Physiologia

This narrative review of rapid eye movement (REM) focuses on its primary etiology and how it fits into the larger framework of neurophysiology and general physiology. Arterial blood flow in the retina may be sensitive to the full overlying ‘weight’ of its adjacent and contiguous vitreous humor caused by the humoral mass effect in the Earth’s gravitational field. During waking hours of the day, this ‘weight’ is continuously shifted in position due to changing head position and eye movements associated with ordinary environmental observations. This reduces its impact on any one point on the retinal field. However, during sleep, the head may maintain a relatively constant position (often supine), and observational eye movements are minimal, leaving essentially one retinal area exposed at the ‘bottom’ of each eye, relative to gravity. During sleep, REM may provide a mechanism for frequently repositioning the retina with respect to the weight it incurs from its adjacent (overlying) vitreous humor. Our findings were consistent with the intermittent terrestrial nocturnal development of ‘gravitational ischemia’ in the retina, wherein the decreased blood flow is accompanied metabolically by decreased oxygen tension, a critically important metric, with a detrimental influence on nerve-related tissue generally. However, the natural mechanisms for releasing and resolving gravitational ischemia, which likely involve glymphatics and cerebrospinal fluid shifts, as well as REM, may gradually fail in old age. Concurrently associated with old age in some individuals is the deposition of alpha-synuclein and/or tau in the retina, together with similar deposition in the brain, and it is also associated with the development of Parkinson’s disease and/or Alzheimer’s disease, possibly as a maladaptive attempt to release and resolve gravitational ischemia. This suggests that a key metabolic parameter of Parkinson’s disease and Alzheimer’s disease may be a lack of oxygen in some neural tissues. There is some evidence that oxygen therapy (hyperbaric oxygen) may be an effective supplemental treatment. Many of the cardinal features of spaceflight-associated neuro-ocular syndrome (SANS) may potentially be explained as features of gravity opposition physiology, which becomes unopposed by gravity during spaceflight. Gravity opposition physiology may, in fact, create significant challenges for humans involved in long-duration space travel (long-term microgravity). Possible solutions may include the use of artificial gravitational fields in space, such as centrifuges.

Purpose: We aimed to assess the effects of one-week betalain-rich beetroot concentrate (BRC) supplementation on high-intensity cycling performance in trained cyclists. Methods: Eighteen male (n = 15) and female (n = 3) cyclists (age: 38.83 ± 8.09; weight: 73.23 ± 10.95 kg; height: 176.86 ± 9.60 cm) were supplemented with a BRC or a placebo (PLA) for six days prior to the experimental trials. On the seventh day, a final dose was administered, and participants completed three all-out 15 s cycling sprints back-to-back, followed by a 4 km cycling time trial (TT). Physiological indicators related to performance were measured throughout the 4 km TT. Results: Sprint performance remained unchanged following PLA treatment. However, BRC treatment led to significant reductions in sprint performance during sprints 2 and 3 compared to sprint 1 (p < 0.05). Time trial performance did not differ between treatments (p > 0.05). Significant increases in physiological and psychological responses during the 4-km time trial were observed following both treatments (p < 0.05). However, heart rate was higher at 2 km compared to 1 km, the respiratory exchange ratio was slightly elevated at 2 km and 4 km relative to 1 km, and VO₂ was slightly higher at 3 km and 4 km compared to pre-TT following BRC treatment only (p < 0.05). Conclusions: One week of a BRC does not enhance 4 km TT performance but may impair repeated-sprint performance in trained cyclists.

Background/Objectives: Hamstring injuries are highly prevalent in sports and often occur, particularly among recreational and professional athletes. Assessing eccentric hamstring strength is critical for injury prevention and rehabilitation, with isokinetic dynamometry being considered the gold standard. However, its accessibility is limited by cost and logistics. This study aimed to evaluate the validity and reliability of the My Jump Lab (version 4.0) mobile application in estimating eccentric peak torque in the break-point angle, compared with isokinetic dynamometry. Methods: Twenty-seven recreational athletes (twenty-six male, one female) were assessed bilaterally using the mobile application and isokinetic dynamometer, which is considered the gold standard for this type of strength assessment. Statistical analysis included Pearson’s correlation, intraclass correlation coefficient (ICC), standard error of measurement (SEM), coefficient of variation (CV), and Bland–Altman plots. Results: Results showed excellent inter-rater reliability (ICC = 0.999; CV = 0.66%) for both smartphone application evaluators and good comparative validity and reliability (ICC ≈ 0.76 with confidence interval: 0.5367–0.876; p < 0.001 and r ≈ 0.705;) when comparing with isokinetic dynamometry. Conclusions: My Jump Lab is a mobile application which can provide a practical and accessible mean for monitoring eccentric hamstring strength in field settings. The app may serve as a feasible field-based alternative to laboratory dynamometry for eccentric strength monitoring.