Slow, Long Distance Cardio Sucks
If you had to pick a form of exercise that would likely have the worst impact on your gains, it would be slow, long distance endurance training (1) (e.g. 10 km running). Long, slow distance endurance training has a different adaption effect compared to resistance training. It doesn't result in a significant increase in strength and power, and it doesn't cause muscle to hypertrophy like resistance training does (1). On its own, the gains you would get are absolutely minimal, if any. Added to a resistance training program, it can interfere with the gains you could make in strength, power, and muscle hypertrophy. Training programs that include both slow, long distance endurance training and resistance training have been shown to produce less gains than programs that only included resistance training (1).
Slow, Long Distance Running Really Sucks
If you had to pick the worst type of slow, long distance endurance training, it would be running. Both running and cycling have been shown to significantly impair lower body strength, power and muscle hypertrophy gains, however, running impaired gains the most (1). When running, the leg muscles experience a very high eccentric load when the lead foot strikes the ground. This high eccentric load repeated enough times (i.e. a long run) can result in a high amount of muscle damage (3). This high amount of muscle damage is believed to have an interference effect with strength, power, and muscle hypertrophy gains. If you have to do some slow, long distance training, but don’t need to be good at running, then opting for other modalities such as cycling, rowing etc., could help to ensure you don't impair your strength, power, and hypertrophy gains as much.
High-Intensity Cardio Is Better
High-intensity cardio, such as high-intensity interval training (HIIT), is a much smarter option if you need to work on your cardiovascular fitness but want to preserve as much of your strength, power, and hypertrophy gains. HIIT is as effective as slow, long distance endurance for improving cardiovascular performance (4), and included in a resistance training program has been shown to produce similar increases in muscle hypertrophy and upper body strength compared to resistance training only programs (2). However, lower body strength gains from resistance training will still likely be less with the inclusion of HIIT compared to a resistance training only program. Using running as your modality for HIIT has been shown to be better than using cycling in mitigating the negative impacts of HIIT on gains (2).
The More You Do, The Worse It Is
It's pretty clear by now that cardio training isn't great for improving strength and power or building muscle. However, this doesn't mean that any amount of cardio is going to have a devastating effect. The total amount (frequency and duration) of cardio you complete will have the greatest influence on how much it impacts your gains (1). If you can avoid it entirely, then you'll get the best lower body strength, power, and hypertrophy gains - I'm looking at you, cardio bunnies, who feel compelled to do cardio after every workout to 'help burn fat.' (FYI - you don't!). If you need to improve/maintain your cardiovascular fitness for your sport, then do the least amount you can get away with.
Your Upper Body Is Fine, It's Just Your Legs!
If you haven't noticed already, all the negative effects of cardio training we've been talking about have been to the lower body - the upper body doesn't get affected at all by cardio that uses the lower body. The effects of cardio are specific to the body area that is involved in the exercise modality. Cycling and running have been shown to only effect strength, power, and muscle hypertrophy gains in the lower body; the upper body's gains are unaffected (1, 2). There hasn't been sufficient research to conclusively determine if cardio training modalities that include the upper body (arm ergometers, swimming, rowing etc.) negatively impact upper body strength, power, and muscle hypertrophy (1), however, given that lower body endurance training modalities can, it's possible upper body modalities will negatively impact gains as well if you do enough of it.
If your main goal is to purely develop as much strength, power, and muscle hypertrophy as possible, it's best to avoid cardio as much as possible. Slow, long distance endurance training will have the worst impact on your gains - especially running. Cycling is a better option. Utilise HIIT as much as possible and keep the total amount of cardio completed to the absolute least needed. If you do decide to use HIIT to work on your cardiovascular fitness, then running is actually a better option than cycling.
Have Your Program Tailored To You
Amanda loves her health and fitness so much so that she has completed multiple degrees including a Bachelor in Sport and Exercise Science with first class honors, a Masters in Biomechanical Analysis, and a Bachelor of Health Science specialising in Naturopathy, Majoring in Nutritional Medicine and Western Herbal Medicine.
Passionate about health and fitness, Daniel changed careers from being a pilot to pursue his love for training. He is a certified strength and conditioner, personal trainer and nutritional advisor.
Michelle creates out of this world recipes of everyday foods we love that are more diet-friendly. She is the girl behind the mouth-watering Instagram page, @peachypalate.