Before we get into whether cardio is detrimental or beneficial to strength training, we must first go over the difference between cardio and conditioning.  The majority of people would likely believe that conditioning = cardio.  This may not be false, but it is incomplete.  “Cardio” is a health-based component of fitness; the ability of our body to deliver oxygen to working muscle, or in other words, how well our heart can pump oxygenated blood to meet energy demands (SOURCE).  

Conditioning, on the other hand, is preparing your body to meet the demands of specific tasks or sports you are taking part in.  Cardio is general, conditioning is specific.  Cardio can make you fit, but you may be poorly conditioned to perform heavy lifts.  A perfect example of this is a marathon runner who is extremely fit, but likely poorly conditioned to deadlift.  

So the main question that many athletes ask is - will conditioning or cardio kill my strength?  And if I include conditioning, what should it look like?  

Benefits of Conditioning 

If you are looking for general fitness levels, the benefits of cardiovascular fitness cannot be ignored.  Although, even if top-tier strength is your goal, there are a number of muscle-specific benefits to performing regular cardio and/or conditioning. 

• Improved Blood Flow to Muscles - Improved cardiovascular abilities have been shown to improve vasodilation, which allows better blood flow and nutrient flow to active muscle tissue (SOURCE).
• Improved Capillary Density in Muscle Tissue - Cardio helps us to create better oxygen delivery and exchange at the cellular level, increasing muscle endurance (SOURCE).
• Improved Cardiovascular Health - Research makes this very hard to argue, as it shows a high percentage of age related diseases are preventable through an active lifestyle. 
• Decreased Vagal Tone - Improved cardiovascular ability helps to decrease your sympathetic nervous system (aka fight or flight) response at rest, which helps to keep heart rate low and stress at bay. 
• Increased Lifting Capacity - As discussed above, with improved oxygen exchange between the heart and muscles, you will better be able to recover and perform high-volume challenging sets.  I don’t care what anyone says, but doing a 10-rep heavy back squat set, or a set of 15 front squats gets you breathing heavier than most running workouts!  
• Improved Recovery of Lactate and Anaerobic Systems - Although strength is a ATP-CP and lactate system process (see graph below), recovery is an aerobic one.  If your aerobic system is at a high level and able to supply oxygen well, it better supports your anaerobic and lactate systems as they work to recover.  As you can tell by the graph, the aerobic system underlies the other two systems and supports them.  You will be able to get your heart rate down faster, and more nutrients and blood flow to your muscles quicker so that you are recovering more efficiently between your sets. 

The benefits of conditioning are pretty obvious, so why might conditioning get a bad rep when it comes to the strength training community?  It is likely because many individuals live under the rule of more is better, and end up doing random, long, ineffective conditioning that is not beneficial at all towards their current programming.  

I remember when I competed in CrossFit, I struggled to take a day off, and so on my rest days, I would do ‘active recovery’ and go out and run 3-4 miles thinking it was helping me get ‘fitter’, but those miles were taking pounds off of my snatch and clean because I was ultimately not allowing my body to recover, and I was not training specifically for my strength goals.  

What Types of Conditioning Are Right? 

When conditioning is properly programmed, you will see improvements in not only fitness, but body composition and performance.  When conditioning is done randomly and in excess to try to burn more calories, or avoid rest days, it can most definitely be a detriment to your progress in strength.  So how do we approach conditioning and knowing what is right?  

1. Assess Energy Systems - Different types of training require different types of energy systems.  If you are a runner or a soccer player, your metabolic demands are very different from someone who is olympic lifting or powerlifting for their main fitness approach.  Runners will need to train mostly their aerobic system with longer, more moderate paced conditioning whereas lifters will utilize their creatine phosphate and lactate (aka anaerobic) systems.  Most power and strength athletes can benefit from 2-4 days per week of higher intensity, short to moderate length conditionings (5-20 minutes).  

2. Know The Limits - When programming and determining how much conditioning to do, we have to be aware of when it becomes too much.  A great rule of thumb for programming is doing the least possible for the highest stimulus. More is never better.  There is a law of diminishing return when it comes to conditioning, and once the level of intensity is lost, the conditioning should end.  Or if we are unable to recover between lifting sessions or losing strength, we need to reevaluate what we are doing outside of our main workouts.  The goal of conditioning for strength athletes is to help improve endurance in lifting sets, as well as the ability to improve recovery between sets and training sessions. Interval style, or shorter conditioning pieces tend to work best.  

3. Always Be Evaluating - As training cycles change, so should conditioning approaches.  If you are in a high volume strength cycle, you would likely want to reduce the intensity, or frequency of your conditioning during that time.  An example of this would be to do more single modality aerobic work (bike, run, row, etc.) at 60% or lower of max HR to help avoid injury or burnout.  

We often consider physical fitness to be somewhat like a soundboard.  You cannot move all different parts of the soundboard up at the same time (the bass, the volume, the frequency, etc.).  This is the same for our fitness.  We cannot expect to improve our endurance, our strength, our explosiveness, and our stability all at the same time.  Different training cycles focus on different things, and this is why you want to take a step back and look at an entire year of your training to plan out periods of aerobic focus, strength focuses, maintenance phases, and deloads in between.  This way, your training program will account for your needs, your weaknesses, and support your goals, all while keeping you safe.