Quality > Quantity when you are stuck on a plateau
Replacing part of your volume with HIIT and strength training provides +3 to +5% performance gains, without overload.
As passionate coaches, we regularly meet well-trained runners who are frustrated by stagnating despite adding more kilometers to their training plan. If you are an intermediate or advanced runner who has already built a solid aerobic base, the scientific truth is clear: targeted strength training and HIIT are now your best levers for progress, far more effective than simply adding more easy kilometers.
The diminishing returns of mileage
When you begin running, every additional kilometer brings substantial gains: your cardiovascular system adapts, your VO2 Max increases, and your running economy improves naturally. But beyond a certain volume (generally 50-70 km/week depending on the individual), returns start to diminish.
⚠️ The Volume Trap
Increasing mileage beyond a moderate volume often provides only minimal returns and significantly increases the risk of injury, chronic fatigue, and overtraining. For well-trained runners, VO2 Max has reached a genetically determined ceiling.
The real question then becomes: how can you use the oxygen available to you more efficiently? This is where running economy comes in, and it is precisely what strength training and HIIT target.
The scientific proof for replacement
Controlled studies show beyond doubt that replacing part of your running volume with explosive strength training or HIIT generates superior performance gains compared with simply adding kilometers.
Result #1: explosive bodyweight strength training
📊 Controlled Study: 32% Substitution = 3% Speed Gain
Well-trained athletes replaced about 32% of their usual running volume with explosive bodyweight exercises (jump squats, plyometric lunges, jumps).
Result: They ran a 5 km 3% faster after 9 weeks.
The control group (which continued running only) saw no performance improvement.
Result #2: HIIT and sprint intervals
🚀 Sprint Interval Training (SIT): 4.5% Improvement in 4 Weeks
Only 4 weeks of sprint interval training (3 sessions per week of 30 seconds at maximal effort) improved 5 km running time by ~4.5%.
These gains are comparable to or greater than what you would get by adding 10-20 weekly kilometers of easy jogging over the same period, but with a fraction of the training time and a drastically reduced injury risk.
These results are not anecdotal: they come from systematic reviews compiling dozens of controlled studies. The science clearly validates the substitution strategy.
The mechanism behind the gains: why it works (without bulking up)
Neuromuscular adaptations, not cardiovascular ones
Here is the crucial point many runners misunderstand: performance gains from strength training and HIIT do NOT come from an improvement in VO2 Max (which remains unchanged in well-trained athletes). They come from:
- Neuromuscular adaptations: Better muscle coordination, more efficient recruitment of muscle fibers
- Biomechanical adaptations: Improved tendon stiffness (leg spring), optimized stride biomechanics
- Improved rate of force development (RFD) : The ability to generate force faster at every stride
Running economy: the holy grail of performance
Running economy measures how much oxygen you consume to maintain a given speed. The more economical you are, the less energy you spend running fast. Strength training and HIIT improve running economy by 2 to 8% depending on the study.
🔑 The Keys to Running Economy
- Increased tendon stiffness: Tendons become stiffer and more elastic, capable of storing and returning more elastic energy (spring effect)
- Reduced ground contact time: You spend less time on the ground at each stride, which reduces braking and improves efficiency
- More powerful propulsion: Each push-off is more explosive, propelling you farther with the same effort
- Lighter, quicker stride: Less energy spent to maintain the same speed
Debunking the bulk myth
A common fear: "Strength training will make me gain muscle and slow me down." That is scientifically false for endurance runners.
Studies show that adding intense strength work (plyometrics or loads) causes no increase in body mass or fat mass in endurance runners. On the contrary, it makes you more powerful, more explosive, and more economical, without making your body heavier.
When and how to replace: the strategic guide
Ideal profile for substitution
This strategy is especially effective for:
- Advanced runners: You already run 40-70 km/week or more and have a solid aerobic base
- Plateaued runners: Your times are stagnating despite regular training
- Time-limited athletes: You cannot increase running volume without compromising your personal life or recovery
- Injury-prone runners: You do not tolerate increases in running volume well
The RenfoRun substitution plan
📅 Optimal Weekly Strategy
Option 1: Partial Substitution (Recommended)
Replace 1 to 2 easy runs (45-60 minutes) with 2 sessions of 30 minutes of HIIT/plyometric strength training (RenfoRun programs).
Gain: You free up 30-60 minutes per week while improving your running economy.
Option 2: Strategic Addition (If Time Allows)
Add 2 sessions of 30 minutes without removing runs, but without increasing mileage.
Warning: Watch for signs of fatigue. Strength training is intense and requires recovery.
Optimal Timing
Place strength sessions after a short easy run or on a separate day, but never the day before a quality session (intervals, threshold).
What RenfoRun sessions contain
RenfoRun programs intelligently combine:
- Bodyweight HIIT: Burpees, mountain climbers, high knees, short and intense circuits
- Plyometrics: Jump squats, jump lunges, forward/ backward/lateral jumps, jump rope
- Runner-specific strength: Core work, single-leg exercises, stabilizer work
Duration: 30 minutes per session, 2 times per week = 1 total hour of weekly strength training for 3-5% gains.
Conclusion: maximize efficiency, not volume
If you are an intermediate or advanced runner looking for progress, the science is clear: adding easy kilometers is no longer your best investment. Explosive strength training and HIIT provide measurable performance gains (3-5% over 5 km) in a fraction of the time, without risk of bulking up, and with reduced injury risk.
RenfoRun was designed precisely for runners who want to break through their plateau: short programs (2×30 min/week), targeted, science-backed, improving your running economy and explosiveness without compromising your running training.
Simple RenfoRun-style version
The substitution plan becomes more concrete with two sample sessions.
- Session 1 — cadence/legs: AMRAP (as many rounds as possible) for 8 min with run in place at 178 steps/min and air squat. Then foot tapping as accessory work.
- Session 2 — HIIT/core: 2 Tabata (20 sec effort / 10 sec rest) blocks with mountain climbers, high knees, hip dips, back extension.
Replace an easy run, never a key workout.
You understand the method. RenfoRun gives you the workout.
No planning, no hesitation — just open the app and follow the session.
- ✓ Guided workouts with timer — just follow along
- ✓ Automatic progressions: your sessions evolve every week
- ✓ 12 to 25-minute sessions, designed to fit your running schedule
- ✓ Built exclusively for runners — road or trail
📚 Scientific Methodology
The data presented in this article come from systematic reviews and randomized controlled trials published in peer-reviewed scientific journals. RenfoRun applies these validated principles to create optimal training programs for road runners.