Richard W. Bragg, John M. MacMahon, Erin K. Overom
Scott A. Yerby, Ph.D.
Director of Experimental Biomechanics Lab, VA Palo Alto RR&D Center
Gordon O. Matheson, M.D., Ph.D.
Associate Professor of Functional Restoration and Director of Sports Medicine, Stanford University
STATEMENT OF PURPOSE:
This project was divided into two distinct phases. The purpose of Phase I was to determine differences in the rheological, or time-dependent, properties between three athletic tapes, each designed for a different purpose, using mechanical tests. The purpose of Phase II was to attempt to correlate these time-dependent mechanical parameters with exercise-induced changes in kinematic properties of the taped ankle using gait testing.
Athletic tape is used to restrict excessive joint motion for athletes in a wide range of sports, from football to gymnastics. Yearly, vasts amounts of money is invested in athletic tape for the prevention of injury, yet it has been commonly reported that it loses much of its structural support after about 20 minutes of exercise. While many studies have addressed the functional performance characteristics of athletic tape, its mechanical properties and their physiological relevance are poorly understood. This project attempts to bridge this gap.
DESCRIPTION OF METHOD:
The tapes studied in this project were selected using a web-based survey of athletic trainers at the professional and collegiate level. The three tapes chosen were Zonas (Johnson & Johnson), the typical white athletic tape used by most trainers for both prophylaxis and rehabilitation; Jaylastic (Jaybird & Mais), the elastic adhesive tape used primarily for support in the case of an injury; and Leukotape, a specialty tape designed specifically for medical purposes such as patellar tracking and arch support.
In Phase I, each tape was subjected to three modes of testing: load to failure, fatigue under load control, and fatigue under displacement control. After the fatigue tests, the tapes were loaded to failure for comparison with the pre-cycling failure tests.
In Phase II, gait analysis using reflective markers and a force plate was performed on a single subject taped with Zonas to identify target parameters to compare with the mechanical test results. The subject was gait tested before and after a rigorous 20 minute exercise protocol, both with and without tape.
In Phase I, load to failure tests (Figure 1) were able to detect significant differences (p<0.001) in failure load, elongation at failure, and stiffness between tapes. Cyclic response data from fatigue tests under both load and displacement control were quantified by calculating logarithmic rate parameters from curve fits. Parameters from displacement control fatigue tests were independent of the loading conditions and significantly different between tapes (p<0.001). After cycling, tapes loaded to failure showed increased stiffness (p<0.001), but no significant changes in failure load or elongation to failure. In each case, Jaylastic was most sensitive to cycling, and Zonas was the least sensitive.
In Phase II, ankle range of motion (peak dorsiflexion to peak plantarflexion) was identified to be the variable most sensitive to the different taping conditions. Relative to the no tape condition, tape resulted in an initial reduction in ankle range of motion (ROM) of 25.4% in walking and 26.7% in jogging. Twenty minutes of exercise with the tape reduced these percentages to 16.7% in walking and 20.6% in jogging. Figure 2 depicts the results of the walking gait tests. Interestingly, the largest difference in these curves occurs during swing phase (approximately 110% of stance phase in the figure).
The mechanical tests performed in this study were successful in distinguishing between time-dependent parameters of three existing tapes. The results of these tests can now be used as benchmarks with which to compare the results of future mechanical tests of athletic tape.
The dynamic gait tests have been useful in identifying peak dorsi-/plantarflexion range of motion as a target parameter for correlation with the time-dependent mechanical parameters. Gait testing will be continued to test more subjects and to include the other tapes.