Intensity and type of physical activity and semen quality in healthy young men

To study the relationship between intensity of physical activity (PA) and semen quality in healthy young men.

A prospective cohort study with repeated measures for each subject.

Healthy high school and university students who did not regularly smoke tobacco, drink alcohol, or take drugs or medicine, with normal body mass index and abdominal circumference.

The participants underwent urologic visit, fasting blood and semen sampling, and anthropometric measurements, and filled in the International Physical Activity Questionnaire, at enrollment and after 4 and 8 months. Duration and frequency of walking, moderate-intensity, and vigorous-intensity activities in the last week were assessed, and a score was computed for total PA.

Semen specimens were taken at each visit through masturbation, after 3-5 days of abstinence, and analyzed by an expert urologist. Sperm concentration, total and progressive motility, and proportion of spermatozoa with normal morphology were measured. Linear and generalized linear mixed models with the Poisson family were fitted to assess the relationships between PA variables and sperm parameters, after adjusting for season, time, and study arm. The shape of the relationship was modeled through restricted cubic spline regression.

A total of 143 male subjects, aged 18-23 years (median, 20 years), were enrolled. They had a median PA of 1,960 (95% confidence interval, 1,055-3,182) Metabolic Equivalent of Tasks in min/wk. Statistically significant differences were found for total, progressive motility, and percent of cell with normal morphology across categories of total PA; the highest medians of total (47%) and progressive motility (34%) and of the percentage of normal morphology cells (7%) were found for medium PA. Positive associations of sperm total motility and normal morphology with medium levels of PA, and negative associations with walking and vigorous-intensity activity emerged. Spline regression analysis confirmed these findings, showing an inverse U-shape relationship, with the highest value of total motility and normal morphology for medium PA, and the lowest values for lower and higher activity.

These findings support the present recommendations to practice moderate PA for health improvement, including semen quality.