Data confirm kinetic, EMG changes

By Jordana Bieze Foster

The static curve of a rocker-bottom shoe does not correlate strongly with its rollover shape during gait, suggesting that other factors such as material stiffness may also contribute, according to research from the University of Salford in the UK.

Investigators analyzed rollover shape in 20 individuals walking at a self-selected speed under four footwear conditions: a flat control shoe, a weighted flat control shoe, a Masai Barefoot Technology (MBT) rocker-bottom shoe, and a prototype rocker-bottom shoe.

Foot-shoe rollover patterns were more curved when participants wore the rocker-bottom shoes than when they wore the flat shoes. However, the only condition for which foot-shoe rollover shape significantly correlated with static sole radius was the MBT condition, and even that correlation was low (r = .32).

This suggests that variables other than the static curve shape are affecting foot-shoe rollover shape during gait, according to Saeed Forghany, a graduate student at the university’s Centre for Health, Sport and Rehabilitation Sciences Research, who presented the group’s findings at the i-FAB congress. One such factor might be that the MBT shoe sole is more compressible than that of the prototype shoe, Forghany said.

The Salford researchers found that curved soles affected foot-shoe rollover shapes but not ankle-foot or knee-ankle-foot rollover shapes, suggesting that the shoes could potentially be used to alter distal gait mechanics without requiring significant changes in coordination strategies proximally.

“These types of footwear might be useful for rehabilitation in patients who have lost some ‘rolling over’ capability,” Forghany said.

In a related study, also presented at the i-FAB congress, the Salford group assessed the effects of curved-sole footwear on kinematics, kinetics, and electromyographic (EMG) muscle activation in the same 20 participants under the same four footwear conditions.

The point of contact with the ground shifted anteriorly in the rocker-sole shoes, which contributed to reduced ankle range of motion and decreases in peak ankle dorsiflexion and plantar flexion moments during early and midstance.

“We’re interested in looking at clinical populations, for example patients with arthritis, whereby modifying some of these variables you can play with the ankle moments,” said Christopher Nester, PhD, director of the center, who presented the second set of findings at the i-FAB congress.

Nester and colleagues also found that curved soles were associated with significant increases in gastrocnemius and soleus EMG during early stance, along with decreased tibialis anterior EMG. These finding are consistent with those of previous studies, in particular a Swiss study published in the January 2006 issue of Clinical Biomechanics.

However, Nester noted, previous studies had limitations, including failure to control for shoe characteristics other than sole curvature. In the current study, the control shoes featured the same last and upper as the prototype rollover shoe, and the weighted control shoe was matched to the weight of the prototype shoe. (Shoe weight was not found to affect any gait parameters.)

The Salford researchers also found no effect of curved-sole shoes on the energy costs of ambulation. Previous studies have reported conflicting results in this area, with a 2011 Mayo Clinic study finding that such shoes decreased oxygen consumption and a 2010 Dutch study reaching the opposite conclusion.

Sources:

Forghany S, Nester C, Richards B. The relationship between sole curvature of roll over footwear and changes in gait. Presented at 3rd International Foot and Ankle Biomechanics Congress, Sydney, April 2012.

Forghany S, Nester C, Richards B, Hatton A. Effect of rollover footwear on metabolic cost of ambulation, lower limb kinematics, kinetics, and EMG muscle activity during walking. Presented at 3rd International Foot and Ankle Biomechanics Congress, Sydney, April 2012.

Romkes J, Rudmann C, Brunner R. Changes in gait and EMG when walking with the Masai Barefoot Technique. Clin Biomech 2006;21(1):75-81.

Hansen AH, Wang CC. Effect of rocker shoe radius on oxygen consumption rate in young able-bodied persons. J Biomech 2011;44(6):1021-1024.

Van Engelen SJ, Wajer QE, van der Plaat LW, et al. Metabolic cost and mechanical work during walking after tibiotalar arthrodesis and the influence of footwear. Clin Biomech 2010;25(8):809-815.