In-situ force plate calibration: 12 years' experience with an approach for correcting the point of force application

Pilot study: validity and reliability of textile insoles used to measure the characteristics of landing tasks during rehabilitation and artistic gymnastics

OBJECTIVES

Artistic gymnastics is a sport where most athletes start at an early age and training volumes are high. Hence, overuse and acute injuries are frequent due to the load endured during landing tasks. During landing, the ground reaction force (GRF) is up to 15.8 times the body weight and therefore reliable GRF measurements are crucial. The gold standard for GRF measurements are force plates. As force plates are mostly used in a constrained laboratory environment, it is difficult to measure the GRF in representative training settings. Textile insoles (novel GmbH, Munich, Germany) exist, which can be used to measure dynamic GRF. Hence, the motivation of this study is to test the validity and reliability of these insoles during landing tasks. GRF was measured during four different exercises, in two test subjects and compared to concurrent force plate data.

RESULTS

Twelve out of 16 statistical parametric mapping plots showed no significant difference between the measured force curves of insoles and force plates. Across conditions, the root mean square error of the maximal vertical GRF was 21 N/kg and an impulse 0.4 Ns/kg. The intraclass correlation coefficient (ICC 2,1) ranged from 0.02 to 0.76 for maximal vertical GRF and from - 0.34 to 0.76 for impulse. The insoles are a valid measurement tool for GRF curve progression and impulse during landing but underestimate the maximal vertical GRF.

Intrinsic foot joints adapt a stabilized-resistive configuration during the stance phase

BACKGROUND

This study evaluated the 3D angle between the joint moment and the joint angular velocity vectors at the intrinsic foot joints, and investigated if these joints are predominantly driven or stabilized during gait.

METHODS

The participants were 20 asymptomatic subjects. A four-segment kinetic foot model was used to calculate and estimate intrinsic foot joint moments, powers and angular velocities during gait. 3D angles between the joint moment and the joint angular velocity vectors were calculated for the intrinsic foot joints defined as follows: ankle joint motion described between the foot and the shank for the one-segment foot model (hereafter referred as Ankle), and between the calcaneus and the shank for the multi-segment foot model (hereafter referred as Shank-Calcaneus); joint motion described between calcaneus and midfoot segments (hereafter referred as Chopart joint); joint motion described between midfoot and metatarsus segments (hereafter referred as Lisfranc joint); joint motion described between first phalanx and first metatarsal (hereafter referred as First Metatarso-Phalangeal joint). When the vectors were approximately aligned, the moment was considered to result in propulsion (3D angle <60^o) or resistance (3D angle >120^o) at the joint. When the vectors are approximately orthogonal (3D angle close to 90°), the moment was considered to stabilize the joint.

RESULTS

The results showed that the four intrinsic joints of the foot are never fully propelling, resisting or being stabilized, but are instead subject to a combination of stabilization with propulsion or resistance during the majority of the stance phase of gait. However, the results also show that during pre-swing all four the joints are subject to moments that result purely in propulsion. At heel off, the propulsive configuration appears for the Lisfranc joint first at terminal stance, then for the other foot joints at pre-swing in the following order: Ankle, Chopart joint and First Metatarso-Phalangeal joint.

CONCLUSIONS

Intrinsic foot joints adopt a stabilized-resistive configuration during the majority of the stance phase, with the exception of pre-swing during which all joints were found to adopt a propulsive configuration. The notion of stabilization, resistance and propulsion should be further investigated in subjects with foot and ankle disorders.