Increased muscle activation during whole-body vibration (WBV) is mainly ascribed to a complex spinal and supraspinal neurophysiological mechanism termed the tonic vibration reflex (TVR). However, TVR has not been experimentally demonstrated during low-frequency WBV, therefore this investigation aimed to determine the expression of TVR during WBV.  Whilst seated, eight healthy males were exposed to either vertical WBV applied to the leg via the plantar-surface of the foot, or Achilles tendon vibration (ATV) at 25Hz and 50Hzfor 70s. Ankle plantar-flexion force, tri-axial accelerations at the shank and vibration source, and surface EMG activity of m. soleus (SOL) and m. tibialis anterior (TA) were recorded from the unloaded and passively loaded leg to simulate body mass supported during standing.  Plantar flexion force was similarly augmented by WBV and ATV and increased over time in a load- and frequency dependent fashion. SOL and TA EMG amplitudes increased over time in all conditions independently of vibration mode. 50Hz WBV and ATV resulted in greater muscle activation than 25Hz in SOL when the shank was loaded and in TA when the shank was unloaded despite the greater transmission of vertical acceleration from source to shank with 25Hz and WBV, especially during loading. Low-amplitude WBV of the unloaded and passively loaded leg produced slow tonic muscle contraction and plantar-flexion force increase of similar magnitudes to those induced by Achilles tendon vibration at the same frequencies. This study provides the first experimental evidence supporting the TVR as a plausible mechanism underlying the neuromuscular response to whole-body vibration.

The purpose of the present study was to quantify vibration transmissibility through the lower extremity during exercise on a whole-body vibration (WBV) platform. Six healthy adults completed 20 trials of 30-second static squat exercise at 30 or 40 degrees of knee flexion angle on a WBV platform working at combinations of 5 frequencies (VF: 20, 25, 30, 35, 40 Hz) and 2 amplitudes (VA: low, 1.5 mm or high, 3 mm). Accelerations induced by the platform were recorded simultaneously at the shank and the thigh using triaxial accelerometers positioned at the segmental center of mass. Root-mean-square (RMS) acceleration amplitude and transmission ratios between the platform and the leg segments were calculated and compared between the experimental conditions. An alpha level of 0.05 was set to establish significance. Shank vertical acceleration was greatest at the lower VF (p = 0.028), higher VA (p = 0.028), and deeper squat (p = 0.048). Thigh vertical acceleration was not affected by depth of squat (p = 0.25), but it was greatest at higher VA (p = 0.046) and lower VF (p = 0.028). Medial-lateral shank acceleration was greatest at higher VF and deeper squat (both p = 0.046) and at higher VA (p = 0.028). Medial-lateral thigh acceleration was positively related to both VF (p = 0.046) and VA (p = 0.028) but was not affected by knee angle (p = 0.46). Anterior-posterior shank acceleration was higher at deeper squat (p = 0.046) and at lower VF and higher VA (both p = 0.028). Anterior-posterior thigh acceleration was related positively to the VA (p = 0.028), inversely to the VF (p = 0.028), and not dependent on knee angle (p = 0.75). Identification of specific vibration parameters and posture, which underpin WBV training efficacy, will enable coaches and athletes to design WBV training programs to specifically target shank or thigh muscles for enhanced performance.

Aim:The aim of this study was to characterize acceleration transmission and neuromuscular responses to rotational vibration (RV) and vertical vibration (VV) at different frequencies and amplitudes.Methods:Twelve healthy males completed 2 experimental trials (RV vs VV) during which vibration was delivered during either squatting (30°; RV vs VV) or standing (RV only) with 20, 25, and 30 Hz, at 1.5 and 3.0 mm peak-to-peak amplitude. Vibration-induced accelerations were assessed with triaxial accelerometers mounted on the platform and bony landmarks at ankle, knee, and lumbar spine.Results:At all frequency/amplitude combinations, accelerations at the ankle were greater during RV (all P < .03) with the greatest difference observed at 30 Hz, 1.5 mm. Transmission of RV was also influenced by body posture (standing vs squatting, P < .03). Irrespective of vibration type, vibration transmission to all skeletal sites was generally greater at higher amplitudes but not at higher frequencies, especially above the ankle joint. Acceleration at the lumbar spine increased with greater vibration amplitude but not frequency and was highest with RV during standing.Conclusions/Implications:The transmission of vibration during whole-body vibration (WBV) is dependent on intensity and direction of vibration as well as body posture. For targeted mechanical loading at the lumbar spine, RV of higher amplitude and lower frequency vibration while standing is recommended. These results will assist with the prescription of WBV to achieve desired levels of mechanical loading at specific sites in the human body.

Despite the well-documented benefits of physical activity (PA), physical inactivity remains a global public health concern. Particularly high levels of sedentarism prevail among young females, making them an important target population for PA behaviour intervention. The effectiveness of interventions designed for this population has not been rigorously analysed and previous reviews of PA interventions and their ability to target specific barriers and subgroups of society have produced inconsistent findings. Ecological models have proven instrumental in categorising factors that influence health behaviours on multiple levels (intrapersonal, interpersonal, organisational and environmental, and, policy and legislative). This narrative systematic review aims to collate, summarise and synthesise evidence pertaining to the characteristics of PA interventions aimed at young females in the UK (14-25 years), explore the measures used to evaluate intervention impact within this population, and to make recommendations for future PA intervention research through an ecological perspective. UK-based PA intervention studies including healthy females aged 14-25 were identified through five electronic databases. Two reviewers independently screened the studies for inclusion, data was extracted based upon agreed criteria, and results were discussed in light of the ecological model of health behaviour. From the 21 articles included in the analysis, 17 interventions took place in educational institutions. PA options were limited across, and within interventions, and only four studies employed qualitative methods to investigate intervention effectiveness. Utilizing the ecological model it was identified that 20 studies investigated intrapersonal factors such as body composition and self-efficacy, and only seven studies explored multiple levels of the model. In conclusion, PA

Introduction Pod Vaping Devices (PVD) such as JUUL have become extremely popular in the US although their uptake and use in the UK remains lower. A key difference between the US and the UK is the nicotine strength legally permitted, typically 59mg/mL in the US but capped at 20mg/mL in the UK and EU. This may limit the ability of EU vaping devices to deliver satisfactory nicotine levels. The primary aim was to compare the EU- (18mg/mL nicotine strength) with the US-JUUL (59mg/mL) on daily smokers’ subjective experiences, craving relief and blood nicotine levels. Methods Double-blind, counter-balanced within-participants design with 2 conditions: 18mg/mL vs. 59mg/mL. On two separate occasions, UK smokers (N=19, 10 Males, 9 Females) vaped ad libitum for 60 mins and provided blood samples at baseline 5, 15, 30 and 60 mins. Subjective effects (incl. satisfaction) were measured at 10 and 60 mins and, craving and withdrawal symptoms (WS) at baseline, 10 and 60 mins. Results Satisfaction did not differ between conditions. There was a significant interaction between Time and Nicotine concentration for Nicotine Hit (p=.045). Mean self-report of Nicotine Hit increased under the use of the 59mg/mL from 10 to 60 mins and decreased under the 18mg/mL. Participants reported higher Throat Hit following use of the 59mg/mL (p=.017). There were no differences in other subjective effects including craving, WS relief (ps&gt;.05). Liquid consumption was doubled under the 18 versus the 59mg/mL (p=.001) and nicotine boost was significantly higher in the 59mg/mL at all time-points (p≤.001). Conclusions The results did not support our hypotheses that satisfaction, craving and withdrawal reduction would be higher with the 59mg/mL JUUL. This could be due to the doubling of liquid consumption in the 18mg/mL. Whether satisfaction and craving relief persists over the longer-term outside of the lab remains to be determined. Implications In a 60-min ad lib vaping session, the EU-JUUL was found to produce comparable satisfaction, craving- and withdrawal-relief as the US-JUUL in this sample of UK smokers. These findings could suggest that the higher nicotine concentrations available in PVDs in the US are not necessary for providing satisfaction and improving craving and WS. However, this was at the expense of a considerable increase in liquid consumption indicative of compensatory puffing.