By Hank Black
A recent study using innovative technology has questioned the potential role of standard running shoes with slightly elevated heels for the prevention and treatment of Achilles tendon pathology.
For many years, inadequate heel offset has been anecdotally implicated as a factor in tendinopathy of the Achilles, and elevating the heel to address this does seem to make sense. Traditional running shoes slightly plantar flex the ankle, which is thought to shorten the muscle-tendon unit and decrease tendon load during gait. However, this effect has not been studied during walking, and studies of footwear’s effect on Achilles load during running have come to mixed conclusions.
One potential limitation of previous studies has been the use of inverse dynamic models to indirectly estimate tendon loads. The new report from researchers at the Queensland University of Technology (QUT) in Brisbane, Australia, uses a recently developed technique: analysis of propagation of acoustic waves along the tendon.
“This is a more direct measure of the tensile load than the commonly used modeling approaches,” said first author Scott C. Wearing, PhD, principal research fellow at QUT’s Institute of Health and Biomedical Innovation. “Acoustic velocity in tendon is proportional to the tensile load to which it is exposed and has a relatively small reported error of less than two percent.”
Medicine & Science in Sports & Exercise published the study in its August 2014 issue.
The researchers also employed another emerging technology, a capacitance-based pressure platform embedded within a variable speed treadmill, to analyze vertical ground reaction force and temporospatial gait parameters.
The study recruited 12 healthy, nonsmoking, recreationally active adult men with no history of Achilles tendon pain or pathology. A custom-built ultrasound probe with a broadband pulse emitter and four receivers was positioned over the midline of the tendon.
After warm-up and with the treadmill at a self-selected gait speed, the participants completed two five-minute walks, one barefoot and one wearing a standard running shoe with a 10-mm heel offset. The researchers’ data analysis found the peak acoustic velocity in the Achilles tendon was significantly higher—suggesting a higher tensile load—during shod walking than during barefoot walking. They found no such difference in minimum acoustic velocity or in the peak rate of change in acoustic velocity during loading.
“We did not determine the specific cause for this increased tensile load in the Achilles,” Wearing said. “It’s possible that heel elevation associated with running shoes may increase muscular activity and cocontraction of the triceps surae and other lower leg muscles during walking.”
In addition, he said, many variables were not assessed in the study, including midsole composition and other properties of the running shoes.
“Our findings are somewhat unexpected, and our next step is to identify which characteristics of running shoes influence Achilles tendon loading during walking and running,” Wearing said.
The researchers also found changes in basic gait parameters associated with walking in running shoes versus barefoot, which Wearing said may help explain the increased tendon load with shoes. Shoes increased mean ankle plantar flexion by 4° during quiet stance as measured by electrogoniometry. When walking with shoes, participants adopted a lower step frequency but greater step length, period of double support, peak vertical ground reaction force, and loading rate than when walking barefoot. The researchers also noted that participants’ stance phase was relatively longer (4%) during shod walking than during barefoot walking.
The study’s use of noninvasive acoustic transmission as a surrogate for measuring tissue load is innovative, said Michael B. Ryan, PhD, who is a Research Fellow at Griffith University in Southport, Australia.
”However, the walking task used by the Brisbane study is not itself thought to contribute to the injury,” Ryan said. “Much must be done before we can understand the influence of heel elevation as a preventive measure for tendinopathy, and, unfortunately, the needed studies are expensive and challenging to organize.”
Wearing SC, Reed LF, Hooper SL, et al. Running shoes increase Achilles tendon load in walking: An acoustic propagation study. Med Sci Sports Exerc 2014;46(8):1604-1609.
Reed LF, Urry SR, Wearing SC. Reliability of spatiotemporal and kinetic gait parameters determined by a new instrumented treadmill system. BMC Musculoskelet Disord 2013;14:249.