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21K Journey: Your Complete Half Marathon
From a comfortable 10K to your half marathon finish line: a 12-week plan to train your legs, your nutrition and your mindset.
21K Journey is a 12-week programme to take you from the 10K distance to your first half marathon, or to target a PB if you've run one before. The plan uses 80/20 polarised running, two strength sessions a week, phased nutrition, and mental preparation for race day. AI adapts everything to your true ability, and your progress is reviewed by a coach, nutritionist, and sports psychologist.
Plan structure
Weeks 1–4: build your aerobic base and strength
Lay a solid foundation: easy runs in zones 1–2, two lower body and core strength sessions per week, long runs starting from your current 10 km. Set goals for each phase and get into your weekly logging habit.
Weeks 5–8: specific block
Bring in the quality: tempo and half marathon pace intervals (e.g. 3x2 km), steadily longer runs with sections at race pace, and your first trial of gels and sports drinks. Mentally, you’ll work on self-talk and managing effort.
Weeks 9–12: taper and race week
Longest run of 18–19 km, progressive reduction of training load in the last 7–10 days, carb-loading protocol (8–12 g/kg/day over the last 48 hours), and your step-by-step race strategy plus a pre-race nerves routine.
Runner’s nutrition: the full cycle
Day-by-day phased fuelling: higher carbs when training volume is up, spaced protein (1.6 g/kg/day), sodium for hydration in sessions over 60 minutes, and gut training for gels in your long runs.
Competition mindset
One guided session each week in the app: phase goals, self-talk for tough kilometres, visualising the course and managing pre-race nerves. The research shows these skills make a measurable difference to endurance performance.
What's included
- AI-personalised 80/20 polarised running schedule from your real starting level: easy runs, focused quality work and progressive long runs up to 18–19 km
- Two 30–40 min weekly strength sessions to boost running economy and help prevent injuries
- Phased nutrition: fuelling for heavy training (5–8 g carbohydrate/kg/day), race week strategies, and on-course fuelling rehearsed in your long runs
- One weekly mindset session (15–20 min): stage goals, self-talk, visualising the route and a pre-race nerves routine
- Deload week every four weeks and a proper taper (rest) over the last 7–10 days before race day
- Genuine feedback from a coach, nutritionist and sports psychologist based on your weekly log of wellbeing and fatigue
Benefits
- You’ll reach the start line in good shape: gradual progression (around 10% weekly volume increases and planned deloads) is designed to lower your risk of overuse injuries, the main reason people drop out
- No race day surprises: you’ll practise pace, breakfast, gels and hydration in at least three long runs before your event
- You train for all three sides of the half: your legs (running and strength), your energy (carbs and sodium) and your mindset (pace control, dealing with the tough final kilometres)
- No generic PDFs: AI adapts your plan weekly, and real professionals check your workload and how you’re feeling
Recommended for
Your typical week
Monday: strength (30–40 min, lower body and core). Tuesday: easy run, 40–50 min in zones 1–2. Wednesday: rest or mobility. Thursday: quality session (tempo or half marathon pace intervals, e.g. 3x2 km). Friday: light strength or rest. Saturday: optional 30-min recovery run. Sunday: progressive long run, from 10 up to 18–19 km depending on phase, with target pace sections in the specific block. Deload every four weeks and reduce load in the final 7–10 days.
Day-by-day phased plan: 5–8 g carbohydrate/kg in peak training weeks, protein spaced through the day (1.6 g/kg), sodium in hydration for any run over 60 minutes. Every Sunday, practise race nutrition: breakfast 3 hours before and gels during the long run. In week 12, carb-loading protocol of 8–12 g carbohydrate/kg in the final 48 hrs, and personalised on-course fuelling plan checked by the nutritionist.
One 15–20 min guided session per week in the app: block goals (weeks 1–4), self-talk and effort management in long runs (5–8), and course visualisation, detailed race strategy and nerves routine (9–12). Plus, weekly log of wellbeing and fatigue, reviewed by the professional team to adjust your plan.
Qué puedes esperar
- Your long run progresses from around 10 km to 18–19 km, carefully monitored, with around 10% weekly increases and structured deload weeks
- Weekly tracking of your intensity split (aim: about 80% easy, 20% quality) and key session paces
- A minimum of 3 race strategy rehearsals in long runs: segment pacing, practiced breakfast, and on-course fuelling (30–60 g carbohydrate per hour)
- Professional team monitors your wellbeing, fatigue and adherence, alongside regular strength work and a pre-race mindset routine
Who this plan is NOT for
- People starting from zero or not yet running 10 km non-stop (try our beginner’s running plan instead)
- Anyone with heart disease, uncontrolled high blood pressure or other cardiovascular risks not yet medically assessed
- Runners with an active injury or ongoing joint pain that has not been checked by a professional
- Pregnant or recently postnatal individuals, or anyone with a history of eating disorders who may be at risk from structured sports nutrition plans
This plan does not replace medical advice. Before preparing for a half marathon, get a sports medical check-up with a stress test, especially if you are over 35, have high blood pressure, diabetes, a family history of heart problems or have been inactive. Stop training and consult a healthcare professional if you experience chest pain, dizziness, palpitations or joint pain that lasts more than 48–72 hours. Do not combine this training with a severe calorie deficit: training hard and eating too little puts your health and performance at risk. Triwell professionals support your training, but do not diagnose or treat medical conditions.
Frequently asked questions
How many weeks do you need to prepare for a half marathon?+
If you’re already running 10K comfortably, 12 weeks is a timeline backed by real-world experience: enough to build your aerobic base, do race-pace specific work and arrive rested after a 7–10 day taper. With less time it’s possible, but you’d have to increase the load faster than is ideal.
Does this plan help me break 2 hours in the half marathon?+
The plan includes goal pace work, and if your 10K PB suggests sub-2 is within reach, the AI will programme your quality sessions and long run pace blocks accordingly (around 5:41/km). We don’t promise any time: it depends on your starting point, consistency and race day. But you do get an intelligent plan to make a serious attempt.
What’s the longest run before a half marathon?+
Here it’s 18–19 km, or roughly 75–90% of race distance. Sports science shows this is enough to prepare for 21.1 km without the fatigue and injury risk of running the whole distance in training.
What should I eat before a half marathon?+
You’ll practise this: carb-loading (8–12 g/kg/day over the last 36–48 hours), high-carb breakfast 3–4 hours pre-race, and 30–60 g carb per hour during the event, with sodium in your hydration. All tested in long runs, so there are no stomach surprises on the day.
Why does a running plan include strength and mindset training?+
Because the evidence is clear: strength work improves running economy and helps avoid overuse injuries, which hit 37–56% of runners each year. Psychological skills (self-talk, effort management, race planning) measurably improve endurance performance. A half marathon is about your legs, your energy and your mindset.
What if I can’t train for a week or feel really tired?+
Log your wellbeing in the app and the plan will adapt: the AI reschedules and the team checks your workload so you’re not tempted to "make up" missed running, which is the fastest route to injury. Missing a week won’t ruin your prep; forcing through to catch up often does.
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