The interplay of footwear and exercise-induced fatigue on substrate partitioning and energy cost of running during steady-state running exercise

The purpose of this study was to assess the interplay of footwear and exercise-induced fatigue (EIF) on substrate partitioning and energy cost of running during steady-state running exercise. Ten trained male distance runners partook first in an incremental test 7 days prior to the experimental session. Participants performed three 8 min treadmill runs in randomized order in minimalist and shod footwear prior to and immediately after an EIF protocol. Cardiorespiratory parameters, substrate partitioning, RPE and blood lactate were measured throughout the experimental sessions. No significant difference was observed pre- to post-EIF on VO₂ during Cr, although VCO₂ production showed a trend towards significance (p = 0.063). Furthermore, there was no significant effect of footwear but there was significant main effect of time (pre- vs. post-EIF) on CHO (p = 0.003) and lipid (p =0.004) oxidation. The caloric cost of running showed no significant difference from pre- to post-EIF (0.98±0.14, 1.00±0.14). Ultimately alteration in substrate contribution to energy production plausibly stems from muscle glycogen depletion. Although not measured muscle glycogen has certainly greatly contributed to maintain running performance during EIF. This is supported by indirect markers of fatigue such as lactate production, RPE score and peak HR.