The mechanical role of the metatarsophalangeal joint in human jumping

Abstract

This study investigated the mechanical role of metatarsophalangeal (MTP) joints in human jumping. Eighteen healthy young men performed three types of single-leg jumps (SJ: squat jump; CMJ: countermovement jump; HJ: standing horizontal jump) on a force plate under barefoot (BARE) and forefoot immobilisation (FFIM) conditions. For FFIM, the forefoot was immobilised around the MTP joints of the dominant leg by a custom-made splint. Force-time components and the centre of pressure (COP) trajectory were measured from the ground reaction force (GRF) in the take-off phase of jumping. The vertical jump heights calculated from the net vertical impulse were lower under FFIM than under BARE during the CMJ (p < 0.05). The HJ distance under FFIM was significantly shorter than that under BARE (p < 0.01). The relative net vertical impulse was lower under FFIM than under BARE during the CMJ (p < 0.05). During the HJ, all the horizontal GRF variables were significantly lower under FFIM than under BARE (p < 0.01), but none of the vertical GRF variables differed between the two conditions. The horizontal relative GRF in the 90-95% of the final take-off phase during the HJ was significantly lower under FFIM than under BARE (p < 0.01). Under FFIM, the COP range in the antero-posterior direction in the take-off phase of the HJ decreased (p < 0.05), whereas its range in the anterior direction for the SJ and CMJ increased (p < 0.05). The results of this study indicate that MTP joint motion can play an important role in regulating force-generating capacities of toe flexor muscles in the take-off phase of human jumping, especially in the horizontal direction of horizontal jumping.

Conflict of interest statement

NO authors have competing interests Enter: The authors have declared that no competing interests exist.

Figures

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

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

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.

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.