Want Strength? Science Says Cut the Cardio

Building strength and size while simultaneously developing endurance is tough. Science compared different ratios of strength vs. endurance training and how they impacted each other.

Building strength and size while simultaneously developing endurance is tough. Sure, it works for beginners. Coach Mark Rippetoe once said, “A novice athlete can ride a stationary bike and his bench press will improve.” But taking your squat from 250 to 300 pounds is a much different process than the journey from 400 to 450 pounds. The former can happen while running twenty miles a week in addition to your strength training. The latter cannot.

This conflict is known as the interference effect. Endurance training somewhat blunts the effect of strength training. An upcoming article from the Journal of Strength and Conditioning Research examined the interference effect in an interesting way. It asked, “If everyone performs the same strength training, how much endurance work can we add before the development of strength and size are inhibited?”

The study examined 24 recreationally trained men, each about 25 years old. All the men had more than two years of experience strength training. The men were divided into four groups that each trained for 6 weeks with a different protocol:

  1. The first group performed only strength training for 3 days per week – let’s call them the “pure strength” group.
  2. The next group performed 1 conditioning session for every 3 strength sessions – let’s call them the “strength bias” group.
  3. The next group performed a conditioning session after every single strength session – let’s call them the “endurance bias” group.
  4. The final group did not train. Instead of training they ate Ho-Hos and watched Duck Dynasty – call them “pathetic” … err … the “control” group.

Every group was tested in strength, endurance, and size before and after the 6-week training cycle.

What were the results? First, all groups that trained experienced some improvement in strength, but only the pure strength and strength bias group experienced significant increases in strength. Furthermore, the pure strength group exhibited far more muscular growth than the other groups. This isn’t the first study to report these types of findings. Therefore, the conclusion is clear: the more endurance work you perform, the more it will inhibit the work you do to build strength and size.

But this isn’t a black and white game. The strength bias group still improved greatly in strength and endurance – just without the significant endurance gains of the endurance bias group. The endurance bias group also improved in strength and endurance – they just didn’t show nearly the strength gains of the other groups that trained.

The amount of endurance work you perform should be commensurate with your goals, and probably even change over the course of your season. Most collegiate athletic programs start the offseason with a hypertrophy phase where conditioning is sacrificed for building size and strength. Slowly over the course of the season more conditioning work is phased in until the team has its lungs back and is still benefiting from the extra size and strength gains from the early offseason.

Training is all about strategic sacrifices. Gains never come for free, so choose your training plan carefully based on your goals and seasonal cycle.


1. Thomas Jones, et. al. Performance and Neuromuscular Adaptations Following Differing Ratios of Concurrent Strength and Endurance Training. Journal of Strength & Conditioning Research (forthcoming). POST ACCEPTANCE, 21 March 2013. doi: 10.1519/JSC.0b013e3182903221

Photo courtesy of Shutterstock.

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