Transmission of Acceleration From a Synchronous Vibration Exercise Platform to the Head During Dynamic Squats

Abstract

Many research studies have evaluated the effects of whole-body vibration exercise on muscular strength, standing balance, and bone density, but relatively few reports have evaluated safety issues for vibration exercises. Knee flexion reduces acceleration transmission to the head during static exercise. However, few studies have evaluated dynamic exercises. The purpose of this investigation was to evaluate the transmission of acceleration to the head during dynamic squats. Twelve participants performed dynamic squats (0°-40° of knee flexion) on a synchronous vertical whole-body vibration platform. Platform frequencies from 20 to 50 Hz were tested at a peak-to-peak nominal displacement setting of 1 mm. Transmissibilities from the platform to head varied depending on platform frequency and knee flexion angle. We observed amplification during 20 and 25 Hz platform vibration when knee flexion was <20°. Vibration from exercise platforms can be amplified as it is transmitted through the body to the head during dynamic squats. Similarly, this vibration energy contributes to observed injuries such as retinal detachment. It is recommended that knee flexion angles of at least 20° and vibration frequencies above 30 Hz are used when performing dynamic squat exercises with whole-body vibration.

Reporting Guidelines for Whole-Body Vibration Studies in Humans, Animals and Cell Cultures: A Consensus Statement from an International Group of Experts

“…Despite some contradictory results reported, Abercromby et al [51], using a fixed configuration (30 Hz and 4 mm), suggested that head acceleration seems to decrease when knee flexion angles are increased from 10 • to 30 • ; however, the authors suggested an increase an in transmissibility above 30 • of knee flexion. These results contrast with previous studies suggesting that flexing the knees results in reduced head transmissibility at all frequencies [48]. It seems that the transmission of vibration to the head is reduced with angles greater than 20 • [48]; in fact, it was recommended to avoid frequencies below 30 Hz, with small knee flexion angles (<40 • ) to reduce the risk of injury at the head level [48].…”

“…These results contrast with previous studies suggesting that flexing the knees results in reduced head transmissibility at all frequencies [48]. It seems that the transmission of vibration to the head is reduced with angles greater than 20 • [48]; in fact, it was recommended to avoid frequencies below 30 Hz, with small knee flexion angles (<40 • ) to reduce the risk of injury at the head level [48]. These suggestions can also be applied to WBV using dynamic movements.…”

“…Mechanical energy transferred to the head can be hazardous, and it is well documented that frequency and knee flexion angles might affect acceleration transmission to the head [48]. As reported in Item 13, certain postures can increase the transmissibility to the head.…”

“…These suggestions can also be applied to WBV using dynamic movements. In a recent study, Caryn and Dickey [48] assessed transmissibility to the head (frequencies between 20 and 50 Hz) during dynamic squats and showed that the response to dynamic exercise is similar to static postures. Hence, summarized, vibration frequency and knee flexion angle interact to affect acceleration submission to the head.…”

Effects of Whole-Body Vibration Training with Different Body Positions and Amplitudes on Lower Limb Muscle Activity in Middle-Aged and Older Women

“…In addition, whole-body vibration training in the static upright is likely to cause head discomfort in older adults. 35 Therefore, static upright and single-leg squats were excluded from the selection of vibration training positions. The study aimed to discuss the effects of whole-body vibration training on lower limb muscle activity in middle-aged and older women with different forms of contraction against self-gravity or with elastic band loading.…”