October 2017

HANDLE WITH CARE: How sports equipment affects biomechanics and injury risk

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Clinicians know that handling a lacrosse stick or other types of sport-specific equipment can affect an athlete’s movement patterns in potentially harmful ways. Now researchers are beginning to quantify these types of effects and explore their clinical implications.

By Jill R. Dorson

If you’re walking down the street carrying two bags of groceries, you’ll move differently than when you’re walking unencumbered. Taking that idea a step further, it makes sense intuitively that carrying a lacrosse stick, football, or any other sports implement will affect an athlete’s biomechanics. This phenomenon, often observed anecdotally by lower extremity clinicians, is increasingly becoming a focus of biomechanical research.

“You’re holding an implement way away from the body, and now your trunk has to compensate for that implement, so the whole [kinetic] chain is compromised,” said Lenny Macrina, PT, SCS, CSCS, cofounder and director of physical therapy at Champion Physical Therapy and Performance in Waltham, MA.

Macrina isn’t the only physical therapist who works with elite athletes to note key changes in the way the body moves when an athlete carries a piece of equipment. In fact, multiple studies1-5 have investigated the particulars of how carrying or holding a piece of equipment affects lower extremity biomechanics.

But it is really on the front lines—from the sidelines, in the training rooms, and in physical therapy clinics—where practitioners see these effects firsthand.

“Because athletes carry an implement of some kind, there is so much need for appropriate hip and spine mobility and stability,” said Dan Lorenz, DPT, PT, LAT, CSCS, director of physical therapy at Specialists in Sports and Orthopedic Rehabilitation in Kansas City, MO. “The implement is an extension of your trunk, so you need a lot of deceleration ability, as well, to control the follow-through.”
In the lab

In the lab

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A 2005 study published in the American Journal of Sports Medicine (AJSM)6 bears out what Lorenz and Macrina see on a day-to-day basis. Athletes were videotaped doing cutting moves, first with no arm constraints and later holding a lacrosse stick, cradling a football with the cutting-side arm, and, finally, cradling a football with the plant-side arm.

The study showed, to varying degrees, the constraints were associated with greater knee abduction moment, which can increase the possibility of anterior cruciate ligament injury, according to lead author Ajit Chaudhari, PhD, FACSM, an associate professor of physical therapy, mechanical engineering, biomedical engineering, and orthopedics at The Ohio State University in Columbus.

A shorter distance between the plant-side arm and the center line of the body—which occurred while carrying the lacrosse stick and carrying the football in the plant-side arm—was associated with significantly greater loading at the knee. The findings suggested, of the three conditions, carrying a lacrosse stick created the most risk.

“Basically, what we’re seeing is the distance between the body and the plant-side or cut-side arm. So we’re thinking from a mechanical point of view, ‘How are these conditions going to predict something?’” Chaudhari said. “The further away, the bigger the lever arm, so it can create more torque. In different conditions, arms are in different positions. … And the more they [lacrosse players and football players carrying the ball on the plant side] brought their arm in more, the bigger the valgus knee moment.”

And, though Chaudhari’s study and others1-5 have shown higher stress on the knee and other joints can be related to carrying a piece of sports equipment, questions remain regarding why and how this happens.

Clinicians and academics all point to changes in arm position, but are quick to add they believe other factors—including playing defense versus offense and gender and distraction—may play key roles in altering how the body moves.

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Sport-specific effects

A 2015 AJSM study7 reported a higher incidence of lower extremity injury during defensive actions versus ball-handling actions in high school basketball players. The study, which collected data over seven years and included 6.4 million athlete exposures, noted no significant differences between offense and defense in soccer for the group overall.

“Defending and ball handling showed an increase in [basketball] injuries, so the supposition was, ‘Why?’” said lead study author Scott Monfort, PhD, who did his doctoral studies in mechanical engineering at Ohio State and is now an assistant professor in the Department of Mechanical and Industrial Engineering at Montana State University in Bozeman. “Our thought is that it is related to some of the sport-specific demands. We know that every sport has constraints—they could be equipment-related; for example, dribbling a basketball with the hand or a soccer ball with the feet, or it could be direct one-on-one defending.”

Although the study did not compare kinematics or kinetics during offensive and defensive actions, Monfort said the effects of ball handling could have been offset by other factors that can also affect biomechanics.

In basketball, defensive moves tend to occur in response to movements by an offensive player that are hard for the defender to anticipate; this may play a greater role in terms of injury risk than any potential effects of ball handling, Monfort noted.

“A defensive move would be representative of a reactive movement, and would put those athletes at more risk for lower extremity injuries because [the movement is] unanticipated,” he said. “We did see that for basketball. In soccer, the demands are different and impose additional constraints on the lower extremities.”

Monfort pointed out that the relevance of particular constraint-related factors can vary for different sports.

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“We found that unanticipated movement may play a greater role in basketball, but with soccer, having to move with the ball may play a more dominant role,” he said.

This phenomenon may also be mediated by gender. In the study, girls had significantly higher rates of ankle injury than boys when ball handling in soccer, but not when playing defense in soccer or when playing basketball.

“The added demands of positioning the ball may play a relatively more dominant role in the multifactorial injury factor in girl soccer players,” Monfort said.

A 2014 meta-analysis published in Sports Medicine8 underscores the relationship between unanticipated movements and injury risk. The analysis of six studies on how unplanned sidestepping affects knee mechanics found athletes had an increased risk of knee injury during unplanned moves, particularly upon landing. The study also noted noncontact ACL injuries were most prevalent during a change of direction.

Losing focus

Carrying a piece of sports equipment can compound the effects of unanticipated movements and other variables that can increase injury risk, experts said. To put it simply, carrying a big stick can take an athlete’s focus off the task at hand.

“The influence of holding something in their hand and having to focus on that, now we’re just relying on response from the lower extremities, and I think you do see a movement that you’re not expecting or that is not ideal because of the inability to use that visual input,” Macrina said. “They are so focused on holding the stick that they [can’t focus] on an unstable surface [or an opponent].”

Chaudhari agrees. He pointed out that his 2005 study wasn’t conducted in a game or practice setting or across enough different sports to develop empirical evidence showing distraction may be a factor affecting biomechanics. Anecdotally, however, Chaudhari believes distractions can have an effect on how the body moves.

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“I think that those [distractions] affect biomechanics, from the standpoint that then you’re spending less of your brain planning how you are going to plant that leg,” he said. “So you are more likely to plant that leg in a way that creates a situation that gets you closer to an ACL tear or other injury.”

Monfort was the lead author of a 2017 study presented in June at the annual meeting of the American College of Sports Medicine9 investigating how visual memory (as determined using the Immediate Post-Concussion Assessment and Cognitive Test [ImPACT] battery) influenced the effect of soccer-ball dribbling on biomechanics in male athletes. Monfort said the results suggest that dribbling a soccer ball is a visually demanding task, and that athletes with diminished capacity for visual memory may be less able to maintain optimal biomechanics while performing sport-specific tasks that require visual attention.

“As someone is making some athletic movement, like dribbling, then they are only periodically looking at the ball and only periodically looking at opponent or field,” Monfort said. “So there is less time to scan the field. In soccer, we saw the demands of [dribbling] are different [than in basketball] and are now imposing additional constraints on the lower extremities.”

Although Monfort’s two studies may appear at odds, they underscore the idea that basketball and soccer, specifically, may have inherently different sport-specific constraints. As such, it can be difficult to compare the effects of equipment-handling constraints on biomechanics, and any resulting effect on injury risk, from sport to sport. Monfort was quick to say more study in this area is needed.

A study from Quinnipiac University in Hamden, CT, presented at the 2016 Combined Sections Meeting of the American Physical Therapy Association also found that knee biomechanics during cutting were affected when a visual-attention task was added.10 However, that study found women were more likely to be affected than men.

Expecting the unexpected

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Both Macrina and Lorenz believe “distractions”—whether an unplanned movement or putting a piece of sports equipment into a player’s hands—are a critical and often overlooked part of the rehab process. In fact, both say that when they’ve added a sport-specific implement to the rehabilitation process, they have seen firsthand that the athlete’s focus is then split.

“Anecdotally, there can’t be any doubt that holding an implement and the changing focus to have to be able to catch a ball, or getting ready for a hit, or feeling the ground beneath them … that vis­ual input and acuity are required,” Macrina said. “It’s unknown, but we’re learning so much about it.”

Lorenz believes elite athletes have a leg up in managing the distractions that go hand-in-hand with on-field play.

“Elite athletes have the ability to anticipate the move before the opponent even does,” Lorenz said. “And they are able to prepare themselves ahead of time.”

That preparation may allow the athlete to compensate for the unexpected move, but as Lorenz has noted in years of working with elite athletes, compensation often comes in the form of raw power. That power, he said, is what separates the elite athlete from the average athlete, and it allows those athletes to overcome potentially high-risk situations that the average human cannot.

“It’s striking to me that the elite athletes I’ve had the ability and privilege to work with are able to overcome deficits with raw natural talent and ability,” Lorenz said. “There is a paper11 about what makes elite athletes different from others in their sport, and without question, in any sport, it came down to power. It had nothing to do with height, weight, bench press, etcetera. It was power.”

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Translational training

Of course, it’s one thing to recognize sport-specific equipment handling as a potential injury risk factor, and it’s another thing altogether to design effective interventions to reduce that risk. However, recent research does suggest training can help address the extent to which unanticipated movements contribute to the problem.

A German study of 24 active women published in March found a combination of perturbation training and plyometric training was associated with significantly reduced knee joint moments during lateral reactive jumps after four weeks.12 And, in a Danish study published in September, a six-week balance training intervention was associated with significant reductions in knee abduction moment during perturbed cutting in 26 healthy men.13

As a way to help rehabilitate injured athletes who participate in equipment-handling sports, experts said it’s important to put an athletic implement into an injured athlete’s hand. Both Lorenz and Macrina said this can have positive mental and physical impacts on the rehabilitation process.

At first, the stick, ball, or glove can be used early in the rehabilitation process just as a way to give the athlete a reminder of what he or she is working toward.

“For me, when someone is going through ACL rehab, if you just put that stick in their hand, it just does so much for their psyche,” Lorenz said. “It gives them a mental boost.”

Later in the rehabilitation process, the clinician can observe how holding the implement changes the way the athlete’s body moves—and how the athlete self-adjusts to the new feature.

“Anecdotally what I’ve seen is, ‘Where are you carrying the implement? Close to your body? Far away? High up?’” Macrina said. “Even team handball players, they’re getting the ball above the head, which changes the body’s landing. It creates changes in the pelvic position, which influences the lumbar area, then the glutes, quads, and hamstrings. Are they now in a poor position to stabilize? You’re influencing muscular positions because you’ve now changed your upper extremity position.”

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And that change in position circles right back to hard research about the effect of carrying a piece of equipment on the lower extremities.

“In rehab, you have to take it in stages,” Chaudhari said. “I think it [holding equipment] should be a goal, that you shouldn’t be done with rehab until you’re able to increase strength/movement with your equipment and the same sorts of distractions as you’d have during a game.”

Chaudhari is also a big believer in giving athletes the proper training early on.

“I’ve heard a lot of people say over the years, ‘We teach kids how to catch and how to throw, but we don’t teach them how to land,’” he said. “We should teach them how to catch while they land. Because they hurt themselves when they land, not so much when they catch and throw.”

A 2012 Australian study5 made similar recommendations, after finding that landing after making an overhead catch was associated with increased peak knee valgus moments, as well as altered lower extremity kinematics.

Theories related to this topic vary, but one thing academics and clinicians can agree on is this: Carrying a piece of sports equipment has an effect on biomechanics, but how those changes happen and the net result of those changes require more study.

“This is an area that is way under researched,” Macrina said. “But it should be highly considered in the advanced phase of rehab and even earlier.”

Jill R. Dorson is a freelance writer based in San Diego, CA.

REFERENCES
  1. Dempsey AR, Elliott BC, et al. Whole body kinematics and knee moments that occur during an overhead catch and landing task in sport. Clin Biomech 2012;27(5):466-474.
  2. Wdowski, MM, Gittoes MJ. Kinematic adaptations in sprint acceleration performances without and with the constraint of holding a field hockey stick. Sports Biomech 2013;12(2):143-153.
  3. Birrell SA, Haslam RA. The influence of rifle carriage on the kinetics of human gait. Ergonomics 2008;51(6):816-826.
  4. Wdowski MM, Gittoes MJ. Kinematic adaptations in sprint acceleration performances with and without the constraint of holding a field hockey stick. Sports Biomech 2013;12(2):143-153.
  5. Dempsey AR, Elliott BC, Munro BJ, et al. Whole body kinematics and knee moments that occur during an overhead catch and landing task in sport. Clin Biomech 2012;27(5):466-474.
  6. Chaudhari AM, Hearn BK, Adnriacchi TP. Sport-dependent variations in arm position during single-limb landing influence knee loading: implications for anterior cruciate ligament injury. Am J Sports Med 2005;33(6):824-830.
  7. Monfort SM, Comstock RD, et al. Association between ball-handling versus defending actions and acute non-contact lower extremity injuries in high school basketball and soccer. Am J Sports Med 2015;43(4):802-807.
  8. Brown SR, Brughelli M, Hume PA. Knee mechanics during planned and unplanned sidestepping: a systemic review and meta-analysis. Sports Med 2014;44(11):1573-1588.
  9. Monfort SM, Pradarelli JJ, et al. Visual memory influences the effect of soccer ball handling on knee valgus angle while cutting. biomechanics of jumping, landing and cutting. Med Sci Sports Exerc 2107;49(5 Suppl):S381
  10. Garbalosa J, Peters L, Plunkett C, Raksnis K. The impact of a visual task and sex on knee biomechanics during a cutting maneuver: preliminary results. J Orthop Sports Phys Ther 2016;46(1):A38.
  11. Lorenz DS, Reiman MP, Lehecka BJ, Naylor A. What performance characteristics determine elite versus nonelite athletes in the same sport? Sports Health 2013;5(6):542-547.
  12. Weltin E, Gollhofer A, Mornieux G. Effects of perturbation or plyometric training on core control and knee joint loading in women during lateral movements. Scand J Med Sci Sports 2017;27(3):299-308.
  13. Souza Oliveira A, de Brito Silva P, Lund ME, et al. Balance training enhances motor coordination during a perturbed side step cutting task. J Orthop Sports Phys Ther 2017 Sept 23. [Epub ahead of print]
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