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How cardio can improve your strength. Concurrent Training, Crossfit and the Hybrid Athlete.


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You spend hours in the gym, avoiding cardio thinking it will ruin your proverbial “gains”. Then you watch the crossfit games and see a bunch of guys with their shirts off, all more jacked than you and yet they do plenty of “Cardio”. What’s that all about?

Concurrent training is defined as “a combination of resistance and endurance training”.

In this week’s newsletter, we will look at what the scientific evidence has to say on concurrent training, shed some light as to why crossfit games athletes are so jacked and whether one form of cardio is better than the other when it comes to training for strength, endurance and power simultaneously.

Jason Khalipa, Crossfit Games Athlete OG, just being a huge dude.

The rise in popularity in hybrid training and crossfit over the past decade has been huge. We have now witnessed hybrid athletes pull, bench and squat very impressive numbers all while running ultra marathons with very impressive times logged, or perhaps witnessed bodybuilding success while concurrently running. Elite crossfit athletes can squat 200 kg, run a sub 5 minute mile and walk on their hands, we have seen it done and know its possible.

Consider the fact that your overall health matters. Cardiovascular disease is currently the leading cause of death globally (Tian & Meng, 2019).

Infact, improving your cardiovascular fitness will not diminish muscle gains and it can help you recover better between strength training sessions. We will cover how exactly this happens below.

If you think your too strong or jacked to include some cardiovascular work of any modality into your training, Mitchell Hooper (the current World’s Strongest Man) includes cardio into his training on the basis of “improved recovery” - his words, not mine.


A systematic review and meta-analysis of 43 studies by (Schumann et al., 2021) found that concurrent aerobic and strength training does not impede muscle growth and strength development. However the meta analysis did find that explosive strength gains may be reduced when aerobic and strength training are performed in the same session as opposed to trained in separate training sessions.

A study by (Petré, H. et al., 2018) compared the difference between HIIT(using Tabata method) and continuous endurance training (40-80 minutes) combined with resistance training in 16 highly trained individuals over a 6 week period. The Results? Lower body maximal strength increased in both groups. However VO2max only increased in the HIIT group. The Authors of this study suggest HIIT to be a better option for people, with regards to similar strength increases but improvement in VO2 max with taking up less time commitment.

A Systematic Review and Meta-analysis by (Petré et al., 2021) looked at 27 different studies to compare the effects of concurrent training vs resistance training only on 1RM leg strength. Findings? 1RM leg press and squat strength was negatively affected by concurrent training in trained individuals only. Moderately trained and beginners found no interference effect. However, the interference when combining the two disappeared when cardio and strength sessions were performed separately.

A really interesting randomised controlled trial I came across by (Davis et al., 2008) took 28 female college athletes, and evaluated the effects of concurrent strength and aerobic training on muscle strength & endurance, body composition and flexibility over an 11 week training programme. Split into two groups, both performed strength and aerobic training in the same session. One group performed a warm up, strength segment, aerobic segment then cool down. The other group mixed the aerobic segment with strength in a crossfit “WOD” style workout. They found that both groups resulted in gains surpassing what had previously been found in scientific literature, yet the group mixing the strength and aerobic work together gained greater adaptations than the separate group.


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For reference: the body relies on 3 energy systems.

  • Anaerobic Alactic (ATP-CP) - Short Duration, Under 10 seconds. Think sprinting or olympic weightlifting.

  • Anaerobic Lactic (Glycolytic) - Short to Medium Duration, 10-90 Seconds. Think 400-800m run, 500m Row, most bodybuilding sets.

  • Aerobic Energy System - Long Duration, over 90 seconds. Endurance training.

See the chart above for reference.

So how can improving our aerobic fitness improve our strength?

Well it’s indirectly increasing our recovery capabilities through ⬇️

Increased Capillary Density - This results in better oxygen and nutrient supply to the muscle and more proficient extraction of metabolic waste (lactate & CO2) due to the greater surface area of capillaries next to the muscle. Resulting in improved work rate and increase muscle time to failure. (Ross et al., 2023)

Increased Blood Volume - This results in larger heart expansions and contractions meaning the heart doesn’t need to work as hard. Resulting in lower heart rates during exercise. Allowing us to recover more between sets 💡 (Convertino, 2007)

Note: A study by (Cocks et al., 2013) found that subjects who performed 4-6 x 30-second max effort sprints on a bike three times per week increased capillary density just as much as participants allocated to do 40-60 minutes cycling at 65% effort 5 times per week.


Volume, Intensity, Compound Lifts, Proximity to Failure and Progressive Overload.

They tick all the boxes above to grow muscle and get stronger.

Despite what you may think if you’ve never stepped into a crossfit box, it’s not all WOD’s or “Circuit” style workouts.

Proper crossfit programming will include:

  • Structured strength progression in the compound lifts ie. Squat, Overhead Press, Deadlift, Bench.

  • Technical practice in the olympic lifts and gymnastics.

  • Single joint isolation exercises for muscular imbalances and hypertrophy.

  • A WOD (Workout of the day) this can vary in time domain and movement selection. However, usually high intensity using multi joint movements and close to failure.

These may be split up into different sessions by whoever is doing that specific crossfit programme. With one day having more strength focus, one day short HIIT style WOD and another with a long 40-60 minute “chipper” style workout. All aimed at improving crossfit performance through the different energy systems in the body. The physique you see is a by-product of that training for performance and GPP (General Physical Preparedness), not specifically training for the physique.


Sure, if you want to be the world’s best powerlifter or set a world record lifting a set of famous stones, the majority of your training volume should be aimed at that goal (sport specific). Cardio, crossfit or HIIT training (which ever modality you chose) may start to affect your recovery and performance towards that goal at certain recoverable volume limits.

But for most of us, the general population, who want to get stronger, fitter and look more jacked, the research shows that concurrent training is a viable option and contrary to popular gym bro mythology, it won’t hinder muscle growth or strength. In Fact it may actually benefit our strength in the long run.

Whether you choose to try crossfit, combine your favourite aerobic activity (Run, Row, Swim or Cycle) with lifting or just increase your daily steps, you don’t need to “pigeon hole” yourself into one style of training. You can improve your aerobic fitness to improve your overall health without harming your muscle gains and strength quest. As shown by the studies above and Mitchell Hooper, the world’s strongest man’s advice!


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Until next week, Happy Lifting!