Anterior subject positioning affects the maximal exerted isometric plantar flexion moment

Abstract

We examined the effect of increased anterior subject positioning toward the dynamometer’s footplate during maximal voluntary isometric contractions (MVCs) on the joint moment, rotation and rate of torque development (RTD). Fourteen subjects, with their hip flexed (110°) and knee fully extended (180°), underwent ramp maximal and rapid voluntary isometric plantar flexion contractions at 4 different positions (0, 3, 6 and 8 cm; randomized). At position “0 cm”, the foot was in full contact with the footplate; at the additional positions, the chair was moved forward. Body kinematics (VICON) and kinetics (HUMAC Norm, PEDAR) were captured synchronously during MVCs and RTDs. The results showed that the maximal exerted joint moment was significantly (p<0.01) increased by >32% from the 0-cm to 8-cm position (126 and 172 Nm, respectively); however, at the “6 cm” and “8 cm” positions, no significant difference was found. The joint rotation was significantly (p<0.01) reduced by >50% (from 15.5 to 7.1°; 0–8 cm). The maxRTD was only significantly higher at “6 cm” compared with the “0 cm” position. The time to reach maxRTD showed shorter tendencies for the “8 cm” position than for all other positions. The results indicate an underestimation of the plantar flexor maximal force potential with the current measuring technique. This could be critical in pre-post study designs where a 2-cm alteration in the chair position can induce an error of ~9% in the joint moment. The joint rotation could be reduced but not completely eliminated. For position standardization purposes, a pressure >220 kPa under the subject’s foot is needed to achieve the maximal joint moment. We discussed the possible origins (fascicle length, neural drive) of the increased joint moment.

Changes in the Plantar Flexion Torque of the Ankle and in the Morphological Characteristics and Mechanical Properties of the Achilles Tendon after 12-Week Gait Retraining

“…The plantar flexion torque of the ankle and the peak plantar flexion torque (T max ) were directly collected from the dynamometer, and then normalized to body weight (dividing by the body weight) [ 9 ]. The peak rate of the plantar flexion torque development (RTD max , Figure 3 ) was obtained by calculating the maximal slope of the plantar flexion torque-time curve, namely, the peak first derivative of the plantar flexion torque [ 20 ].…”

Ankle joint rotation and exerted moment during plantarflexion dependents on measuring- and fixation method

“…To reduce the ankle joint movement, commercial dynamometer manufactures are suggesting securing the foot on the dynamometer footplate with inextensible straps. The majority of the conducted research [ 5 – 7 , 13 – 15 ] used the proposed fixation method but nonetheless other researchers [ 2 , 3 , 8 , 9 , 12 , 16 – 19 ] avoided to implement that procedure. A possible explanation could be the reliance on the increased rigidity of the custom-made dynamometer device or the scope of the research project.…”

“…It is known from the literature that during the plantarflexion efforts, an inevitable joint rotation occurs [ 1 , 12 , 20 ]. The origin of the joint rotation was identified on the compliance of the dynamometer-subject system [ 21 ], the cushioning pads [ 22 ] and the soft muscular tissue [ 23 ].…”

“…With the subsequent straightening of the knee joint, the cushioning pads were compressed and a firmer contact of the foot to the dynamometer plate was ensured. In a recent attempt [ 12 ] we showed that with a similar method, a foot pressure of ~220kPa was necessary in order to achieve the maximal plantarflexion moment and to reduce the ankle joint rotation (>32% and >50% respectively), compared to initial condition. That outcome raised the question, if the use of a fixation method (straps) is necessary to achieve the maximum moment and minimum joint rotation during plantar flexion efforts or if only chair adjustments is needed [ 12 , 25 , 26 ] to reach similar results.…”

“…Nonetheless, to assess the kinematics of the ankle joint during plantarflexion efforts, researchers implemented digital [ 1 , 26 ], infrared cameras [ 12 , 25 , 27 ], electrical goniometers [ 3 , 5 , 13 ], potentiometers [ 4 ] or simply measured the crank angle provided by the isokinetic dynamometer [ 28 , 29 ]. For example, Magnusson and colleagues (2001) [ 3 ] measured the joint rotation during plantarflexion efforts by placing an electrical goniometer on the distal part of the fifth metatarsal and the posterolateral aspect of the fibula.…”