Concurrent Training & the Interference Effect

Concurrent training means doing endurance (cardio) and resistance training in the same program. The interference effect, first described by Robert Hickson in 1980, is the idea that the endurance work blunts strength and muscle gains compared with lifting alone. It is one of the most repeated fears in the gym. Current meta-analyses show it is much narrower than that reputation.

Muscle size and maximal strength: no measurable cost. Schumann et al. 2022 (Sports Medicine) pooled 43 studies of healthy adults, each comparing concurrent training with an identical strength program done without cardio, for at least 4 weeks. The standardized mean differences were:

• Muscle hypertrophy: −0.01 (95% CI −0.16 to 0.18), no effect.
• Maximal strength: −0.06 (95% CI −0.20 to 0.09), no effect.
• Explosive strength: −0.28 (95% CI −0.48 to −0.08), a small but real reduction.

These results held regardless of cardio type (cycling vs running), frequency (more or fewer than 5 concurrent sessions per week), training status (untrained vs active), and age (under or over 40). A 2026 umbrella review (Held et al., Sports Medicine: 17 meta-analyses, 144 studies, 1,492 participants) reached the same conclusion. Compared with lifting alone, concurrent training produced comparable strength, power and hypertrophy, and significantly better aerobic capacity.

Where the cost actually shows up: explosive strength, same session. Explosive strength covers jump height, rate of force development, and power output. In Schumann 2022 its attenuation was significant when cardio and lifting were done in the same session, but not when the sessions were at least 3 hours apart. The authors found no evidence that the order within the session drove this; proximity did.

Exercise order within a session. Eddens, van Someren & Howatson 2018 (Sports Medicine, 10 studies, programs of 5+ weeks) compared lifting-then-cardio with cardio-then-lifting:

• Lower-body dynamic strength (1RM in squat, leg press or leg extension) improved about 6.9 percentage points more with lifting first (95% CI 1.96 to 11.87; p = 0.006).
• Order had no effect on lower-body hypertrophy (1.15%, p = 0.40), isometric strength, VO2max or body fat.
• Caveat: 6 of the 10 studies used untrained participants, mostly under 30.

Held et al. 2026 likewise found no significant sequence effects overall, with a tendency favouring lifting first for strength.

Practical rules.

• If you want muscle and general fitness, do your cardio; it won't cost you growth.
• If lower-body strength is the priority and both are in one session, lift first.
• If jump or sprint power matters (athletes), separate cardio and power work by at least ~3 hours, or put them on different days.

• People lifting for muscle or general fitness who also want to run, ride, row or do classes.
• Strength-focused lifters deciding where cardio goes in the week.
• Field- and court-sport athletes, for whom jump and sprint power matters (they have the most reason to separate the two).

• Elite athletes: data from highly trained to elite athletes are scarce (Held et al. 2026). The findings are strongest for recreational and untrained people.
• Cardio intensity isn't settled. The major reviews couldn't analyse intensity consistently, and HIIT formats differ (see the Research trail).
• Order data come from younger, mostly untrained people. 6 of the 10 studies in Eddens 2018 used untrained participants, mostly under 30.
• Fatigue still counts. Very high total training volume without enough food or rest is a recovery problem, whatever the mix (see Recovery — Overview).

Dani wants bigger legs and to run a 10 km race in the spring. She has 4 days a week.

1. Default: she doesn't drop running for fear of "losing gains". Muscle growth and max strength weren't measurably reduced when cardio was added (Schumann 2022).
2. Week layout:
   • Mon: lower-body lifting
   • Tue: easy 40-minute run
   • Thu: upper-body lifting, then a 20-minute easy run after lifting
   • Sat: lower-body lifting in the morning; intervals that evening, more than 3 hours later
3. Why this order: on lifting-plus-running days she lifts first, because lower-body strength is a priority for her (Eddens 2018). Keeping her hard intervals ≥3 hours away from leg sessions avoids the one clear cost: explosive strength in same-session training.
4. Check-in after 8 weeks: her squat and her 5 km time are both improving. No change needed.

Next lesson: Hybrid / Concurrent (Strength + Cardio) Program. See these rules built into a full week of lifting and cardio. This lesson sits in both the Build Muscle and Get Stronger paths, so its next step is the same in both: the program shows the rules working, whichever goal brought you here.

• Adding cardio doesn't measurably reduce muscle growth (SMD −0.01) or max strength (SMD −0.06) versus the same lifting program alone (Schumann et al. 2022, 43 studies).
• Explosive strength is the exception (SMD −0.28), and mainly when cardio and lifting share a session; ≥3 h apart showed no significant effect.
• Order: lifting first gave ~6.9 percentage points more lower-body 1RM gain, with no difference in muscle growth (Eddens et al. 2018, 10 studies).
• Fiber-level growth shows a small negative effect (SMD −0.23), with a type I fiber hit for running but not cycling. This is preliminary (Lundberg et al. 2022).
• Concurrent training improves aerobic capacity more than lifting alone, with comparable strength and hypertrophy (Held et al. 2026 umbrella review, 17 meta-analyses).
• The evidence is thin for elite athletes.