Planning strength and conditioning in the same week: the interference effect

An athlete needs to be both strong and enduring at the same time. But these two adaptations trigger different signaling pathways at the cellular level and can partially inhibit each other. This is called the interference effect. The good news: the size of the effect has been overstated, and it can be largely managed with the right programming.

What is the interference effect?

Strength training activates signaling pathways that stimulate muscle protein synthesis. Endurance training triggers a different pathway that increases mitochondrial production and energy efficiency. High-volume endurance work can somewhat limit strength and especially power gains.

Important distinctions:

• Strength is affected less, power more: Maximal strength gains are largely preserved; explosive power and jump performance are more sensitive.
• The effect is dose-dependent: 2–3 moderate-intensity endurance sessions per week cause no problem; high daily volume does.
• Running affects it more than cycling: Running's eccentric component causes muscle damage and prolongs recovery.

Six rules to reduce interference

1. Put them on separate days

If possible, strength and high-intensity endurance are done on different days. This ensures both sessions are performed fresh.

2. If the same day is unavoidable, leave 6+ hours

Research shows that a longer gap between sessions reduces interference. Strength in the morning and conditioning in the evening is a workable model.

3. Sequencing: priority first

If done in the same session, whichever capacity is the priority comes first. In athlete programs this is usually strength or power. Heavy lifting done while fatigued both lowers quality and increases risk.

4. Choose your endurance mode

Cycling, SkiErg and rowing cause less muscle damage than running. These options can be preferred in blocks where strength gains are the priority.

5. Control volume

More than 3 high-intensity endurance sessions per week significantly limit strength gains. Zone 2 work, on the other hand, produces relatively little interference even at high volume.

6. Support it with nutrition

Adequate energy and protein intake reduces the impact of interference. Being in a calorie deficit at the same time makes the problem worse.

The block approach

Another solution is to prioritize the two capacities in phases:

This approach focuses on one capacity in each phase while keeping the other in maintenance. Our periodization article covers this structure in detail.

A realistic model for team-sport athletes

In team sports, sport practice already includes a high conditioning load. In this case, extra endurance work is kept limited and the weight room is dedicated to strength and power. A practical distribution:

• 2 strength sessions (one heavy, one power-focused)
• 1 Zone 2 session (recovery and base)
• 1 RSA or game-format conditioning session
• Sport practice and matches

Strength for endurance athletes

There's also the reverse question: should runners and cyclists do strength training? The evidence is clear: yes. Heavy strength training improves running economy and boosts performance; concerns about gaining muscle mass don't materialize with low-volume heavy work. 2 short sessions per week (heavy sets of 3–5 reps) are ideal for most endurance athletes.

Common mistakes

1. A long run right after strength: The combination that undermines strength gains the most.
2. Making every session “mixed”: Constant circuit-style work provides enough stimulus for neither strength nor conditioning.
3. Combining it with a calorie deficit: You can't carry two stimuli at once on insufficient energy.
4. Doing power work while fatigued: Power is the capacity most sensitive to interference.

Frequently asked questions