Source credit: PubMed / Journal of Strength and Conditioning Research. DOI: 10.1519/JSC.0000000000005595.
Short summary: A June 29 Journal of Strength and Conditioning Research study tested whether 12 weeks of combined aerobic and strength training affected movement velocity during later strength-loading bouts. Thirty-two men were assigned to lower-body HIIT plus lower-body strength, lower-body HIIT plus upper-body strength, or lower- and upper-body strength training. The main signal was practical rather than absolute: squat movement velocity was more vulnerable when the conditioning and strength work both targeted the lower body, while bench-press velocity did not show the same pattern when HIIT and strength targeted separate muscle groups.
Why it matters for lifters
Concurrent training is not automatically a progress killer, but this paper supports a programming detail many lifters already feel in the gym: hard conditioning placed on the same muscle groups as heavy or explosive lifting may leave more of a mark on bar speed. For athletes chasing power, sprint carryover, or velocity-based training targets, the finding argues for smarter separation between hard lower-body intervals and lower-body strength sessions instead of treating all cardio as the same stress.
The study is also a reminder to judge interference by the quality of the lift, not just whether the workout was completed. If mean propulsive velocity drops across a loading bout, the athlete may still be moving weight but losing the explosive intent that the session was meant to train.
What to watch next
Watch for larger studies in trained lifters, women, team-sport athletes, and mixed training plans that vary recovery time, exercise order, and HIIT modality. The most useful follow-up would show whether separating muscle groups, splitting sessions across the day, or moving intervals away from key lower-body lifts preserves strength velocity over a full training block.
Health note: This article is informational and is not medical advice. Consult a qualified professional for medical, injury, nutrition, supplement, or individualized training decisions.