Effect of a load distribution system on mobility and performance during simulated and field hiking while under load.

This study was conducted to test a modular scalable vest-load distribution system (MSV-LDS) against the plate carrier system (PC) currently used by the United States Marine Corps. Ten Marines engaged in 1.6 km load carriage trials in seven experimental conditions in a laboratory study. Kinematic, kinetic, and spatiotemporal gait parameters, muscle activity (electromyography), heart rate, caloric expenditure, shooting reaction times, and subjective responses were recorded. There was lower mean trapezius recruitment for the PC compared with the MSV-LDS for all conditions, and muscle activity was similar to baseline for the MSV-LDS. Twenty-seven Marines carrying the highest load were evaluated in the field, which measured an increase in energy expenditure with MSV-LDS; however, back discomfort was reduced. The field evaluation showed significantly reduced estimated ground reaction force on flat-ground segments with the MSV-LDS, and the data suggest both systems were comparable with respect to mobility and energy cost. Practitioner summary: This study found that a novel load distribution system appears to redistribute load for improved comfort as well as reduce estimated ground reaction force when engaged in hiking activities. Further, hiking with a load distribution system enables more neutral walking posture. Implications of load differences in loads carried are examined. Abbreviations: AGRF: anterior-posterior ground reaction forces; CAREN: Computer Assisted Rehabilitation Environment; GRF: ground reaction forces; HR: heart rate; ML-GRF: mediolateral ground reaction forces; MOLLE: Modular Lightweight Load-carrying Equipment; MSV-LDS: modular scalable vest-load distribution system; NHRC: Naval Health Research Center; PC: plate carrier; PPE: personal protective equipment; RPE: rating of perceived exertion; SAPI: small arms protective insert; sEMG: surface electromyography; USMC: United States Marine Corps; VGRF: Ground reaction forces in the vertical.

Changes in combat task performance under increasing loads in active duty marines.

UNLABELLED: U.S. Marines perform mission tasks under heavy loads which may compromise performance of combat tasks. However, data supporting this performance decrement are limited. PURPOSE: The aim of this study was to determine the effects of load on performance of combat-related tasks. METHODS: Subjects (N=18) ran a modified Maneuver Under Fire ([MANUF], 300 yards [yd] total: two 25-yd sprints, 25-yd crawl, 75-yd casualty drag, 150-yd ammunition can carry, and grenade toss) portion of the U.S. Marine Corps Combat Fitness Test under 4 trial conditions: neat (no load), 15%, 30%, and 45% of body weight, with a shooting task pre- and post-trial. RESULTS: There was a significant increase in total time to completion as a function of load (p<0.0001) with a relationship between load and time (r=0.592, p<0.0001). Pre- to post-MANUF shot accuracy (p=0.005) and precision (p<0.0001) was reduced. CONCLUSION: Short aerobic performance is significantly impacted by increasing loads. Marksmanship is compromised as a function of fatigue and load. These data suggest that loads of 45% body weight increase time to cover distance and reduce the ability to precisely hit a target.

Lesions of the dorsal noradrenergic bundle augment the renin response to blood loss but do not alter hypothalamic Fos expression.

The goal of this study was to determine if the dorsal noradrenergic bundle (DNAB) plays an essential role in mediating increased plasma renin activity (PRA) and hypothalamic activation, as indicated by increased Fos expression, in response to a small volume blood loss in unanesthetized animals. Male Sprague-Dawley rats were prepared with bilateral 6-hydroxydopamine or sham lesions of the dorsal noradrenergic bundle. In both groups of animals, blood pressure decreased by only 10-15 mmHg following hemorrhage (10 ml/kg over 15 min). Plasma renin activity increased similarly in both groups after 5 ml/kg blood loss, but showed a significantly greater increase after 10 ml/kg blood loss in animals with 6-hydroxydopamine lesions than in those with sham lesions (increase of 13.8 +/- 2.0 ng/ml/h versus 8.4 +/- 1.2 ng/ml/h; P < 0.025). There were numerous Fos-immunoreactive cell nuclei in the supraoptic nucleus (SON) and parvicellular paraventricular hypothalamic nucleus (PVN) of hemorrhaged animals. The number of Fos-positive neurons did not differ between groups, indicating that the dorsal noradrenergic bundle does not convey the primary drive for supraoptic and paraventricular nucleus activation during blood loss. However, one or more of the forebrain regions innervated by the dorsal noradrenergic bundle may attenuate the sympathetic outflow that initiates renin release in response to hemorrhage.

Pregnancy alters lateral parabrachial nucleus but not hypothalamic Fos expression following hypotensive hemorrhage.

The goal of these experiments was to determine if hemorrhage-induced Fos expression in the hypothalamus and lateral parabrachial nucleus (LPBN) is altered by reproductive cycle phase or pregnancy. Conscious unrestrained female Sprague-Dawley rats were subjected to a 16 ml/kg hemorrhage on the morning of the metestrus or proestrus phases of the estrous cycle, or on day 12-14 of pregnancy (mid-gestation). Hemorrhage induced a significant increase (p < 0.01) in the number of Fos-immunoreactive cell nuclei in the supraoptic nucleus, and in both the magnocellular and parvicellular components of the paraventricular hypothalamic nucleus, that did not differ between groups. In virgin females, hemorrhage also induced a significant increase in LPBN Fos expression that did not differ between metestrus and proestrus. In pregnant animals, there was an increase in basal LPBN Fos expression, but hemorrhage induced no further increase in the number of Fos-immunoreactive neurons in the LPBN. Mean arterial pressure decreased (p < 0.001) and plasma renin activity increased (p < 0.01) to a similar extent in all three groups after 16 ml/kg blood loss. In summary, the number of paraventricular and supraoptic nucleus neurons activated by hemorrhage is unaffected by estrous cycle phase or pregnancy. In contrast, pregnancy significantly attenuates the LPBN response to hemorrhage.

Heart rate and blood pressure quantitative trait loci for the airpuff startle reaction.

The airpuff startle reaction is a probe of sensori-autonomic processing and is useful for studies of genetic control of stress-induced cardiovascular activity. Using a Wistar-Kyoto-Spontaneously Hypertensive Rat F2 cross, we reported an airpuff-elicited strain-dependent and trial-dependent bradycardia, the absence of which cosegregated with hypertension. Here, we use the mapping power of the HXB-BXH recombinant inbred rat strains (n=23) to locate quantitative trait loci (QTL) for this and associated cardiovascular phenotypes. Rats (12 weeks old), with indwelling femoral arterial catheters, were subjected to repeated airpuff startle stimuli (100 ms, 12.5 psi, 28 trials). Basal mean arterial pressure (MAP), delta MAP, and delta heart rate response to airpuff stimuli were analyzed as the average over 28 trials. There was a significant strain effect on the cardiovascular phenotypes measured. One QTL for the bradycardia elicited by the first airpuff stimulus was identified on chromosome 2 (D2rat 62/63; logarithm of odds [LOD] 2.9) mapping near a reported blood pressure locus. Further QTL were identified for basal MAP (RN08), stimulus-elicited tachycardia on trials 2 to 5 (RNO1 and RNO10), and delta MAP (RNO6). Our results indicate that chromosomes 1, 2, and 10 are involved in heart rate responses to airpuff startle stimulus, and chromosomes 6 and 8 are involved in pressor responses. This study is the first to identify stress-related heart rate loci and provides additional support for our prior cosegregation results. Furthermore, we have established the utility of this experimental paradigm to identify loci responsible for cardiovascular regulation during stress in genetic hypertensive models.