Circadian rhythm of myoglobin serum concentrations in healthy subjects demonstrated by cosinor analysis.

In order to evidentiate whether a circadian rhythm of the myoglobin serum concentration is present in humans, we measured serially the myoglobin levels in blood samples of 21 healthy subjects (10 females and 11 males), at bed rest, by means of a sensitive and accurate radioimmunological method. The data obtained were then evaluated according to the single and mean cosinor analysis, to assess the presence of a significant circadian rhythm. Eighteen of the 21 subjects showed a significant circadian rhythm. The calculated equation for the mean cosinor was: Y = 19.12 + 4.09 cos (15t-128.24) and the F-value for the zero amplitude test was 19.9 (p less than 0.001). Our data demonstrate that circadian variations of myoglobin serum concentration are likely to occur in humans. These findings strongly emphasize the need to take the time of sample collection into account when employing serum myoglobin as a marker for muscle damage.