Fig 1.
Forefoot immobilisation (FFIM) with a splint.
Several pieces of wood sticks were cut and adjusted to the length of the forefoot, and these pieces were jointed parallel with vinyl tape so that this splint could be bent in a small range at the sagittal plane of the foot. The size of the splint was approximately 9.5 cm long, 13.8 cm wide and 48.0 g. The splint was fixed on the dorsal side of the dominant forefoot by taping. White arrows show the direction of overlap around the dorsal side of the forefoot.
Fig 2.
Typical raw data of ground reaction force during the squat jump (SJ), countermovement jump (CMJ) and horizontal jump (HJ) under barefoot conditions.
Take-off phase: The range from the onset of the vertical GRF change to the take-off during the ground contact of the SJ, CMJ and HJ; Fz_max: Maximum vertical ground reaction force; Fz_mini: Minimum vertical ground reaction force; Fy_max: Maximum horizontal ground reaction force; VI (grey area): Net vertical impulse; HI (grey area): Net horizontal impulse.
Fig 3.
Relative differences in jump performance for the squat jump (SJ), countermovement jump (CMJ) and horizontal jump (HJ) under forefoot immobilisation (FFIM).
Values are mean and SD. Jump heights in the SJ and CMJ were calculated from the net vertical impulse (Jump height _impulse). The dashed line at 100% indicates the level without a splint (BARE). + and * denote significant differences between BARE and FFIM at p < 0.05 and p < 0.01, respectively.
Table 1.
Comparison of jump performance during the squat jump (SJ), countermovement jump (CMJ) and horizontal jump (HJ) under barefoot (BARE) and forefoot immobilization (FFIM) conditions.
Fig 4.
Relative changes in the ground reaction force (GRF) during the take-off phase of the squat jump (SJ), countermovement jump (CMJ) and horizontal jump (HJ) under barefoot (BARE) and forefoot immobilisation (FFIM) conditions.
BARE: Black line (mean) and bar (SD); FFIM: Grey dashed line (mean) and grey dotted bar (SD). * denotes a significant difference between BARE and FFIM at p < 0.01.
Fig 5.
The statistical parametric mapping (SPM) in relative changes in the ground reaction force (GRF) during the take-off phase of the squat jump (SJ), countermovement jump (CMJ) and horizontal jump (HJ).
Grey dotted lines are the critical threshold points where are considered significantly different between BARE and FFIM. Grey area is significant difference between BARE and FFIM.
Table 2.
Comparison of ground reaction force (GRF) related variables during the take-off phase of the squat jump (SJ), countermovement jump (CMJ) and horizontal jump (HJ) under barefoot (BARE) and forefoot immobilization (FFIM) conditions.
Table 3.
Comparison of the centre of pressure (COP) related variables during the take-off phase of the squat jump (SJ), countermovement jump (CMJ) and horizontal jump (HJ) under barefoot (BARE) and forefoot immobilisation (FFIM) conditions.
Fig 6.
Schematic model of the force amplification mechanism of the toe flexors.
MTC, Muscles, tendon, fascia & aponeurosis complex; MTP, metatarsophalangeal joints. Gray arrow and dashed lines show the schema in which the vertical load applied to the talus bone is transmitted to the metatarsal and the calcaneus bones, thenceforward increasing in the tension of the MTC of the toe flexors and enhancing the force generation at the push-off.