A methodological proof-of-concept of the teeter-totter effect.

The Nike Vaporfly 4% (VP4) shoe is popular due to its unique design and reported performance benefits. However, the underlying mechanisms responsible for the improvements remain unclear. One proposed mechanism is the teeter-totter effect. This study aimed to 1) experimentally test the teeter-totter theory by estimating the teeter-totter moment (M TT ) in the VP4 compared to a flat shoe (CONTROL) and 2) quantify the change in the anterior-posterior position of the centre of pressure (Δx a-p ) in the VP4 compared to the CONTROL. Plantar pressures and high-speed video were recorded from 15 runners in two shoe conditions. The VP4 generated a larger propulsion moment, M P , ( ∫ M P dt  = 90.46 ± 38.87 Nms; p  < 0.001, d  = 1.95), suggesting the presence of an M TT in the VP4 ( ∫ M TT dt  = 57.16 ± 24.35 Nms) when compared to the CONTROL ( ∫ M P dt  = 33.30 ± 14.52 Nms). Δx a-p was greater in the VP4 (Δx a-p  = 9.48 ± 6.08 mm; p  < 0.001, d  = 2.07) compared to the CONTROL (Δx a-p  = 0.54 ± 0.67 mm). This study provides a methodological proof-of-concept for the teeter-totter theory. The findings highlight the possibility of a teeter-totter effect resulting in greater heel propulsion while running in an AFT shoe construction, assuming a constant muscle moment and pivot point.