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Running on the treadmill is not typically an athlete’s first choice—you got into triathlon to enjoy the outdoors, not stare at a wall. But a treadmill is a godsend for keeping your training on track when you’re facing adverse weather conditions or have a limited workout window. Just make sure you don’t expect a treadmill run to be the equivalent of a road run, says Richard Diaz, endurance sports coach and founder of California-based Diaz Human Performance. An important distinction between running inside and outside is that treadmill running is “rate independent—the treadmill is going to do what it’s going to do, and you’re just trying to keep up with it,” he says. “When you’re outside, you’re not going anywhere unless you push or pull yourself through space.”
The biggest problem with putting yourself on a treadmill belt, Diaz believes, is the potential for over-striding, especially as you start to fatigue—outdoors, you’d just slow down rather than try to keep up with the belt. By over-striding, you’re overloading your posterior chain, which can lead to hamstring injuries. Repetitive treadmill running also opens yourself up to other overuse injuries, says elite triathlon coach and running biomechanics expert Bobby McGee. When you’re running outside, small changes in the environment (curbs, hills, rocks) cause you to make minute movements with tiny stabilizers, keeping your muscles and joints more balanced. However, the uniformity of a flat treadmill belt and a steady pace give you a too-consistent foot strike, which can overtax your muscles and bones.
The fix to the injury potential? “There is plenty of research that if you jack the treadmill up to one to two percent [incline], you can mimic road imperfections,” McGee says. Mixing up your speed and incline throughout your workout—even using those pre-programmed hill workouts—can add enough variety to help stave off injury.
To make the most of your treadmill runs, you also need to know that not all machines are created equally. “You get what you pay for,” says McGee, who uses a Woodway 4FRONT (which costs over $6,000) with his athletes. Even though he’s working with what he calls the “Rolls Royce of treadmills,” with its high-quality belt and deck, he notes that all treadmill dashboards are notoriously inaccurate. As the belt stretches and the mechanical components wear down, treadmills need to be recalibrated often (it happens even sooner with heavier athletes on low-quality treadmills).
With his elite athletes, McGee uses a hand-held tachometer to keep their treadmill speed workouts on track, since accuracy is so important. However, for the average triathlete who runs on the treadmill occasionally, Diaz wouldn’t worry about the reported speed being a little off. “I look at time as a more important variable than speed,” he says—he prescribes workouts as time against effort (i.e., a number of minutes in a specific heart rate zone). Ultimately, like any training device, the treadmill can greatly benefit you as an athlete as long as you keep its limitations in mind. “It’s a powerful tool,” Diaz says. “Being on a treadmill is not a death sentence—it’s an opportunity to really focus on your skill sets.”