Thursday, June 11 2026
Stop sabotaging your race with outdated methods and one-size-fits-all plans. Learn the 7 most common half marathon training mistakes and the scientific fixes to get you to the finish line strong.
TL;DR: Most half marathoners plateau or get injured because they treat every run like a race, ignore strength work, and follow rigid "one-size-fits-all" PDFs. Success comes down to smart load management, respecting the taper, and using periodisation to fit training around your actual life, not the other way around. I’m launching a 16-week Cardiff Half Marathon block on June 14th to help you avoid these traps.
The half marathon is the "Goldilocks" of running distances. It’s long enough to require serious respect and a dedicated half marathon training plan, but short enough that you can still have a life outside of your trainers.
However, because it feels "doable," many runners fall into the same avoidable traps. They end up at the start line with heavy legs, nagging injuries, or the feeling that they’ve left their best performance on a Tuesday night training run.
I’ve seen it hundreds of times as a running coach. Whether you are aiming for your first 5K or you're a seasoned ultra-runner, the principles of human physiology don't change. If you want to smash the Cardiff Half this October, you need to stop making these seven common mistakes.
1. The "Too Much, Too Soon" Trap
This is the most common reason runners end up in my inbox with an injury. You feel motivated, you download a running training programme, and you immediately jump from 10 miles a week to 25.
The result? Your aerobic system might keep up, but your tendons and joints haven't had time to "absorb the load." This leads to poor load management, which is the process of balancing the physical stress of training with your body's ability to recover and adapt.
The Fix: The old "10% rule" is basically a myth. It only tracks volume, ignores intensity, and takes no account of individual response, which is exactly why it falls apart in the real world. I use the Acute-to-Chronic Workload Ratio (ACWR) to compare your current load (acute) against the rolling average of the previous 3–6 weeks (chronic), alongside session RPE so we can measure the internal cost of the work, not just the miles on a watch. In simple terms, we’re looking for a workload "sweet spot" of roughly 0.8 to 1.3, while anything creeping above 1.5 is a red flag and a higher-risk zone for heavy legs, breakdown, and injury. I also factor in life stress, because poor sleep, work stress, and general life chaos act on the same physiological pathways as training load. That’s why a one-size-fits-all plan so often fails: it only sees the session, not the full system. This is the scientific, coach-led approach that helps us decide when to push, when to hold steady, and when to adjust before a niggle becomes a proper problem.
2. Running Your Easy Runs Too Fast
If most of your runs feel "comfortably hard," you’re stuck in the "Grey Zone." You aren't going slow enough to build your aerobic base, and you aren't going fast enough to trigger high-end speed adaptations.
Running too fast on easy days is a one-way ticket to burnout. It prevents your muscles from recovering, meaning when it’s time for a hard interval session, you’re already depleted.
The Fix: Your easy runs should be at a "shuffling" pace where you could comfortably hold a conversation. If you’re huffing and puffing, you’re working too hard. If you struggle to judge that effort, my Traffic Light Effort System can help you match the session to how your body is actually responding on the day.
3. Relying on Generic App-Based Plans
Generic plans don't know that you had a 12-hour shift yesterday. They don't know that you’ve got a "niggle" in your calf or that you slept poorly. A PDF doesn't care about your life; it only cares about the schedule.
When you use an online running coach, you get a plan that breathes. We adjust the volume based on how you actually feel, ensuring you stay consistent without breaking.
The Fix: Personalised coaching is the key to longevity. A plan should adapt to you, not the other way around.
4. Neglecting Strength and Mobility
Many runners think that to get better at running, you just need to run more. While volume is important, strength work is what keeps you on the road. Without a solid foundation, the repetitive impact of 13.1 miles will eventually find the weakest link in your chain. If your body is repeatedly compensating through poor biomechanics, that load has to go somewhere.
The Fix: You don't need to become a bodybuilder. Two 30-minute sessions a week focusing on single-leg stability, glutes, core, and better movement control will transform how you handle the flat, fast stretches of the Cardiff Bay area. If you think movement quality is part of the issue, my online gait analysis will help you understand what to look for.
5. The "No-Taper" Hero
I see this every year: runners get nervous two weeks before the race and decide to "test" their fitness with a long, fast run. All they do is show up to the start line with deep fatigue.
You need a proper taper, which is the phase at the end of a training block where you reduce your volume to shed fatigue and freshen up your legs. The work is already done; the taper is just about letting the gains "soak in."
The Fix: Trust the process. In the final 10–14 days, less is almost always more.
6. Fueling Fails
You wouldn't try to drive to London on an empty tank, yet many runners try to tackle 2-hour long runs on nothing but a cup of black coffee.
If you don't practice your nutrition during training, your stomach will likely rebel on race day. You need to learn how your body handles carbohydrates while moving at pace.
The Fix: Use your long runs as "dress rehearsals." Practice with the gels or hydration mixes you plan to use in Cardiff.
7. Ignoring "Real World" Periodisation
Most people fail because they try to follow a pro-athlete schedule while living a regular life. This is where periodisation comes in: the strategic division of a training programme into specific phases to ensure you reach peak performance on race day. If you want a clearer view of how the bigger picture fits together, have a look at The Macrocycle.
I specialise in fitting high-level UESCA principles around 12-hour shifts, family commitments, and the general chaos of life. If the plan isn't sustainable, it isn't working.
The Fix: Look at your training as a "system management" task. If work is high-stress, your running intensity should temporarily decrease to compensate.
The Path to a PB in Cardiff
The Cardiff Half Marathon is one of the best races in the UK, but the flat course can be deceptive. It's easy to go too fast too early and pay the price at mile 10.
That’s why we’ve built the 16-week Cardiff Half Marathon Block. It’s not just a list of runs; it’s a fully supported coaching experience designed to get you to the finish line feeling strong, not just "finished."
What you get:
- A bespoke plan built entirely around your schedule.
- Direct access to me for feedback and adjustments.
- Guidance on strength, nutrition, and race-day strategy.
- A human approach that understands "life happens."
The deadline to join this specific block is June 14th. This gives us exactly 16 weeks to build your base, sharpen your speed, and nail your taper.
Ready to stop guessing and start progressing? Let’s get to work.
Looking for a deeper dive into the science? Mention the "PFM Running Terminology Guide" when you contact Steven to get your free PDF copy.
Join the Cardiff 16-Week Training Block Here
Key Takeaways
- Load management is king: Don't let your enthusiasm outpace your recovery.
- Keep easy runs easy: Slow down to get faster.
- Personalisation beats generic plans: Your life isn't a template; your plan shouldn't be either.
- Respect the taper: Fresh legs are faster than tired ones.
- Sign up by June 14th: Start your journey to the Cardiff finish line with expert support.
FAQ
Q: Is 16 weeks too long to train for a half marathon?
A: Not if we use proper periodisation. The first few weeks are about building a healthy base, which reduces injury risk later in the block. If you want to understand that foundation properly, read The Base Phase.
Q: I’m a beginner: can I still join the Cardiff block?
A: Absolutely. I coach everyone from 5K first-timers to 200-mile ultra-runners. The principles of a good half marathon training plan apply to everyone; we just scale the volume to fit your current ability.
Q: Do I need a gym membership for the strength work?
A: No. Most of the mobility and strength work we prescribe can be done at home with minimal equipment. Consistency is more important than heavy weights.
