Higher Vertical Ground Reaction Forces Associated with Louder Landing Sound

Research Review: Higher Vertical Ground Reaction Forces Associated with Louder Landing Sound

By Stefanie DiCarrado DPT, PT, MSCS, NASM CPT, CES, PES

Edited by Brent Brookbush DPT, PT, COMT, MS, PES, CES, CSCS, ACSM H/FS

Original Citation: Wernli, K., NG L., Phan, X., Davey, P., Grisbrook, T. (2016) The Relationship Between Landing Sound, Vertical Ground Reaction Force, and Kinematics of the Lower Limb During Drop Landings in Healthy Men. Journal of Orthopaedic & Sports Physical Therapy. 46(3) 194-199 ABSTRACT

Caption: Practicing Hop Down to Single Leg Touch Down in the Transverse Plane with a Soft Landing

Practicing Hop Down to Single Leg Touch Down in the Transverse Plane with a Soft Landing

Why is this relevant?: Ground reaction force is the equal and opposite force exerted back on our body when it makes contact with the ground, generally via foot strike (1). If not properly attenuated via soft tissue structures and force transmission throughout the entire kinetic chain, this force can overly stress, bones, joints and soft tissues and lead to stress fractures and soft tissue injury (2). Reducing ground reaction forces during training and rehabilitation programs should be considered, as it may reduce the volume of stress placed on the body during training, and if carry-over affect is had, reducing the total volume of stress of daily and sporting activity. This article provides evidence that the amount of sound made upon foot strike/landing, may be used as an indicator and potentially a cue for optimizing the attenuation of ground reaction forces.

Study Summary

Caption: Vertical Drop to Soft Landing to Balance

Vertical Drop to Soft Landing to Balance

Review & Commentary:

The authors created a unique study, as previous research did not quantitatively measure sound in decibels (db), but relied only on the hearing and the subjective report of volume from the researchers. This study implemented instrumental assist in determining soft, normal, and loud landing sounds to more accurately correlate volume with vertical ground reaction forces (vGRF) and joint kinematics.

This is a strong study with a clearly described objective, proper literature review, sufficient subject selection and a standardized methodology that is reproducible. The authors provided a clear description of the issue addressed - the relationship of lower extremity injury to high vGRF, and their objective to quantify the relationship between vGRF, landing sound, lower extremity kinematics, and potentially, risk of injury. The authors cited several studies as examples of softer landing sounds being associated with reduced ground reaction forces, as well as studies correlating increased ankle, knee and hip motion with softer landings. The authors of this study determined the gap in the research was prior studies provided qualitative rather than quantitative data. A stronger data set, one that includes quantitative analysis of landing sounds, would improve the validity and reliability of the conclusions made by the researchers in all cited studies related to soft-landings.

The researchers required 26 subjects to produce statistically significant data; the subject demographics are summarized in the chart above with all 26 subjects. Subject selection did not need to be specific, as the purpose was to quantify a relationship noted qualitatively in previous research. Future research can build upon this study to investigate specific populations.

Standardization ensures that the data collection process is not influenced by factors other than what the study intends to analyze. All subjects wore the same reflective markers in the same spots according to the same protocol. Subjects performed the same 10-minute warm-up prior to testing while wearing the reflective motion capture sensors and were given the same testing instructions. The authors demonstrated the expected motion to the subjects, and allowed for ample practice time to ensure high quality data during motion capture. To eliminate interference by order of experimentation, the subjects landed as they normally would for a baseline sound, vGRF, and kinematic reading, and then they were either asked to land louder or softer based on a randomly chosen value via coin flip. Each condition (baseline sound, louder sound, and softer sound) was performed 5 times with a 1-minute rest between conditions. All subjects performed the test with their right leg.

This study is clearly outlined and reproducible due to the level of detail provided. Kinetic and kinematic data collection required use of a force plate and motion analysis system for which the authors provided company and settings information. Researchers collected sound data with a shotgun microphone and a sound-level meter and again provided all details and specific placement information. Prior to testing, the microphone placement was tested (as close as possible to the subject's landing foot without interfering with the landing).

The authors provided the exact instructions given to the subjects during the exercise, and provided citations of previous research used to determine a height that appropriately replicated the force of "work, sport, and leisure" (pg 195). The authors did not specifically describe placement markers for the motion analysis, but named and cited the protocol used: Plug-in-Gait full-body marker set (3).

The study is simple in its design, demonstrates statistically significant data and correlations, but is not without limitations. The authors noted that subjects were a homogeneous sample, comprised only of healthy, limit the transferability of findings. This does not invalidate the statistical significance of the data, nor the ability to infer conclusions among other populations, but further research using a broader population should be considered. Another possible limitation is the variability within each individual's movement system - the researchers did not evaluate for movement dysfunction or compensation patterns. The authors felt the training and familiarization with the task allowed for a consistent sample, which is what was detected in the data. Regardless of dominant side, all subjects were tested using their right leg. The authors do not acknowledge this as a limitation, but it may have been interesting to compare sides to see if kinetic and kinematic variations exist. Future research may want to compare one side to the other, as well as single leg landings to double leg landings. The subjects were not blinded and may have altered their landing techniques based on landing sound instruction, however, the authors noted this is unlikely a factor as the subjects were unaware of the expected results based on landing sound.

Although not a limitation of this study given the study's intent, future studies may provide details regarding specific foot/ankle, knee, and hip motion to investigate if the greater excursion is sagittal, frontal, or transverse plane. Previous research has found increased injury associated with altered hip, knee, and ankle mechanics during landing, especially in the frontal and transverse plains (4,5,6).

Why is this study important?

This study provides an quantitative data of a relationship between landing sound and vGRF. This relationship has been previously researched , but data was qualitative. Further, this study provides kinematic data, correlating increased excursion of the knee and ankle with softer landings and lower vGRF.

How does it affect practice?

The results of this study offer a simple way of assessing and reducing the stress placed on the body during landing tasks. Vertical ground reaction forces are typically measured via force plate, but this study along with previous research provides evidence that force plates may not be necessary to cue/train a reduction in vGRF. Clinicians can rely on their hearing and that of their patients, to assess and cue softer landings. This is easily implemented during various exercises and may be applied to home exercise programs. The authors suggest future research should investigate decibel reading smartphone apps for reliability which will assist clinicians in tracking a patient's progress.

How does it relate to Brookbush Institute Content?

"It is not enough to increase the quantity of movement if we can also increase the quality of movement" (Brookbush Institute - quotes that inspire ). The predictive models of Upper Body Dysfunction (UBD) , Sacroiliac Joint Dysfunction (SIJD) , Lumbo Pelvic Hip Complex Dysfunction (LPHCD) , and Lower Leg Dysfunction (LLD) focus on the quality of movement. The Brookbush Institute's goal of improving the quality of movement led to the development of assessment techniques designed to identify compensatory movement patterns and their root causes. This article noted increased ankle excursion during softer landing and a correlation to decreased vGRF. Proper assessment is then needed to ensure an individual has the appropriate range of motion in their ankles to allow for this excursion without compensatory excessive eversion (Feet Flatten ) or tibial external rotation (Feet Turn Out ). These are both compensations described in LLD  and LPHCD . Hip excursion increased during hard landing along with decreased ankle movement. This may imply that individuals without proper ankle dorsiflexion or arch stabilization may compensate with excessive hip motion to help dampen vGRF. On the Overhead Squat Assessment , this may be seen as an excessive forward lean, or if only one ankle is restricted, an asymmetrical weight shift.

In addition to assessing and correcting movement dysfunction, each predictive model includes exercises to improve the body's ability to react to forces applied to it. These exercises are referred to as "Reactive Integration" exercises which initially begin with higher velocity movements that end in a soft landing and maintaining balance, and progress to be more plyometric activities. Any jumping or landing exercise always includes cues for soft landing, for example "land like a ninja", or "landing is to be seen, and not hear". This article supports these cues as softer landing sounds are associated with decreased vGRF, which may be associated with a decreased risk of lower extremity injury.

The following videos demonstrate proper technique and form during reactive integration exercises involving landing.

Tibialis Posterior Reactive Integration:

Hop Down to Stabilization

Hop Down to Single Leg Touchdown to Balance

Gluteus Medius Reactive Activation: Side Hop Progression

Multiplaner Skaters:

Lateral Hop To Vertical To Balance

Single Leg Box Jump:

Lateral Hop To Single Leg Box Jump

Sources

1. Ground Reaction Forces. The Free Dictionary Available at: [http:// medical-dictorionary.thefreedictionary.com/ground+reaction+force](http:// medical-dictorionary.thefreedictionary.com/ground+reaction+force)
2. Zadpoor, A.A., Nikooyan, A.A. (2011) The relationship between lower-extremity stress fractures and the ground reaction force: a systematic review. Clin Biomech. 26:23-28.
3. Input Devices and Music Interaction Laboratory. Plug-in-Gait Marker Placement. Available at: http://www.idmil.org/mocap/Plug-in-Gait+Marker+Placement.pdf
4. Review: Hewett, T. E., Myer, G. D., Ford, K. R., Heidt, R. S., Colosimo, A. J., McLean, S. G., & Succop, P. (2005). Biomechanical measures of neuromuscular control and valgus loading of the knee predict anterior cruciate ligament injury risk in female athletes A prospective study. The American journal of sports medicine, 33(4), 492-501
5. Review: Dos Reis, A. C., Correa, J. C. F., Bley, A. S., Rabelo, N. D. D. A., Fukuda, T. Y., & Lucareli, P. R. G. (2015). Kinematic and Kinetic Analysis of the Single-Leg Triple Hop Test in Women With and Without Patellofemoral Pain. journal of orthopaedic & sports physical therapy, 45(10), 799-807.
6. Review: Smith, J. A., Popovich, J. M., & Kulig, K. (2014). The influence of hip strength on lower limb, pelvis, and trunk kinematics and coordination patterns during walking and hopping in healthy women. Journal of Orthopaedic & Sports Physical Therapy, (Early Access), 1-23.

© 2016 Brent Brookbush

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