Effect of increased bending stiffness on running economy and joint biomechanics in uphill running and running on unstable terrain: is there any evidence for embedding carbon plate in trail running footwear?

The emergence of carbon-plated trail running footwear has spurred a re-evaluation of their effects on metabolic power and joint biomechanics. This study investigates the influence of increased longitudinal bending stiffness (LBS) on these parameters during uphill running and on irregular terrain. Ten amateur trail runners wore two conditions of footwear: with and without carbon plates. For each condition, metabolic power was assessed on level and uphill treadmill running (11.6 ± 1.2 km/h and 7.8 ± 0.6 km/h, respectively), while 3D kinematics and kinetics of lower limb joints were evaluated in a laboratory setting on unstable terrain. Subjective assessment of plantar feedback during running on irregular terrain was collected. Regarding biomechanics, discrete variables were extracted as surrogates for joint control on unstable terrains (e.g. normalised jerks, frontal peak angles, and ranges of motion). Because there is no consensus on the quantification of joint stability, the biomechanical analysis was completed with Bayesian statistical parametric mapping to depict differences in-between shoe conditions over the entire signals. Results revealed no footwear effect on metabolic power on level terrain but showed an increase in uphill running metabolic power with the plated condition (2 ± 2%, p = .04). No differences were observed in biomechanical parameters or plantar feedback between conditions. These findings suggest that while increasing LBS does not affect metabolic power during level running, it leads to performance degradation during uphill running. Therefore, the benefits of increased LBS may not be applicable to technical trail running scenarios where running paces are very low. Embedding carbon plates in trail running footwear may lack physiological or biomechanical advantage, underscoring the necessity of considering contextual factors in footwear design for specific activities.