Affiliations: [a] Institute of Biomedicine, Physiology, University of
Kuopio, Kuopio, Finland | [b] Department of Sports Science and Health, Suleyman
Demirel University, Isparta, Turkey
Note: [] Address for correspondence: Zekine Lappalainen, Institute of
Biomedicine, Physiology, University of Kuopio, PO Box 1627, FI-70211, Kuopio,
Finland. Tel.: +358 17 163108; Fax: +358 17 163112; E-mail:
[email protected]
Abstract: Circadian rhythms are known to influence muscular performance and
regulate leptin hormone secretion, which assists in the regulation of body
weight and energy homeostasis. In this study we examined the time-of-day effect
on skeletal muscle eccentric contractile properties and the response of serum
leptin to acute eccentric exhaustive isokinetic exercise. Male subjects
(n = 26) performed a bout of exhaustive eccentric exercise on
an isokinetic dynamometer in the morning or late afternoon time on different
days. The test was repeated after 7–10 days at different time-of-day. Blood
samples were collected at baseline and immediately after exercise for
determination of serum leptin. Leg extensor muscle torque and work parameters
were recorded, and compared with the time-of-day. Maximal eccentric torque
values were not significantly affected by time-of-day. The maximal work
performed during single repetition as well as total work values were
significantly higher in the afternoon time. Leptin levels significantly
decreased after exercise, but no time-of-day effect on serum leptin could be
observed. Diurnal variations during short-term isokinetic exhaustive eccentric
exercise seem to reflect muscle work capacity, with higher contractile
efficiency towards the evening time. Although short-term exhaustive eccentric
exercise decreased serum leptin, the levels did not to have a significant
diurnal variation.
Keywords: Diurnal variation, eccentric exercise, leptin, muscle work
