Study shows reduced vertical stress when driving a stroller

Study shows reduced vertical stress when driving a stroller

For many parents with young children, getting back into the running routine means breaking out the jogging stroller. While it's no surprise that pushing a bulky tricycle feels more difficult and changes the way you run, a new study led by researchers at Penn State Berks has found that runners experience less impact with each step, reducing their overall risk of injury.

The study published in the journalPLUS onealso showed a possible compromise. While the shock load per step is lower when running with a stroller, the torsional or twisting forces increase when the foot is pushed off the ground. However, this movement is not as commonly associated with injury as a kick impact, the researchers said.

“Although there is a lot of data on running economy and effort, this is the first to examine how loading forces change when running with a stroller,” said Allison Altman Singles, associate professor of kinesiology and mechanical engineering and senior author of the study.

Understanding this “biomechanical trade-off” could inform stroller design, training strategies, and injury prevention and rehabilitation protocols for those who walk with strollers.”

Allison Altman Singles, Associate Professor of Kinesiology, Pennsylvania State University

According to the research team, up to 79% of runners suffer injuries each year. The researchers said they wanted to examine whether and how the key forces on the body associated with common overuse injuries change when walking with a stroller.

They examined metrics related to vertical load and torsional load—the extent to which the foot twists on the ground as a runner pushes off the ground and moves forward. High vertical loading rates – or how quickly force is transmitted through the body – are associated with an increased risk of overuse injuries such as knee pain, stress fractures and plantar fasciitis. Increased torsional stress is also associated with stress-related injuries in the lower leg.

For this study, researchers recruited 38 healthy runners - men and women who were injury-free and ran at least five miles per week. Each participant walked with and without a stroller over a force plate that measured the impact of each step.

The researchers found that running with a stroller resulted in a significant reduction in all vertical load metrics of at least 8% and up to 17%. In other words, the load per step was lower, indicating a potential reduction in injury risk.

"When we walk with a stroller, we relieve ourselves vertically because we put our hands on the handlebars and lean in a little. This allows some of our weight to shift and go through the stroller instead of our legs," Singles said.

On the other hand, the torsional load values ​​increased significantly when driving the stroller, with some measurements increasing by more than four times. The arms and torso rotate naturally as you run to counterbalance the natural movement of the legs. Holding the handlebars could limit rotation of the upper body, the researchers explained, which in turn increases rotational forces under the feet to compensate. Driving the stroller may also require more rotational forces to propel the stroller forward and move it in a straight line.

While the increase in torsional load may be a concern, Singles said it is much less established as an injury risk factor compared to vertical load metrics and may be addressed through improved stroller design or running cues. However, further research is needed.

"The most important finding is that walking in a stroller is not dangerous. This study shows that in many cases the risk of overuse injury is lower because of the stroller itself," Singles said.

The research team continues to study stroller running, including examining these biomechanical changes and the types of injuries stroller runners experience.

Additional authors of the paper include first author Joseph Mahoney, who was previously an associate professor of mechanical engineering and kinesiology at Penn State Berks and is currently an associate professor of mechanical engineering at Alvernia University, and Benjamin Infantolino, an associate professor of kinesiology at Penn State Berks. Amy Lista and Diego Carbajal, who both earned bachelor's degrees from Penn State Berks, also contributed to the article.

This work was supported by funding from Penn State and Alvernia University.

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