1. Just Don’t Overtrain. Before I go into the details on the research, let me say that you really shouldn’t base how you exercsie on testosterone levels. And the reason is simple: there is no evidence that any form of exercise dramatically raises or lowers testosterone with one exception: if you overtrain for an extended period of time, you can hammer your testosterone levels. For details, read my pages on Overtraining and Testosterone and The Best Signs of Overtraining. If you look at the studies on the pages, you’ll see that typical drops from overtraining are 20-30%, but you can tank them even more in severe cases. It can take months or even years to recover from overtraining as well with minimal exercise in some cases.
So, when it really gets right down to it, the best form of exercise is the one that you will keep doing throughout the entire year without hurting yourself. I am not sure why, but a huge percentage of people feel that exercise has to be “punishing.” Well, that’s great for all the masochists out there, but your body begs to differ.
2. Weight Lifting is the Only Winner (But Not By Much). My favorite form of exercise is weight lifting. I don’t know why I enjoy it so much, but I just do. So it makes me happy to report that weight lifting is the only form of exercise that I know of that improves baseline testosterone levels according to (a small amount) of research. However, us weight lifters have little to brag about, because the studies – and there isn’t much out there – only show an increase of about 15% at best. You can read more about it in my page on Testosterone and Weight Lifting.
4. Endurance Training Often Lowers Baseline Testosterone. Multiple studies have shown that endurance training – biking, long distrance running, etc. – lower baseline testosterone levels roughly 20-30%. Now that’s a pretty steep drop, but a lot of men don’t even notice it, because they get nice increases in nitric oxide, neurotransmitters, etc. The theory always was that endurance training was a stressor and increased cortisol levels. However, a recent study found that this was not really the case: cortisol levels dropped actually.  Furthermore, they verified that luteinizing hormone (LH) pulses did not change either. LH is the trigger hormone from the pituitary that tells the testes to produce T. In other words, we don’t really know why endurance training lowers testosterone, but we have enough studies to conclude with a high likelihood that thisis the case.
My personal opinion is that, if you feel good and are showing no signs of overtraining, then I wouldn’t worry about a smallish drop in testosterone as usually the benefits will outweight the negatives. After all, the healthiest people on the planet, the Tarahumara, are essentially ultramarathoners and they enjoy exceptional longevity as well. But I would monitor yourself using one of these: Inexpensive Testosterone Labs.
1) JCEM, First Published Online: Jul 01 2013, “Endurance Training Decreases Serum Testosterone Levels in Men without Change in Luteinizing Hormone Pulsatile Release ”
2) J Endocrinol Invest, 2012 Dec, 35(11):947-50, “Testosterone responses to intensive interval versus steady-state endurance exercise”
3) Eur J Appl Physiol, 2013 Jul, 113(7):1783-92, “Effect of acute DHEA administration on free testosterone in middle-aged and young men following high-intensity interval training”