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Injury Biomechanics Laboratory

• Research Overview
• Current Projects
• Members

Dr. Scott McLean

1240 CCRB
401 Washtenaw Avenue
Ann Arbor, MI 48109-2214
Phone: (734) 647-1669

Research Overview

Research conducted within the Injury Biomechanics Laboratory focuses on identifying the underlying mechanisms of sports related injuries and the subsequent development of successful injury screening and prevention strategies.

Recent Science Daily article on Dr. McLean's research

Current Projects

Currently, our research focuses on two primary sports related injury concerns: non-contact anterior cruciate ligament (ACL) injuries and shoulder and elbow injuries in the young overhead athlete.

A. Mechanisms of Non-Contact ACL Injury

The deleterious impact of non-contact ACL injuries on athlete health and performance has precipitated extensive efforts towards their prevention. In particular, recent research has focused on identifying underlying neuromuscular control predictors of ACL injury risk, as such factors are readily amenable to training, and in essence, preventable. Neuromuscular training programs continue to evolve out of this research, which attempt to modify what are considered abnormal and potentially hazardous movement strategies. Despite the ever-increasing complexity and number of these programs however, ACL injury rates, and the associated sex-disparity in these rates, have not diminished. Rather than accept this as inevitable, we suggest that current prevention programs evidently continue to exclude key components of the non-contact ACL injury mechanism. Large-scale prevention is thus unlikely unless the precise mechanism/s of injury can be successfully elucidated.

Non-contact ACL injuries most likely stem from a complex interaction of anatomical, hormonal and neuromuscular factors. An equally complex integrative research design thus appears necessary to clearly determine how these combined factors manifest within the injury. With this in mind, we continue to utilize a combination of state-of-the-art experimental, cadaveric and model simulation methods to more effectively understand the causal factors of non-contact ACL injury. Through such an approach, successful screening of subject rather than population-specific injury risk may also eventually be possible. This in turn would facilitate more effective prevention methods that promote successful neuromuscular adaptation within individual non-modifiable constraints. Such steps appear necessary, if non-contact ACL injuries are to be ultimately eradicated. Considering these facts therefore, our research into non-contact ACL injury mechanisms currently focuses on the following:

Temporal Effects of Neuromuscular Fatigue on Anterior Cruciate Ligament Injury Risk in the NFL Athlete

Non-contact anterior cruciate ligament (ACL) injury is a potentially traumatic sports related injury suffered by a disproportionately large number of athletes playing within the National Football League (NFL). This injury typically necessitates surgical reconstruction, followed by a difficult and lengthy rehabilitation program, culminating in the athlete being sidelined for an extended period. Further, despite ongoing advances in surgical repair techniques, few athletes return to their pre-injury competitive levels, drastically shortening their professional careers. Injury also predisposes the NFL athlete to a significant long-term risk of degenerative osteoarthritis, often pre-empting the need for total knee replacement. With these facts in mind, identification of the mechanisms of non-contact ACL injury and the means through which they can be prevented is paramount within the NFL. Altered or abnormal lower limb neuromuscular control during the landing, cutting and pivoting maneuvers synonymous with football, is increasingly suggested as a key risk factor of non-contact ACL injury. Specifically, it is purported that these neuromuscular abnormalities culminate in dynamic joint postures that compromise the integrity of the ACL. Football is a sport that necessarily requires sustained maximal physical effort, meaning that player fatigue is largely unavoidable. It may be that the fatigue effects cumulatively incurred throughout a football game increase the likelihood of performing a movement resulting in ACL injury. Unfortunately, this information is not yet available. Furthermore, the extent to which the potentially deleterious effects of fatigue, and hence ACL injury risk, may vary throughout the course of a single season is also unknown. With these facts in mind, the specific aims of this research project therefore are to:

To achieve the above goals, we will use state of the art high-speed motion analysis and electromyography (EMG) techqniques to measure three-dimensional joint (hip, knee and ankle) motions and loads and muscle activation strategies of forty-five football athletes performing a series of anticipated and unanticipated jump-landing movements. Subjects will be tested on four separate occasions within a single season (31 weeks), incorporating, pre, within and post season sessions. At each tesing session, subjects will a series of dynamic landing movements both before and during exposure to a cumulative general fatigue protocol. The joint biomechanics and muscle EMG data obtained during each jump series, across each test session, will then be compared to precisely quantify the effects of decision making and how these effects depend on both fatigue, leg (dominant versus non-dominant) and time of season. We expect that the deleterious combined effects of fatigue and decision making will be more pronounced in the initial and latter stages of a single season, when athlete fitness levels are typically compromised. By teaching tailoring prevention strategies to within-season variations in athlete strength and conditioning, more successful program outcomes and hence, reduced injury rates, are likely.

Combined Effects of Neuromuscular Fatigue and Anticipation on Non-Contact ACL Injuries in Females

Non-contact anterior cruciate ligament (ACL) injury is a potentially traumatic sports related injury suffered by a disproportionately large number of female athletes. Hence, identification of the mechanisms of female non-contact ACL injury is paramount. Recent studies suggest that both neuromuscular fatigue and unanticipated movements may in isolation contribute to non-contact ACL injury risk. To date however, the combined impact of these factors has not been investigated. Sports participation often requires sustained maximal physical effort, meaning that player fatigue is largely unavoidable. Similarly, the random nature of sports activity necessarily precipitates execution of unanticipated movement responses. Considering fatigue manifests through both central and peripheral pathways therefore, poor reactions, decisions and hence movement responses appear feasible in the presence of fatigue. Considering these facts, the specific aims of this research project are to:

Forty female recreational athletes have been recruited for the purpose of this study. Specifically, they will have lower limb biomechanics and muscle EMG data recorded during a series of anticipated and unanticipated single leg landings via state-of-the-art motion analysis techniques, both before and during exposure to a generalized fatigue protocol. For unanticipated trials, subjects will be required to rapidly respond and adjust movement responses while in the air immediately prior to landing, based on a series of randomly activated light stimuli.

During the fatigue protocol, subjects will perform continuous series of three single leg squats followed immediately by a landing trial until squats can no longer be performed. We expect that females will demonstrate potentially hazardous knee motion, load and muscle activation strategies when performing unanticipated landings, particularly in the presence of fatigue. We further expect that specific muscle activation timings during simple reaction tasks will predict high risk knee load states, such as increased knee abduction torques. This result will have immediate implications for improved injury screening and prevention methods.

B. Mechanisms of Shoulder and Elbow Injury in the Young Overhead Athlete

Baseball is one of the most popular sports in the United States. Unfortunately, a large number of injuries couple this participation, particularly in young developing pitchers where repetitive stresses applied at the shoulder and elbow can perpetuate significant joint debilitation. Equally disconcerting is that these injuries are often the catalyst for significant long-term joint degradation, career ending surgeries, and restriction in routine upper limb function. Information regarding the causal factors of shoulder and elbow injuries in young overhead athletes however is currently limited. We intend to address this void directly in our ongoing research within the laboratory, with the following representing our initial exploits:

Effect of Pitching Load and Between Bout Rest on Muscle Degradation and Pitching Mechanics: Implications for Shoulder Injury in Young Pitchers.

Shoulder injuries are a common and potentially traumatic injury in young baseball pitchers. With the mechanisms of such injuries still elusive, pitch counts and days rest between pitching bouts are currently viewed as the most effective preventative strategy. To date, there is a paucity of scientific data relating pitching load to muscle and/or joint degradation, particularly in young skeletally immature populations. It is thus plausible that current guidelines may in fact contribute to rather than reduce injury rates. It is also unclear whether muscle degradation is coupled with fatigue induced adaptations in the pitching action. The specific aims of this study therefore, are to 1. Compare exercise-induced changes in the rotator-cuff muscles across a variety of pitching loads, and 2. Determine whether the onset of muscle damage correlates with simultaneous alterations in pitching mechanics.

A total of 24 young pitchers (12-15 years) will be recruited to the study and randomly allocated to one of four groups, characterized by a predefined total pitch count (40, 50, 60, 70 pitches). T2 weighted magnetic resonance (MR) images of the rotator cuff muscles in the pitching arm will be obtained immediately prior to and after pitching, and once daily for five days post pitching. These data will be compared to determine the relative impact of pitch count on muscle damage, as evidenced by the amount of intramuscular water. Changes in upper limb joint motions and loads will also be quantified across the pitching bout, and correlated with MR data as a means of determining mechanical predictors of muscle damage onset. This study represents the first step in our long-term research goal of determining the causal factors of shoulder injuries in the young overhead athlete. Elucidating the link between pitching load and injury risk would immediately afford more effective and stringent guidelines pertaining to safe pitch counts. Understanding the relationship between pitching load, pitching mechanics and injury risk would also enable more effective injury screening and prevention strategies to be formulated. These combined actions would contribute directly to a significant reduction in shoulder injuries in the overhead athlete.

Members

Faculty:
    Scott McLean, Ph.D. (mcleansc@umich.edu), Director
Undergraduate Student(s):
    Julia Samorezov (jsamorez@umich.edu)
    Mike Beel-Bates (mikepbb@umich.edu)
Collaborators:
    James Ashton-Miller, Ph.D. (jaam@umich.edu), Research Professor, Biomedical and Mechanical Engineering; Senior Research Scientist, Institute of Gerontology, University of Michigan
    Uwe Kersting, Ph.D. (u.kersting@auckland.ac.nz), Assistant Professor, Department of Sports Science, The University of Auckland
    Riann Palmieri-Smith, Ph.D. (riannp@umich.edu), Assistant Professor, Athletic Training, Movement Science, and Orthopaedics, University of Michigan
    Ton van den Bogert, Ph.D. (bogerta@ccf.org), Assistant Staff, Department of Biomedical Engineering, The Cleveland Clinic
    Edward Wojtys, M.D. (edwojtys@umich.edu), Medical Director, Medsport Sport; Medicine Program Professor, U-M Department of Orthopaedic Surgery


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