Cardio can cause gains to be lost Cardio workouts are often viewed as limiting “gains” or preventing muscle growth. Research shows that cardio can also inhibit resistance training’s muscular adaptations.
Concurrent training is a combination of cardio and weight training. This helps to understand the science and research behind the potential downsides.
Heather Hart is an ACSM-certified exercise professional, RRCA-certified running coach, and co-owner of Hart Strength and Endurance coaching. We spoke to Heather Hart about how they can maximize their results in the gym.
Hart states that there is not enough evidence to prove cardio can hinder muscular adaptations in weightlifting or other strength training exercises.
Hart says that “numerous studies have shown that concurrent strength and cardio training can lead to decrements in strength, power and muscular hypertrophy.” However, other studies show that adding cardio and resistance training can not hinder strength or muscle gains. Hart cites a recent review in Sports Medicine.
Studies examining the possible adverse effects of concurrent training on muscle strength and muscle adaptations found that concurrent training only affects explosive strength, not muscle hypertrophy or strength. A 2018 review was published in the Sports Journal.
Journal found that some cardio exercises, such as HIIT, have a lower or negligible effect on resistance-training-induced muscle adaptations.
Hart explains the possible mechanisms behind cardio exercise being counterproductive to your hard work in the gym. Hart says that cardio exercise can cause interference with molecular pathways involved in adaptations to strength training.
Hart explains that there are two pathways to cell metabolism and growth in our bodies when it comes down to adapting to exercise. The mTOR pathway is activated during resistance training and the AMPK pathway is activated during aerobic exercise (cardio). The AMPK pathway could be inhibited or downregulated by concurrent training. A decrease in mTOR may cause inhibition of protein synthesis or interfere with the building of muscle.
Hart states that this could mean that resistance training may not yield the desired results if you combine cardio or aerobic exercise with strength training. This can also inhibit muscle hypertrophy.
“Another theory states that cardio and resistance training can cause individuals to be fatigued and to deplete their energy stores, which in turn causes them not to lift as much or with the same frequency and volume that they would have if they were doing it alone. This could inhibit their potential gains,” says Syas Hart.
You won’t get the same results if you try to do too many workouts in one session, or eat too little between them, and you won’t be as able to push your body to the limit and reap the same rewards if you are fully rested.
Hart states that prolonged cardio (greater then 90 minutes) increases the chance that your body will use protein as a source for energy and speeds up muscle protein breakdown. While muscle protein synthesis following exercise can replenish the protein lost (in combination with protein and/or amino acid consumed through food), it typically brings the muscle protein balance back down to net neutral.
Translation: You aren’t losing muscle mass but you aren’t gaining it.
Hart believes it is possible to combine cardio and weight training without compromising your gains. Here are her top tips on concurrent training.
- You can space out your workouts. Rather than doing cardio and resistance training in one session, try spacing them by at least six hours. 24 hours would be a good option.
- Hart suggests prioritizing the type of exercise you want to do based on your goals. Hart states that cardio and weight training should be done in the same session. She says that if your goal is to increase strength or muscle size, you will want to lift weights first before doing your cardio. Cardio should not be more than 90 minutes if your goal is muscular hypertrophy. This is when protein breakdown occurs.
- You must fuel right. Cardio can cause muscle loss and weakening if you don’t eat enough calories or get the proper nutrients. Hart says that you will need to increase your caloric intake to give yourself enough energy for both exercises. Hart also suggests that you need additional’materials’ in order to repair and build muscle. Hart adds that for those who focus on strength training, this could mean eating more carbs to support their cardio. Cardio fans such as runners and cyclists may need to add strength training. This could mean eating more protein to support hypertrophy.
Fasting cardio affect muscle growth?
Hart says that there is a possibility. She says that glycogen is the preferred energy source for steady-state aerobic exercise. “When glycogen is scarce, our bodies can convert protein (from muscle) to amino acids. These amino acids are then converted into glucose, providing energy that contributes up to 18%.
She explained that while exercise can inhibit protein synthesis (or the building, repairing and growth of muscles), it is stimulated immediately after an exercise. Most of the time, protein can be replenished by eating protein after exercise. Fasted cardio can change this situation.
Hart says that studies show that it is more difficult to replace protein lost after fasted cardio because muscle protein breakdown is likely to be greater in the fasted state. Hart says that muscle protein synthesis must be greater than muscle protein breakdown in order to cause hypertrophy. Without adequate food intake, this cannot happen.”
Hart cites the AMPK metabolic pathway as being activated in energy-depleted state like steady-state cardiovascular exercise. This is especially true when it fasts. This could in turn lower the mTOR pathway and inhibit muscle growth.