For athletes and fitness enthusiasts looking to optimize their performance and physique, the question of how to effectively combine strength and endurance training is a crucial one. While both forms of exercise offer unique benefits, there has long been debate about whether performing them concurrently leads to compromised adaptations - a phenomenon known as the "interference effect." In this article, we'll dive into the latest research on concurrent training to determine if endurance work truly impairs strength and muscle gains.
The Interference Effect: What Does the Research Say?
The concept of interference between endurance and strength training was first proposed by Dr. Robert Hickson in 1980 [1]. His seminal study found that individuals who performed both strength and endurance training saw impaired strength development compared to a strength-only group. This sparked decades of research attempting to further elucidate the interference effect.
A 2012 meta-analysis by Wilson et al. examined 21 studies on concurrent training, finding small but significant negative effects on strength, power, and muscle hypertrophy when endurance training was added to a resistance program [2]. However, the magnitude of interference appeared to depend on several factors:
1. Training volume and frequency: Higher endurance training volumes, especially when performed 3+ times per week, led to greater interference.
2. Exercise modality: Running appeared to cause more interference than cycling.
3. Training experience: Untrained individuals saw less interference than trained subjects.
More recent research has continued to investigate these factors. A 2019 meta-analysis by Petré et al. examined the effects of concurrent training on maximal strength development in subjects of different training statuses [3]. They found:
- Trained individuals showed significant interference (effect size = -0.35)
- Moderately trained individuals showed a small, non-significant interference effect (-0.20)
- Untrained individuals showed no interference (0.03)
Importantly, the negative effect in trained individuals only occurred when strength and endurance were performed in the same session. When done on separate days, no significant interference was observed.
Mechanisms of Interference
Several physiological mechanisms have been proposed to explain the potential interference effect:
1. Residual fatigue: Endurance exercise may cause acute fatigue that impairs force production in subsequent strength training.
2. Competing cellular signaling: Endurance and strength training activate different molecular pathways that may inhibit each other.
3. Overtraining: High total training volumes may exceed recovery capacity.
4. Fiber type shifts: Endurance training may cause a shift towards more fatigue-resistant but less powerful muscle fibers.
However, it's important to note that these mechanisms are still being investigated, and the degree to which they impact real-world training outcomes is debated.
Practical Implications for Optimizing Concurrent Training
While the interference effect is a real phenomenon, especially for trained individuals, it doesn't mean that concurrent training is ineffective. In fact, many studies show that well-designed concurrent programs can lead to improvements in both strength and endurance [4]. Here are some evidence-based strategies to minimize interference and maximize adaptations:
1. Separate strength and endurance sessions: As shown by Petré et al., performing strength and endurance training on different days appears to minimize interference [3]. If same-day training is necessary, allow at least 6 hours between sessions.
2. Prioritize the most important fitness quality: Place the highest priority training first in the day/week when you're freshest.
3. Periodize training focus: Use block periodization to emphasize either strength or endurance development in different training phases.
4. Moderate endurance volume: Keep endurance training to 2-3 sessions per week at moderate intensities when strength is the priority.
5. Choose low-impact endurance modes: Cycling or swimming may interfere less than running with lower body strength development.
6. Fuel appropriately: Ensure adequate carbohydrate and protein intake to support recovery from both training modalities.
7. Focus on recovery: Prioritize sleep and manage overall stress to enhance adaptation to the combined training load.
Conclusion
While concurrent endurance and strength training can potentially lead to interference in strength adaptations, especially in trained individuals, this effect can be minimized with proper programming. By separating training sessions, periodizing training focus, and managing overall training stress, it's possible to make significant gains in both strength and endurance simultaneously.
The key is to design your program based on your individual goals, training status, and recovery capacity. For most recreational athletes and fitness enthusiasts, the benefits of a well-rounded fitness program incorporating both strength and endurance training likely outweigh any small interference effects. However, athletes with very specific strength or power requirements may need to more carefully periodize their endurance work to maximize performance in their sport.
As always, individual responses to training can vary greatly. Experiment with different approaches, track your progress, and adjust your program as needed to find the optimal balance of strength and endurance training for your goals.
References:
1. Hickson RC. Interference of strength development by simultaneously training for strength and endurance. Eur J Appl Physiol Occup Physiol. 1980;45(2-3):255-63.
2. Wilson JM, Marin PJ, Rhea MR, Wilson SM, Loenneke JP, Anderson JC. Concurrent training: a meta-analysis examining interference of aerobic and resistance exercises. J Strength Cond Res. 2012 Aug;26(8):2293-307.
3. Petré H, Hemmingsson E, Rosdahl H, Psilander N. Development of Maximal Dynamic Strength During Concurrent Resistance and Endurance Training in Untrained, Moderately Trained, and Trained Individuals: A Systematic Review and Meta-analysis. Sports Med. 2021 May;51(5):991-1010.
4. Murlasits Z, Kneffel Z, Thalib L. The physiological effects of concurrent strength and endurance training sequence: A systematic review and meta-analysis. J Sports Sci. 2018 Jun;36(11):1212-1219.
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