Forefoot bending stiffness, running economy and kinematics during overground running

Abstract

Previous research has shown that altering forefoot (FF) bending stiffness can enhance running economy; however, the mechanism behind the changes in running economy remains unknown. Therefore, the purpose of this study was to investigate the relationship between forefoot bending stiffness, running economy, and lower limb kinematics during overground running. Eighteen aerobically fit recreational male athletes performed overground running using a portable metabolic analysis system to measure oxygen consumption in two footwear conditions with different forefoot bending stiffness. Sagittal plane kinematic data of the metatarsophalangeal, ankle, and knee joints were recorded using a high-speed camera. On average, there was no difference in running economy when running in the Stiff shoe ( _ VO 2 D 38.1 § 5.4 mL/kg/min) compared to the Control shoe ( _ VO 2 D 37.7 § 5.8 mL/kg/min, p D 0.11). On an individual basis, 10 athletes (Responders) improved their running economy with increased FF bending stiffness (Δ _ VO 2 D ¡2.9%), while eight athletes (Non-Responders) worsened or did not improve their running economy in a stiff shoe (Δ _ VO 2 D C1.0%). In stiff footwear, Responders experienced kinematic changes at the ankle joint (decreased angular velocity) that likely resulted in decreased energy requirement for muscular contractions due to a presumed shift on their individual forceÀvelocity relationship. The lack of improvement in running economy by the Non-Responders may be attributed to a presumed lack of a shift in the forceÀvelocity relationship of the calf musculature. Instead, Non-Responders experienced kinematic changes (increased ankle plantarflexion during push phase with stiff footwear) that likely hindered their moment-generating capability potentially due to a shift on their individual forceÀlength relationship. These findings represent important progress towards explaining inter-individual changes in running economy with different footwear bending stiffness.

Adding carbon fiber to shoe soles does not improve running economy: a muscle-level explanation

“…12–16 To date, two studies have reported that adding optimally stiff carbon fiber plates to shoe soles improves running economy by 0.8 12 and 1.1% 13 , while another three studies reported that adding carbon fiber plates to shoe soles does not affect running economy. 14–16…”

“…Based on lower limb-joint analyses, which do not necessarily reflect muscle dynamics, 21, 22 metatarsophalangeal- and ankle-joint dynamics are more affected during running with the addition of carbon fiber plates to shoe soles than knee- and hip-joints. 13, 14, 23–25 Further, intrinsic foot muscles do not directly affect running economy, 26 indicating that altered plantar flexor dynamics during running with versus without carbon fiber plates added to shoe soles may help explain changes in running economy.…”

“…28, 29 Additionally, running with stiffer footwear may decrease plantar flexor shortening velocity, reducing muscle metabolic energy expenditure per contraction. 14 For example, increasing footwear bending stiffness may yield greater plantar flexor force generation because the anterior shift of the athlete’s center of pressure yields a longer moment arm between the ground reaction force ( F GRF ) and the ankle-joint center ( R GRF ). 13, 23 Consequently, this longer moment arm leads to a greater GRF-induced ankle-joint flexion moment.…”

“…33 Hence, deeming that muscle pennation changes are relatively small, increased MT force may further stretch spring-like tendons (tendon length: L T ) and yield shorter in-series operating muscles ( L M ). Lastly, adding carbon fiber plates to shoe soles may decrease plantar flexor muscle fascicle shortening velocity during ground contact, 14, 27 eliciting more economical muscle contractions. 28, 29 Absent of meaningful changes in ankle-joint mechanical power ( P ank ) and plantar flexor MT moment arms ( r MTs ), increasing plantar flexor MTs force ( F MTs ) decreases ankle-joint angular velocity ( ω ank ).…”

Special issue: Bending stiffness: performance and injury effects

“…Their results also indicate that athletes may respond to a medium level of stiffness, with higher and lower stiffness shoes resulting in decreased performance. Madden, Sakaguchi, Wannop, and Stefanyshyn (2016) collected oxygen consumption and kinematic data on athletes performing overground running in different magnitudes of forefoot bending stiffness. The study identified kinematic differences of runners who responded positively (increased performance) in stiff footwear and those who responded negatively (decreased performance) in stiff footwear.…”