You don’t have to become overly devoted to a gym to feel and see major physical benefits to your health. Even walking briskly for half an hour and doing push-ups a few times a week can change your life, believe it or not, according to Gregory A. Hand, Ph.D., MPH, the associate dean of academic affairs for the Arnold School of Public Health at the University of South Carolina and an expert on the importance of exercise for HIVers. Hand has a study coming out in the journal AIDS Care that shows how even small amounts of exercise can dramatically improve what is known as “functional capacity” in HIVers.

You can imagine your functional capacity as a glass of water, Hand explains. Every time you exert energy, even to check the mailbox, you take a sip. If your glass is particularly empty to begin with, you’re going to tire yourself out before the day is up. But if you increase your functional capacity level all the way to the brim and beyond, you’ll have more energy for both everyday life and an exercise routine.

Hand says the participants in his study were sedentary HIVers in their 20s and 30s whose functional capacities were as low as those of healthy individuals twice their age. The participants walked on a treadmill for 30 minutes and did some light weight lifting for another half an hour just twice a week. After only six weeks their functional capacity increased a whopping 20%, which, Hand says, “is simply unheard-of.”

Hand recently heard from one of the study participants, a man who had been living in public housing and was unable to work. “He called to tell me that he felt so good from keeping up his exercise program,” Hand says, “that he’d gotten a job and an apartment and was living a very happy life.”