Samuel J. Allen

Neuromuscular function in healthy occlusion

This study aimed to measure neuromuscular function for the masticatory muscles under a range of occlusal conditions in healthy, dentate adults. Forty-one subjects conducted maximum voluntary clenches under nine different occlusal loading conditions encompassing bilateral posterior teeth contacts with the mandible in different positions, anterior teeth contacts and unilateral posterior teeth contacts. Surface electromyography was recorded bilaterally from the anterior temporalis, superficial masseter, sternocleidomastoid, anterior digastric and trapezius muscles. Clench condition had a significant effect on muscle function (P = 0.0000) with the maximum function obtained for occlusions with bilateral posterior contacts and the mandible in a stable centric position. The remaining contact points and moving the mandible to a protruded position, whilst keeping posterior contacts, resulted in significantly lower muscle activities. Clench condition also had a significant effect on the per cent overlap, anterior-posterior and torque coefficients (P = 0.0000-0.0024), which describe the degree of symmetry in these muscle activities. Bilateral posterior contact conditions had significantly greater symmetry in muscle activities than anterior contact conditions. Activity in the sternocleidomastoid, anterior digastric and trapezius was consistently low for all clench conditions, i.e. <20% of the maximum voluntary contraction level. In conclusion, during maximum voluntary clenches in a healthy population, maximum masticatory muscle activity requires bilateral posterior contacts and the mandible to be in a stable centric position, whilst with anterior teeth contacts, both the muscle activity and the degree of symmetry in muscle activity are significantly reduced.

Trade-offs between horizontal and vertical velocities during triple jumping and the effect on phase distances.

The triple jump is an athletic event involving three ground contact phases during which athletes must trade off the maintenance of horizontal velocity against the generation of vertical velocity. Previous studies have indicated that individual athletes have a linear relationship between the loss in horizontal velocity and the gain in vertical velocity during each phase. This study used computer simulation to investigate the effects of constraining the takeoff velocities in the hop phase on the velocity trade-offs in this and subsequent phases. Kinematic data were obtained from an entire triple jump using a Vicon automatic motion capture system, and strength and anthropometric data were collected from the triple jumper. A planar 13-segment torque-driven subject-specific computer simulation model was used to maximise the distance of each phase by varying torque generator activation timings using a genetic algorithm. Vertical takeoff velocities in the hop phase were constrained to be 100%, ±10%, ±20%, and ±30% of the performance velocity, and subsequent phases were optimised with initial conditions calculated from the takeoff of the previous phase and with no constraints on takeoff velocity. The results showed that the loss in horizontal velocity during each contact phase was strongly related to the vertical takeoff velocity (R(2)=0.83) in that phase rather than the overall gain in vertical velocity as found in previous studies. Maximum overall distances were achieved with step phases which were 30% of the total distance of the triple jump confirming the results of experimental studies on elite triple jumpers.

Running Technique Is An Important Component Of Running Economy And Performance

Despite an intuitive relationship between technique and both running economy (RE) and performance, and the diverse techniques used by runners to achieve forward locomotion, the objective importance of overall technique and the key components therein remain to be elucidated. Purpose This study aimed to determine the relationship between individual and combined kinematic measures of technique with both RE and performance. Methods Ninety-seven endurance runners (47 females) of diverse competitive standards performed a discontinuous protocol of incremental treadmill running (4-min stages, 1-km·h−1 increments). Measurements included three-dimensional full-body kinematics, respiratory gases to determine energy cost, and velocity of lactate turn point. Five categories of kinematic measures (vertical oscillation, braking, posture, stride parameters, and lower limb angles) and locomotory energy cost (LEc) were averaged across 10–12 km·h−1 (the highest common velocity < velocity of lactate turn point). Performance was measured as seasons best (SB) time converted to a sex-specific z-score. Results Numerous kinematic variables were correlated with RE and performance (LEc, 19 variables; SB time, 11 variables). Regression analysis found three variables (pelvis vertical oscillation during ground contact normalized to height, minimum knee joint angle during ground contact, and minimum horizontal pelvis velocity) explained 39% of LEc variability. In addition, four variables (minimum horizontal pelvis velocity, shank touchdown angle, duty factor, and trunk forward lean) combined to explain 31% of the variability in performance (SB time). Conclusions This study provides novel and robust evidence that technique explains a substantial proportion of the variance in RE and performance. We recommend that runners and coaches are attentive to specific aspects of stride parameters and lower limb angles in part to optimize pelvis movement, and ultimately enhance performance.

Models incorporating pin joints are suitable for simulating performance but unsuitable for simulating internal loading

Simulation models of human movement comprising pin-linked segments have a potential weakness for reproducing accurate ground reaction forces during high impact activities. While the human body contains many compliant structures such a model only has compliance in wobbling masses and in the foot-ground interface. In order to determine whether accurate GRFs can be produced by allowing additional compliance in the foot-ground interface, a subject-specific angle-driven computer simulation model of triple jumping with 13 pin-linked segments was developed, with wobbling masses included within the shank, thigh, and trunk segments. The foot-ground interface was represented by spring-dampers at three points on each foot: the toe, ball, and heel. The parameters of the spring-dampers were varied by a genetic algorithm in order to minimise the differences between simulated GRFs, and those measured from the three phases of a triple jump in three conditions: (a) foot spring compression limited to 20 mm; (b) this compression limited to 40 mm; (c) no restrictions. Differences of 47.9%, 15.7%, and 12.4% between simulation and recorded forces were obtained for the 20 mm, 40 mm, and unrestricted conditions, respectively. In the unrestricted condition maximum compressions of between 43 mm and 56 mm were obtained in the three phases and the mass centre position was within 4mm of the actual position at these times. It is concluded that the unrestricted model is appropriate for simulating performance whereas the accurate calculation of internal forces would require a model that incorporates compliance elsewhere in the link system.

Exploiting 3D printing technology to develop robotic running foot for footwear testing

Results of modern automatic footwear testing technology based on the biomechanics of the human foot have limitations due to use of the passive imitative foot. On the other hand, many studies on the humanoid walking robot, orthotic ankle, and prosthesis for amputees have been presented. However, these studies only focused on the ankle joint and walking gait. In this paper, the authors proposed a framework for developing a robotic running foot-leg for footwear testing. This prosthesis has four controlled degrees of freedom at the hip, knee, ankle and metatarsophalangeal joints. Along with two active joints (i.e. the ankle and metatarsophalangeal joints) and one passive joint (i.e. the midtarsal joint), the foot model also includes the windlass mechanism formed by the hindfoot, metatarsals and plantar fascia springs. In addition, the framework includes iteration for rapid prototyping and developing the cover of the robotic foot by simultaneous multi-material 3D printing technology.

Optimisation of phase ratio in the triple jump using computer simulation.

The triple jump is an athletic event comprising three phases in which the optimal proportion of each phase to the total distance jumped, termed the phase ratio, is unknown. This study used a whole-body torque-driven computer simulation model of all three phases of the triple jump to investigate optimal technique. The technique of the simulation model was optimised by varying torque generator activation parameters using a Genetic Algorithm in order to maximise total jump distance, resulting in a hop-dominated technique (35.7%:30.8%:33.6%) and a distance of 14.05m. Optimisations were then run with penalties forcing the model to adopt hop and jump phases of 33%, 34%, 35%, 36%, and 37% of the optimised distance, resulting in total distances of: 13.79m, 13.87m, 13.95m, 14.05m, and 14.02m; and 14.01m, 14.02m, 13.97m, 13.84m, and 13.67m respectively. These results indicate that in this subject-specific case there is a plateau in optimum technique encompassing balanced and hop-dominated techniques, but that a jump-dominated technique is associated with a decrease in performance. Hop-dominated techniques are associated with higher forces than jump-dominated techniques; therefore optimal phase ratio may be related to a combination of strength and approach velocity.

Position tracking control in torque mode for a robotic running foot for footwear testing

Available automatic footwear testing systems still lack flexibility and bio-fidelity to represent the human foot and reproduce the wear conditions accurately. The first part of this article introduces a new design of the robotic running foot for footwear testing using cable conduit mechanisms. This robotic running foot is integrated with an upper leg mechanism to form a complete integrated footwear testing system. The cable conduit mechanisms help remove the bulky actuators and transmissions out of the fast-moving robotic foot. Thus, this robotic running foot design not only allows high-power actuators to be installed, but also avoids a significant dynamic mass and inertia effects on the upper leg mechanism. This means that the integrated footwear testing system can have multiple powered degrees of freedom in the robotic running foot and simulate much higher human running speeds than other available systems. However, cable conduit mechanisms cause significant challenges in control approaches, especially in high-speed systems, due to their nonlinear transmission characteristics. Furthermore, the robotic running foot actuators must operate in a torque/force control mode to reproduce the foot–shoe interaction during gaits while it is critical to control the foot joints’ position in the swing phase of gaits. The latter part of this article presents a study on position tracking control in torque mode for the robotic running foot joints using adaptive and proportional–integral–derivative control designs to evaluate the system’s ability to mimic the human foot kinematics in running. Both controllers proved their effectiveness, implying that the proposed control approach can be implemented on the integrated footwear testing system to control the foot joints’ position in the swing phase of running gaits.

The effect of increasing strength and approach velocity on triple jump performance.

The triple jump is an athletic event comprising three phases in which the optimal phase ratio (the proportion of each phase to the total distance jumped) is unknown. This study used a planar whole body torque-driven computer simulation model of the ground contact parts of all three phases of the triple jump to investigate the effect of strength and approach velocity on optimal performance. The strength and approach velocity of the simulation model were each increased by up to 30% in 10% increments from baseline data collected from a national standard triple jumper. Increasing strength always resulted in an increased overall jump distance. Increasing approach velocity also typically resulted in an increased overall jump distance but there was a point past which increasing approach velocity without increasing strength did not lead to an increase in overall jump distance. Increasing both strength and approach velocity by 10%, 20%, and 30% led to roughly equivalent increases in overall jump distances. Distances ranged from 14.05m with baseline strength and approach velocity, up to 18.49m with 30% increases in both. Optimal phase ratios were either hop-dominated or balanced, and typically became more balanced when the strength of the model was increased by a greater percentage than its approach velocity. The range of triple jump distances that resulted from the optimisation process suggests that strength and approach velocity are of great importance for triple jump performance.