Effect of relaxation time on hysteresis of human tendon in vivo.

OBJECTIVES: The purpose of this study was to investigate the effect of relaxation time on tendon hysteresis. METHODS: Subjects exerted isometric plantar flexion torque from rest to maximal voluntary isometric contractions within around 0.5 s, followed by relaxation with six different times (0.3, 0.5, 0.7, 1, 3, and 5 s). During each trial, tendon elongation in the medial gastrocnemius muscle was measured by ultrasonography. The area within the exerted torque-tendon elongation loop, as a percentage of the area beneath the curve during ascending phase, was calculated as tendon hysteresis. RESULTS: Between the 0.3 and 1 s relaxation time conditions, the hysteresis values were significantly greater for the shorter relaxation time conditions (except between the 0.5 and 0.7 s conditions). In contrast, no significant differences in tendon hysteresis were found between 1 and 5 s of relaxation time conditions. Furthermore, the relationship between relaxation time and tendon hysteresis showed a significantly negative correlation under 1 s or less of relaxation time, but no significant correlation was observed under conditions of 1 s or more. CONCLUSION: These results suggest that relaxation time greatly affects tendon hysteresis under condition that relaxation time was less than 1 s.

Predicting the Early-Age Time-Dependent Behaviors of a Prestressed Concrete Beam by Using Physics-Informed Neural Network.

This paper proposes a physics-informed neural network (PINN) for predicting the early-age time-dependent behaviors of prestressed concrete beams. The PINN utilizes deep neural networks to learn the time-dependent coupling among the effective prestress force and the several factors that affect the time-dependent behavior of the beam, such as concrete creep and shrinkage, tendon relaxation, and changes in concrete elastic modulus. Unlike traditional numerical algorithms such as the finite difference method, the PINN directly solves the integro-differential equation without the need for discretization, offering an efficient and accurate solution. Considering the trade-off between solution accuracy and the computing cost, optimal hyperparameter combinations are determined for the PINN. The proposed PINN is verified through the comparison to the numerical results from the finite difference method for two representative cross sections of PSC beams.

Effect of different positions of splinting on flexor tendon relaxation: a cadaver study.

We performed a cadaver study to evaluate how six different static heat-moulded splints affect flexor tendon relaxation. Each splint positioned the wrist and metacarpophalangeal (MCP) joints in different positions. We evaluated the tendon relaxation in 12 fresh adult cadaver forearms by measuring the flexor tendon displacement between two solid markers for each splint. The wrist position ranged from 30° flexion to 45° extension and the MCP joints from 30° to 60° flexion. For each splint, tendon relaxation was achieved relative to the neutral reference position. Tendon relaxation was greatest when the MCP joints were positioned in 60° flexion. We also noted the persistence of tendon relaxation when the wrist was positioned in extension (30° or 45°) as long as MCP joint flexion was maintained (30° or 60°). We conclude that the wrist extension with the MCP joints flexion may optimize tendon relaxation during immobilization after flexor tendon repairs.