Biorhythm means rhythm of life. Our lives are governed by cycles that start at our day of birth. The theory has been applied in the past to accident prevention. Many companies have studied biorhythms and their effects on airline pilots and athletic teams.
From the day we are born, we are governed by cycles.
The 28-day cycle called the emotional or sensitivity cycle governs one's temperament.
The 33-day cycle, called the intellectual cycle, influences our intellect or thinking capacity.
The 23-day cycle called the physical cycle governs the condition of one's body.
Critical days are those during which a cycle crosses from plus to minus (or minus to plus). The term critical is relative. It is a period of change where our system is in a state of flux.