057 - Does Cardio Kill Gains? Not Exactly
This systematic review and meta-analysis examined 15 studies with 300 healthy adults comparing concurrent aerobic and strength training versus strength training alone, focusing specifically on muscle fiber hypertrophy (Type I and II).
What They Found:
Concurrent training led to a small, statistically borderline reduction in overall muscle fiber hypertrophy (SMD −0.23, p = 0.05).
Type I fibers showed more pronounced interference, especially when aerobic training was running-based (SMD −0.81).
Type II fibers were less affected (SMD −0.13, p = 0.31).
No significant differences were found in outcomes related to training order, frequency, or modality (same-day vs different-day training).
Cycling as aerobic training posed less risk of interference than running.
What This Means:
Contrary to past conclusions about whole muscle hypertrophy, this meta-analysis suggests that at the muscle fiber level, concurrent training, particularly when pairing running with lifting, can slightly blunt hypertrophic gains.
This matters because fiber-level adaptations often precede whole-muscle changes and inform the early stages of strength development and tissue remodeling.
While not a dealbreaker for concurrent programming, this nuance underscores the importance of aerobic modality selection, especially in populations where strength and muscle mass retention is critical to operational readiness.
Tactical Implications:
Select Your Aerobic Tool Wisely: Opt for cycling over running when combining aerobic work with hypertrophy training to minimize Type I fiber interference.
Periodize With Precision: During hypertrophy-focused training blocks, reduce high-impact aerobic work. Instead, isolate or separate modalities if endurance must be maintained.
Monitor Individual Response: Use strength and muscle assessments to detect early signs of interference and adjust training balance accordingly, especially in combat prep or return-to-duty contexts.
Reframe Fiber-Specific Goals: Tactical populations relying on fatigue-resistance may benefit from maintaining Type I size, so interference from endurance training could be a double-edged sword depending on operational demand.
Questions To Consider:
Are you choosing endurance modalities based on tradition or tactical outcome?
Could cycling better support hypertrophy and reduce joint stress in your program?
Do your concurrent training protocols reflect the specific fiber adaptations you need?
How are you measuring hypertrophy, at the macro (whole muscle) or micro (fiber) level?
What does your current program sacrifice in the name of “doing it all”?
Lundberg TR, Feuerbacher JF, Sünkeler M, Schumann M. The Effects of Concurrent Aerobic and Strength Training on Muscle Fiber Hypertrophy: A Systematic Review and Meta-Analysis. Sports Med. 2022;52(10):2391-2403. doi:10.1007/s40279-022-01688-x