Men more likely to father female offspring during high-level soccer training
Among a cohort of professional male soccer players in Chile, those who took part in high-intensity training when they conceived a child with their partner were more likely to have a girl, researchers reported in Human Reproduction.
“To the best of our knowledge, this is the first study that assesses the influence of exercise-sports training load on the sex of the offspring of male soccer athletes,” Diana Vaamonde, PhD, professor of human anatomy and embryology in the department of morphological sciences in the School of Medicine and Nursing at Universidad de Cordoba in Spain, and colleagues wrote. “The results reveal a significant bias in the sex ratio toward females as a result of higher-load volume and/or intensity of training. The observed bias toward greater female offspring is in opposition to the general statistical data for sex ratio of live births in the region to which the teams belonged, which is consistently around 51% males, as well as worldwide.”
Researchers recruited 75 professional soccer players from first division teams in Chile to participate in a retrospective, observational, cross-sectional study from August to October 2017. Participants were players actively engaged in training when they conceived a child with their partners. All individuals were required to have been engaged in normal sports activities just before their partner’s pregnancy and had to know their training volume and intensity.
To evaluate training load, players were considered to be taking part in low workloads of low-volume and low-intensity training during a rest period, medium workloads of low-volume and moderate- or low/moderate-intensity training while competing in the championships, and high workloads of high-volume and high-intensity training during the preseason. Researchers quantified low-training volume as less than four training sessions per week, moderate volume as six to eight training sessions per week and high volume as more than eight sessions per week. The Borg Rating of Perceived Exertion scale from 1 to 10 was used to quantify intensity. A score of less than 6 indicated low-intensity training, 6 to 8 was categorized as moderate intensity and a score of higher than 8 was considered high intensity.
The study population conceived 122 live child births, of whom 52 were male and 70 were female. The volume and intensity of training had an influence on the child’s observed sex. Of those who engaged in high-intensity training, 45 players fathered girls and 15 players fathered boys (P < .001). Among players who took part in high-volume training, there were 36 girls born vs. seven boys (P < .001).
When evaluating training intensity, there was a higher number of girls born from players engaged in high-intensity training (n = 45) than those who had moderate-intensity (n = 12) or low-intensity training (n = 13; P < .001). A similar pattern was not found when looking at male children.
In subgroup analysis, researchers compared participants who took part in high-load training with players who had low-load training (n = 53). The bias was greater in this subgroup, with 80% of the high-load participants fathering girls vs. 52% girls in the low-load group.
“Intense exercise has been linked to several altered semen parameters as well as increased sperm DNA fragmentation, increased presence of macrophages, increased reactive oxygen species and a decreased total antioxidant capacity,” the researchers wrote. “It is clear that the type of sports training, athletic performance level and the physical exercise effort can potentially modulate these reproductive responses and as such may impact the specific time point of conception.”
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