According to the d20 SRD regarding carrying capacity:
A character can lift as much as his or her maximum load over his or her head.
What is the maximum load? Is it the same as the "heavy load" column shown in Table: Carrying Capacity?
Yes, that is precisely it.
The Heavy Load column on the Carrying Capacity table indicates how much your character can carry and still move about for long periods of time, even if his reaction time is slowed down and he cannot run. The maximum Heavy Load is his maximum load.
In the Player's Handbook this is made clear in the first paragraph on page 162, where it states
Tordek can't quite manage to carry her and her gear, because doing so would put him over his 200-pound maximum load.
which is the maximum heavy load listed for a character with Strength 15.