TRT for Endurance Athletes: What Cyclists and Runners Need to Know

By Dr. Farhan Abdullah, DO | Medical Director, Magnolia Functional Wellness | Southlake, TX

He'd ridden 9,000 miles the previous year. He could hold a steady pace on a Saturday group ride for four hours in August, with the Texas heat coming up off the asphalt like an oven door left open. And yet, sitting across from me, he described himself as "flat." Tired in a way sleep didn't fix. No drive, no snap in his legs on hard efforts, a libido that had quietly packed up and left. His lab work from another clinic showed a total testosterone in the low 200s, and someone had already suggested he just start injections.

I'm Dr. Farhan Abdullah, and at Magnolia Functional Wellness in Southlake, I see some version of this man every few weeks. Sometimes it's a cyclist. Often it's a marathoner or a triathlete in his forties who's been training seriously for a decade or more. The question is always the same: should an endurance athlete with low testosterone be on TRT?

The answer is more interesting than yes or no. Sometimes it's yes. Surprisingly often, it's "not yet, and maybe not at all." And the reasons have a lot to do with how endurance training itself talks to your hormones.

Why Serious Endurance Training Can Push Testosterone Down

Most people assume exercise always raises testosterone. For moderate training, that's roughly true, or at least it doesn't hurt. But high-volume aerobic work is a different animal. For decades, exercise physiologists have documented that men who log big miles often carry lower resting testosterone than their less-trained peers.

Dr. Anthony Hackney at the University of North Carolina has spent much of his career on this. In a 2020 review in Frontiers in Endocrinology, he laid out a useful distinction. Some men develop low testosterone acutely, tied to low energy availability or overtraining, and it tends to be transient. It improves once the underlying problem is fixed. Others develop a more chronic pattern that persists over years of training, which his group calls the "Exercise-Hypogonadal Male Condition."

That distinction matters enormously for treatment. One version is a fueling and recovery problem wearing a hormone costume. The other may be a longer-lasting adaptation of the hypothalamic-pituitary-gonadal axis.

How low can it go? Lower than you'd expect in fit, healthy men. A 2019 study by Hooper and colleagues in the International Journal of Sports Physiology and Performance drew blood from 22 men competing at the 2011 Ironman World Championships in Kona. Before the race, only 9 had clearly normal testosterone. Another 9 sat in a gray zone, and 4 had levels suggestive of actual deficiency. Testosterone then fell further in the days after the race. These weren't sedentary men with metabolic disease. They were among the fittest amateur athletes on the planet.

So when a runner tells me his testosterone came back at 280, my first thought isn't "he needs testosterone." It's "what is his training doing to him, and is it reversible?"

Fuel First: The Low Energy Availability Problem

I see this pattern constantly. A guy in his forties gets serious about cycling or running. He wants to get leaner because lighter is faster, especially on climbs. He cuts carbs, trims portions, and adds volume. His weight drops. His power-to-weight ratio looks great on paper. And over a few months, his body quietly decides it can't afford a fully functioning reproductive system.

This is what sports medicine now calls Relative Energy Deficiency in Sport, or REDs. The idea is simple. After you subtract the energy you burn training, there's not enough left over to run everything else properly: bone remodeling, immune function, thyroid output, and yes, testosterone production. The 2023 International Olympic Committee consensus statement on REDs, led by Mountjoy and published in the British Journal of Sports Medicine, makes clear this isn't just a female athlete issue. Men get it too. They just get diagnosed less often, partly because nobody's looking.

Male endurance athletes with low energy availability tend to show a recognizable cluster:

• Low or low-normal testosterone, often with low or "inappropriately normal" LH
• Persistent fatigue and stalled performance despite consistent training
• Reduced libido and fewer morning erections
• Stress fractures or low bone density, particularly in cyclists, since riding isn't a bone-loading sport
• Frequent colds, poor sleep, irritability

What I tell my patients is this: if energy deficiency is driving your low testosterone, putting you on TRT is like turning up the radio to drown out a strange engine noise. You'll feel better for a while. The engine is still making the noise.

Fixing it usually means eating more, especially carbohydrate around training, and sometimes cutting volume or adding real recovery weeks. Is that the answer an ambitious masters athlete wants to hear? Not usually. But I've watched men recover their testosterone into a normal range over a few months just by fueling like athletes instead of dieters. That's a better outcome than lifelong therapy.

When TRT Actually Makes Sense for a Runner or Cyclist

None of this means endurance athletes can't or shouldn't be on testosterone. Some absolutely should. Low testosterone from a true testicular or pituitary problem doesn't care how many miles you log. And some men, after we've fixed their fueling and given it an honest trial, still have low levels and real symptoms.

Before I consider testosterone replacement therapy for an endurance athlete, I want a few things nailed down:

• At least two early-morning total testosterone levels, drawn on a normal training day, not the morning after a century ride or a long run.
• Free testosterone and SHBG. Lean endurance athletes can run higher SHBG, which changes how much testosterone is actually available to tissues.
• LH and FSH. These tell me whether the problem starts in the testes or upstream in the brain. Low testosterone with low or normal LH points toward a central, often functional cause.
• A frank conversation about calories, training load, and sleep. Sometimes I'll ask for a few days of food logging. It's often eye-opening.
• Fertility plans. Testosterone therapy suppresses sperm production. For a 38-year-old runner who wants more kids, that changes everything about the plan.

If the labs confirm genuine hypogonadism, the symptoms fit, and we've addressed energy availability without improvement, TRT can be a very reasonable choice. Men in that situation often report better recovery, steadier mood, and the return of that drive they'd lost. I'd be careful with expectations, though. Testosterone at physiologic replacement doses isn't a performance drug in the way people imagine. It restores normal. It doesn't turn a 3:30 marathoner into a Boston qualifier.

The Hematocrit Problem Endurance Athletes Can't Ignore

This is the part of TRT that deserves extra attention in runners and cyclists, and it's where I see other clinics get sloppy.

Testosterone stimulates red blood cell production. That's well established. A 2022 network meta-analysis of randomized trials by Nackeeran and colleagues in the Journal of Urology found that every testosterone formulation studied raised hematocrit compared with placebo, with intramuscular cypionate or enanthate producing an average increase of about 4 percentage points.

For a sedentary man starting at a hematocrit of 42, that's usually manageable. Endurance athletes add some wrinkles:

Dehydration concentrates blood. Train through a North Texas summer and draw labs the next morning, and your hematocrit can read higher than it really is. I want labs drawn well hydrated, and I pay attention to timing.

Altitude stacks on top. If you spend a week riding in Colorado or doing an altitude block, your body makes more red cells on its own. Add testosterone, and numbers can climb fast.

Thicker blood isn't free. Once hematocrit goes past about 54 percent, most guidelines recommend holding or reducing therapy, because blood viscosity and clotting risk rise. An athlete who already pushes his cardiovascular system hard for hours at a time doesn't need that extra load.

In practice, this means closer monitoring for athletes than for my average TRT patient. We check hematocrit and blood pressure at each follow-up, adjust dose or frequency when needed, and sometimes recommend blood donation. Smaller, more frequent doses can smooth out the peaks, too.

If You Race, Read This Part Twice

Testosterone is on the World Anti-Doping Agency's prohibited list at all times, in and out of competition. If you race in events governed by USA Cycling, USA Triathlon, or other bodies that follow the WADA code, you can be tested, and masters athletes do get tested.

A Therapeutic Use Exemption (TUE) is possible, but the bar is high. WADA's physician guidance on male hypogonadism generally doesn't support exemptions when low testosterone is functional, meaning driven by things like overtraining or under-eating. That's another reason the workup matters so much. If you're a competitive athlete, sort out the TUE question before you start therapy, not after a positive test. Local fun runs and the weekend group ride out toward Grapevine Lake are a different story, but it's worth knowing where the lines are.

What a Smart Plan Looks Like

At Magnolia, an endurance athlete with low testosterone usually goes through something like this:

First, confirm it. Repeat morning labs at the right time in the training cycle, plus the supporting panel: free testosterone, SHBG, LH, FSH, estradiol, prolactin when indicated, thyroid, CBC, ferritin, and a metabolic panel. Iron deficiency is common in runners and can mimic a lot of the same fatigue.

Second, look for the reversible stuff. Energy availability, sleep, training load, alcohol, medications, and weight changes. For many men, a structured 8 to 12 week period of eating more and managing training stress moves the numbers meaningfully.

Third, recheck. If testosterone has recovered and symptoms have improved, great. We keep monitoring, and no prescription was needed.

Fourth, treat when it's warranted. If true hypogonadism persists, we talk through TRT honestly: the benefits, the hematocrit issue, fertility, and anti-doping implications. If we start, we monitor closely and adjust.

If you're weighing the bigger picture on testosterone therapy in North Texas, our guide for men over 30 considering TRT covers the fundamentals.

The athletes who do best are the ones who treat this like they treat their training. They're curious, they track things, and they're willing to change course when the data says so. That mindset makes them great patients.

The Bottom Line for Runners and Cyclists

Low testosterone in an endurance athlete isn't the same diagnosis as low testosterone in a sedentary man with a big waistline and sleep apnea. The causes differ, and so should the treatment. Sometimes the fix is a prescription. Often, it starts with a bigger breakfast, a recovery week, and an honest look at how hard you've been pushing.

If you're a runner, cyclist, or triathlete in the Southlake area and you've been feeling flat despite doing everything "right," I'd love to help you figure out why. At Magnolia Functional Wellness, we'll look at the whole picture, from your training log to your lab panel, and build a plan that respects both your health and your goals on the road.