Most states don't provide students with enough physical education, a new report finds.

Just 19 states require elementary school students to take physical education classes for a set amount of time, and only 15 set minimum rules for middle school students.

Only Oregon and the District of Columbia require the amount of physical education time recommended by national experts. That's 150 minutes a week for elementary students, and 225 minutes for older kids.

Get Breaking News Delivered to Your Inbox

In 62 percent of states, students are allowed to substitute other activities for their required physical education credit. Many states let schools withhold physical activity or use it to punish students, according to the 2016 Shape of the Nation report.

The report was released by Voices for Healthy Kids, an initiative of the American Heart Association and the Robert Wood Johnson Foundation, and by SHAPE America -- Society of Health and Physical Educators.

"The benefits of physical education ring clear as a school bell," Nancy Brown, chief executive officer of the American Heart Association, said in a Voices for Healthy Kids news release. "With effective physical education, we can keep kids' hearts healthy and their minds in gear to do their best at school every day."

The good news is that school districts, under a recent law, will be able to get federal funding to improve their programs, the report said.