Effects of Caffeine Ingestion on Human Standing Balance: A Systematic Review of Placebo-Controlled Trials

Caffeine ingestion may influence balance control via numerous mechanisms. Although previously investigated using various study designs and methods, here we aimed to create the first evidence-based consensus regarding the effects of caffeine on the control of upright stance via systematic review (PROSPERO registration CRD42021226939). Embase, PubMed/MEDLINE, SPORTDiscus and Web of Science databases were searched on 27 January 2021 to identify placebo-controlled trials investigating caffeine-induced changes in human standing balance. Reference lists of eligible studies were also searched. Overall, nine studies involving a total of 290 participants were included. All studies were moderate to strong in quality according to the QualSyst tool. Balance-related outcome measures were collected across a range of different participant ages, stances and sensory conditions. The results show that younger participants’ balance was generally unaffected by caffeine ingestion. However, a significant balance impairment was observed following caffeine ingestion in all studies involving older participants (average age >65 years). Our results therefore suggest an age-dependent effect of caffeine ingestion on human standing. Further research into this effect is warranted as only one study has directly compared younger and older adults. Nonetheless, an important implication of our findings is that caffeine ingestion may increase fall risk in older adults. Furthermore, based on our findings, caffeine ingestion should be considered as a potential confounding factor when assessing human standing balance, particularly in older adults.

Long-Lasting Event-Related Beta Synchronizations of Electroencephalographic Activity in Response to Support-Surface Perturbations During Upright Stance: A Pilot Study Associating Beta Rebound and Active Monitoring in the Intermittent Postural Control

Movement related beta band cortical oscillations, including beta rebound after execution and/or suppression of movement, have drawn attention in upper extremity motor control literature. However, fewer studies focused on beta band oscillations during postural control in upright stance. In this preliminary study, we examined beta rebound and other components of electroencephalogram (EEG) activity during perturbed upright stance to investigate supraspinal contributions to postural stabilization. Particularly, we aimed to clarify the timing and duration of beta rebound within a non-sustained, but long-lasting postural recovery process that occurs more slowly compared to upper extremities. To this end, EEG signals were acquired from nine healthy young adults in response to a brief support-surface perturbation, together with the center of pressure, the center of mass and electromyogram (EMG) activities of ankle muscles. Event-related potentials (ERPs) and event-related spectral perturbations were computed from EEG data using the perturbation-onset as a triggering event. After short-latency (<0.3 s) ERPs, our results showed a decrease in high-beta band oscillations (event-related desynchronization), which was followed by a significant increase (event-related synchronization) in the same band, as well as a decrease in theta band oscillations. Unlike during upper extremity motor tasks, the beta rebound in this case was initiated before the postural recovery was completed, and sustained for as long as 3 s with small EMG responses for the first half period, followed by no excessive EMG activities for the second half period. We speculate that those novel characteristics of beta rebound might be caused by slow postural dynamics along a stable manifold of the unstable saddle-type upright equilibrium of the postural control system without active feedback control, but with active monitoring of the postural state, in the framework of the intermittent control.

The Negative Cascade Effect – Impact of a Rotated Mandible

The human body is a vertical bilaterally balanced entity capable of locomotion on two legs. The entity maintains an upright stance because of an intricately connected musculo skeletal system. This system works in synchrony with a vast number of muscles, tendons and nerves, which holds the bony parts as one unit allowing them to move as joints, thus making it possible for the human body to carry out complex physical tasks. The mandible, is housed right at the top, just below the brain. This is a unique bone having a bilaterally connected joint with similar muscle attachments on either side. Any imbalance in the bilateral symmetrical function of the muscles can trigger of a variety of complex interactions leading to major problems in the entire musculo skeletal system right till the feet. In addition this asymmetry also impacts internal organs unfavourably. This sequence of events has been termed by Smylist® as the negative cascade effect. This article explains how an imbalanced (rotated) mandible can cause a vast variety of problems and issues in the human body.

Processing moving visual scenes during upright stance in elderly patients with mild cognitive impairment

Background The ability to maintain balance in an upright stance gradually worsens with age and is even more difficult for patients with cognitive disorders. Cognitive impairment plays a probable role in the worsening of stability. The purpose of this study was to expose subjects with mild cognitive impairment (MCI) and healthy, age-matched controls to moving visual scenes in order to examine their postural adaptation abilities. Methods We observed postural responses to moving visual stimulation while subjects stood on a force platform. The visual disturbance was created by interposing a moving picture in four directions (forward, backward, right, and left). The pre-stimulus (a static scene for 10 s), stimulus (a dynamic visual scene for 20 seconds) and post-stimulus (a static scene for 20 seconds) periods were evaluated. We separately analyzed the total path (TP) of the center of pressure (COP) and the root mean square (RMS) of the COP displacement in all four directions. Results We found differences in the TP of the COP during the post-stimulus period for all stimulus directions except in motion towards the subject (left p = 0.006, right p = 0.004, and away from the subject p = 0.009). Significant RMS differences between groups were also observed during the post-stimulus period in all directions except when directed towards the subject (left p = 0.002, right p = 0.007, and away from the subject p = 0.014). Conclusion Exposing subjects to a moving visual scene induced greater destabilization in MCI subjects compared to healthy elderly controls. Surprisingly, the moving visual scene also induced significant aftereffects in the MCI group. Our findings indicate that the MCI group had diminished adaptation to the dynamic visual scene and recovery. These results suggest that even mild cognitive deficits can impair sensory information integration and alter the sensory re-weighing process.

Persistent visual and vestibular impairments for Postural control following concussion

ObjectiveThe purpose of this study was to examine sensory reweighting for upright stance in three groups (i.e., sub-acute concussion, concussion history, control).BackgroundBalance impairments are common following concussion; however, the physiologic mechanisms underlying these impairments are not well understood.Design/methodsThere were 13 participants (8 women, 21 ± 3 years) between 2 weeks and 6 months post-injury who reported being asymptomatic at the time of testing (i.e., sub-acute concussion group), 13 participants (8 women, 21 ± 1 year) with a history of concussion (i.e., concussion history group, >1 year following concussion), and 26 participants (8 women, 22 ± 3 years) with no concussion history (i.e., control group). We assessed sensory reweighting by simultaneously perturbing participants' visual, vestibular, and proprioceptive systems. The visual stimulus was a sinusoidal translation of the visual scene at 0.2Hz, the vestibular stimulus was ±1 mA binaural monopolar galvanic vestibular stimulation (GVS) at 0.36Hz, and the proprioceptive stimulus was Achilles' tendon vibration at 0.28Hz. The visual stimulus was presented at two different amplitudes (low vision = 0.2m, high vision = 0.8m). We computed center of mass gain to each modality.ResultsThe sub-acute concussion group (95% confidence interval = 0.078-0.115, p = 0.001) and the concussion history group (95% confidence interval = 0.056-0.094, p = 0.038) had higher gains to the visual stimulus than the control group (95% confidence interval = 0.040-0.066). The sub-acute concussion group (95% confidence interval = 0.795–1.159, p = 0.002) and the concussion history group (95% confidence interval = 0.633–1.012, p = 0.018) had higher gains to the vestibular stimulus than the control group (95% confidence interval = 0.494-0.752). There were no group differences in gains to the proprioceptive stimulus and there were no group differences in sensory reweighting.ConclusionsFollowing concussion, participants responded more strongly to visual and vestibular stimuli during upright stance, suggesting they may have abnormal dependence on visual and vestibular feedback. These findings may indicate an area for targeted rehabilitation interventions.