- The angle at which a person leans their torso forward as they run affects their risk of injury, finds a study from the University of Colorado.
- The feet hit the ground harder when people lean forward as they run.
- Leaning forward places stress on the hips, knees, legs, and feet that can lead to overuse issues.
Many people consider running to be an activity that occurs primarily from the waist down. However, a new study from researchers at the University of Colorado in Denver has shown that the angle of a runner’s torso has a lot to do with how they run and their likelihood of injuries.
Leaning forward too far when running increases the chances of developing overuse injuries.
The study, which appears in the journal Human Movement Science, explores the effects of a runner’s trunk flexion, which is the angle at which they hold their torso as they run. The researchers found that even small changes in trunk flexion can have a profound effect on the motion, or “kinematics,” of the lower limbs and how hard they hit the ground when running.
Despite running not obviously involving the trunk, arms, and head, these parts of the body constitute about 68% of its mass.
To test the effects of trunk flexion on running, the researchers had to devise an experimental scenario that made it possible to hold runners’ torsos at specific angles without impeding their ability to run.
“We had to create a way,” says lead author Anna Warrener, Ph.D., “in which we could reasonably force someone into a forward lean that didn’t make them so uncomfortable that they changed everything about their gait.”
The researchers found that having a lightweight, plastic dowel behind treadmill runners’ heads caused them to lean forward to avoid hitting it. The higher the position of the dowel, the less the runners ducked out of its way, and the straighter their trunk flexion. As the researchers lowered the dowel, the runners leaned forward more.
The researchers recruited recreational runners with no injuries, ranging in age from 18 to 23 years. Each individual ran brief 15-second trials at 3 meters per second. They performed trials at their preferred trunk flexion and trials tilting forward at three angles that the researchers specified: 10, 20, and 30 degrees.
“We thought,” reports Dr. Warrener, “that the more you lean forward, your leg would need to extend further to keep your body mass from falling outside the support area. As a result, overstride and stride frequency would go up.”
However, the results were unexpected. “The relationship between strike frequency and stride length surprised us,” Dr. Warrener recalls. “The inverse was true. Stride length got shorter, and stride rate increased.”
The runner’s average stride length decreased by 13 centimeters, while stride frequency went up from 86.3 to 92.8 strides per minute.
Overstride relative to the hip — where the foot lands too far ahead of the hip — increased by 28% when runners leaned forward.
Trainer Sarah Pelc Graca of Strong with Sarah explained to Medical News Today, “To break it down, when you’re overstriding, you’re not setting up your joints to be at the best angle to propel you forward properly while running.” She noted that overstrides “can lead to patellofemoral pain syndrome, iliotibial band syndrome, and plantar fasciitis.”
Dr. Warrener’s suspicion is that overstriding occurs due to a decrease in the amount of time that runners’ feet spend in the air between steps when they run leaning forward. There’s less forward travel during this airtime, so the runners take a higher number of shorter steps.
Dr. Bert Mandelbaum, sports medicine specialist and orthopedic surgeon at Cedars-Sinai Kerlan-Jobe Institute in Los Angeles and author of The Win Within: Capturing Your Victorious Spirit, spoke with MNT about the study.
Dr. Mandelbaum said that in running, “it’s about efficiency and energy dissipation.”
He warned that “the more inefficient we are and the less we can dissipate energy, the higher proclivity there will be to creating an overuse situation and stress injury.”
The briefer airtime that the researchers saw in the study leads to an overall increase in energy use, says Dr. Warrener: “The act of swinging your leg is really expensive as you’re running. Swinging it faster as you lean forward may mean a higher locomotor cost.”
The researchers saw several ways in which a higher trunk flexion was harder on a runner’s body, creating imbalances that provided an opening for more injuries.
Leaning further forward changes the position of the runner’s foot and lower limb position, causing them to hit the ground harder. Runners also had a more flexed hip and more bent knee joint as they ran.
“As a runner,” Graca advised, “it’s important to focus on a forward lean. However, know your muscles because if you have a muscle imbalance, you might end up leaning a bit too far forward, which can be a cause for injury.”
“The big picture takeaway is that running is not all about what is happening from the trunk down — it’s a whole body experience. Researchers should think about the downstream effects of trunk flexion when studying running biomechanics.”
– Dr. Warrener
“You know, we should never underestimate the importance of the modifiable factors,” Dr. Mandelbaum told MNT. Trunk flexion is just one of these, and there are many others, he said, ranging from diet to adequate running shoes. “You’re only as good as your weakest link.”
Dr. Mandelbaum encouraged everyday runners to try out different running postures to find a “highly efficient position where they feel good with it, and they’re able to move, and they get rewarded.”
When a runner finds their “sweet spot,” said Dr. Mandelbaum, they feel “like they’re almost floating.”