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Related Concept Videos

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Consider a man with a mass of 70 kg seated in a chair connected to a pin support through a member BC. If the man maintains an upright position, the task is to determine the horizontal and vertical reactions of the chair on the man when the member makes a 45° angle with the horizontal. At this moment, the man has a speed of 5 m/s, increasing at a rate of 1 m/s².
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Newton's third law states that every action has an equal and opposite reaction. Consider a swimmer pushing off the side of a pool. They push against the wall of the pool with their feet and accelerate in the direction opposite to that of their push. This occurs because the wall exerts an equal and opposite force on the swimmer. Here, the forces do not cancel out each other as they are acting on different systems. In this case, there are two systems: the swimmer and the wall. If we select...
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In terms of human respiration, the act of expelling air, known as exhalation (or expiration), operates on the principle of pressure gradients. During expiration, the pressure within the lungs exceeds that of the surrounding atmosphere. Under normal conditions, quiet breathing involves passive exhalation and is free of muscular contractions. This is because the exhalation process is driven by the natural elastic recoil of the lungs and chest wall, both of which have an inherent tendency to...
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Related Experiment Video

Updated: Sep 11, 2025

Quantifying Arms and Legs Contributions during Repetitive Electrically-Assisted Sit-To-Stand Exercise in Paraplegics: A Pilot Study
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Increasing seated reaction forces with lower body negative pressure.

Suhas Rao Velichala1, Jonathan Kim2, Alan R Hargens3

  • 1Department of Orthopaedic Surgery, University of California, San Diego, San Diego, CA, USA. suhasraov@gmail.com.

NPJ Microgravity
|August 13, 2025
PubMed
Summary
This summary is machine-generated.

Seated lower body negative pressure (LBNP) effectively simulates Earth

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Area of Science:

  • Space physiology
  • Human adaptation to microgravity
  • Cardiovascular and musculoskeletal responses

Background:

  • Spaceflight leads to musculoskeletal deconditioning and cardiovascular changes.
  • Simulating Earth's gravity in microgravity is crucial for astronaut health.
  • Lower body negative pressure (LBNP) is a potential tool for gravitational simulation.

Purpose of the Study:

  • To evaluate ground reaction forces and cardiovascular responses during seated lower body negative pressure (LBNP).
  • To assess the safety and efficacy of seated LBNP as a microgravity countermeasure.

Main Methods:

  • Ten healthy subjects were exposed to graded seated LBNP (-10 to -40 mmHg).
  • Gluteal, foot, and total reaction forces were measured.
  • Heart rate and blood pressure were monitored throughout the protocol.

Main Results:

  • Ground reaction forces significantly increased with increasing LBNP levels (P < 0.05).
  • Forces doubled by -30 mmHg LBNP compared to baseline.
  • Cardiovascular parameters remained stable, indicating no acute hemodynamic risk.

Conclusions:

  • Seated LBNP is a safe method for simulating gravitational loading.
  • It effectively increases ground reaction forces, mimicking Earth's seated posture.
  • Seated LBNP shows promise as a countermeasure for spaceflight-induced deconditioning.