Cardio does not kill your gains after all

Gym folklore has long held that cardio blunts the results of lifting, an idea known as the interference effect. Both athletes and recreational exercisers routinely perform high volumes of aerobic and strength work at the same time, so the question of whether the two modes are compatible matters to a huge number of people. Earlier evidence left the picture unclear, particularly around which adaptations, if any, actually suffer. This updated review set out to establish whether combining the two costs you muscle, maximal strength or explosive strength compared with lifting alone.

The authors systematically searched six databases, with the search updated in March 2021, for studies of healthy adults of any age and sex. To qualify, a study had to compare supervised concurrent aerobic and strength training lasting at least 4 weeks against an identical strength-only prescription. The outcomes were maximal strength, explosive strength and muscle hypertrophy. In all, 43 studies made the cut, and subgroup analyses probed whether cardio type, session order, weekly frequency, age or training status changed the result.

Concurrent training made no meaningful difference to maximal strength or muscle growth compared with lifting alone. Explosive strength was the exception: it showed a small but statistically significant shortfall in the concurrent groups. That shortfall was more pronounced when aerobic and strength work were performed within the same session than when sessions were separated by at least 3 hours. None of the other factors mattered: cycling versus running, more or fewer than 5 weekly sessions, untrained versus active participants, and being under or over 40 all left the conclusion unchanged.

This updates a long-running debate about concurrent training and narrows the supposed interference effect considerably. Rather than cardio sabotaging all lifting adaptations, the pooled evidence points to a specific cost to explosive strength, with muscle size and maximal strength apparently safe. The finding that same-session training worsens the effect offers a practical lever, though the review cannot explain why the interference happens. How this plays out in highly trained athletes over long training periods remains an open question.

If you lift and also run, ride or row, this is a reason to relax about losing muscle or top-end strength: the pooled evidence found no such penalty. The nuance concerns power. If rapid, explosive force matters to you, these data suggest the timing of sessions is where interference shows up, with same-session combinations linked to the biggest shortfall. For most people whose goals are size and general strength, the two training modes look compatible.