Advanced footwear technology does not affect local dynamic stability during treadmill running

Abstract

Advanced footwear technology (AFT) running shoes have a thick midsole of highly compliant and resilient foam, contributing to improved running economy (RE) of, on average, 2–4% (Burns & Joubert, Citation2024). However, this thick layer of compliant foam may result in reduced stability (Burns & Joubert, Citation2024), which in turn has been linked to a worsening of RE (Schütte et al., Citation2018). This effect, termed the ‘cost of instability’, has been suggested to partially explain why RE does not improve when increasing stack height beyond 40 mm (Burns & Joubert, Citation2024). One method to assess running stability is through local dynamic stability (LDS), which can be quantified by calculating the maximum Lyapunov exponent (LyE) of any stationary kinematic time-series signal and describes the ability to withstand small perturbations (Winter et al., Citation2023). Although LDS has proven valuable in clinical gait research, it has received limited attention in footwear science with only one study investigating footwear effects on LDS (Frank et al., Citation2019; Winter et al., Citation2023). Despite a hypothesised reduction in stability caused by AFT, no study has investigated the effects of AFT running shoes on LDS directly.