Add two new elemental planes, those of Positive Energy and Negative Energy.

The Plane of Positive Energy:

• The full level is lit.
• Has lots of yellow lights, trees, and whatever plant-based monsters exist in the game.
• Everything is treated as if it has regeneration. The player can regenerate current HP past its maximum, but if this gets too far past the maximum, they instantly die from being unable to contain the energy (there are warning messages to this effect as you approach this point).
• Items in the player’s and monsters’ inventories can randomly get blessed, enchanted, or charged - even if this runs the risk of overenchanting and destroying them.
• Eating any food restores HP as well as nutrition.
• All exercisable attributes are exercised at regular intervals.
• All sleep effects are negated.

The Plane of Negative Energy:

• The full level is dark.
• Contains lots of undead.
• Everything constantly loses hit points. If you have regeneration, it either nullifies or only partly nullifies this effect.
• Items in the player’s and monsters’ inventories can randomly get cursed or lose enchantment or charges (going negative on things which are capable of being negative).
• You lose several times as much nutrition per turn as normal.
• All abusable attributes are abused at regular intervals.

Eating healthy foods (fruits, vegetables, royal jelly?) should exercise Constitution, and eating unhealthy foods (candy bar, cream pie, etc) should abuse it.

Seperately track every different source of exercising an attribute, with diminishing returns for repeated use of the same exercise source until that attribute changes value, which resets it. This prevents you from spamming an easy-to-do exercise source such as pushing boulders around or writing Elbereth, and makes you diversify your sources of exercise.

Possibly weight the different exercise sources (e.g. successfully finishing studying a spellbook should be worth more for Wisdom exercise than successfully casting that spell is).

Quaffing a potion of speed should exercise dexterity. Possibly only if it is non-cursed.

The “vitamin” effect of a pill shouldn’t give a big chunk of nutrition. It should give a token amount of nutrition (say 10 or 20), but its main effect should be to exercise all attributes that can be exercised several times.

Wearing a blessed ring of sustain ability lets you exercise attributes, but not abuse them. A cursed one lets you abuse attributes, but not exercise them. It continues to block all other sources of ability score change. If wearing two rings of sustain ability, determine what happens by averaging the beatitude of the two.

It gets increasingly hard (maybe even exponentially hard) to raise a stat through exercise as the stat approaches its racial maximum.

Walking up stairs exercises Strength.

Define a new set of ability score maximums which represents the highest the score can reach via exercise. These caps are always equal to or higher than the existing maximums, which represent the highest a stat can be increased to through potions of gain ability or other stat-boosting effects. In some cases, the exercise maximum should stay the same and the non-exercise maximum may need to be decreased.

It’s an open question on whether restore ability should be able to restore points to their exercise-only maximums, or just up to the gain-ability maximums.

Exercise or abuse Charisma as a result of consorting with foocubi.

Merge the rings of sustain ability and slow digestion into a “ring of stasis”. Double-edged effects: slows down digestion like normal, but also slows down healing, energy regeneration, timer effects like confusion and sickness, any timing-out intrinsics, prevents exercise from happening, blocks or reduces to 1 effects that directly change attributes.

Kicking down doors exercises Str and not Dex.

Intelligence can be abused and exercised, but unlike other stats, exercise will never bring it above its base value (or the value you have raised it to through gain ability).

Sources of abuse: mind flayer brain eating, zombie attacks. Sources of exercise: reading spellbooks, writing spellbooks, writing scrolls, learning a new spell, getting a major Oracle consultation for the first time, possibly some of the uncommon, non-farmable ways stolen from the things that exercise Wisdom.

If attribute changes from exercise and abuse are blocked due to the ring of sustain ability, they accumulate, and once you take the ring off they will all gradually apply over the next few exercise cycles.