###### Abstract  
Physical performance in sport performance such as football is influenced by sleep quality, but there are only a few studies about this and the behaviour of muscle force at knee flexors and extensors. The aim of this study is to make an analysis of sleep, an analysis of muscle force parameters (flexors and knee extensors), and a study of the correlation between sleep quality and muscle force. The study includes 18 junior women footballers, average age 14.75 years old, who participated in a training programme of 90 min, three times/week. The evaluation includes sleep quality evaluation using the sleep quality scale (SQS), sleepiness evaluation using the Cleveland Adolescent Sleepiness Questionnaire (CASQ), and muscle force evaluation using dynamometry for knee flexor and extensor muscles. We recorded maximal muscle force, medium maximal muscle force, and duration of maintained muscle force. We observed that more than 83% of subjects scored below 50% on the maximal SQS score and all participants scored less than 40 points (50%) on the CASQ's maxim score, meaning a small level of sleepiness. With regard to muscle force, left-right symmetry for medium maximal force shows a predominance of the right-hand side and the value was 1.64%, for knee extensors and for knee flexors the difference was 7.58%, meaning that for knee extensors the symmetry is better than that of knee flexors. Statistical analysis regarding muscle parameters shows that there are no significant statistical differences between the left- and right-hand sides. Because the duration of the maintained maximal muscle force could indicate muscle fatigue, we observed that there was no link, and that sleep quality or sleepiness do not influence muscle fatigue. Our research concludes that muscle asymmetry of the left-right side of knee extensor and flexor muscles is minimal and does not correlate with sleep quality or sleepiness. There is no statistical correlation between muscle force parameters and sleep quality. muscle force; sleep quality; muscle symmetry; athletes +
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by different situations that involve the athletes [6]. A good sleep-like quality influences physical performance and this aspect is important in the context of good fitness and limits the risk of injuries. There have been many questionnaires that evaluate the sleep quality of athletes, and the studies refer to sleep disorders, such as the deprivation of sleep, that could affect physical performance. The problem is that there is only a small number of studies on the sleep quality of athletes, or if the studies exist, they include a small number of athletes without underlining the specificity or any link between physical performance, fitness components, and sleep. There are not enough studies on the sleep quality of women football players. In addition, there is a small evidence base about the sleep evaluation. This needs to have evidence-based information because in the present conditions we observe an increase in the number of women footballers, and much more, this implication is more visible in young girls. Many studies speak about the sleep of women football players and demonstrate that there is a large variability in sleep duration and sleep quality during competitions and that players develop different sleep patterns [4; 7; 8]. Starting from these aspects, we could consider that there are a lot of different methodology approaches to understanding and interpreting the sleep of athletes and a lot of validated tools for sleep assessment. Research has been carried out, but studies include a small number of people and are of a short duration. Thus, this topic seems to need a new approach to sport activity. In this context there are some studies that investigate the effect of a decrease in sleep duration on physical performance, such as muscle force [9; 10; 11; 12], anaerobic power [13; 14; 15; 16; 17], endurance [18], or aerobic capacity. In their analysis of physical performance, [PERSON] et al.