The musculo-skeletal response of athletes to various activities during training exercises has become a critical issue in order to optimize their performance and minimize injuries. However, dynamic and kinematic measures of an athlete’s activity are generally limited by constraints in data collection and technology. Thus, the choice of reliable and accurate sensors is crucial for gathering data in indoor and outdoor conditions. The aim of this study is to validate the use of the accelerometer of a high sampling rate (13440.277778emHz) Inertial Measurement Unit (IMU) in the frame of running activities. To this end, two validation protocols are imposed: a classical one on a shaker, followed by another one during running, the IMU being attached to a test subject. For each protocol, the response of the IMU Accelerometer (IMUA) is compared to a calibrated industrial accelerometer, considered as the gold standard for dynamic and kinematic data collection. The repeatability, impact of signal frequency and amplitude (on shaker) as well as the influence of speed (while running) are investigated. Results reveal that the IMUA exhibits good repeatability. Coefficient of Variation CV is 1%()8.58±0.06m/normals2 on the shaker and 3%()26.65±0.69m/normals2 while running. However, the shaker test shows that the IMUA is affected by the signal frequency (error exceeds 10% beyond 800.277778emHz), an observation confirmed by the running test. Nevertheless, the IMUA provides a reliable measure in the range 0–100 Hz, i.e., the most relevant part in the energy spectrum over the range 0–150 Hz during running. In our view, these findings emphasize the validity of IMUs for the measurement of acceleration during running.

This main goal of this study is to investigate the link between both aerodynamics and physiological responses of an international level middle-distance runner, when running either alone or in drafting position behind two pace makers. A simulation model based on Computational Fluid Dynamics (CFD) methods are used to analyze aerodynamic effects while physiological parameters are experimentally recorded using a lightweight ambulatory respiratory gas exchange system (Cosmed K5 © ). Experiments were performed at submaximal effort during a 1000 m on-track running test, and simulations were carried out under similar conditions in terms of speed and runners spacing. The results indicate that compared to the baseline (running alone), the drafting position shows a significant aerodynamic reduction in drag area (-33%), which should be responsible for the measured decrease in the following physiological parameters: oxygen consumption (-6%), heart rate (-1%) and energy cost (-33%). The findings of this study suggest running behind two pace makers meaningfully influences the runner's physiology by minimizing air resistance.

Cotterell and Rice theory (Int J Fract 16 (2): [155][156][157][158][159][160][161][162][163][164][165][166][167][168][169] 1980) on the kinking of a crack submitted to a biaxial loading in a homogeneous material is revisited. Using both an energetic and a stress fracture criteria (Leguillon, Eur J Mech A/Solids 21:61-72, 2002) allows defining a positive threshold of the T-stress T c below which no branching can occur (Selvarathinam and Goree, Eng Fract Mech 60(5-6):543-561, 1998) provided the inhomogeneities size is small compared to the Irwin length. The absence of such a threshold would definitely condemn experimental procedures like the double-cantilever beam (DCB) or compact tension (CT) tests, which result in a positive T-stress at the crack tip. The stress intensity factors K I and T are computed using a contour integral. Calculations provide a very good agreement with the analytical results of the infinite Centrally Notched (CN) plate in tension for instance. An asymptotic analysis makes it possible to define the branching angle as a discontinuous function of T with a jump from 0 • to some significant positive value as T reaches T c . Furthermore, for non vanishing K II , a similar analysis is carried out, a positive T-stress increases the kinking angle due to K II alone.