Combining Endurance and Strength: The Interference Effect

Can You Train Endurance and Strength at the Same Time?

Yes, endurance and strength can be trained simultaneously with great results. In the current meta-analysis, the often-feared interference effect is not detectable for muscle growth and maximal strength; explosive strength may be attenuated. Both training modalities have their place, and research shows how to combine them optimally.

What Is the Interference Effect?

The interference effect describes the phenomenon where concurrent endurance and strength training can slightly reduce strength gains. 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 (signal for muscle growth)
• Endurance training: AMPK pathway

AMPK inhibiting the mTOR pathway is considered a possible mechanism of the interference. This mechanism comes from experiments in rodents. In a study of ten healthy, moderately trained men, the mTOR pathway after heavy strength training was not inhibited by 30 minutes of cycling (Apró et al., 2013). The mechanism behind the interference effect has not been clarified (Coffey & Hawley, 2017).

How Strong Is the Effect Really?

A meta-analysis by Wilson et al. (2012) in the Journal of Strength and Conditioning Research covering 21 studies found mean effect sizes of:

• Hypertrophy: 1.23 (strength training), 0.85 (combined training), 0.27 (endurance training)
• Maximal strength: 1.76 (strength training), 1.44 (combined training), 0.78 (endurance training)
• Explosive strength: 0.91 (strength training), 0.55 (combined training), 0.11 (endurance training), all three groups significantly different

A more recent meta-analysis of 43 studies (Schumann et al., 2022) found no impairment of muscle growth and maximal strength with combined training; explosive strength was attenuated.

Important: For muscle growth and maximal strength, a meta-analysis of 43 studies found no impairment from additional endurance training (Schumann et al., 2022). Explosive strength may be attenuated, especially when both types of training take place in the same session.

How Do You Optimally Combine Endurance and Strength Training?

Factors that have been studied include the time gap between sessions (at least 6 hours), the order of the sessions and the type of endurance training.

1. Temporal Separation

A study by Robineau et al. (2016) of 58 amateur rugby players compared gaps of 0, 6 and 24 hours between the strength and endurance sessions over 7 weeks (strength always first):

• 0 hours apart: smaller gains in maximal strength than with 6 and 24 hours apart and than with strength training alone
• 6 hours apart: smaller gains in strength during fast movements and in maximal oxygen uptake than with 24 hours apart
• 24 hours apart: greater gains in maximal oxygen uptake than with 0 and 6 hours apart

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

2. Order of Training

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

Strength before cardio, if dynamic leg strength matters to you. A meta-analysis of ten studies (Eddens et al., 2018) found a 6.9% advantage in dynamic leg strength with the order strength before endurance, but no difference in leg muscle growth. In a study by Schumann et al. (2014) of 29 physically active men, maximal strength (1 repetition maximum) improved similarly over 24 weeks with both orders (13% and 17%). The initial difference in testosterone concentration in the two days after the session with endurance before strength had disappeared after the training period and did not appear to be related to strength development.

3. Type of Cardio

According to the meta-analysis by Wilson et al. (2012), the interference depends on the type, frequency and duration of the endurance training. With running, but not with cycling, muscle growth and strength were significantly lower when combined with strength training. A more recent meta-analysis of 43 studies (Schumann et al., 2022) found no significant differences for either the type of endurance training (cycling or running) or the weekly frequency of combined training (more or fewer than 5 sessions).

How Should You Plan Training Based on Your Goal?

The optimal split between strength and endurance training depends on your individual goal. Here are the recommendations for the most common objectives.

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)

Goal: Endurance Event

Priority: Sport-specific training

• Endurance training: 3-5x/week
• Strength training: 1-2x/week
• Strength as a complement to endurance training

A review of endurance-trained runners and cyclists (Rønnestad & Mujika, 2014) concludes: with heavy or explosive strength training, running economy improves and running performance can increase; in cyclists, heavy strength training shows the clearest additional benefit.

HIIT vs. Zone 2

High-Intensity Interval Training (HIIT)

• Improves VO2max in healthy young to middle-aged adults slightly more than traditional endurance training (Milanović et al., 2015)

Zone 2 Training (LISS)

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

Seiler (2010) analysed studies of endurance athletes at national and international level who train 10 to 13 times per week: around 80% of training sessions are in the low-intensity range (about 2 mmol/l lactate), and around 20% consist of high-intensity phases. In a 9-week study of 48 well-trained endurance athletes, polarised training improved the key performance variables the most, compared with threshold training, high-intensity interval training and high-volume training (Stöggl & Sperlich, 2014).

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

Sample Weekly Plans

Muscle Building Focus

Balanced Fitness

Recovery Matters

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

• 7-9 hours of sleep (National Sleep Foundation recommendation for adults, Hirshkowitz et al., 2015)
• Adequate protein; the linked article gives the guideline value for requirements
• Plan deload weeks with reduced load when needed; how best to schedule them has not been researched (Bell et al., 2023)
• Adjust load and recovery according to how you feel

Conclusion

The interference effect exists, but according to the current meta-analysis it mainly affects explosive strength and less so muscle growth and maximal strength. With proper planning - temporal separation, appropriate cardio modality, adjusted volume - you can benefit from both training modalities.

Further Reading

• Strength Training for Beginners: The Key Fundamentals
• Recovery Myths: What Really Helps with Regeneration
• Sleep & Recovery: The Underrated Success Factor
• Calculating Calorie Needs: BMR, TDEE & Macros
• Calorie Calculator

Sources:

• Wilson JM, Marin PJ, Rhea MR, Wilson SMC, Loenneke JP, Anderson JC (2012). Concurrent training: a meta-analysis examining interference of aerobic and resistance exercises. Journal of Strength and Conditioning Research, 26(8), 2293-2307. DOI: 10.1519/JSC.0b013e31823a3e2d
• Robineau J, Babault N, Piscione J, Lacome M, Bigard AX (2016). Specific Training Effects of Concurrent Aerobic and Strength Exercises Depend on Recovery Duration. Journal of Strength and Conditioning Research, 30(3), 672-683. DOI: 10.1519/JSC.0000000000000798
• Rønnestad BR, Mujika I (2014). Optimizing strength training for running and cycling endurance performance: A review. Scandinavian Journal of Medicine & Science in Sports, 24(4), 603-612. DOI: 10.1111/sms.12104
• Schumann M, Walker S, Izquierdo M, Newton RU, Kraemer WJ, Häkkinen K (2014). The order effect of combined endurance and strength loadings on force and hormone responses: effects of prolonged training. European Journal of Applied Physiology, 114(4), 867-880. DOI: 10.1007/s00421-013-2813-6
• Hickson RC (1980). Interference of strength development by simultaneously training for strength and endurance. European Journal of Applied Physiology and Occupational Physiology, 45(2-3), 255-263. DOI: 10.1007/BF00421333
• Seiler S (2010). What is Best Practice for Training Intensity and Duration Distribution in Endurance Athletes? International Journal of Sports Physiology and Performance, 5(3), 276-291. DOI: 10.1123/ijspp.5.3.276
• Eddens L, van Someren K, Howatson G (2018). The Role of Intra-Session Exercise Sequence in the Interference Effect: A Systematic Review with Meta-Analysis. Sports Medicine, 48(1), 177-188. DOI: 10.1007/s40279-017-0784-1
• Schumann M, Feuerbacher JF, Sünkeler M, Freitag N, Rønnestad BR, Doma K, Lundberg TR (2022). Compatibility of Concurrent Aerobic and Strength Training for Skeletal Muscle Size and Function: An Updated Systematic Review and Meta-Analysis. Sports Medicine, 52(3), 601-612. DOI: 10.1007/s40279-021-01587-7
• Apró W, Wang L, Pontén M, Blomstrand E, Sahlin K (2013). Resistance exercise induced mTORC1 signaling is not impaired by subsequent endurance exercise in human skeletal muscle. American Journal of Physiology Endocrinology and Metabolism, 305(1), E22-E32. DOI: 10.1152/ajpendo.00091.2013
• Coffey VG, Hawley JA (2017). Concurrent exercise training: do opposites distract? The Journal of Physiology, 595(9), 2883-2896. DOI: 10.1113/JP272270
• Stöggl T, Sperlich B (2014). Polarized training has greater impact on key endurance variables than threshold, high intensity, or high volume training. Frontiers in Physiology, 5, 33. DOI: 10.3389/fphys.2014.00033
• Milanović Z, Sporiš G, Weston M (2015). Effectiveness of High-Intensity Interval Training (HIT) and Continuous Endurance Training for VO2max Improvements: A Systematic Review and Meta-Analysis of Controlled Trials. Sports Medicine, 45(10), 1469-1481. DOI: 10.1007/s40279-015-0365-0
• Hirshkowitz M, Whiton K, Albert SM et al. (2015). National Sleep Foundation’s sleep time duration recommendations: methodology and results summary. Sleep Health, 1(1), 40-43. DOI: 10.1016/j.sleh.2014.12.010
• Bell L, Strafford BW, Coleman M, Androulakis Korakakis P, Nolan D (2023). Integrating Deloading into Strength and Physique Sports Training Programmes: An International Delphi Consensus Approach. Sports Medicine - Open, 9(1), 87. DOI: 10.1186/s40798-023-00633-0