PMC:4719559 / 1835-3908
Annnotations
{"target":"https://pubannotation.org/docs/sourcedb/PMC/sourceid/4719559","sourcedb":"PMC","sourceid":"4719559","source_url":"https://www.ncbi.nlm.nih.gov/pmc/4719559","text":"Background\nExposure to actual [1–3] or simulated [2, 4–7] microgravity reduces tolerance for physical exertion and alters cardiovascular responses to exercise in humans. Most [2, 4–6, 8], but not all [9] studies have shown impaired reflex responses to static exercise or cold pressor tests. However, the extent to which spaceflight or bedrest influences these reflexes, or whether other factors are responsible for the modulated reflex activity, remains unclear.\nBy employing various stressors, it is possible to characterize afferent and efferent reflex pathways and determine how environmental adaptations (e.g., spaceflight, bedrest, fasting) modulate neural and cardiovascular responses. Static handgrip to fatigue elicits increases in blood pressure (BP), heart rate (HR), and muscle sympathetic nerve activity (MSNA) [10]. The primary mechanisms responsible for the neural and cardiovascular responses are activation of central command, a feedforward control mechanism via stimulation of the cardiovascular center from descending central neural pathways, and the exercise pressor reflex, a feedback control mechanism emanating from mechano- and metaboreceptors in skeletal muscles [10, 11]. Reflex pathways originating from cold nociceptors in the skin and involving central vasomotor centers can be assessed by sympathetic and pressure responses to the cold pressor test [9, 12].\nA recent study [13] reported that astronauts were in negative energy balance (~30 %) during a 17-day shuttle mission. Hypocaloric intake reduces HR, BP, and sympathetic activity [14–16], and we have documented reduced orthostatic tolerance following caloric restriction [17]. However, the impact of reduced caloric intake alone and in conjunction with microgravity adaptation on neural control of the cardiovascular system during static exercise or cold pressor is not known. Accordingly, the purpose of this study was to test the hypothesis that caloric restriction reduces the responses to cold pressor and static handgrip exercise, and to a greater extent when combined with bedrest.","divisions":[{"label":"title","span":{"begin":0,"end":10}},{"label":"p","span":{"begin":11,"end":462}},{"label":"p","span":{"begin":463,"end":1386}}],"tracks":[{"project":"TEST0","denotations":[{"id":"26793301-20-25-73074","span":{"begin":31,"end":32},"obj":"[\"8872635\", \"11513320\", \"16306254\"]"},{"id":"26793301-39-44-73075","span":{"begin":50,"end":51},"obj":"[\"11513320\"]"},{"id":"26793301-42-47-73076","span":{"begin":53,"end":54},"obj":"[\"10696809\", \"14701716\", \"11515805\", \"8828644\"]"},{"id":"26793301-165-170-73077","span":{"begin":176,"end":177},"obj":"[\"11513320\"]"},{"id":"26793301-9-14-73078","span":{"begin":179,"end":180},"obj":"[\"10696809\", \"14701716\", 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