Exhaustive endurance exercise activates brain glycogen breakdown and lactate production more than insulin-induced hypoglycemia

Diet-induced diabetes is associated with lower hippocampal glycogen and reduced glycogenolysis following local exogenous insulin

Brain fuel (specifically, glucose) supply and metabolism are well-established to be limiting factors for cognitive performance, with the largest body of data being for hippocampally mediated tasks. Consistent with this, disease states such as Alzheimer's disease and insulin-resistant diabetes, that impair cognitive metabolism, impair cognition with this being shown again most prominently for hippocampally mediated processes. In addition to glucose supplied from the blood, brain oxidative metabolism can use local glycogen stores (within astrocytes) as a fuel source via conversion to lactate; both lactate and glycogen have been shown to be important contributors to regulation of cognitive metabolism. Insulin has been shown to be a key regulator of hippocampal cognitive and metabolic processes; in the periphery, insulin facilitates glycogen synthesis and storage, but the impact on brain glycogen is unclear. Furthermore, the impact of diet-induced diabetes on hippocampal glycogen levels and/or metabolism is unknown. Here, we show that in rats with high-fat diet-induced diabetes, hippocampal glycogen is reduced and is less responsive to acute intrahippocampal administration of insulin, which significantly reduces glycogen in the hippocampi of control animals: Our data suggest that impaired fuel availability from glycogen may be a contributing factor to the cognitive impairment seen in disease states that include central insulin resistance.

The Problem of Effort Distribution in Heavy Glycolytic Trials with Special Reference to the 400 m Dash in Track and Field

Simple Summary

Short, intensive, but above lactate threshold physical trials or competitions which last <1 min but are close to this time limit, are on the border between glycolytic and aerobic efforts. The distribution of effort is critical in these tasks to achieve the best possible results. However, it is still unclear which of the general rules, descending from the theory, should be adopted by athletes (or any other subject facing a similar task). The 400 m dash competition of track and field has been taken in this systematic review as a paradigm for surveying the determinant factors which influence the pacing strategy and the end of effort. From the literature it emerges that there are several approaches, grounded in the philosophical basis of effort, which determine effort distribution. The problem is still open and a clear direction has not yet emerged from the available studies on the topic.

Abstract

Background. Biological factors are ultimately responsible for the cessation of effort in short, maximal glycolytic efforts. However, how these factors are sensed by the brain and act in a loop or feedforward way to regulate the distribution of effort is still unclear. Methods: A systematic review of existing literature on short term glycolytic exercise has been performed on publicly available databases (Google Scholar and Pudmed). Results: The problem of effort termination in fast maximal glycolytic activities after 100 years of research is still open. It is not clear if a central governor of effort exists, if the limitations are in the energy transport and utilization system, or in the psycho-social factors. Conclusions. The solution probably resides in a mixture of factors, but how the different components interact is still a mystery for science due to the philosophical grounding of the experimental approaches.