Researchers looked at 2,569 young people who were participating in a longitudinal study in southwest England that included numerous health factors, including activity level—including intensity of that exercise—and bone mineral density. They analyzed the effect of intensity on the difference in bone health from age 12 to age 25, and found that those who pursued more high-intensity physical activity had significantly greater density at a later age than those who did only light-intensity activity. Since this type of bone strength is an important marker of the future risk of osteoporosis, the researchers noted, that means the exercise they were doing as teens could have a preventative effect as they aged—offering protection even decades later.
Building Bone Strength
The fact that low-intensity or low-impact activity didn’t provide many bone changes doesn’t come as a surprise, according to Belinda Beck, PhD, of Griffith University in Australia and director of The Bone Clinic, a health service focusing on bone, muscle, and joint health. “We know from past research that bone only responds to high-intensity activity, and that’s true at any age,” she says. “We also know that improvements in bone density due to that type of activity can continue even if you stop exercising, although ideally, you would pursue activity throughout your life.” Although it’s important to stay active no matter what your age, adolescence and early adulthood is particularly crucial. That’s when peak bone strength occurs, the researchers note in the recent study. Maintaining that bone density through continued high-intensity activity is what creates a protective effect throughout adulthood. Jumping, running, and any other activity that works with gravity is especially helpful, Beck says, because it stresses bones in a way that fosters growth. For example, a study on plyometric jump training by adolescent girls found that activities like hopping and box jumps led to higher bone mass, in addition to other advantages like improved knee extensor strength, balance, and leg strength.
What Qualifies as Intense?
With the recent study as well as others looking at the effects of training, intensity matters. But what qualifies as truly intense? One classic workout is high-intensity interval training, which means working out for a shorter amount of time but with greater effort, and might including loading up the bones through resistance or jumping. Other examples of high-intensity activity include:
RunningTabata trainingFast hikingPlyometric exercisesJump ropingSpeed walkingCross-country skiingSprinting
There’s no precise definition of high intensity, but you can measure it in a few ways, including monitoring your heart rate and doing a “talk test” during cardio exercise, which means the higher your intensity level, the more challenging it will be to talk in more than a few words before getting out of breath, says Ariel Osharenko, CSCS, a sports performance physical therapist and trainer. When increasing your intensity, either in cardio or strength training, it’s helpful to think about your perceived rate of exertion, also called PRE. This is a subjective measure, but it’s useful for increasing intensity over time. For example, working at around a 7 out of 10 on the PRE scale can keep you from increasing your intensity too quickly, he suggests. Coaches who are training teenagers will likely use PRE—as well as observation—to ensure that athletes are staying challenged without fatiguing too quickly, but this is also an easy tactic for people of any age to tailor their workouts for intensity, he adds.
More Advantages
In addition to providing a protective effect on bone health as you age, high-intensity activity can have a range of other benefits for kids and teens, says Disa Hatfield, PhD, chair of the Department of Kinesiology at the University of Rhode Island College of Health Sciences. Those run the gamut from behavioral advantages to physical improvements. She notes that consistent, high-intensity activity can affect:
Self-esteemBody perceptionSocializationAcademic performanceMental disciplineBalance and mobilityPostureOverall quality of life
“In general, this can be the start of a lifelong exercise habit, not just because it has protective health effects that a child or teen will benefit from later, but because it’s fun,” says Hatfield.
