Basya Tsybukmakher
Berakhot 32b teaches that four things require strengthening: Torah, good deeds, prayer and the ordinary pursuits of life.
With Torah and prayer, it is easy to understand that we have an obligation to strengthen our commitment to them. “Good deeds” refers to good character traits, which also need strengthening. Thus, these are the “three things on which the world stands”: Torah, service and good deeds (“service” means prayer, and “good deeds” means good character traits).
As for the “ordinary pursuits of life,” Rashi comments in Berakhot: “If he is a craftsman, [let him strengthen himself] in his craft; if he is a merchant, in his trade…”
This includes all the body's needs.
We have an obligation to strengthen ourselves in these areas too, so that we can be healthy and capable of fulfilling Torah, prayer and good deeds.
Sefer HaChinukh (488) states that the body needs four things: food, sleep, rest and joy.
This means that joy is also one of the body's needs. It gives us strength and energy, as Mesillat Yesharim explains. Joy is usually a natural part of a person's life. We see young children playing and rejoicing all the time. Only when they lack something do they stop being joyful. In the same way, every person is happy when they have what they want. This concerns the body's needs.