This is old news. In the early to mid 1900's, scientists like Broda Barnes and Hans Selye made stress their career; later ,Ray Peat and Sapolskly continue this same understanding.
"Thus, exercise training in rats seems to elicit the fall in TPO activity and T4 plasma concentration at rest but without changing hepatic 5’DI activity and rT3 plasma concentrations. A decline in T3 plasma concentration, observed in rats trained with the lowest exercise intensities, could be regarded as transitional effect in adaptation to chronic exercise.Eur J Appl Physiol. 2003 Jan;88(4-5):480-4. Epub 2002 Nov 22.
Resting thyroid and leptin hormone changes in women following intense, prolonged exercise training.
Baylor LS, Hackney AC.
. Resting metabolic rate (RMR) was significantly decreased by 8% after training despite the preservation of fat-free mass (FFM). Accordingly, plasma norepinephrine (NE) concentrations, NE appearance rate, and plasma levels of triiodothyronine (T3), free T3, and total thyroxine (T4) were lower after training. Metabolism. 1997 May;46(5):499-503.
Endurance training with constant energy intake in identical twins: changes over time in energy expenditure and related hormones.
Tremblay A, Poehlman ET, Despres JP, Theriault G, Danforth E, Bouchard C.
Cytochrome oxidase in the brain can also be increased by mental stimulation, learning, and moderate exercise, but excessive exercise or the wrong kind of exercise (“eccentric”

can lower it (Aguiar, et al., 2007, 2008), probably by increasing the stress hormones and free fatty acids. Sedentary living a high altitude has beneficial effects on mitochondria similar to moderate exercise at sea level (He, at al., 2012.” Ray Peat, PhD.
Besides causing stress, estrogen levels are increased by stress. For example, a male runner’s estrogen is often doubled after a race. Men and women who are hospitalized for serious sickness typically have greatly increased estrogen levels. Estrogen’s role in terminal illness, a vicious circle in which stress decreases the person’s ability to tolerate stress, is seldom appreciated.” Ray Peat, PhD.