Large amounts of endurance exercise and being very lean are both associated with lower testosterone levels.
In fact, some research on male athletes participating in endurance sports, such as marathons and long-course triathlons, reports testosterone levels that are just 50% of those found in comparable age-matched, non-exercising men.
The common characteristics and traits of men displaying the so-called Exercise-Hypogonadal Male Condition (EHMC for short) include:
– They have low resting basal testosterone levels, typically 50–75% that of normal, healthy, age-matched sedentary men.
– Their low testosterone levels do not appear to be a transient phenomenon related to the acute stress-strain of exercise.
– In many cases, it appears an adjustment in the regulatory axis (to allow a new lower set-point for circulating testosterone) has occurred.
– They typically have a history of early involvement in organized sport and exercise training. This has resulted in these men having many years of almost daily exposure to physical activity.
– The type of exercise training history most frequently seen in these men is prolonged, endurance-based activities such as distance running, cycling, race walking, and triathlon training.
However, there are several reasons why EHMC is something most people don’t need to worry about.
For one, it’s a phenomenon that’s typically observed in endurance athletes who are very lean and training for events like triathlons, ultramarathons, that type of thing.
Rather than being caused by steady-state cardio per se, it has more to do with low energy availability, a result of the highly restrictive diet necessary to maintain such a low body fat percentage.
If you get someone to diet for long enough, their T levels will dip sooner or later, irrespective of how much cardio they’re doing.
For example, there was an interesting case-study that looked at a professional drug-free bodybuilder while he was dieting down for a contest.
By the time of the show, testosterone had dropped to just 25% of its normal resting level.
That’s despite the fact he was doing mainly resistance training (5 hours per week) and HIIT (40 minutes per week), with only 30 minutes devoted to steady-state cardio.
In most cases, that amount of exercise by itself wouldn’t be a problem. The real issue was the reduced energy intake combined with a very low level of body fat (this guy was down to 4.5% by the time of the contest).
Even with no exercise at all, such an extreme level of leanness will cause T levels to take a dive.
In short, too much exercise, be it steady-state cardio, HIIT, or resistance training, especially when it’s combined with prolonged dieting, can have an adverse effect on hormone levels.
However, it’s not cardio by itself that’s causing the problem, but large amounts of exercise combined with a restrictive diet and low body fat percentage.