Combining Endurance and Strength: The Interference Effect

The Question of Balance

Cardio or strength? The question is wrong. Both training modalities have their place — and research shows how to combine them optimally.

The Interference Effect

In 1980, Robert Hickson published a study showing that concurrent endurance and strength training can reduce strength gains. This phenomenon is known as the “Interference Effect” or “Concurrent Training Effect.”

Molecular Explanation

Endurance and strength training activate different signalling pathways:

• Strength training: mTOR pathway —> muscle protein synthesis —> hypertrophy
• Endurance training: AMPK pathway —> mitochondrial biogenesis —> endurance adaptations

AMPK can inhibit mTOR — hence the potential interference.

How Strong Is the Effect Really?

A meta-analysis by Wilson et al. (2012) in the Journal of Strength and Conditioning Research found:

• Hypertrophy: No significant difference
• Maximal strength: Slightly reduced (-5-10%)
• Strength endurance: Significantly reduced

Important: The effect is minor at moderate training volumes. For most recreational athletes, it is practically irrelevant.

Practical Optimisation

1. Temporal Separation

A study by Robineau et al. (2016) examined the optimal gap between sessions:

• <6 hours apart: Significant interference
• >8 hours apart: Minimal interference
• 24 hours apart: No measurable interference

Recommendation: If possible, schedule strength and endurance training on different days or with at least 6-8 hours between them.

2. Order of Training

When both training types must be done on the same day:

Strength before cardio — when muscle building is the priority. A study by Schumann et al. (2014) showed that cardio before strength reduces the testosterone response and increases cortisol.

3. Type of Cardio

Not all cardio is equal. Interference varies depending on the modality:

High interference:

• Running (high eccentric load, especially for the legs)
• Long, intense endurance sessions

Low interference:

• Cycling
• Rowing
• Swimming
• Short, moderate cardio

A study by Wilson et al. (2012) found that cycling interferes less with strength gains than running.

Training Planning by Goal

Goal: Muscle Building

Priority: Strength training

• Strength training: 3-4x/week
• Cardio: 1-2x/week, moderate, preferably cycling
• No cardio directly before leg training

Goal: General Fitness

Balance between both

• Strength training: 2-3x/week
• Cardio: 2-3x/week
• At least 1 rest day per week

Goal: Fat Loss

Calorie deficit is more important than training type

• Strength training: 3x/week (to preserve muscle!)
• Cardio: As desired, but not at the expense of recovery
• Increase NEAT (non-exercise activity)

A study by Villareal et al. (2017) showed that strength training during a diet preserves more muscle mass than cardio alone.

Goal: Endurance Event

Priority: Sport-specific training

• Endurance training: 3-5x/week
• Strength training: 1-2x/week
• Strength as a supplement for injury prevention

Interestingly, research shows (Ronnestad & Mujika, 2014) that strength training improves endurance performance, particularly running economy.

HIIT vs. Zone 2

High-Intensity Interval Training (HIIT)

• Time-efficient (15-25 minutes)
• High calorie expenditure
• Rapidly improves VO2max
• But: stresses the nervous system, limited frequency (2-3x/week)

Zone 2 Training (LISS)

• Longer sessions at low intensity
• Builds the aerobic base
• Promotes mitochondrial biogenesis
• Supports active recovery

A study by Seiler (2010) showed that elite endurance athletes train ~80% of their time in Zone 2. This “polarised training” is often more effective than moderate intensities.

Recommendation: A mix of 1-2x HIIT and 1-2x Zone 2 per week.

Sample Weekly Plans

Muscle Building Focus

Day	Training
Mon	Strength — Upper Body
Tue	Light Cycling (30 min)
Wed	Strength — Lower Body
Thu	Rest
Fri	Strength — Full Body
Sat	Zone 2 Cardio (40 min)
Sun	Rest

Balanced Fitness

Day	Training
Mon	Strength — Upper Body
Tue	HIIT or Running
Wed	Strength — Lower Body
Thu	Light Cardio or Yoga
Fri	Strength — Push/Pull
Sat	Longer Endurance Session
Sun	Rest

Recovery Matters

Combined training means a greater total training load. Recovery must be adjusted accordingly:

• 7-9 hours of sleep
• Adequate protein (1.6-2.2g/kg)
• Deload weeks every 4-6 weeks
• Watch for overtraining symptoms

Conclusion

The interference effect exists but is not a problem for most recreational athletes. With proper planning — temporal separation, appropriate cardio modality, adjusted volume — you can benefit from both training modalities.

---

Sources:

• Wilson JM et al. (2012). Concurrent training: a meta-analysis examining interference of aerobic and resistance exercises. Journal of Strength and Conditioning Research.
• Robineau J et al. (2016). Specific Training Effects of Concurrent Aerobic and Strength Exercises Depend on Recovery Duration. Journal of Strength and Conditioning Research.
• Ronnestad BR & Mujika I (2014). Optimizing strength training for running and cycling endurance performance: A review. Scandinavian Journal of Medicine & Science in Sports.
• Schumann M et al. (2014). Acute neuromuscular and endocrine responses and recovery to single-session combined endurance and strength loadings. Applied Physiology, Nutrition, and Metabolism.
• Villareal DT et al. (2017). Aerobic or Resistance Exercise, or Both, in Dieting Obese Older Adults. New England Journal of Medicine.