Why Runners Should Lift Weights: The Science of Tendon Stiffness and Economy

Introduction

A saying has long circulated in Taiwan’s running community: “Runners who lift weights get bulky, slow, and stiff.” Over the past decade, sports science research has completely debunked this notion. In reality, the higher the level of endurance runner, the more they need strength training—not to build muscle mass, but to change a physical property you can’t see or touch, yet one that determines how efficiently you run: tendon stiffness.

Tendons: The Spring System of Running

With every stride, your Achilles tendon and plantar fascia are stretched and store elastic energy, which is released upon landing. This “Stretch-Shortening Cycle” (SSC) contributes roughly 30–50% of overall propulsion. The stiffer the tendon, the more energy it can store and release within a shorter ground contact time—this is precisely the visual sensation of elite marathoners “bouncing off the ground the moment their foot touches down.”

Conversely, a low-stiffness tendon is like a loose rubber band: it requires a longer ground contact time to generate rebound force, consuming a bit more oxygen with every step. Over a full marathon, that adds up to a 5–10 minute difference.

What Running Economy Is

Running Economy (RE) refers to the oxygen uptake (VO₂) required to maintain a given pace; the lower the value, the more efficient the running. Between two runners with similar VO₂max, the one with better RE is usually the one who ultimately runs faster.

Below are the main factors affecting RE and their relationship with strength training:

What the Research Says

Multiple controlled experiments by Norwegian running scientist Bent Rønnestad and New Zealand researcher Beattie show that heavy-load strength training performed twice per week, 30–40 minutes per session, over 8–12 weeks, improves RE in middle- and long-distance runners by 3–8% and 5K performance by approximately 3%. The key point is that none of these subjects gained body weight—some even lost weight—because the training volume was kept within the low-rep, neural-adaptation range.

How to Train

• Frequency: Twice per week, scheduled after easy run days or on separate days
• Exercise selection: Squats, deadlifts, single-leg squats, calf raises
• Intensity: 3–5 sets × 4–6 reps @ 80–90% 1RM
• Tempo: Explosive concentric, 2-second eccentric
• Rest: 3+ minutes between sets

Practical Advice

For runners new to strength training, start with a 4–6 week “movement learning phase,” keeping loads below 60% 1RM to first master squat and deadlift form. Most gyms in Taiwan lack dedicated coaches to assist with technique, so beginners can start with trap-bar deadlifts and dumbbell split squats—these have a high safety margin and a short learning curve.

During the final 2 weeks before race day, switch strength training to a maintenance mode (once per week, half the volume but maintaining intensity). This preserves adaptations without interfering with freshness during race week.

Conclusion

Running fast isn’t just about cardiorespiratory fitness—it’s also about material mechanics. Treat your tendons as adjustable springs, give them two high-load stimuli each week, and a few months later you’ll notice: at the same pace, your heart rate is lower; with the same training volume, fatigue is reduced. That is the gift strength training gives to runners.

Related Reading

• Runner-Specific Strength Training: Why Endurance Runners Should Lift Weights
• Combining Running and Strength Training: Why Runners Need to Lift
• Why Endurance Athletes Need Strength Training: The Dual Key of Economy and Injury Prevention
• A Runner’s Strength Prescription: From Hip Drive to Lower-Limb Stiffness—Gym Strategies to Improve Running Economy