The Brain on Bikes: Voluntary Performance & the Hemodynamic Response In the Prefrontal Cortex During Exhaustive Exercise

Fatigue can produce many outcomes. “Almost all chronic diseases may evolve with fatigue. The differential diagnosis includes infections; anemia; neoplastic, connective tissue, endocrine, neurological, chronic kidney, chronic liver, metabolic and ionic diseases; sleep and psychiatric alterations; and many others” [1]. Fatigue also plays an important role in human performance. During performance the body relies upon energy production. When fatigue sets in, performance struggles. Yet fatigue is a somewhat vague term.
To probe into fatigue requires a definition, and for our purposes, fatigue will be defined as “the failure to maintain the required or expected force” [2]. Though this is not the only definition of fatigue [3]. We understand poor diet, exercise, or sleep habits can lead to fatigue. We also understand what fatigue can cause, such as, higher levels of stress, chronic illness, and depression [1]. What we are currently lacking is the exact mechanism that is fatigue. There are currently two hypotheses which seem to each contain partial answers. These are that of peripheral fatigue, and that of central fatigue.
Peripheral fatigue indicates that fatigue originates somewhere outside of the Central Nervous System (CNS). This origin could be muscular, chemical, other variables [4],[5],[6]. Central fatigue argues that the muscles and all other peripheral components are merely byproducts of the CNS running the show. The idea focuses on the brain’s survival instincts and its ability to shut down peripheral organs to ensure its own success [7]. This study aimed to build upon the known knowledge of central fatigue. Specifically, the study tested two hypotheses:

1. That voluntary alterations in performance would be directly correlated with Prefrontal Cortical Oxygenation.
2. That Hyper-performances or Hypo-performances would be directly correlated to mean Prefrontal Cortical Oxygenation. To measure the CNS, functional Near Infrared Spectroscopy (fNIRS) was used for quantitative measurements. In addition, a rate of perceived exertion (RPE) was taken for qualitative measures.
   Peripheral measures were made through muscle Near Infrared Spectroscopy (mNIRS), cycling performance, and blood lactate samples. By incorporating these technologies, the study provided data from an abundance of data enabling correlational results.