Second Wind Phenomenon

Medspeak A substrate-dependent variation of exercise tolerance, in which previously fatiguing exercise can be performed with relative ease, after a period of rest
Metabolic disease A finding typical of patients with glycogen storage disease V, in which the first phase of exercise is characterised by progressive fatigue and weakness of the exercised muscles, followed by a phase of adaptation, in which rest results in rapid and complete recovery and a sustained ability to exercise without difficulty, attributed to increased cardiac output, changes in metabolic pathways and increased EMG activity
Rheumatology A surge of subjective 'energy' that follows rest, which is typical of the mid-afternoon fatigue of rheumatoid arthritis