With the 2026 FIFA World Cup wrapping up in North America, after some of the sport’s biggest games took center stage in Atlanta, some Georgia State University researchers remain focused on a challenge familiar to athletes at every level: injuries to the ACL.
Anterior cruciate ligament injuries affect athletes across sports and are one of soccer’s most common setbacks. Behind every successful return to play is a growing body of biomechanics research that informs how injuries are prevented, diagnosed and treated, so players have the best possible recovery and a better outlook for both short- and long-term success.
“We are looking ahead and focusing on how to get you back to sport safely and quickly, but also on how to keep you active for a longer time,” said Liang-Ching Tsai, a professor of physical therapy at Georgia State.
BETTER TREATMENT PROTOCOLS
Of particular focus in physical therapy are knees, which are tricky joints. If the muscles, bones, ligaments and cartilage aren’t operating in harmony, it can lead to pain in the knee or up and down the leg.
One notably persistent problem, especially in soccer players, is tearing an ACL. When the load on the knee is too much — whether from making a sharp turn or being involved in a collision — the ligament can be damaged. ACL tears almost always require surgery and often end a player’s season.
Despite how common ACL tears are — studies have shown that 400,000 ACL reconstruction surgeries are done in the U.S. each year — people are still not walking out of rehab perfectly healthy.
Research in the field has found that people who’ve torn an ACL have a 4-to-10-times-greater chance of developing osteoarthritis in that knee than if they hadn’t been injured.
They also have an increased risk of needing a knee replacement 15 years later.
Experts at Georgia State are trying to lower the rates of such long-term effects by studying how athletes are being rehabbed today, and what might work better. That work has been one focus of Tsai’s research during his more than 10 years at Georgia State. Over the past decade, he has published more than 30 studies in physical therapy and rehabilitation science, including research on biomechanical injury mechanisms and rehabilitation strategies.
In one National Institutes of Health-funded study, Tsai and his team are looking at how knee rehabilitation, including rehab for ACL tears, can preserve long-term knee cartilage health.
“When you go see an orthopedic surgeon or physical therapist, it’s not that they don’t care about your long-term health, but they need to focus on your immediate, short-term recovery first,” Tsai said. “They’re not going to be paying too much attention to something that’s going to happen five to 10 years down the road.”
And while ACL patients will have physical therapy after surgery, they may not see another physician for this injury for some time unless the joint starts hurting again due to degeneration.
“This rehab window that we have immediately after the initial injury is key,” he said.
He and other GSU scientists are looking at what approaches to rehab work best. Their work includes human studies into the implications of favoring one side or the other after an injury and of walking speed after surgery. Researchers are also looking at what factors may lead to re-injury.
This kind of work is possible because of Georgia State’s Biomechanics and Motor Control Laboratory, a state-of-the-art research facility equipped with motion-capture technology, light sensors and biomechanical tools that can provide insight into injury, recovery and motion. In addition to studying ACL injury recovery, the lab is also doing research on people with cerebral palsy, knee osteoarthritis and other lower extremity disorders.
Tsai has conducted preclinical research to explore optimal rehab principles that can best preserve the knee joint following traumatic injuries.
“Once we have that information, our ultimate goal is to apply it to rehabilitation through clinical trials to see if any of those modifications would improve patient outcomes,” he said.
This kind of data helps inform better rehabilitation methods that can directly translate to patient care.
KEEPING ATHLETES ON THE FIELD
While Tsai advances the science of injury prevention and rehabilitation through research, other Georgia State experts put that knowledge into practice, helping student-athletes stay healthy, recover from injuries and return to competition.
Jake Irwin is a clinical associate professor and physical therapist for GSU’s Athletics Department, overseeing care for Georgia State University student-athletes. He says NCAA Division I athletes are like Formula 1 cars.
“One little piece moving wrong at the level they’re competing at, and they’re going to break down somewhere,” he said.
He says his role is to “look for that little piece that might be missing” and correct it. That kind of specificity and focus is key for athletes at their peak performance level and for preventing injury before it happens. As part of his teaching, Irwin leads a course on how to work with elite athletes.
“Most people come into it thinking it’s about lifting heavy and coming up with some crazy exercise someone’s never seen before,” he said.
But those athletes are going to be able to lift more weight than the general public. Instead, he wants his students to focus on the basics.
“It’s a matter of how they move that weight, and is there some small link in the chain that’s causing a breakdown? Usually, you can find a problem with a very simple fix, and when they put it into the whole chain, it makes everything function better with less chance of injury.”
DEVELOPING FUTURE THERAPISTS
Deborah Ruiz, a second-year Doctor of Physical Therapy student at GSU who played soccer for Georgia Southern University, knows how important proper ACL rehab can be.
She tore her left knee ACL as a sophomore in high school, then tore the right knee ACL as a first-year student in college. She tore it a second time two weeks after getting cleared to play again.
She says she can tell the difference between her knees. When she was in high school, the rehab timeline was 6 to 9 months whereas now it’s a year. Her high school treatment was also very conservative, with two to three sessions per week, and without a distinction made between “pain that’s hurting you and doing actual damage, and pain of discomfort having just had surgery to build muscle back,” she said.
In college, her rehab regimen consisted of seeing a trainer every day at the start and, over time, dropped to three times then to twice a week. On days she wasn’t in physical therapy, she was seeing a strength-training coach. Today she has far fewer problems with her right knee than her left.
The experience led her to want to work as a physical therapist, and her personal journey is informing her skills. She knows exactly what kind of pain her patients are going through as well as the mental aspects of being hurt and itching to get back to their sport.
No matter what area of practice she lands in after getting her doctorate, she knows the time she’s spent working with different kinds of athletes will help her improve the lives of the patient populations she serves.
“I have a huge passion for any sort of physical activity, and with any kind of injury that’s holding people back physically, I really want to help them,” Ruiz said.
That future could include working with high school athletes, college competitors like herself or professionals at the highest level. And as research at Georgia State University continues to advance the science of biomechanics and injury recovery, its impact is expected to reach athletes far beyond Atlanta — including those competing on soccer’s world stage for years to come.
Story by Jen Miller
Photos by Jenni Girtman
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