Will cardio kill my gains?

No, not at normal volumes. Interference becomes a genuine concern only with high volumes of hard, especially high-impact, cardio alongside heavy lifting. Separating sessions, choosing lower-impact modes, and eating enough resolves most of it.

What the interference effect actually is

Concurrent training can blunt strength and hypertrophy adaptations under certain conditions, mostly involving high frequency and high intensity of endurance work performed close to lifting sessions. It is a real effect, but it is dose-dependent and modest at the volumes most people actually do. Two or three easy sessions a week is not the problem.

What raises the risk

• High weekly volumes of hard running, particularly downhill or with heavy eccentric loading.
• Hard cardio immediately before or shortly after a lifting session.
• Insufficient calories to support both types of training.
• Poor sleep, which compresses the recovery available for either.

How to keep both

Separate hard cardio from heavy lower-body sessions by at least six hours, and ideally put them on different days. Favour cycling, rowing, or the elliptical over running when lifting volume is high, since the eccentric damage is much lower. Lift first if the two must be in the same session and strength is your priority.

Eat for the total workload

A great deal of what gets blamed on interference is simply under-eating. Adding four cardio sessions without adding any food creates an unintended deficit, and progress in the gym stalls accordingly.

What you gain by keeping cardio

Better recovery between sets and sessions, improved work capacity, better cardiovascular health, and a higher energy expenditure that makes managing bodyweight easier. Removing cardio entirely to protect muscle is usually a poor trade.

A workable default

Two or three easy aerobic sessions of 20 to 40 minutes plus a daily step target sits comfortably alongside a serious lifting programme. Add hard intervals only if a specific goal requires them, and watch your strength numbers as the indicator. The lifting side is covered in Principles of Strength Training.