CHRONOBIOLOGY INTERNATIONAL, 2025 (SCI-Expanded, Scopus)
The aim of this study was to investigate the effect of circadian rhythmicity (CR) on lower extremity strength and balance performance in 22 female athletes (19-24 y). Participants underwent isokinetic knee strength, Single Leg Hop Tests (SLHT), Y Balance Test (YBT), and isokinetic static/dynamic balance tests. All measurements were randomized and performed at 9:00, 14:00, and 19:00 to assess CR variation. In total, 3 angular strength, 5 jump, and 2 balance tests were analyzed. When comparing results across time zones, body temperature, isokinetic 60 degrees/sec extension (Ext) strength, and several bipedal static balance parameters Forward-Backward Standard Deviation (SBFD), Average Forward-Backward Speed (AFBS), and Ellipse Area (EA)) showed statistical significance (p>0.05). No significant differences were found in other isokinetic strength tests, all SLHTs, Y balance, or dynamic balance tests (p>0.05). Significant CR effects on lower extremity strength were observed only in the 60 sec extension, with overall strength peaking at 14:00. Strength asymmetry remained similar across time points. These findings suggest that time-sensitive performance parameters like strength and static balance are influenced by CR, while balance and coordination parameters appear more stable. Accordingly, scheduling strength-based training during midday hours may optimize performance by leveraging CR-related variations.