Chocobos are sorted into two Classes:
Mental     and    Physical.
 
It's important to read about and learn the difference between these two categories, as it directly affects which type of Careplan you
put your Chocobo on, even from the very start.

The two Stats that directly coincide with Physical Chocobos are:
Strength & Endurance.

Strength:  Affects the Chocobo’s running speed.  This encompasses both your personal
usage of your Chocobo (calling on Whistle or during the Hot-and-Cold game), as well as when you race it via the Chocobo Bucks Racing NPC near each stable or in the Chocobo Racing Arena.

The majority of Chocobo Raisers, in the end, want a fast Chocobo to mainly get them around as quick as possible.  If this is your goal, you will want to focus on bringing up Strength as much as possible, as well as Endurance.
Also if you are just using your Chocobo for a means of transport instead of Racing it, it's not important to acquire any Physical Abilities.

Strength also affects the aesthetics of your Chocobo.  Religiously following a Physical Program from the start should grant you Average Strength+ by day 30.
Acquiring average Strength by day 29 (Adulthood) grants your Chocobo a particular appearance:  Larger feet and thicker legs result.  Note:  If your Chocobo does not attain average Strength by day 29, you will not acquire either of these physical traits.

Strength and Endurance are directly affected by food and Careplans.  Most raisers typically use Vomp Carrots and Sharug Greens to help boost Physical Stats. During the Chick Phase, Carrot Pastes may be used.

Careplans such as Taking a walk and Carrying Packages later on boost both Physical Attributes.
If you want to isolate Strength boosts, your careplan options are:  Exercising Alone and Delivering Messages later on.

The Caretaker Long Walks and Compete against Others boost Strength and Endurance as well.

Endurance:  Affects the Chocobo’s riding duration.  If Endurance is your Chocobo's dominant attribute, this results in a patient personality.
In Chocobo Racing, increased Endurance affects the chocobo's stamina.

Many Chocobo Diggers will attempt to bring up Endurance after they have learned both Bore and Burrow and have maxed Discernment, so that their Chocobo can stay out longer during
a Dig Session.

Your Chocobo's Endurance should slightly increase faster than your Chocobo's Strength counterpart.  Therefore, it should hit Average a bit faster than Strength does.  Having Endurance at Average or above before day 29 will permanently alter the Chocobo's physical appearance as an adult. The Chocobo's tailfeathers will appear elongated.  Note:  If
your Chocobo does not attain average Endurance by day 29, you will not acquire this physical trait.

The Chocobo Stables offer a few Careplans that Isolate and Boost Endurance:
Exercise in a Group and Acting in a Play later on.


Some Raisers follow a Mental Program until both abilities are acquired, either inherited + learnt, or both learnt, then switch to a Physical Program to bring up Physical Stats.
To learn in-depth about this Multi-Step Physical + Mental Program, read the Careplan section carefully.