Sébastien Duc

Transmission of whole body vibration to the lower body in static and dynamic half-squat exercises

Abstract Whole body vibration (WBV) is used as a training method but its physical risk is not yet clear. Hence, the aim of this study is to assess the exposure to WBV by a measure of acceleration at the lower limb under dynamic and static postural conditions. The hypothesis of this paper is that this assessment is influenced by the frequency, position, and movement of the body. Fifteen healthy males are exposed to vertical sinusoidal vibration at different frequencies (20–60 Hz), while adopting three different static postures (knee extension angle: 180°, 120° and 90°) or performing a dynamic half-squat exercise. Accelerations at input source and at three joints of the lower limb (ankle, knee, and hip) are measured using skin-mounted accelerometers. Acceleration values (g) in static conditions show a decrease in the vibrational dose when it is measured at a more proximal location in the lower extremity. The results of the performed statistical test show statistically significant differences (p < 0.05) in the transmissibility values caused by the frequency, the position, and to the presence of the movement and its direction at the different conditions. The results confirm the initial hypothesis and justify the importance of a vibration assessment in dynamic conditions.

Analysis of muscular activity and dynamic response of the lower limb adding vibration to cycling

ABSTRACT Vibration in cycling has been proved to have undesirable effects over health, comfort and performance of the rider. In this study, 15 participants performed eight 6-min sub-maximal pedalling exercises at a constant power output (150W) and pedalling cadence (80 RPM) being exposed to vibration at different frequencies (20, 30, 40, 50, 60, 70 Hz) or without vibration. Oxygen uptake (VO2), heart rate (HR), surface EMG activity of seven lower limb muscles (GMax, RF, BF, VM, GAS, SOL and TA) and 3-dimentional accelerations at ankle, knee and hip were measured during the exercises. To analyse the dynamic response, the influence of the pedalling movement was taken into account. The results show that there was not significant influence of vibrations on HR and VO2 during this pedalling exercise. However, muscular activity presents a significant increase with the presence of vibration that is influenced by the frequency, but this increase was very low (< 1%). Also, the dynamic response shows an influence of the frequency as well as an influence of the different parts of the pedalling cycle. Those results help to explain the effects of vibration on the human body and the influence of the rider/bike interaction in those effects.

Effect of vibration frequency and angle knee flexion on muscular activity and transmissibility function during static whole body vibration exercise.

Whole bodyvibrations (WBV) created by the useof vibrating platform exercise were largely studied for their impact on muscular activity, neuromuscular and postural control (Fratini et al. 2009). Lower limb muscle response to vibration depends on static body position, muscle stiffness, amplitude and frequency of the mechanical vibration (Pollock et al. 2010). Nevertheless, the effect of body position and frequency of vibration on electromyography (EMG) signal are still discussed as several previous studies reported muscular activity increase (Fratini et al. 2009; Pollock et al. 2010; Giminiani et al. 2013), whereas recent studies indicate no significant variation in EMG activity (Avelar et al. 2013). These differences could be due to the vibrations parameters, i.e. amplitude (1–5mm) and frequency (5–55Hz), the degree of knee flexion (5–908) used and the muscle studied. Moreover, most of the time, these studies used closed chain configuration since subjects hold bodypositiononvibratingplatformswithhandsgraspingona front support. The aim of this study was to study the response of lower limb tissues to varied vibration frequencies and angle knee flexion during static body position by measuring thigh and leg muscles activity and the transmissibility function of input vibration across lower body joints.

Principal Componant Analysis between perceptions and kinematics of the subject. An ergonomic case study at office work

Nowadays, musculoskeletal disorders (MD) account for 80% of professional pathologies (INRS 2008). MD contains the peri-articular pathologies that affect muscles, articulations and nerves (INRS 2008). World Health Organization published a report in 2004 that showed prevalence of lumbar back pain was about 60%. The main risks factors of MD are repeatability of a task, bad posture maintaining and static muscle activity (INRS 2008). Videman et al (1990) showed a relationship between back pain and office working according to their low activity. Identification and prevention of risk of MD are usually based on ergonomic studies. Ergonomy focuses on comfort and discomfort, specially with sitting workers. However, few studies have been carried out in order to connect the cognitive approach and biomechanics, aiming to better evaluate the links between the biomechanics of comfort and its perception by a subject (Baucher and Leborgne 2006). These studies interested only on the subjectives comfort’s parameters and postural balance of the subject regardless of the upper joint or spine kinematics. The aim of this study is to show the relationships between comfort’s perception and biomechanics. This approach presents through a case study.

Transmission of whole-body vibration to lower limb during dynamic squat exercise

Whole-body vibration (WBV) exercise has been used for several years to improve neuromuscular performance in athletes or patients. One parameter measured to study the response of the human body to vibration is the transmissibility function. Transmissibility can be determined from the ratio of forces, displacements, velocities or accelerations. Several studies have measured the transmissibility of input vibration delivered by a platform in a standing or flexed position (Avelar et al. 2013) and using different frequencies (Kiiski et al. 2008) and/or amplitudes (Pollock et al. 2010). The majority of these studies have been conducted in a static position. To the best of our knowledge there are no studies that evaluate this physical risk with movement. If movement and vibration exposure are present at the same time, it could be assumed that the movement affects the transmitted dose of vibration throughout the human joints. This could be because movement is a continuous change of position in the human body and it also changes the absorption of energy in the involved segments. So, the aim of this work was to measure the vibration transmissibility (T) according to (1) the movement represented as the relative angle between the segments (u) and its direction, and (2) to measure the excitation frequency of the vibration (v).