Constitution (HP) Guide Edit
This guide will be formatted the exact same as Strength, Defence, and Attack.
Constitution affects your in-game hitpoints (The amount of damage you can take before you die).
Raising this skill will increase how much damage you can take.
The max level for all skills is 120 at ~104.5m experience. Levels past 99 do affect your combat abilities.
Hitpoints is levelled at one-third of the rate of Attack, Strength, Defence, Ranged and Magic, as for every 3 experience you gain in these skills: You only gain 1 HP/Constitution experience.
There are currently 50+ players with 200m Hitpoints experience. It is one of the most commonly maxed skills in the game.
Training 1-120 Edit
You should train Constitution passively, as you only gain EXP (As much as you gain in the following skills, divided by three) in this skill whilst training Attack, Strength, Defence, Magic and Ranged. Therefore it trains three times slower than one of these single skills.