The Interference Effect of Concurrent Strength and Endurance Training and How to Resolve It

Introduction

“Strength training + endurance” (concurrent training) is an inevitable issue for endurance athletes. Research has found that when performing both types of training simultaneously, strength gains are interfered with by endurance training—this is the so-called “interference effect.” But this doesn’t mean you have to pick a side; understanding the mechanisms behind the interference will help you find the optimal way to schedule your training.

What Is the Interference Effect

Hickson’s classic 1980 study found that a pure strength training group improved strength by 39%, while the group doing both strength and endurance training improved by only 22%. Subsequent research has confirmed that this effect does exist, mainly due to:

1. Molecular level: Endurance training activates the AMPK pathway, which suppresses the mTOR pathway involved in muscle synthesis
2. Energy level: Glycogen depletion limits the quality of strength training
3. Fatigue level: Neural fatigue affects subsequent training performance
4. Time level: Limited recovery time

What Determines the Degree of Interference

Five Principles for Mitigating Interference

Principle 1: Separate the Sessions (Most Important)

Allow at least 6 hours between strength and endurance sessions. If possible, split them into two sessions per day:

• Morning: Strength training
• Evening: Endurance

Principle 2: Strength First

If you can only train on the same day and the interval is insufficient, do strength training first. After endurance work, muscles are fatigued and the quality of strength training will drop significantly.

Principle 3: Separate Intensity by Day

Hard strength days + easy endurance days; easy strength days + hard endurance days. Avoid making both hard on the same day.

Principle 4: Separate Movement Patterns

Upper-body strength days + lower-body-dominant endurance days (e.g., cycling); lower-body strength days + upper-body-dominant endurance days (e.g., swimming).

Principle 5: Get Nutrition Right

Consuming 20–40g of protein + 60–100g of carbohydrates within 30 minutes after training can significantly reduce the interference effect.

Periodization Example

Off-season Building Phase (Strength Priority)

• Strength training 3x/week (emphasis phase)
• Endurance 4x/week (high volume, low intensity)
• Strength days paired only with easy endurance

Pre-season (Balanced)

• Strength training 2x/week (maintenance)
• Endurance 5x/week (including 2 intensity sessions)
• Intensity days separated from strength days

In-season (Endurance Priority)

• Strength training 1x/week (maintenance)
• Endurance 6x/week (race-season mode)
• Strength volume halved, intensity preserved

Intensity Matching Chart

Practical Advice

• Keep a training log: Track subjective fatigue and adjust immediately if you notice excessive fatigue
• Eat enough carbs: 5–8 g/kg of body weight per day to support the dual training load
• Sleep is king: 8+ hours is needed to recover from the fatigue of combined training
• Deload weeks should reduce both: Cut back both types of training during deload weeks, not just endurance

Conclusion

The interference effect is real, but that doesn’t mean you can’t train both. By understanding the mechanisms and scheduling smartly, you can absolutely have both strength and endurance. Remember the three key principles: separate by time and day, distribute intensity, and support with nutrition—this will minimize the interference effect and let you enjoy the combined benefits of both types of training.

Related Reading

• The Interference Effect Between Strength and Endurance Training: How to Schedule Without Losing Out on Either
• Combining Strength Training with Endurance Sports: Building Strength and Cardio Simultaneously
• The Interference Effect of Concurrent Training: When Strength and Endurance Fight Inside Your Body
• The Interference Effect Between Muscle Gain and Endurance: Why These Two Goals Pull Against Each Other and How to Schedule Both