Concurrent Training

Concurrent training is the simultaneous pursuit of both strength/hypertrophy and aerobic fitness within a training program. It is the norm rather than the exception — most recreational athletes, competitive CrossFit athletes, bodybuilders managing body composition, and anyone who runs or cycles alongside lifting is training concurrently. The interference effect describes the observation that combining strength and aerobic training attenuates the adaptations of each compared to training either in isolation. Understanding when interference is meaningful, and how to minimize it, is the core practical question.

The Interference Effect

Hickson (1980) was the first controlled demonstration: subjects trained for strength only, aerobic only, or both concurrently. The concurrent group gained less strength than the strength-only group over the 10-week study despite matched strength training volume. The mechanism was not clarified until molecular biology tools became available decades later.

Molecular basis (Coffey & Hawley 2017): strength and aerobic training activate partially antagonistic molecular signaling pathways:

• mTORC1 — the primary anabolic signaling pathway activated by resistance training; drives muscle protein synthesis and hypertrophy
• AMPK — activated by energetic stress (aerobic exercise); drives mitochondrial biogenesis but phosphorylates and downregulates mTOR signaling when active

When aerobic exercise follows immediately after strength training, residual AMPK activation blunts the post-strength mTOR response. The result is attenuated hypertrophy adaptation from the strength session.

Wilson et al. (2012) meta-analysis of 21 studies quantified the interference effect:

• Hypertrophy: concurrent training produced ~31% less muscle growth than strength-only training
• Strength: ~18% less strength gain compared to strength-only
• Power: ~23% less power development
• Aerobic adaptations were largely preserved in concurrent training

Moderators: When Interference Is Large vs. Small

The interference effect is not fixed — it is modulated by how concurrent training is programmed:

1. Training Order Within the Same Session

When performing both modalities in the same session:

Order	Effect on strength adaptation
Strength → Aerobic	Moderate interference (aerobic performed in fatigued state)
Aerobic → Strength	Greater interference (pre-fatigue impairs strength quality; AMPK still active)

Recommendation: if same-session training is required, perform strength work first.

2. Separation Between Modalities

Separation	Interference level	Notes
Same session (back-to-back)	High	AMPK maximally elevated during mTOR window
< 3 hours same day	Moderate–High	Some AMPK clearance; mTOR window still partially blunted
6+ hours same day	Low	AMPK largely returned to baseline; mTOR response mostly intact
Different days	Minimal	Full molecular recovery between stimuli

Recommendation: separate strength and aerobic sessions by at least 6 hours when programming on the same day. Different-day training is preferable for maximizing both adaptations.

3. Aerobic Modality

Running generates eccentric mechanical stress in the lower body. Following a heavy leg session with running creates compounding muscle damage — both physiological interference and physical fatigue.

Modality	Lower-body interference	Notes
Running	High	Eccentric loading; DOMS; mechanical overlap with squat/hinge
Cycling	Low	Concentric-dominant; minimal muscle damage; preferred for strength athletes
Rowing	Low	Low eccentric component; good for full-body concurrent programs
Swimming	Minimal	No lower-body mechanical stress; useful for injury contexts

Recommendation: for athletes primarily focused on lower-body strength development, substitute cycling or rowing for running when possible.

4. Aerobic Volume and Intensity

Wilson et al. (2012) found the interference effect was significantly larger for running than cycling, for high volumes over moderate volumes, and for same-day vs. different-day training.

Aerobic parameter	Interference risk
Low volume (< 30 min, 2–3×/week)	Low
Moderate volume (30–60 min, 3–4×/week)	Moderate
High volume (> 60 min, 5+×/week)	High
LISS at Zone 2	Lower than equivalent HIIT
HIIT	Higher per session (greater AMPK activation)

How Much Does Interference Matter in Practice?

For most recreational athletes, the interference effect is a second-order concern. The practical hierarchy of factors affecting outcomes is:

1. Progressive overload (primary driver of strength/hypertrophy)
2. Adequate protein intake (1.6+ g/kg/day)
3. Sufficient sleep (7–9 hours)
4. Training consistency over months
5. Program periodization
6. Interference effect (meaningful at high training volumes; small at low–moderate volumes)

The interference effect becomes practically significant for:

• Athletes training 5–6 days per week with high total volume
• Competitive strength athletes in peaking phases
• Athletes targeting maximal hypertrophy specifically (the 31% hypertrophy attenuation is meaningful over a full year)

For most trainees doing 3–4 strength sessions plus 2–3 aerobic sessions per week at moderate volume, the concurrent training tradeoff is acceptable and the health/recovery benefits of aerobic training outweigh the marginal interference.

Practical Concurrent Training Templates

Template A: Strength-Primary (minimal interference)

Day	Morning	Afternoon/Evening
Mon	Strength (lower)	—
Tue	Strength (upper)	—
Wed	—	Zone 2 cycling 45 min
Thu	Strength (lower)	—
Fri	Strength (upper)	—
Sat	Zone 2 cycling 60 min	—
Sun	Rest / walk	—

Aerobic work placed on separate days from heavy lower-body sessions.

Template B: Balanced Concurrent (moderate interference)

Day	Session
Mon	Strength AM + Zone 2 cycling PM (6 h separation)
Tue	Rest
Wed	Strength
Thu	Zone 2 cycling
Fri	Strength
Sat	Zone 2 or HIIT
Sun	Rest

Template C: Same-Session (high convenience, higher interference)

Sequence	Duration
Strength work	45–60 min
10-min transition	—
Zone 2 cycling	20–30 min

Strength first, aerobic second, keep aerobic duration short to limit post-session AMPK duration.

How Systems Differ

• Powerlifting: Interference is most meaningful during peaking phases where maximal strength expression is the goal. Aerobic work in the 8–12 weeks before competition should be reduced to 1–2 low-volume Zone 2 sessions per week, kept on separate days from main lifts.
• Bodybuilding: The 31% hypertrophy attenuation is meaningful over a full hypertrophy block. For athletes specifically focused on muscle growth, minimizing interference (different days, cycling preferred, moderate volume) is worth the scheduling effort. During a cutting phase, aerobic work serves primarily for energy expenditure — interference with hypertrophy is less relevant.
• Olympic Weightlifting: Technical sessions require fresh neuromuscular state. Any aerobic work that creates residual lower-body fatigue impairs snatch and clean mechanics. Zone 2 cycling post-technical session or on rest days avoids this. Aerobic volume is typically kept lower than in other strength sports.
• CrossFit: Concurrent training is the entire premise of the sport — strength and aerobic capacity are both competitive variables. The programming challenge is achieving both without maximally compromising either. The prescription: ensure at least one true Zone 2 session per week (not moderate-intensity conditioning), and program dedicated strength blocks at sufficient intensity to drive strength adaptation.
• Calisthenics: Running is often a recreational addition to calisthenics practice. The eccentric loading from running creates more interference with calisthenics skill work than cycling would. For athletes pursuing advanced calisthenics skills that require maximal relative strength, running volume should be managed carefully.