There is considerable interest in understanding the physical factors that affect an athlete’s ability to perform at the highest level without sustaining an injury. Current tests to assess an athlete’s ability to perform the movements required in a given sport or evaluate risk for injury are fairly simple, based mainly on anecdotal evidence, and do not discriminate among athletes’ current abilities to perform given movements (as determined from literature and correspondence with athletic trainers, physical therapists, and coaches). Including quantitative biomechanical tests in these athlete evaluations would allow variables believed to influence performance and injury risk to be quantified, tracked over time, and their actual affects on performance and injury risk determined. Such information is needed to develop science-based injury prevention guidelines. Currently, injury prevention guidelines are rather limited because little information is available regarding basic injury mechanisms and the state of the musculoskeletal structures prior to injury. The purpose of this study was to develop a portable instrumentation system that can record biomechanical quantities believed to affect lower extremity athletic performance and injury risk. To this author’s knowledge, no such portable system currently exists. The system was designed for in-the-field testing to increase athlete accessibility and to allow the quantities of interest to be tracked over time, thus providing a database that can be used to test various theories regarding factors affecting performance and overuse injury mechanisms.

A set of biomechanical quantities deemed most relevant to lower extremity athletic performance and injury risk was selected from careful inspection of clinical and research literature, and discussion with athletic trainers and coaches. The instrumentation system consists of standard biomechanical components necessary to collect the selected quantities. Tape measures and goniometers are used to determine basic anthropometric measurements (height, weight, leg length, foot arch height, and Q-angle). A manual goniometer is used to quantify ankle, knee and hip flexibility/range of motion (ROM). Force transducers and a customized limb testing fixture are used to quantify absolute isometric strengths and strength ratios for the hamstrings, quadriceps, gastrocnemius/soleus and tibialis anterior. A single camera video system is used to record sagittal plane ankle, knee and hip kinematics while the athlete performs prescribed movements. A Bertec force plate is used to measure ground reaction forces during the prescribed movements. Electromyography (EMG) data are collected to quantify activation timing and magnitude of the previously mentioned muscles. Video, force plate, and EMG data are synchronized. The synchronized force plate and video data are utilized in an inverse dynamics analysis to determine the net forces and moments acting at the knee and ankle throughout the movement. The net forces and moments can be used in a lumped parameter model and distribution analysis to estimate forces in individual structures. This information can then be used to identify movement strategies that can reduce structure loads. A custom reaction timing test involving a visual and audio cue and EMG is used to quantify reaction time.

The instrumentation system met all portability design criteria, allowing for timely data collection at outdoor locations easily accessible to athletes. The system was also successful in collecting the selected quantities that have been proposed to affect lower extremity athletic performance and injury risk. While some video and force components sacrificed a small amount of accuracy or precision for portability, overall accuracy and precision of the system allowed for meaningful biomechanical analysis.

A multifactorial analysis of the collected quantities combined with performance and injury incidence reports provided data needed to determine the relationship between these quantities, performance and injury risk. Interactions of quantities were investigated to provide a more thorough description of performance and injury risk. For example, low levels of knee flexion combined with large ground reaction forces during jump stops and running impacts can reveal movement mechanics that may be damaging to an athlete’s anterior cruciate ligament. Subtle modifications to the athlete’s mechanics may improve performance and reduce injury risk. The portable data acquisition system provides an opportunity to obtain the data necessary to test various theories regarding performance and non-contact, overuse injury mechanisms. Data tracked over time for specific populations may reveal quantity thresholds required to achieve a particular performance level or to avoid injury for specific tasks. Ultimately, systems such as this will provide the data needed to establish science-based guidelines for screening athletes for performance capabilities/limitations and injury risk and thus serve as a valuable tool for the coach, trainer, and athlete.