Glossary

Core biological terms

Circadian rhythm: The internal biological timing system that regulates sleep, alertness, and physiological processes across the 24-hour day.
Sleep homeostasis: The biological process that increases pressure to sleep the longer a person remains awake.
Sleep debt: The cumulative effect of insufficient sleep over time, influencing fatigue, cognition, and recovery.
Sleep inertia: A period of reduced alertness and performance immediately after waking.

Fatigue: A biological and cognitive state reflecting reduced capacity for sustained performance, influenced by sleep, circadian timing, workload, and health.
Fatigue risk: The likelihood that fatigue will impair performance, increase error probability, or affect safety.
Fatigue management: Strategies used to monitor, mitigate, and reduce fatigue in individuals and operational environments.
Fatigue accumulation: The progressive increase in fatigue across time due to extended wakefulness, workload, or insufficient recovery.
Physical fatigue: Reduction in muscular performance and endurance resulting from exertion and metabolic demand.
Neuromuscular fatigue: Decline in the ability of muscles to generate force due to neural and muscular factors.
Muscle recovery: Physiological restoration following exertion or strain.
Exertional fatigue: Fatigue resulting from sustained physical effort.

Alertness: A state of readiness that enables effective perception, attention, decision-making, and response.
Vigilance: The ability to sustain attention and detect important signals over time.
Cognitive readiness: The mental capacity to perform tasks requiring attention, decision-making, and situational awareness.
Wakefulness regulation: Biological and behavioral processes that maintain alertness across the day.
Stimulants: Substances that influence neural activity and alertness, often interacting with sleep and circadian regulation.
Light exposure: Environmental light, particularly in specific wavelengths and timing, which affects circadian rhythms and alertness.

Reaction time: The interval between a stimulus and a behavioral response, often used as a measure of alertness and performance.
Performance variability: Fluctuations in accuracy, speed, or decision quality associated with fatigue and alertness.
Decision fatigue: Decline in decision quality after prolonged cognitive activity or stress.
Situational awareness: The perception and understanding of environmental conditions needed for effective performance.

Fatigue-related impairment: Reduction in performance or safety margin associated with fatigue.
Human performance limitation: Constraints on capability related to biological, cognitive, or environmental factors.
Operational readiness: The ability to perform effectively in demanding or safety-critical environments.
Error probability: The likelihood of mistakes occurring under conditions of fatigue or degraded alertness.

Chronic fatigue: Persistent fatigue associated with medical, neurological, or psychological conditions.
Sleep disorder: A condition affecting sleep quality, duration, or timing.
Recovery: Physiological and cognitive restoration following exertion, illness, or sleep loss.
Resilience: Capacity to maintain performance despite stress, fatigue, or environmental demands.

Biometric monitoring: Measurement of physiological signals used to assess fatigue, sleep, and alertness.
Wearable technology: Devices that collect data on sleep, activity, and physiological state to inform readiness.
Predictive fatigue modeling: Use of data and algorithms to estimate fatigue and performance risk.
Readiness assessment: Evaluation of cognitive and physiological capacity to perform tasks safely and effectively.