Excessive Cardio & Testosterone: The free T / Cortisol Ratio Revisited | Plus: Why Even a 72% Decrease in fT/C May be Less Significant for Your Gains Than You Thought It'd Be

Cardio - Only "too much" can hurt you.

Let me get this straight: this is not an anti-cardio article. There's not just little, there's rather absolutely no doubt that a sane amount of endurance training is nothing but healthy for us, but done in excess, especially "running has been demonstrated to provide a large physiological stress to the body, resulting in large neuroendocrine system responses" (Anderson. 2016) - more specifically, running to exhaustion will have the hypothalamic–pituitary–adrenal (HPA) axis overproduce the glucocorticoid hormone, cortisol, which in turn appears to suppress the production of testosterone.

Now, cortisol - you've learned that in previous articles - is not the villain as which it is portrait by companies that are trying to sell you useless and potentially counter-productive "cortisol blockers". Rather than ruining your results, normal amount of cortisol will aid in substrate mobilization (including the use of body fat during your workouts) and can even improve your running performance.
Surprised? Well, I guess you will be likewise surprised to hear that the well-established connection between high cortisol and low testosterone levels that are characteristic of overtraining is likewise not as black-and-white as you may have heard. In 2005, for example, Brownlee et al. were able to show that the significant decline in total testosterone in response to exercise goes hand in hand with a disassociation of testosterone and its binding globulin SHBG that triggers an increase in free and thus bio-active testosterone levels - an increase that correlates with the exercise-induced increase in cortisol (as Brownlee et al. point out this is probably due to "an adrenal cortex contribution of fT or disassociation of fT from sex hormone binding globulin" | Brownlee. 2005).

Figure 1: Free testosterone and cortisol in young mend during recovery from 60-90min intense exercise (Brownlee. 2005).

In that, it is important to acknowledge that this finding of which the scientists rightly say that it "would seem to support the notion that the observed testosterone reductions following certain forms of physical exercise could be related to cortisol elevations in response to that exercise" does not "indicate a cause and effect relationship" (Brownlee. 2005).
What it does do, however, is tell us that we cannot restrict post-workout hormone essays to cortisol and total testosterone - unfortunately, the many currently available studies do just that... and what's more: they also fail to "assess the time course required for the neuroendocrine system to return to a resting homeostatic state" (Anderson. 2016) - even though

"[s]uch information is potentially vital to the coach and athlete in establishing timeline guidance forthe number of rest days necessary after strenuous exercise, such as might occur in a competition" (Anderson. 2016).

It is thus only logical that Travis Anderson and colleagues conducted a study to assess
the dynamics (!) of cortisol and testosterone concentration during recovery, following an exhaustive exercise bout. A study the results of which gain significance to the researchers' choice of subjects.

Table 1: Subject characteristics - Certainly not a bad thing to use elite athletes instead of noobs (Anderson. 2016).

12 elite endurance runners who reported to the laboratory on seven separate occasions each time being required to adhere to the preassessment guidelines, which included being 2.5 h fasted, abstaining from strenuous activity, alcohol and sexual activity for 24 h, and abstaining from caffeine consumption for 12 h.

Table 2: Exhaustive exercise session (X ± SD) | VO 2 oxygen uptake, HR heart rate, RPE rate of perceived exertion, VT ventilatory threshold (Anderson. 2016).

Following a 7-day wash-out period, participants took part in a standardized exhaustive exercise test -- a prolonged exercise run on the treadmill until volitional fatigue, running at 100 % +/-3% (see Table 3) of their pre-determined ventilatory threshold (VT | ventilatory threshold refers to the point during exercise at which ventilation starts to increase at a faster rate than VO2, the VT thus reflects the levels of anaerobiosis and lactate accumulation).

Complete exhaustion is key to the ill effects of "cardio"
.
To ensure "a truly fatiguing exercise session", strong "verbal encouragement" was given to subjects towards the end of the exercise session (the RPE levels in Table 2 indicate that this worked - the subjects, elite athletes or not, were truly exhausted) after which the subjects completed a ~5 min cool down, prior to a post-exercise blood sample being taken (+0 h).

Figure 2: Free testosterone (left, top), cortisol (left, bottom) and fT:cortisol ratio (right | Anderson. 2016).

Subjects reported back to the laboratory at the same time of day 24 (+24 h), 48 (+48 h), and 72 (+72 h) hours after the exhaustive exercise bout, where blood samples were again drawn. Subjects
were asked to maintain a similar diet and activity level compared to the pre-EES period during this 72 h of recovery, and the latter involved only activities of daily living and no exercise training. The analysis of these samples revealed the following results:

• free testosterone - as far as fT is concerned the researchers observed a significant decrease in fT following EES compared to pre-EES time points (−48 to 0 h; p = 0.053 to p = 0.001) that persisted for up to +48 h into recovery, before returning to baseline (pre-EES) levels at +72 h,
• cortisol - the scientists' REPANOVA and post hoc analysis revealed increases and decreases in C following EES compared to pre-EES. At +0 h, C was increased (p < 0.001) and decreased at +24 h (p < 0.002) before returning to baseline (pre-EES) levels,
• free testosterone : cortisol ratio - the analysis of the ratio of the two measured hormones revealed significant differences with post hoc analysis showing fT:C was significantly decreased at +0 h (0.167 ± 0.084) relative to all other time points (p < 0.005), interestingly enough, it took only 24h for the fT:C to return to pre-EES, with no significant differences between +48 h or +72 h compared to any pre-EES values,