*By Brian Bozarth—former World Cup triathlete and AltaBrio coach*
### Introduction
The off‑season is where races are won. Each winter at AltaBrio I see athletes either lay the groundwork for breakthrough performances or squander months on unstructured training. In 2024, sports scientists closely tracked the training of elite U23 female triathletes across a season【136320157926609†L209-L224】. Their findings reinforce what seasoned coaches preach: **consistent volume, polarized intensity distribution and smart periodization** lead to significant gains. As we turn the calendar to 2025, now is the perfect time to build your aerobic base, develop strength and set up your year for success.
In this article I’ll distil lessons from recent research and two decades of coaching to show how to structure your off‑season and early‑season training. We’ll look at the training characteristics of top performers, explore periodization models, discuss the 80/20 concept, and introduce heart‑rate variability (HRV) as a feedback tool. Whether you’re targeting a spring sprint or a late‑season IRONMAN®, these principles will help you arrive strong, motivated and injury‑free.
### Lessons from elite U23 female triathletes
A 2024 study published in *Sports* followed three under‑23 elite female triathletes throughout their competitive season. The researchers documented every session, measured physiological changes and assessed performance【136320157926609†L209-L224】. Several insights stand out:
– **Consistent training volume.** The athletes averaged over **10 hours per week**, with peaks above 15 hours during key phases【136320157926609†L209-L224】. Even at the elite level, it was overall volume—not heroic single sessions—that produced gains.
– **Polarized intensity distribution.** About **82 %** of training time was spent in low‑intensity “Zone 1”, **6 %** in moderate “Zone 2” and **12 %** in high‑intensity “Zone 3”【136320157926609†L209-L224】. This 80/20 split allowed the athletes to accumulate volume without chronic fatigue while still stimulating high‑end adaptations.
– **Performance improvements.** Over the season, **VO₂max increased 6.9–10 % in cycling and 7.1–9.1 % in running**, and power at VO₂max improved 5–9 %【136320157926609†L209-L224】. Swimming speed at lactate threshold improved 1.2–4 %, and body fat decreased slightly【136320157926609†L209-L224】.
– **Periodization.** The athletes combined traditional linear periodization (gradually increasing intensity through the season) with focused “block” periods emphasising one discipline【136320157926609†L209-L224】. This hybrid approach enabled them to address individual weaknesses without compromising general fitness.
These athletes are fast, but the principles apply to all of us. If you train consistently, emphasise low‑intensity aerobic work and sprinkle in targeted high‑intensity sessions, you will see improvements. Let’s look at how to apply those principles to your 2025 season.
### Periodization strategies for age‑groupers
Periodization simply means planning how training load varies over time. Two common models are **linear periodization**, where you gradually progress from base to build to peak, and **block periodization**, where you concentrate on one main focus (such as cycling endurance or run speed) for a short period while maintaining the others.
A hybrid approach works well for busy adults. For example:
1. **Base Phase (January–February).** Focus on building aerobic endurance with lots of Zone 1 training. Include strength training and technique work in all three sports. Weekly hours might increase from 6 to 10, depending on your background.
2. **Build Phase (March–May).** Introduce more Zone 2 and Zone 3 sessions: tempo rides, threshold runs and swim sets near lactate threshold. Retain at least 70 % of volume in Zone 1 to avoid burnout.
3. **Specific Block (June).** Spend 2–3 weeks emphasising a weaker discipline. For example, if hills crush your run, add two weekly hill sessions and reduce swim volume slightly. If cycling is your limiter, do a block of long rides with sustained threshold intervals.
4. **Taper and Race Prep.** Reduce volume by 40–60 % in the last 10‑14 days before a key race while retaining a few short, sharp workouts.
This structure mirrors what the elite study observed—a mix of traditional progression and focused blocks【136320157926609†L209-L224】. Importantly, schedule recovery weeks every 3–4 weeks where volume drops 30 % and intensity is lower. Your body adapts during rest, not during the workout itself.
### Polarized training: why 80/20 works
“Polarized” refers to the distribution of training intensity: most sessions are easy, a small portion are very hard, and very little falls in the middle. This approach produces greater improvements in VO₂max and lactate threshold than training mostly at moderate intensity. The U23 athletes spent **82 % of their time in low intensity**, **6 % at moderate intensity** and **12 % at high intensity**【136320157926609†L209-L224】. Age‑groupers should aim for a similar distribution.
Practically, that means most rides and runs should be performed at an effort where you can hold a conversation. Hard sessions (intervals, hill repeats, race‑pace swims) should feel uncomfortably challenging but are kept short and separated by easy days. Avoid the “grey zone” where you’re too tired to go hard yet too rushed to go easy. If you’re pressed for time, swap a moderate session for a short, high‑intensity one rather than making every workout medium.
### Strength and conditioning for triathletes
Off‑season is the ideal time to build strength. Research shows strength training improves running economy, cycling power and reduces injury risk. Focus on:
– **Lower‑body compound lifts** (e.g., squats, lunges, deadlifts) to develop maximal force.
– **Unilateral exercises** (single‑leg deadlifts, step‑ups) to address imbalances.
– **Core stability** (planks, Pallof presses) for better posture in aero position and during the run.
– **Upper‑body pulling** (rows, pull‑ups) to support swimming and maintain shoulder health.
Keep sessions short (30–45 min) and perform them twice per week. Increase weight slowly and avoid going to failure; your goal is neuromuscular adaptation, not bodybuilding.
### Altitude training and HRV: monitoring adaptation
Many triathletes in the Rocky Mountain region take advantage of altitude to boost red blood cell production. But adaptation varies by individual. Monitoring **heart‑rate variability (HRV)** is a simple way to gauge recovery and readiness. A 2021 article on HIITScience notes that after high‑intensity training or altitude exposure, resting heart rate may rise and HRV may drop; as adaptation occurs, HRV trends upward and resting heart rate returns toward baseline【653264913789109†L40-L90】. The authors also point out that variability in HRV responses can identify “responders” and “non‑responders”【653264913789109†L63-L90】.
To track HRV:
1. **Measure daily.** Use a validated smartphone app like HRV4Training; it’s been shown to reliably measure heart rate and HRV using the phone’s camera【653264913789109†L114-L128】. Take readings first thing in the morning while still supine.
2. **Look for trends.** Don’t react to a single low reading; instead, observe 7‑day moving averages. If HRV trends downward and resting heart rate trends upward, you may need more recovery.
3. **Adjust training.** Use HRV data to decide whether to proceed with a planned hard session or substitute an easy workout. This responsiveness helps prevent overtraining and maximises gains from altitude camps.
### Nutrition and fueling in the base phase
Winter is a good time to dial in your nutrition. When training volume is lower, caloric needs decrease; focus on nutrient‑dense whole foods and adjust portion sizes. As you increase endurance work, practice **carbohydrate periodization**—eat more carbs around hard or long sessions and fewer on easy days. Adequate protein (1.6–1.8 g/kg/day) supports muscle repair and adaptation. Don’t neglect micronutrients such as iron (especially important at altitude) and vitamin D.
Hydration is often overlooked in winter because cold temperatures blunt thirst. Aim for 30–35 ml/kg/day of fluid, more if training indoors. Electrolyte intake remains important for long indoor rides or runs on the treadmill.
### Mental preparation and goal setting for the new season
Off‑season is prime time to reflect on last year’s performances and set goals for 2025. Write down process goals (e.g., “do two strength sessions per week”) and outcome goals (e.g., “complete my first 70.3 in under six hours”). Use visualisation during long aerobic sessions to rehearse race scenarios. Building mental strength now pays dividends when the race gets tough.
### Conclusion
January isn’t the time to hammer every workout; it’s the time to build a robust engine. The 2024 study of elite U23 triathletes shows that **consistent volume, a polarized intensity distribution, and thoughtful periodization** lead to measurable improvements in VO₂max and performance【136320157926609†L209-L224】. By adopting a similar approach, integrating strength training, monitoring recovery through HRV【653264913789109†L40-L90】【653264913789109†L114-L128】, and planning your nutrition and mental strategies, you’ll start 2025 with momentum. Build your foundation now and you’ll thank yourself when you’re flying down the home stretch of your target race.
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**References**
1. Domínguez, R. et al. *Training Characteristics, Performance, and Body Composition of Three U23 Elite Female Triathletes throughout a Season*. **Sports**, 2024【136320157926609†L209-L224】.
2. Torre, F. et al. *The Rhythm of Readiness: Leveraging Heart Rate Variability for Smarter Training*. **HIITScience**, 2021【653264913789109†L40-L90】【653264913789109†L114-L128】.