Central vs peripheral fatigue
LoadTwo distinct fatigue components: central (nervous system) and peripheral (muscle), with different recovery timescales.
Peripheral fatigue originates in the muscle: glycogen depletion, acidosis, myofibrillar damage. It resolves in 24-72h depending on intensity. Central fatigue originates in the nervous system: reduced motor drive, altered perception of effort (RPE). It's more insidious : the athlete 'feels fine' but maximal power or pace is depressed. In Ironman, both accumulate simultaneously. The day after a long brick or a 5h+ fasted ride, central fatigue can persist even if the legs feel light: a frequent trap during high training load periods.
In TriPaced:
In TriPaced, the Load & Form block (CTL/ATL/TSB) captures overall fatigue but doesn't distinguish central from peripheral. If you feel mentally depleted despite a neutral TSB, it's often central fatigue: the planner may then suggest a short or active session rather than a long endurance effort.