We studied the nature of biphasic changes in serum creatine kinase (CK) activity with transient weight training.
Six untrained healthy men (21-24 yr) participated in the programme. Six different types of weight training (70-80% maximum muscular strength) were imposed. Blood specimens were collected on nine separate occasions and CK activity, calcium (Ca), inorganic phosphate (Pi), zinc (Zn) and polyamine concentration were measured.
Muscle soreness was also examined by asking the men to fill out a questionnaire.
Muscle soreness appeared one hour after training and was considerable one and two days after the training.
CK activity showed a typical biphasic change. The extreme mean values (highest or lowest) of Ca, Pi, Zn and polyamines appeared between two and three days after the training. This period of time corresponded to that between the first and second peaks of CK activity. The first peak of CK activity after weight training was assumed to be related to muscle soreness. We propose that changes in blood Ca, Pi, Zn, polyamines and muscle soreness reflect a series of different histopathological reactions including muscle damage, repair and regeneration in subjects given transient weight training. Each peak of the biphasic change in serum CK activity may be different in nature, histologically and/or biochemically.

Serum creatine kinase (CK) activity and myoglobin (Mb) level showed biphasic changes due to transient weight training. The first peak appeared within one day and the second peak appeared within several days after training.
We investigated the characteristics of each peak by measuring the total CK and CK isoenzymes (CK-MM, -MB, -BB) activities.
The results were as follows:
1) The first peak of Mb level appeared sooner than that of total CK activity. In two untrained subject, the second peak of total CK activity and Mb level were higher than the first peak.
2) The CK activity within four hours after training was that of CK-MM. CK-MB and -BB activities did not appear immediately after training, but they appeared within one day after training. CK-MB activity showed the highest value on the fifth day, and CK-BB activity was highest on the seventh day. Appearance of CK-BB activity was more apparent in the untrained than in the trained subjects.
3) The mean ratio of CK-MB activity to total CK activity was 5.3 % on the fifth day, and that of CK-BB activity was 2.9 % on the seventh day. These ratios were the highest among ratios in the post-training period.
It is suggested that the first peak represents a transient enzyme leakage into the blood stream, as the result of damaged muscles, especially in untrained subjects, while the second peak which appeared within several days after training represents, at least to some extent, the participation of ontogenetic muscle regeneration.