Franz Konstantin Fuss

Comparison of Non-Invasive Individual Monitoring of the Training and Health of Athletes with Commercially Available Wearable Technologies

Athletes adapt their training daily to optimize performance, as well as avoid fatigue, overtraining and other undesirable effects on their health. To optimize training load, each athlete must take his/her own personal objective and subjective characteristics into consideration and an increasing number of wearable technologies (wearables) provide convenient monitoring of various parameters. Accordingly, it is important to help athletes decide which parameters are of primary interest and which wearables can monitor these parameters most effectively. Here, we discuss the wearable technologies available for non-invasive monitoring of various parameters concerning an athletes training and health. On the basis of these considerations, we suggest directions for future development. Furthermore, we propose that a combination of several wearables is most effective for accessing all relevant parameters, disturbing the athlete as little as possible, and optimizing performance and promoting health.

Design and evaluation of smart wearable undergarment for monitoring physiological extremes in firefighting

For workers in extreme environments, such as firefighters, thermal protective clothing is essential to protect them from exposures to high heat and life threatening risks. This study will investigate the design of a new smart protective clothing system, which incorporates sensors in the undergarment to measure physiological data, such as skin temperature, heat flux and heat rate to assess the thermal status of the worker. The aim of this paper is to outline the design of the smart wearable undergarment and the evaluation process for testing the smart undergarment in a controlled environment.

Nonlinear Visco-Elastic Materials

Linear visco-elastic models in the simplest form require three parameters, two springs and one damper, as two-parameter models, i.e. Maxwell and Kelvin–Voight models, either relax stress or creep, but are not capable of doing both. Three-element linear models can be expanded by adding further linear elements (Wiechert model). Nonlinearity can be attributed to linear models, e.g., by power Hertzian springs and exponential functions applied to springs and dampers. Still, the basic structure of such models is linear, as long as they consist of springs and dampers. In visco-elastic materials such as polymers, the Young’s modulus is commonly used for the materials’ stiffness characterisation, often without referring to the strain rate applied. Dependency of the Young’s modulus on the strain rate is an inherent property of visco-elasticity. By definition, the Young’s modulus is determined at small strain as is the Poisson’s ratio.

The Loss Tangent of Visco-Elastic Models

When modelling visco-elasticity, be it linearly (standard linear solid with two springs and one damper) or non-linearly (power and log models), it is important to know on which model parameters the viscous energy loss depends on. In this paper, the dependency of the loss tangent (tan δ, ratio of loss modulus to storage modulus) and the phase angle δ on elasticity E and viscosity η parameters and on the excitation frequency f is derived and evaluated in three visco-elastic models. In the Zener model (standard linear solid of Voight form), tan δ and δ depend on E, η, and f. f and η are linked together and always occur as the product fη. Tan δ is smaller than π/2. The transient part of the stress function is an exponential function; the steady state part comprises of sine and cosine functions. In the power model, tan δ and δ depend on η only; (0 ≤ η < 1). η has no relationship with f in tan δ. Tan δ is smaller than π/2. The transient part of the stress function is a Maclaurin series; the steady state part is a sine function with ηπ/2 phase shift. In the log model, tan δ and δ depend on E, η, and f; but at the same f, larger E/η have larger tan δ and δ. The viscosity constant appears as a stand alone η, and as the product of η and log 2πf. Tan δ can be larger than π/2 at small E/η (high viscosity) and small frequencies (large cycle periods with small strain rates). The transient part of the stress function comprises of cosine and sine integrals; steady state part consists of sine and cosine functions.