Fatigue isn’t just “feeling tired”—it’s a deep, often overwhelming exhaustion that affects physical stamina, mental clarity, emotional stability, and overall recovery trajectory. For athletic trainers, physical therapists, and sports medicine professionals, understanding the physiological roots and clinical manifestations of post-concussion fatigue is essential for guiding athletes back to health and function.
Emerging research highlights that fatigue is far more than a secondary complaint. It may, in fact, be a primary marker of ongoing brain dysfunction and incomplete neurological recovery. This article explores the neurophysiological causes of fatigue after concussion, and offers research-supported strategies for managing and monitoring this complex symptom.
Why Is Fatigue So Common After a Concussion?
Fatigue is frequently one of the earliest symptoms after a concussion and often one of the last to resolve. According to a study published in Physiological Reports, adolescents who had recently sustained a concussion exhibited heightened levels of fatigue, which correlated with autonomic nervous system (ANS) dysregulation—a disruption in the body’s ability to manage stress, heart rate, and energy balance (source).
Concussion-induced fatigue stems from multiple interacting systems:
- Neurological: A concussion alters the brain’s ability to manage neural energy, leading to reduced efficiency in cognitive processing and motor coordination. Tasks that once required minimal effort—like focusing during class or walking across campus—may now drain significant energy reserves.
- Autonomic Dysfunction: The ANS, responsible for regulating “fight or flight” and “rest and digest” responses, is often disrupted post-concussion. This dysregulation contributes to poor sleep quality, reduced exercise tolerance, and cardiovascular instability, all of which feed into persistent fatigue. A comprehensive review published in Current Sports Medicine Reports explains how ANS imbalance impairs sleep-wake cycles, cardiovascular control, and energy regulation (source).
- Endocrine and Hormonal Changes: Growth hormone deficiency (GHD) has emerged as an underdiagnosed contributor to chronic fatigue in individuals with mild traumatic brain injury. GHD affects metabolism, mood, and cognition—factors that collectively diminish energy. A study published in Journal of Neurotrauma highlights that patients with GHD following concussion experienced notable fatigue and mental fog, warranting endocrine screening in long-recovery cases (source).
- Neuroinflammation: Beyond structural damage, concussion triggers a cascade of inflammatory responses within the brain. These neuroinflammatory changes can persist well after the initial trauma, disrupting normal neurotransmission and contributing to a state of ongoing fatigue, as described in this Springer publication on combat-related fatigue and neuroinflammation (source).
How Fatigue Affects Daily Function After a Concussion
Fatigue after concussion isn’t confined to the sidelines or the training room—it spills over into every part of life. Reaction time, memory recall, and decision-making slow down significantly. According to a study in The Journal of Head Trauma Rehabilitation, fatigue was among the top-reported symptoms affecting driving performance in recently concussed individuals. It impaired neurocognitive function and prolonged reaction times, raising real concerns for activities requiring split-second decision-making (source).
Clinically, we see this reflected in athletes who return to class but can’t concentrate, or who rejoin practice only to hit a wall mid-session. Physical activity, social interaction, even screen time can become exhausting. This isn't simply physical deconditioning—it’s the brain using an inefficient operating system and burning excess fuel just to perform routine tasks.
