Abstract
Purpose Sleep has been identified as an important factor influencing performance, as well as sex and chronotype. The study aimed to investigate: (I) sleep changes in tennis season periods; (II) sleep influence on balance and lower-limb strength; (III) sex and chronotype influences. Methods Participants filled out a questionnaire to evaluate their chronotype. Sleep habits, balance, and lower limbs strength were evaluated in two season periods: off- and in-season. Forty percent of participants worsened their sleep duration from off- to in-season. Based on this, two groups were made: the worsened sleep group (WSG) and the improved sleep group (ISG). Results The WSG showed a decrease in balance performance across all test conditions. This was evidenced by significantly higher Sway Path Length (SPL) and Sway Average Speed (SAS) values in double-leg stance (DLS) both with eyes open (EO) and eyes closed (EC) (p range from 0.043 to<0.001), as well as in single-leg stance (SLS) (p range from 0.018 to 0.010) from off-season to in-season period. Furthermore, gender-specific differences were also observed. Females had significantly worse SPL and SAS values in right SLS (p≤0.043), while males significantly increased SAS in DLS with EO (p=0.044), and SPL, SAS, and Sway Ellipse Area (SEA), in DLS with EC (p≤0.018). No sleep effects were found in jumping performance. Evening types showed the lowest SEA in left SLS than the other chronotypes, and at in-season compared to off-season (all p<0.001). Conclusions Sleep remains a critical determinant of performance. Indeed, a reduction in sleep quantity was associated with a significant decline in balance performance, while no effect on jumping performance was observed. The strength of this association may be affected by athletes’ transition from off-season to in-season. This study suggests that individual factors such as sex and chronotype can influence these associations. These results offer valuable insights that require further investigations.