Research to Reader: fertility science
There are so many incredible benefits of exercise for those undergoing fertility treatments but it is possible to have too much of a good thing. If you participate in a number of hours of endurance exercise each week and you will be providing a sperm sample for analysis or fertilisation, then read on!
A Delicate Balance
When we are getting an athlete ready for competition it is a delicate balance to ensure they have quality training sessions yet have sufficient time to recover and repair, ensuring optimal adaptations and performance. If we overload an athlete their performance suffers and we see alterations in their biochemical, physiological and psychological profiles.
With increases in training stress we experience increases in oxidative stress. Oxidative stress is important in stimulating training adaptations but too much and it can have negative implications. Sperm is quite susceptible to oxidative stress and indeed research has shown that high levels of oxidative stress (indicated by the lipid peroxidation marker MDA) are associated with increases in DNA fragmentation (1) – not great for baby making.
How Many Hours a Week?
In endurance athletes training 4-5 days per week for ~2hrs (VO2max 62ml/kg/min) sperm parameters such as semen volume, motility, and number of spermatozoa were all lower when compared to recreational exercisers (VO2max 50ml/kg/min) undertaking ~4-5 hours per week at low to moderate intensities (1).
In high level triathletes (VO2max 70 ml/kg/min) with 5 years racing history and training approx. 416 km of swimming, 13,000 km of cycling and 2,600 km of running per year, semen parameters were at the lower end of the ‘normal’ reference range set by the World Health Organization (ranges used in laboratories to determine sperm quality) (2). DNA fragmentation was high (2), supporting similar studies that suggest that high volumes and intensities of endurance training may have negative effects on sperm quality (2, 3).
Put That Mountain Climb on Hold...
Sperm are very susceptible to damage as a result of exposure to oxidative stress. High volumes and intensities of exercise may overwhelm our antioxidant defences designed to counteract oxidative stress, with damaging effects on sperm. Oxidative stress levels also rise when we are exposed to environments where oxygen delivery may be compromised. If you undertake any altitude training or training in a simulated hypoxic environment it would be recommended that you avoid this, particularly in the weeks prior to sample collection.
Exposure to altitude in animals induces changes to reproductive hormones, and reversible fertility impairments in humans (4). In healthy, but older (~47years), mountain climbers a five day climb to Mount Kilamanjaro’s summit (900m to 5895m) led to a reduction in the forward motility of sperm (5). If you are not acclimatised to living at altitude then exposure to extreme altitudes is not conducive to reproduction.
Is Lycra Your Attire of Choice?
If you are partial to donning some lycra and hitting the asphalt it may be time to consider the type of activities you are participating in and whether swapping off on the front on the next bunch ride is going to give your little swimmers the best chance of making healthy embryos.
In trained cyclists undertaking 16 weeks of prescribed training (371 km/wk for 8 weeks then 659 km/wk for 8 weeks) following a four week off season, sperm parameters were negatively affected compared to before training (6). The cyclists had an average training history of just under six years with VO2max values of 64 ml/kg/min). While sperm motility recovered after 7 days of rest, the number of sperm were reduced and sperm abnormalities increased after 30 days of no exercise. In combination with another study that has shown cycling for more than five hours a week is associated with a 92% chance of low sperm concentration (7), it appears that intense and prolonged cycling negatively influences male fertility.
If your preferred mode of exercise is cycling then you may need to reduce the time spent on the bike and importantly limit the number of high intensity exercise sessions.
1. Tartibian B, Maleki BH. Correlation between seminal oxidative stress biomarkers and antioxidants with sperm DNA damage in elite athletes and recreationally active men. Clin J Sport Med. 2012; 22: 132-9.
2. Vaamonde D, Algar-Santacruz C, Abbasi A, Garcia-Manso JM. Sperm DNA fragmentation as a result of ultra-endurance exercise training in male athletes. Andrologia. 2017.
3. Hajizadeh B, Tartibian B, Eghbali M, Asri-Rezaei S. Comparison of seminal oxidants and antioxidants in subjects with different levels of physical fitness. Andrology. 2013; 1: 607-14.
4. Verratti V, Giulio CD. High-altitude hypoxia and reproduction: is there an environmental limit to the human male reproductive system? Sport Sciences for Health 2012; 7: 39-40.
5. Verratti V, Di Giulio C, D'Angeli A, Tafuri A, Francavilla S, Pelliccione F. Sperm forward motility is negatively affected by short-term exposure to altitude hypoxia. Andrologia. 2016; 48: 800-6.
6. Hajizadeh Maleki B, Tartibian B. Long-term Low-to-Intensive Cycling Training: Impact on Semen Parameters and Seminal Cytokines. Clin J Sport Med. 2015; 25: 535-40.
7. Wise LA, Cramer DW, Hornstein MD, Ashby RK, Missmer SA. Physical activity and semen quality among men attending an infertility clinic. Fertility and sterility. 2011; 95: 1025-30.