Acute and delayed responses of steroidal hormones, blood lactate and biomarkers of muscle damage after a resistance training session: time-of-day effects.

Background: The present study aimed to investigate the effect of time-of-days (TOD) on some biochemical and hormonal responses after resistance training sessions.

Methods: Ten trained subjects (22±2 years) performed, in randomized order, three resistance-training-sessions at 7 a.m., 1 p.m. and 5 p.m. Each training-session included six upper and lower body resistance exercises with 3×10 repetitions. Blood lactate (Lac), creatine kinase (CK), lactate dehydrogenase (LDH), cortisol (C) and testosterone (T) were collected at rest, 3 min and 48 h after each-session.

Results: At rest, steroidal hormones were higher in the morning compared to the evening (P<0.01), whereas, no significant TOD effect on Lac, CK or LDH was observed. 3min after training, whatever the TOD, Lac, CK and T increased significantly (P<0.001). However, a significant decrease in C and a significant increase of T/C ratio were registered only after morning training. 3 min and even 48 h after training, the diurnal variations (i.e., morning to evening) of CK and C have been altered with higher early evening values of CK and lower one of C; whereas, T, Lac and LDH conserved their resting diurnal variation. Additionally, 48 h after the morning session, CK and T/C ratio remained elevated compared to the baseline levels.

Conclusions: In conclusion, resistance exercises soliciting both lower and upper limbs seems to alter the diurnal variation of CK and C, to enhance the morning anabolism/catabolism status and to produce more favorable environment for muscular adaptation up to 48 h post-training.