Strength score if you move at least 10 feet on foot immediately before the jump. When you make a standing long jump, you can leap only half that distance. Either way, each foot you clear on the jump costs a foot of movement.
This assumes that the height of your jump doesn’t matter, such as a jump across a stream or chasm. You must succeed on a DC 10 Athletics check to clear a low obstacle (no taller than a quarter of the jump’s distance), such as a hedge or low wall or DC 15 Athletics check to clear a high obstacle (no taller than a half of the jump’s distance). Otherwise, you hit it.
When you land in difficult terrain, you must succeed on a DC 10 Acrobatics check to land on your feet. Otherwise, you land prone. If you jump from a height of higher than 10 feet you must make a Dexterity Saving Throw to take half fall damage. The DC for this save starts at 10 and increases by 5 for every 5 additional feet you fall.
High Jump. When you make a high jump, you leap into the air a number of feet equal to 3 + your Strength modifier if you move at least 10 feet on foot immediately before the jump. When you make a standing high jump, you can jump only half that distance. Either way, each foot you clear on the jump costs a foot of movement. In some circumstances, you can Use an Action to make an Athletics check to jump higher than you normally can, adding 1/5 of the roll to your maximum jump height.
You can extend your arms half your height above yourself during the jump. Thus, you can reach above you a distance equal to the height of the jump plus 1½ times your height.

Grappling

When you want to grab a creature or wrestle with it, you can use the Attack action to make a special melee attack, a grapple. If you’re able to make multiple attacks with the Attack action, this attack replaces one of them.
The target of your grapple must be no more than one size larger than you and must be within your reach. Using at least one free hand, you try to seize the target by making a grapple check instead of an attack roll: a Athletics check contested by the target’s Athletics or Acrobatics check (the target chooses the ability to use). If you succeed, you subject the target to the Grappled condition. The condition specifies the things that end it, and you can release the target whenever you like (no action required).
Escaping a Grapple: A grappled creature can use its action to escape. To do so, it must succeed on an Athletics or Acrobatics check contested by your Athletics check.
Moving a Grappled Creature: When you move, you can drag or carry the grappled creature with you, but your speed is halved, unless the creature is two or more sizes smaller than you.

Shoving a Creature

Using an Attack or Bonus Action, you can make a special melee attack to shove a creature, either to knock it prone or push it away from you. If you’re able to make multiple attacks with the Attack action, this attack replaces one of them. The target must be no more than one size larger than you and must be within your reach. Instead of making an attack roll, you make a Lifting check contested by the target’s Lifting or Acrobatics check (the target chooses the ability to use). If you win the contest, you either knock the target prone or push it 5 feet away from you. If you succeed by a vast margin you can push the creature an additional 5 feet for every 5 you beat their roll by.

Weapon Wielding

Beyond simple lifting and movement, Strength dictates the maximum kinetic force a creature can control in combat. It determines the ability to withstand the recoil of heavy firearms, the torque of massive melee weapons, and the structural integrity required to utilize military-grade ordnance without injury.
Weapons scale through 8 distinct Damage Tiers. Tiers 1, 2, and 3 are standard and can be used by any functional weapon found in the world. Tiers 4 through 8 require reinforced, custom construction to handle the immense forces involved. A standard weapon forced to output damage at these tiers will shatter upon use.
A wielder's Strength score and proficiency determine the maximum damage tier they can effectively handle. Base scaling grants access to higher tiers for every 10 points of Strength. Proficiency provides a specific one-tier boost starting at 15 Strength. A creature with 1 to 9 Strength is limited to Tier 1 and must subtract their Strength modifier from the damage dealt when using Melee Weapon. If you attempt to attack with a weapon you don't have the Strength to wield it will miss and fall out of your hands.

Damage Tiers

The Heavy trait increases a weapon's damage by one tier but carries significant logistical downsides. This allows a wielder to punch above their weight class. For example, a wielder who meets the requirements for Tier 3, such as having 20 Strength and Proficiency, can utilize a Heavy weapon to achieve Tier 4 damage output. Talented Engineers can also Augment weapons to make them more wieldy to lower Tiers of Strength at the cost of Tech Points.