The combination of aerobic and strength loads is called competitive or parallel training. For a long time, gyms believed that cardio "burns muscles", and runners avoided the barbell, fearing "overpumping". The editors break down what is really known about the mutual influence of these loads and how to make a plan in which they help, not hinder, each other.
What is the interference effect
The term "interference effect" appeared after the classic work of Robert Hickson in 1980. In his study, participants trained either only for strength, only for endurance, or a combination of both. Up until about week seven, strength in the combined group increased as much as in the pure strength group, but then its gains slowed and even decreased slightly, while the "pure" strength groups continued to progress.
It is worth remembering the conditions of that experiment: the loads were very heavy — strength training five days a week and six days of endurance, some of which were intense intervals. Such a total volume rarely happens in the life of an ordinary hall visitor, so the result cannot be mechanically transferred to moderate programs.
The physiological explanation of interference has long been based on molecular signaling pathways. Strength training activates the mTORC1 complex, which triggers protein synthesis in muscles, and long-term aerobic work activates AMPK, an "energy deficit sensor" that inhibits some of the anabolic processes. However, in living people, these signals are short-lived and partially diluted in time, so direct "turning off" of muscle growth is not confirmed.
More practical causes of interference are fatigue and under-recovery. If the legs are "clogged" after a long run, squats are performed with less weight and less volume, and therefore the stimulus for strength growth is weakened. Similarly, a chronic deficit of calories with a large volume of cardio limits resources for the synthesis of muscle tissue.
What modern meta-analyses say
A meta-analysis by Wilson et al. (2012) summarized data on a combination of aerobic and strength training and found that explosive strength and power were most affected, while hypertrophy and maximal strength were reduced less. The authors also observed that running had a more negative effect on lower extremity strength results than cycling, and that the effect depended on the frequency and duration of cardio sessions.
A later review by Murach and Bagley (2016) directly questioned the universality of interference for hypertrophy: in many studies, moderate cardio did not interfere with muscle fibre growth, and in untrained individuals sometimes even enhanced it. An updated meta-analysis by Schumann and colleagues (2022) confirmed that competitive training does not reduce gains in muscle mass and maximal strength, but may limit the development of explosive strength, especially when both loads are performed in the same session.
So, the current picture is as follows: for health, body composition and general physical form, the combination is quite compatible. For athletes with critical power — sprinters, jumpers, weightlifters — the volume and type of cardio should be dosed more carefully.
| Index | Effects of adding cardio | What it depends on |
|---|---|---|
| Muscle hypertrophy | Minimal or absent at moderate volume | Total calories, cardio volume |
| Maximum strength | Small effect, more often in trained people | Frequency and duration of aerobic sessions |
| Explosive strength and power | Most noticeable | Same-day sessions, long-distance running |
| Aerobic endurance (VO₂max) | Strength training has little negative effect | Regularity of aerobic work |
It is also important that strength training, in turn, does not harm endurance, and for runners and cyclists, it often improves the economy of movement. Therefore, it is more correct to consider interference as an asymmetric and dose-dependent effect, and not as an "either-or" law.
Order, interval and type of cardio
The easiest way to reduce conflict is to spread the load over time. If the schedule allows, strength training and aerobic training are best done on different days or at least several hours apart. Researchers often cite a guideline of around six hours or more between sessions, although the exact value depends on the intensity.
When both loads have to be combined in one workout, the one that is the priority is usually put first. For a person who wants to build strength, it is logical to work with a barbell first, and do cardio afterwards. To prepare for the race, the order can be reversed. For general health, the difference between the options is small.
The type of cardio also matters. Exercise bikes and rowing machines create less shock and eccentric load on the legs than running, so they interfere less with squats and deadlifts. Inclined walking or swimming are even gentler options for recovery days.
High-intensity intervals save time and develop aerobic capacity well, but they themselves tire the neuromuscular system. Putting in heavy leg intervals before a heavy day of squats is a common mistake that leads to "failed" strength training.
Nutrition and recovery during competitive training
Much of what people perceive as "cardio eating away muscle" is actually due to an energy deficit. An additional 3-4 hours of aerobic work per week can mean significant energy expenditure that must be compensated if the goal is to gain or maintain mass. For weight loss, a deficit is deliberately created, but then it is especially important to maintain sufficient protein intake.
For people who exercise regularly, sports nutritionists' consensus documents usually call for a range of about 1.2–2.0 g of protein per kilogram of body weight per day. A meta-analysis by Morton et al (2018) found that gains in lean mass from protein-supplemented strength training plateau at around 1.6 g/kg per day, although some people may benefit from more.
Carbohydrates are the main fuel for intense cardio and heavy strength sessions. If both workouts are scheduled on the same day, glycogen stores are depleted faster, so eating a meal with carbohydrates and protein between sessions helps restore performance. Strict restriction of carbohydrates during high volumes of competitive training often reduces the quality of both types of exercise.
- Protein: distribute evenly over 3–5 meals, 20–40 g each.
- Carbohydrates: increase on days with two sessions or long cardio.
- Fluid and electrolytes: especially during prolonged aerobic exercise in the heat.
- Sleep: 7–9 hours — the basic condition for recovery after any exertion.
Among the supplements with proven effectiveness for such a regimen, we can mention creatine monohydrate, which supports strength work and does not interfere with aerobic exercise, as well as caffeine before intensive sessions. No supplement, however, can compensate for chronic sleep deprivation and malnutrition.
How to plan a week
The starting point is the 2020 WHO recommendations for adults: at least 150–300 minutes of moderate aerobic activity or 75–150 minutes of vigorous activity per week plus strength training for major muscle groups at least twice per week. These figures show that a combination of both types is not a compromise, but the norm of a healthy lifestyle.
For a person who primarily wants to increase strength and muscle mass, a reasonable option is 3–4 strength training sessions and 2–3 moderate aerobic sessions of 20–40 minutes each, preferably on other days or after strength work for the upper body. Intensive intervals — no more than 1-2 times a week.
For a runner who adds strength, the logic is mirrored: the basis remains running training, and 2 strength sessions per week are built around basic exercises with a moderate volume. It is better to put heavy strength on days of easy running, and not before a key tempo training.
Regardless of the goal, the progression of the volume of cardio should be carried out gradually and monitor the markers of under-recovery: a drop in working weights, worsening of sleep, constant soreness of muscles, decrease in motivation. If they appear, the less priority type of load is reduced first.
Editorial conclusions
The interference effect is real, but it is greatly exaggerated. It is most prominent for explosive strength and very high volumes of cardio, while for muscle growth and health a moderate combination is perfectly safe and beneficial.
The key tools are to divide the sessions in time, prioritize the load first, choose less traumatic types of cardio for the legs and cover energy needs, especially protein and carbohydrates.
Competitive training is the best way to simultaneously improve cardiovascular health, body composition, and functional strength when approached with an understanding of recovery principles.
The editors also recommend reading our materials on protein standards for athletes, on creatine and endurance, and on signs of overtraining.
List of used literature
- Hickson RC. Interference of strength development by simultaneously training for strength and endurance. Eur J Appl Physiol Occup Physiol. 1980;45(2-3):255â263.
- Wilson JM, Marin PJ, Rhea MR, et al. Concurrent training: a meta-analysis examining interference of aerobic and resistance exercises. J Strength Cond Res. 2012;26(8):2293â2307.
- Murach KA, Bagley JR. Skeletal muscle hypertrophy with concurrent exercise training: contrary evidence for an interference effect. Sports Med. 2016;46(8):1029â1039.
- Schumann M, Feuerbacher JF, Sünkeler M, et al. Compatibility of concurrent aerobic and strength training for skeletal muscle size and function: an updated systematic review and meta-analysis. Sports Med. 2022;52(3):601â612.
- Morton RW, Murphy KT, McKellar SR, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. Br J Sports Med. 2018;52(6):376â384.
- Bull FC, Al-Ansari SS, Biddle S, et al. World Health Organization 2020 guidelines on physical activity and sedentary behaviour. Br J Sports Med. 2020;54(24):1451â1462.
- Thomas DT, Erdman KA, Burke LM. American College of Sports Medicine Joint Position Statement. Nutrition and athletic performance. Med Sci Sports Exerc. 2016;48(3):543â568.
