Crossing a half marathon finish line often sparks a new running goal: a full marathon! After all, if you’ve already run 21.2K, doubling the distance can seem like the logical progression. But the transition from half to full isn’t so straightforward.

…the transition from half to full isn’t so straightforward.

While a few aspects of half marathon training translate to the full marathon, including the types of workouts you need, marathon training amplifies the demand put on both your body and your mind. The increased race distance means longer training cycles, more time on your feet, and a greater need to dial in the details that might not matter as much in a half.

Runners moving from a half to a full marathon often experience the same few pitfalls, but once you know what they are, they’re usually fixable.

We spoke to RRCA-certified run coach, certification instructor, and principal lecturer at Coastal California University, Christine Rockey, who reveals the three most common mistakes runners make when transitioning from a half to a full marathon for the first time, and how you can avoid them.

1. Not Prioritising Fuelling
Failing to prioritise fueling is the single biggest issue Rockey sees with athletes making the jump from a half to a full.

In a half marathon, many runners can get through a race with minimal fuelling or by grabbing one or two gels sporadically throughout a race. The marathon is a completely different physiological challenge, and will certainly overwhelm someone with a haphazard fuelling strategy, Rockey explains. The longer duration means your body will run low on readily available energy if you don’t take in carbohydrates along the way.

When runners aren’t fuelling during training, warning signs often show up in subtle ways before race day arrives. “You’re going to see fatigue, lack of motivation, not wanting to do the workouts you’re scheduled to do,” Rockey says. “One of the things that [you can measure] is a spike in your resting heart rate.” These signals often indicate that your body isn’t recovering properly between runs.

Prioritising pre-run and post-run meals is an easy way to start righting that ship. Prerun meals should include a balance of macronutrients, with a focus on carbs. Post-run fuelling should prioritise carbs, but also include some protein, within 30 to 60 minutes of finishing your effort.

You should also rehearse your race-day nutrition routine.

You should also rehearse your race-day nutrition routine. “If you’re going to run in the morning, you should practice fuelling with whatever you plan to eat on race day to make sure it sits well,” Rockey explains.

Even more crucial: practicing midrun fuelling. Rockey has seen many athletes who assume they can figure it out close to race day, but that approach can backfire. As soon as your plan calls for runs of 90 minutes or more, “you’re going to want to start practising doing some fuelling,” Rockey says.

2. Undertraining
Another common mistake for runners moving into full marathon training is inconsistency and the resulting undertraining issues that come from it.

Most runners who have completed a half marathon understand the importance of a structured training plan in keeping them consistent. However, many people can also successfully train for and race 21.1K with cracks in their plan, but those cracks can create big problems when going for 42.2K. Undertraining, not running fast, far, or frequently enough, has greater consequences in a marathon because of the physiological demands late in the race.

Oftentimes, skipping workouts can lead to undertraining. And while it’s rarely intentional, when you start missing more workouts than you realise, the probability of a bad race skyrockets. “You could get injured,” Rockey says. “But there’s the mental side of things, too. You can feel like a failure if things don’t go the way you expected.”

One of the best ways to lower the risk of undertraining is by having a solid base before you even begin your marathon plan. “I really think [runners] should have at least 500 to 800 kilometres of a base,” says Rockey. “Just get an idea of your life as a runner.” If it’s only been a few weeks since your half, you probably have a base already, so the key shifts to maintaining consistency.

One of the telltale signs of undertraining is stagnation. If you’re simply not getting faster in your training over a month or so, it may be time to check your training log for skipped runs, especially quality efforts like interval workouts or long runs.

The bottom line: Missing one workout every so often isn’t detrimental, just something to keep an eye on. However, if you regularly skip your quality workouts or miss full weeks of training, it may be time to reevaluate and build up toward a more manageable goal.

3. Misjudging the Challenge
Even runners who trained really well for their half marathon will experience unexpected challenges, both physical and mental, when moving up to a full marathon.

“When you hit the 21K mark, you’re not halfway there, even though on paper you are,” Rockey says. Essentially, you have physically travelled half the distance, but you haven’t experienced the full scope of the challenge yet.

In the later stages of a marathon, your body is operating in new territory. Glycogen stores run low, muscle fatigue mounts, and your ability to maintain pace becomes increasingly tied to fuelling and mental resilience, Rockey says. If you’ve only done half marathons before, you simply don’t know what that feeling is like. “I’ve done about 100 marathons, and in every one around 32K I’m still like, ‘Oh my god, why did I sign up for this?’” Rockey says.

Getting as ready as possible for that moment at 32K comes during race prep, especially on long runs where you’re spending extended time on your feet without the energy of race-day crowds to push you, explains Rockey. “At home, you’re literally running by yourself,” she says. “The only person to hold you accountable is you.”

The first step in holding yourself accountable and building mental resilience is simply getting out the door consistently, as mentioned above. Once you’re out running, work on your mental game just as much as your physical. Some strategies to consider include positive self-encouragement, running with a buddy, or Rockey’s suggestion: “I play games with myself,” she says. “I’ll try to do math problems or count backwards from 100.”

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