Undesirable Slowed Pace After Running a Half Marathon

Lately I seem to get tired more quickly when I run, my pace is a lot slower, and sometimes I cannot finish my planned mileage without walking or taking a break. I ran a 10k about ten months ago after training with a team. Then I joined an intermediate training team for a half marathon. I ran 5 days a week ranging from 3–5 miles during the week and then the gradual increase of miles on weekends. I started out running about a 10-minute mile and over the course of training knocked it down to about a 9-minute mile. On race day I ran an 8:30-mile pace with a time of 1:51:25. About a week or two after the race I signed up for another half marathon in about two months. I didn't really take any time off — maybe a week — and started at the beginning of my previous training schedule again. Over the past month and a half my pace has gotten much slower, somewhere between 10 and 11 minute miles. My legs just feel exhausted while I don't really feel winded. What should I do? – Andrea, Richmond, VA, USA

Hi Andrea,

Thank you for writing in — and for giving such a clear picture of your training history. That detail makes it much easier to work out what is likely going on.

Here's what we'll cover:

1. Why your legs are heavy when your lungs feel fine
2. The role group training played — and what to do about it
3. How to use low heart-rate running to rebuild properly
4. What to realistically expect from the half marathon in two months

1. Why Your Legs Are Heavy When Your Lungs Feel Fine

The combination you describe — heavy legs but no breathlessness — is a specific and recognisable pattern. It tells us that your cardiovascular system is coping fine. Your heart and lungs are not the problem. The problem is in the muscles: they are fatigued and have not had enough time to rebuild.

Think about what happened in that half marathon. You raced at 8:30 per mile. But your easy training pace was around 10 minutes per mile, and over the course of training you pushed it to 9 minutes per mile. Running a race at 8:30 per mile when your comfortable pace is 9:00 to 10:00 means you were working at a very high intensity — possibly 85 to 90 per cent of your maximum effort — for nearly two hours. That is an enormous muscular load.

A half marathon at that intensity typically calls for around two weeks of genuine recovery — a common rule of thumb is roughly a day of easy running for every mile raced — before you resume structured training. You took roughly one week. So your muscles — still rebuilding from the race — were asked to start training again almost immediately. The result is what you are experiencing now: persistent fatigue that shows up in the legs because that is where the damage is.

The good news is that this is very fixable. Nothing is permanently broken. You just need to stop fighting the fatigue and start working with it.

2. The Role Group Training Played

Training with a group has real advantages — the social accountability, the structured schedule, the shared experience. But there is one consistent drawback: the group tends to set the pace, and the group's pace is often faster than what is right for you individually.

Looking at your numbers, I suspect this is part of the story. You went from 10-minute miles to racing at 8:30 in one training block. That is a significant jump — and it likely means a lot of your training runs were at 9-minute-mile pace or faster, rather than at a genuinely easy aerobic effort. Short-term, this produces rapid improvement. You feel fitter, you get faster, race day goes well. But when the aerobic base has not been built progressively — when you have been running harder than your system can sustain — the payback arrives in the weeks after the race.

I am not saying the group training was wrong. It got you to 1:51 in your first half marathon, which is a solid result. But the pattern of training-hard-throughout-the-cycle, racing hard, taking minimal recovery, and immediately starting again is a recipe for the fatigue you are now experiencing. Your body needs more than a week to absorb a near-two-hour race effort — and it needs that recovery before it can adapt and improve, rather than just survive.

This is not a criticism. It is a very common pattern, especially for runners who train with groups and are motivated to keep up.

3. The Fix: Low Heart-Rate Base Running

Here is what I would do. For the next four to six weeks, run only at a genuinely easy pace — one where your heart rate stays in Zone 1. There are two reliable ways to find that zone.

The first is to use a heart-rate calculator. I recommend either the Zoladz heart-rate calculator or the Karvonen heart-rate calculator — both will give you your Zone 1 ceiling based on your resting and maximum heart rate. The second is the rough Maffetone formula: 180 minus your age. Both approaches point you towards a similar intensity — low, controlled, and aerobic.

What does this feel like in practice? At first, it may mean slowing to 11, 12, or even 13 minutes per mile. You may need to walk on uphills to keep your heart rate from spiking. That can feel frustrating — especially if you were recently racing at 8:30 per mile. But I want you to reframe it: that pace is not regression, it is base building. Your aerobic system is consolidating. The heavy legs will ease. And after four to six weeks of this kind of running, something interesting happens — your easy pace naturally picks up, and then it surpasses what it was before. See the base running page for a full explanation of why this works.

The principle is simple: you cannot build fitness on a foundation of fatigue. Easy running first — everything else follows.

4. The Upcoming Half Marathon in Two Months

I would not focus on this race right now. Do not build a training plan around it, and do not pressure yourself to hit a specific time.

That said, if you spend the next six to eight weeks doing steady low-HR easy running and start to feel genuinely better — legs lighter, energy restored, running feeling enjoyable again — you could absolutely show up at that half marathon and run it for the experience. Keep it relaxed, run at an easy aerobic effort, and enjoy the day. It is a great distance and there are plenty of opportunities to race it seriously once you are properly recovered.

The half marathon is not going anywhere. What matters more right now is that you rebuild your base properly so that the next serious training block does not leave you in the same position. Listen to your body, keep the effort low, and trust that the pace will come back — because it will.

I hope that helps, Andrea. Give yourself some grace — you ran a strong race and your body is simply asking for more time than you gave it. That is understandable, and very fixable.

Kind regards,

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