Video Analysis
Using contemporary technology to improve clinical assessment.
By Brian Hoke, PT, DPT, SCS, CGFI Andrew Altman, PT, MPT, ATC David Volkringer, PT, MPT, and Katie Johnson, PT, DPT
What is the common element in the following events: a soccer player lands a jump, a pitcher throws a ball, a long distance runner makes contact with the ground, and a golfer makes impact with the ball on the tee? They all take place in less than one second, and the movement that occurs cannot be accurately assessed with the unaided eye. The integration of video technology solves this clinical dilemma by capturing the motion and allowing the clinician to replay the motion at a much slower rate to analyze posture, joint positions, and symmetry. Video technology has evolved greatly from the days of the first tape-based systems. Some will recall the VHS and Sony Beta technology of yesteryear, with its large recording units and cameras. The cost of the equipment was high and slow motion playback was often “fuzzy” with poor definition. Fast forward to modern technology for video capture and playback, and the user is provided with several video options that are more compact, affordable, and produce a much higher definition playback for slow motion clinical analysis. In our physical therapy practice, we use video capture- to analyze landing patterns that reveal a higher risk of anterior cruciate ligament (ACL) injuries
- to analyze the throwing motion in baseball
- to analyze the swing path and body positions during the golf swing
- to analyze gait patterns for walking and running
ACL Injury Risk Evaluation
In the United States alone, there are more than 200,000 ACL injuries annually. Of these, approximately 65 percent will undergo reconstructive surgery. This has consequentially created an increase in the numbers of rehabilitative cases seen in the physical therapy outpatient setting. As a result, there has been much attention toward designing a physical therapy training program that will not only result in predictably good outcomes, but also one that is able to test and predict the level of injury and or re-injury.
There have been many efforts toward determining various risk factors that lead to ACL injuries, and high valgus moments, especially with anterior tibial forces, have been determined to result in strain and increase the risk of rupture of the ACL1,2,3,4. A Drop Jump Test objectively measures the athlete’s ability to control lower limb axial alignment in the frontal plane.
To perform the video analysis, the patient jumps off a box on to the ground and then immediately jumps in to a maximum vertical jump. The camera captures the jump in four specific phases; just as the toes are touching the ground (pre-landing), the landing (deepest position), the take-off in to the maximum jump, and the maximum jump.
The knee valgus angle can also be measured to objectively document the higher risk athlete who demonstrates greater valgus angle on landing.
Clinically, we have found that the video analysis of the drop jump test is a standardized, time-efficient measurement tool that can be performed easily in a physical therapy office.
Biomechanical Throwing Analysis
High-speed video analysis can be a valuable tool to assess a baseball player’s faulty mechanics as they perform the movement of throwing. A portable system is necessary to video at a baseball field, which can be analyzed and reviewed at your physical therapy practice with the player, coach, and parents. To perform a good quality video analysis for a baseball pitcher:- The player should wear clothing that affords good exposure of the throwing arm, trunk, and legs. Have the player shirtless or in tight clothing so that all land marks and joints can be identified. Sliding shorts or bike shorts are useful to video the lower trunk and hips.
- Mark necessary landmarks with small retroreflective markers such as ScotchLite® Adhesive Tape. You can also use a permanent felt-tip marker.
- Film three to five pitches from three different views: second base view (behind pitcher), home plate view (front view), and open side (left handed pitcher would be from first base and a right handed pitcher would be from third base.)
During analysis, identify the biomechanical faults observed in the thrower’s motion to decrease the athlete’s risk of injury and/or improve a thrower’s performance and development of maximal pitch velocity. After reviewing your analysis with the athlete and other key individuals, such as parents, coaches, and sports agents, it is not uncommon for them to recommend the analysis to other players and coaches.
Gait Analysis for Walking and Running
During walking the foot is only on the ground for six tenths of a second, and when we run stance phase is as short as 2/10 of a second.
Integrating video into the evaluative process enables the clinician to observe the gait pattern in a frame-by-frame manner and find the exact moment in gait where the subject reaches maximal pronation. At this point we are able to use an angle tool to compare the difference between the left and right subtalar joints. As a result of the analysis, the plan of care may include strengthening for the lower limb decelerators, a footwear recommendation, or orthotic therapy. A marked difference between the left and right sides may also lead the clinician to look further up the kinetic chain to determine if there is a reason behind the difference, such as a limb length discrepancy, pelvic asymmetry, or scoliosis.
Vertical displacement of the center of mass is another predictor of running efficiency. Decreasing vertical displacement improves performance by using less energy to go up and down and spend more we have for moving forward. We use the video software to find the lowest and highest points during the subject’s gait cycle and use the calibrated line segment tool to determine the distance that the runner travelled up and down.
Video capture and playback software enables the clinician to slow down movements that are too fast for the naked eye to see and educate the athlete regarding their biomechanical faults or movement inefficiencies and identify excessive or inadequate motion that can be altered to improve performance or reduce the potential for injury.
Golf Swing Analysis
Down-The-Line Golf Swing Video Capture
Face-On Golf Swing Video Capture
Video analysis of golfers’ swings is a common practice by teaching golf professionals and on sports coverage of televised professional golf events. For the clinician, a brief analysis of a golfer’s swing can assist in detecting faults that can increase the risk of injury and also impair a golfer’s performance.
The video analysis of a golfer’s swing is typically done from two views: “face on” and “down the line.” The “face-on” view (Figure A) is done by filming facing the player as they swing. This provides useful information regarding proper weight transfer during the swing as well as lateral sway of the hips and pelvis during the swing. The second view is “down the line” (Figure B) filmed by standing behind the player facing their target. This view is extremely helpful in analyzing the golfer’s posture, swing plane, and rotation of the hip and pelvis.
What You Need to Get Started
Knee extension of trail leg leading to Reverse Pivot swing fault
Takeaway and swing path
To begin video analysis, you will need a camcorder, preferably with the ability to record in high definition, a tripod to keep the camera steady while filming, and a computer with a memory card reader or USB cable to connect the camera to load the video for analysis. For the analysis itself, you may choose from many user-friendly software packages. Some of the more commonly used programs available for purchase are Dartfish, Sports Motion Analysis, and Coach’s Eye. There are also very useful public domain programs for the clinician, such as V1 Home and Kinovea.
Capturing and printing the video frames that reveal the most useful information can be helpful and providing video images to the patient is a marketing opportunity. People love to see themselves on the video since it is a perspective that they cannot otherwise obtain, and they will often share this information with other athletes and coaches. When the patient has been referred by a physician or coach for the video analysis, make sure the referral source also gets a copy of the video images, as well as a concise summary of the significant findings.
Summary
The integration of video analysis into clinical practice can open the door to more accurate analysis of functional movements, particularly in the high velocity movements of common sports. The information obtained can assist the clinician in identifying factors that increase the risk of injury, cause the body to move into abnormal patterns of compensation, and impair optimal sports performance. From this information, corrective measures can be developed, and subsequent analysis can further assess the effectiveness of treatment interventions. In addition to providing an extremely valuable clinical tool for the clinician, this novel service can also be a new source of revenue for the clinical practice. This is particularly true in the absence of injury, where the goal is injury risk reduction and improved performance. If people in your community value this service, it can provide significant cash-based revenues.
The following are examples of four common swing faults that can be demonstrated on the video and linked to specific problems that can be addressed by a physical therapist:
Reverse Pivot: If a golfer allows the trail leg to move into knee extension during the backswing (Figure C) and subsequently fails to make proper weight transfer to their lead foot in the downswing, they will hit “off their back foot.” This can often be corrected with core stabilization of the lower trunk musculature, lower extremity postural stabilization exercises in a flexed knee position, and better proprioceptive awareness and balance ability.
Improper Swing Path: If the golfer swings the club outside the ideal swing path on the backswing, they will repeat the path on the downswing imparting a left to right sidespin to the subsequent ball flight (“slicing”). When this is observed in the video analysis, it may reflect a lack of thoracic rotation or inadequate shoulder external rotation range of the trailing shoulder.
Loss of Golf Posture: In an ideal golf swing, the golfer maintains a consistent spine angle from takeaway to impact with the ball. This creates consistency in bringing the club head back to a “square” position as the club is brought through the impact zone. When the loss of golf posture occurs, the golfer fails to maintain a stable spine angle (Figure B) during the swing, becoming more upright during the golf swing. This can be related to inadequate strength and stability in the hip and pelvis and can frequently be corrected with core stabilization exercises for the gluteals and lower abdominal musculature.
Shortened Swing Arc: A golfer’s swing arc is related to the power developed and ultimately the distance that the ball travels. When the golfer fails to bring the club back fully in the backswing there is a loss of power and distance. The video analysis provides an easy tool to observe the length of the arc of a golfer’s swing (Figure D). Tightness in the posterior shoulder of the lead arm, loss of hip internal rotation of the trail leg, and limitation of trunk rotation can all lead to a shorter backswing.
Brian Hoke, PT, DPT, SCS, CGFI, is a PPS member, co-owner of Atlantic Physical Therapy, PC, in Virginia Beach, VA, and a Titleist Certified GolfFitness Instructor. He can be reached at hokeptscs@aol.com.
Andrew Altman, PT, MPT, ATC, is co-owner of Atlantic Physical Therapy, PC. He can be reached at aatlmanpt@aol.com.
David Volkringer, PT, MPT, OCS, is a physical therapist with Atlantic Physical Therapy, PC. He can be reached at dvolkringer@gmail.com.
Katie Johnson, PT, DPT, is a physical therapist with Atlantic Physical Therapy, PC, and a former Division 1 soccer athlete. She can be reached at katieannj@gmail.com.
Notes
1. Boden BP, Dean GS, Feagin JA Jr, Garrett WE Jr. Mechanisms of anterior cruciate ligament injury. Orthopedics 2000; 23: 573-8.
2. Boden BP, Torg JS, Knowles SB, Hewett TE. Video analysis of anterior cruciate ligament injury: abnormalities in hip and ankle kinematics. Am J Sports Med. 2009;37(2):252-259.
3. Ford KR, Myer GD, Hewett TE. Valgus knee motion during landing in high school female and male basketball players. Med Sci Sports Exerc. 2003;35(10):1745-1750.
4. Hewett TE, Myer GD, Ford KR, et al. Biomechanical measures of neuromuscular control and valgus loading of the knee predict anterior cruciate ligament injury risk in female athletes: a prospective study. Am. J. Sports Med. 2005; 33: 492-501.
5. Zebis MK, Andersen LL, Bencke J, et al. Identification of athletes at future risk of anterior cruciate ligament ruptures by neuromuscular screening. Am. J. Sports Med. 2009; 37: 1967-73.