Since January 2026, the World Anti-Doping Agency has been screening blood and urine samples for traces of two weight-loss agents: semaglutide and tirzepatide. Although they are not banned, they are still being monitored. They would be of little use to anyone in elite sports: Those who are already extremely slim will mainly lose muscle mass from a weight-loss injection. For the rest of the MTB scene, things look different. Those who have been spending money for years to shave off every gram from their frames can now target their own bodies directly for a fraction of that cost. Is this the next logical step in weight optimization, or does it go too far? The trail leads back to 1988, to a carbon-fiber frame.

Six euros per gram

In 1988, the American manufacturer Kestrel built one of the first production carbon frames for mountain bikes with its MXZ model. Five years later, the Trek 9900, weighing 1,288 grams, was considered the world’s lightest production frame. Since then, the shift to carbon has turned into a battle over every single gram. Swiss manufacturer DT Swiss sells the EXC 1200 Classic carbon wheels for 2,499 euros at 1,644 grams, and the EX 1700 Classic aluminum wheels for 749 euros at 1,916 grams. Those who opt for the carbon version pay 1,750 euros more for 272 grams less. That’s about 6.40 euros per gram saved. Extrapolated, that would amount to over 6,400 euros for a whole kilogram—just for a pair of wheels. This calculation could be repeated for frames, brakes, or drivetrains.

For pure racing hardtails, frame development has continued, with the lightest models now weighing around 800 grams. For full-suspension bikes, the picture is more nuanced. The lightest carbon full-suspension bikes are cross-country and marathon racers, optimized for climbing, and even they weigh between 1.5 and 2.5 kilograms—heavier than the 1993 Trek hardtail. For enduro and downhill bikes, weight isn’t the top priority. Stability and control on the descent matter more. The sport itself has also evolved. Today, the frame itself has to withstand more: space for wider tires, mounts for more suspension travel, and reinforcements against harder impacts.

At this point, there’s very little left to gain from the material. Every additional gram costs more than it’s worth to many riders. A revolution is now taking place in our own bodies—one as significant as the switch to carbon once was—only this time, it comes from a syringe.

What the injection really costs

One subcutaneous injection per week. In clinical trials, people on semaglutide lose an average of about 15 percent of their body weight, and those on tirzepatide lose up to 22.5 percent. However, about 25 to 45 percent of this loss is not fat but muscle mass. For elite athletes, who are usually among the leanest people in their discipline anyway, this is a bad deal: Those with hardly any fat reserves lose strength above all else.

For the rest of the MTB community, the option looks tempting at first glance. A four-week supply of Wegovy costs around 179 Swiss francs in Switzerland without insurance coverage—a fraction of the price of a carbon wheelset. It’s hard to say how long a fit, normal-weight mountain biker would need to use the injection to lose two kilograms. All efficacy data comes from overweight or obese individuals with much larger weight loss goals, not from lean athletes. If someone also meets the medical criteria for coverage—a specific body mass index combined with a comorbid condition—basic health insurance will help cover the cost. However, no well-trained mountain biker who wants to shed two kilograms for a climb or the next race meets these criteria. The injection is prescribed for morbid obesity. A higher wattage is not a recognized indication. Anyone who wants it anyway must pay the full price, needs a prescription, and a doctor willing to prescribe it outside of this diagnosis. Anyone who has the money can buy carbon. The injection, however, is not.

Legal, but under scrutiny

Hard to get doesn’t mean it’s banned. It isn’t banned in either elite or recreational sports. Its use is being monitored nonetheless: Since early 2025, WADA has been testing blood and urine samples for traces of weight-loss agents to determine how widespread their use in sports already is. This data will help determine whether the substance will be added to the Prohibited List in the future. Nike’s carbon-plate shoe, the “Vaporfly,” was also legal at first, until world records began falling one after another and the International Association of Athletics Federations limited sole thickness to 40 millimeters in 2020. Norwegian sports philosopher Sigmund Loland sums up what this is all about: the question of whether a performance can still be attributed to a person’s talent and effort, or to the technology they use. It took four years from the first world records to the ban on the Vaporfly sole. How long will it take with the weight-loss injection?

WADA is already considering a possible ban ahead of the 2028 Olympic Games in Los Angeles—about two and a half years after monitoring began—significantly faster than in the case of the Vaporfly shoe. The injected active ingredient can be detected directly in urine samples, as has long been routine in elite sports. The weight-loss injection acts within the body itself. Lighter material only affects the rider from the outside. This is therefore about more than just weight: it’s about the risk an athlete takes to become lighter. There has been little research into the side effects the injection has on a healthy body over the years, and long-term safety data is lacking.

What is certain, however, is that the weight-loss injection was not developed for sports. In elite sports, it offers little benefit—if anything, the opposite. In recreational sports, it’s hard to come by and has hardly been tested. Carbon, on the other hand, continues to deliver exactly what it was developed for: lightweight yet sturdy components. For the vast majority, material weight optimization remains the simpler and safer choice. Ultimately, everyone must decide for themselves whether the risk is still worth it.