The interplay of aerobic and strength training: a hybrid training approach
In the realm of fitness and athleticism, the combination of aerobic and strength training—known as concurrent training—has emerged as a strategy to target a broad spectrum of physical demands within a single program.
This approach seeks to unify the endurance and cardiovascular benefits of aerobic exercises with the muscle hypertrophy, strength, and power gains attributed to resistance training. Yet, the compatibility of these two distinct training modes and their impact on athletic performance and physical health has been a subject of ongoing debate and research.
Unraveling the concurrent training conundrum
A meta-analysis by Wilson and colleagues laid the groundwork for understanding how aerobic training might interfere with the adaptations typically seen in exclusive strength training (1).
Concurrent training, despite its practical appeal, showed potential decrements in strength, hypertrophy, and power when compared to resistance training alone. This finding sparked further investigations into the phenomenon often referred to as the "interference effect."
However, the story is not one-sided. Subsequent studies and a more recent systematic review and meta-analysis have painted a more holistic picture, indicating that concurrent training does not universally reduce developments in maximal strength and muscle hypertrophy (2).
Instead, these outcomes appear largely unaffected by the integration of aerobic exercises, regardless of the aerobic training types (i.e. cycling vs. running), frequencies (i.e. > 5 vs. < 5 weekly sessions), participant training status (i.e. untrained vs. active), age groups (i.e. < 40 vs. > 40 years), and training modalities (i.e. same session vs. same day vs. different day).
Explosive strength and individual variability
A consistent finding across studies is the specific vulnerability of explosive strength to concurrent training, particularly when aerobic and resistance exercises are performed in close succession within the same training session.
This suggests an interference effect, one that selectively impacts the neuromuscular adaptations necessary for rapid force production — a critical component in many athletic endeavours.
What's more, individual responses to concurrent training exhibit significant variability, with some athletes experiencing reductions in performance outcomes, while others see substantial improvements.
This individual variability underscores the complexity of predicting concurrent training outcomes and emphasizes the need for personalized training programs.
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The underlying mechanisms: a tale of two muscle fibres
The interference hypothesis suggests that the root of these mixed outcomes lies in the conflicting physiological adaptations elicited by aerobic versus resistance training.
Aerobic exercises tend to increase mitochondrial density and may favour the hypertrophy of type 1 muscle fibres, associated with endurance. In contrast, resistance training promotes the growth of type 2 fibres, which are crucial for strength and power.
At the molecular level, aerobic and resistance exercises stimulate protein synthesis in different muscle subfractions, with potential implications for the mTOR signalling pathway—central to muscle building. This divergence hints at why combining these training modes might lead to compromised outcomes in some areas, particularly explosive strength.
Practical implications for athletes and fitness enthusiasts
For those aiming to incorporate both aerobic and strength training into their regimen, the evidence offers valuable insights:
Exercise order and timing
To minimize interference effects, particularly on explosive strength, it may be beneficial to separate aerobic and strength training sessions by at least 3 hours, if not scheduling them on different days.
Training modality selection
Choosing an aerobic training modality that complements the athlete's sport-specific demands can help mitigate potential negative impacts. For example, cyclists and runners might focus on their respective disciplines to support, rather than hinder, strength and power development.
Volume and intensity considerations
Balancing the volume and intensity of aerobic training is key. For example, high-intensity, short-duration sessions may offer a way to preserve or even enhance explosive strength while still reaping the cardiovascular benefits.
The future of fitness programming
While concurrent training presents a physiological puzzle, it also offers a promising avenue for achieving comprehensive fitness outcomes. Tailoring training programs to the individual athlete's needs, goals, and responses to training can leverage the benefits of both aerobic and strength exercises.
As research continues to evolve, so too will our strategies for integrating these diverse training modalities, ensuring athletes and fitness enthusiasts alike can achieve their optimal physical health and performance.
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References
Wilson JM, Marin PJ, Rhea MR, et al. Concurrent training: a meta-analysis examining interference of aerobic and resistance exercises. J Strength Cond Res. 2012;26(8):2293–307.
Schumann, M., Feuerbacher, J. F., Sünkeler, M., Freitag, N., Rønnestad, B. R., Doma, K., & Lundberg, T. R. (2022). Compatibility of concurrent aerobic and strength training for skeletal muscle size and function: an updated systematic review and meta-analysis. Sports medicine, 1-12.