Why training one sport wins this year and loses in five

Training changes exactly what you use. Run, and you get better at the muscles, joints and nerve signals of running. Nothing else trains them as well.

In one study, well-trained athletes added extra training for eight weeks. Over 3.2 kilometres, the extra running took 26 seconds off their time. The same extra time spent swimming took off half as much. The group that added nothing barely changed.

So in the first year, the athlete who only runs will usually be the faster runner. That is real. It is why so many people train that way.

The catch is that running is hard on the legs. Around four in ten runners get injured in a year.

Injuries come with the hours. Across 13 studies, recreational runners had about eight injuries for every 1,000 hours of running. The more of your week you spend running, the more of those hours you collect.

When you stop, you start losing fitness within weeks. Researchers asked seven endurance athletes to stop training altogether. Their VO₂max, the most oxygen they could take in and use, fell seven percent in three weeks.

So a six-week injury does not cost six weeks. It costs the six weeks, then the weeks of climbing back to where you were. And the injury does not stay in the past. Across many studies of long-distance runners, one of the strongest predictors of a running injury was an earlier one.

Fitness is built on top of the fitness you already have. Every year starts from where the last one ended. A runner who loses a season starts the next one from lower down.

Your heart and lungs grow from how long and how hard you work, whatever the sport. So do the roads in your muscles, the tiny blood vessels that carry oxygen to every fibre. Base effort builds them best. That is the steady effort you could hold for hours, about three out of ten.

A review of seven trials compared people who trained only by running with people who trained only by cycling. Their VO₂max came out much the same. The engine moves between sports. The part that belongs to running, the stride and the spring in your tendons, still has to be trained on foot.

That changes what an injury means. When your shin is sore from running, you can still ride and swim. You keep training your engine at base, threshold and VO₂max while your shin heals. You come back with most of your fitness intact.

And swimming and riding are not only there for bad weeks. They are endurance in their own right, and being good at them opens up a lake, a coastline or a mountain road.

Spreading the work helps before anything hurts, too. In a study of running shoes in Luxembourg, 264 recreational runners were followed for 22 weeks. Runners who did an extra hour a week of other sports had about 15 percent less risk of a running injury.

Running works your muscles thousands of times against a light load. It builds the engine. It does not make you strong, and it does not take your joints through their full range. Those are qualities of their own.

Kettlebells build the strength and power to lift, carry and jump. Yoga builds the range to squat, reach and get up off the floor, and a breath you can control. Strength also makes endurance cheaper and cuts injuries in many sports.

In elite endurance sport, the longer the event, the later athletes reach their best, from about 20 for short swims to nearly 40 for ultra-distance cycling. In the longest events, athletes keep getting better for many years.

Put those together and the five years look different from the first one. The runner is ahead after a year. But injuries come with running hours, and she spends all of hers running. Each injury costs her the weeks off and the weeks back, and makes the next one more likely. Every push to do more lands on the same feet, shins and knees.

The athlete who mixes is a little slower at first. He trains the same hours, but fewer of them land on the same tissue. When one part is sore, he keeps his engine going in another sport. He builds strength and range that running never gave him. Over five years, the weeks he never lost make him the better athlete, and he is a swimmer and a rider as well as a runner.

This matters most when time is short. If you have four hours a week, mixing does not ask for a fifth. It asks you to spend the four differently.

Running is the clearest case only because it has the most studies. A rider who only rides, or a swimmer who only swims, also repeats one movement for years.

Triathletes train three sports, and they still get hurt. Over four seasons, 46 of 50 elite Australian triathletes were injured. Most of the injuries came in training, and the ankle, foot and lower leg were hurt most often.

Three sports did not stop the injuries. The number of sports is not what protects you.

What makes mixing pay is how the pieces fit together. A swim, a ride, a run, a kettlebell and a mat each ask something different of you. Thrown into a week at random, they can add up to more strain, not less. Jonas did not pull ahead by doing more things. He pulled ahead because the things he did fitted together, and that takes some care. The rest of this part is about that care.