Heart rate has been reported to increase during nausea and has therefore been used as an indicator of motion sickness. However, the relationship between heart rate and subjective ratings of motion sickness has received little attention, and the autonomic origins of any increase in heart rate during motion sickness are unknown. Spectral analysis of heart rate variability can quantify the degree of sympathetic and parasympathetic stimulation of the heart, as reflected by the low frequency (LF) power and high frequency (HF) power components, and the ratio of LF:HF power (“autonomic balance”). This experiment investigated changes in heart rate and heart rate variability prior to and during the development of nausea. Forty subjects (20 male, 20 female) sat within an optokinetic drum (a visual stimulus) rotating at 5 rpm for a maximum of 32 minutes. Heart rates, measures of heart rate variability, and ratings of sickness were recorded during a resting pre-exposure period and during optokinetic stimulation. Heart rates increased significantly with increasing subjective ratings of sickness (P < .001). This appeared to be attributable to a net increase in sympathetic stimulation of the heart, (P < .05). Sickness ratings were greater for females than males (P = .09), consistent with a significantly greater history of motion sickness reported by females than males over the previous 12 months (P < .02). The findings suggest that a simple measure of heart rate may be a useful indicator of small changes in the degree of sickness that can be of interest in motion sickness research.

The purpose of this study was to investigate the consequences of a high-speed boat transit on physical performance. Twenty-four Royal Marines were randomly assigned to a control (CON) or transit (TRAN) group. The CON group sat onshore for 3 h whilst the TRAN group completed a 3-h transit in open-boats running side-by-side, at 40 knots in moderate-to-rough seas, with boat deck and seat-pan acceleration recorded. Performance tests (exhaustive shuttle-run, handgrip, vertical-jump, push-up) were completed pre- and immediately post-transit/sit, with peak heart rate (HRpeak) and rating of perceived exertion (RPE) recorded. Serial blood samples (pre, 24, 36, 48, 72 h) were analyzed for creatine kinase (CK) activity. The transit was typified by frequent high shock impacts, but moderate mean heart rates (<45% HRpeak). The TRAN group post-transit run distance (-219 m, P < 0.01) and vertical-jump height (5%, P < 0.05) were reduced, the CON group showed no change. The TRAN group post-transit test RPE increased (P < 0.05), however, HRpeak was similar for each group (98%). Post-transit CK activity increased in the TRAN group up to 72 h (P < 0.01) and also, but less markedly, in the CON group (24 and 48 h, P < 0.05). Post-transit run and jump performances were reduced despite mean transit heart rates indicating low energy expenditure. The greater TRAN CK activity suggests muscle damage may have been a contributory factor. These findings have operational implications for Special Forces/naval/police/rescue services carrying out demanding, high-risk physical tasks during and immediately after high-speed boat transits.

National and International Standards (e.g. BS 6841 and ISO 2631-1) provide methodologies for the measurement and assessment of whole-body vibration in terms of comfort and health. The EU Physical Agents (Vibration) Directive (PAVD) provides criteria by which vibration magnitudes can be assessed.However, these standards only consider upright seated (90°) and recumbent (0°) backrest angles, and do not provide guidance for semi-recumbent postures. This paper reports an experimental programme that investigated the effects of backrest angle on comfort during vertical whole-body vibration. The series of experiments showed that a relationship exists between seat backrest angle, whole-body vibration frequency and perceived levels of discomfort. The recumbent position (0°) was the most uncomfortable and the semi-recumbent positions of 67.5° and 45° were the least uncomfortable. A new set of frequency weighting curves are proposed which use the same topology as the existing BS and ISO standards.These curves could be applied to those exposed to whole-body vibration in semirecumbent postures to augment the existing standardised methods.Keywords: whole-body vibration, human comfort, backrest angle Running header: "Backrest angle and whole-body vibration"Relevance statement Current vibration standards provide guidance for assessing exposures for seated, standing and recumbent positions, but not for semi-recumbent postures. This paper reports new experimental data systematically investigating the effect of backrest angle on discomfort experienced. It demonstrates that most discomfort is caused in a recumbent posture and that least was caused in a semi-recumbent posture.

High-speed RIB transits followed immediately by high-intensity activity are intrinsic to contemporary maritime operations; suspension seats can maintain post-transit physical performance, thereby enhancing safety and operational effectiveness.

This study investigated the effects of reclined backrest angles on cognitive and psychomotor tasks during exposure to vertical whole-body vibration. Twenty participants were each exposed to three test stimuli of vertical vibration: 2-8 Hz; 8-14 Hz and 14-20 Hz, plus a stationary control condition whilst seated on a vibration platform at five backrest angles: 0° (recumbent, supine) to 90° (upright). The vibration magnitude was 2.0 ms −2 root-mean-square. The participants were seated at one of the backrest angles and exposed to each of the three vibration stimuli while performing a tracking and choice reaction time tasks; then they completed the NASA-TLX workload scales. Apart from 22.5° seat backrest angle for the tracking task, backrest angle did not adversely affect the performance during vibration. However, participants required increased effort to maintain performance during vibration relative to the stationary condition. These results suggest that undertaking tasks in an environment with vibration could increase workload and risk earlier onset of fatigue. Practitioner SummaryCurrent vibration standards provide guidance for assessing exposures for seated, standing and recumbent positions, but not for semi-recumbent postures. This paper reports new experimental data systematically investigating the effect of backrest angle on human performance. It demonstrates how workload is elevated with whole-body vibration, without getting affected by backrest angle. PADDAN, G.S. ... et al., 2012. The influence of seat backrest angle on human performance during whole-body vibration. Ergonomics, 55 (1), pp. 114 -128.