Cardio and Lifting: How to Do Both Without Killing Your Progress

There is an old idea in strength training that cardio kills your gains. Like most absolutes in fitness, it takes something that can happen under certain conditions and turns it into a rule that supposedly applies to everyone. Cardio does not automatically prevent you from getting stronger or building muscle, and for most people there is no reason they cannot improve their cardiovascular fitness while continuing to make progress in the weight room. The problem begins when the cardio you are doing creates enough fatigue, muscular stress, or recovery demand that it starts compromising the lifting responsible for the result you actually care about.

This is why the first question should not be whether cardio is good or bad for muscle growth. The better question is why you are doing cardio in the first place. Someone walking to increase energy expenditure during a fat-loss phase, someone doing moderate aerobic work for cardiovascular health, and someone preparing for a marathon are all technically “doing cardio,” but they are solving completely different problems. The purpose of the cardio should determine the modality, frequency, intensity, and amount you use, as well as how much of your recovery you are willing to dedicate to it.

Why Are You Doing Cardio?

For someone primarily focused on body composition, cardio is usually a tool for increasing activity and energy expenditure. In that situation, there is very little reason to immediately choose the hardest form available. Daily walking, incline treadmill work, easy cycling, or other low-intensity activity can increase expenditure while creating relatively little additional fatigue. For some people, simply increasing daily steps will accomplish what they need. If more activity is necessary, adding 20–30 minutes of low-intensity cardio after lifting sessions is a reasonable place to start and can be increased only when the goal actually requires it.

Cardio for general health serves a different purpose. Here the objective is to improve cardiovascular fitness and aerobic capacity rather than simply burn additional calories. Regular moderate aerobic work that can be repeated and recovered from makes sense, and something in the range of 20–40 minutes two or three times per week can be a practical starting point. This work does not need to become another maximal training session. HIIT can have a place, but harder work is not automatically more useful when the desired adaptation can be achieved with a lower recovery cost.

Endurance performance changes the conversation again because specificity now matters. If you want to become a better runner, you eventually have to run enough to improve at running. If you are preparing for a marathon, the volume, frequency, and specificity of the endurance work have to become large enough to drive those adaptations. At that point, cardio is no longer simply supporting your lifting program; it has become one of the primary goals of the training phase. Some reduction in the rate of hypertrophy may come with that shift, but that is not necessarily a programming mistake. It is the predictable cost of prioritizing a different quality.

Where the Interference Actually Comes From

Combining resistance training and endurance work is commonly referred to as concurrent training, and the potential reduction in strength or hypertrophy adaptations is usually called the interference effect. This has often been interpreted to mean that cardio somehow burns muscle or shuts down muscle growth, but that is an overly dramatic way to describe what is usually a much simpler problem. Concurrent training generally does not appear to produce a large reduction in whole-muscle hypertrophy under normal conditions, although some forms of aerobic work seem to create more interference than others. The practical issue is usually the total amount of stress being accumulated and whether the person can continue recovering well enough to train productively.

Three variables are especially useful when thinking about that stress: frequency, intensity, and modality. The more often you perform cardio, the harder those sessions are, and the more muscular damage or impact the modality creates, the more likely it is to compete with the resistance training you are trying to prioritize. There is no universal number of sessions where cardio suddenly becomes excessive because recovery capacity differs from person to person. Someone sleeping well, eating enough, and performing relatively low-fatigue aerobic work may tolerate a considerable amount. Someone dieting aggressively, training legs hard several times per week, sleeping poorly, and adding frequent running sessions may reach their limit much sooner.

Intensity changes the cost of the work considerably. Walking, incline treadmill work, and easy cycling generally create relatively little fatigue, which is why they can usually be performed more frequently. Hard intervals and sprint work are different. They may be more time-efficient, but they also create a larger recovery demand and overlap more heavily with the high-intensity muscular work already being performed in the weight room. If the purpose of cardio is simply to increase energy expenditure during a body-composition phase, turning every session into HIIT often creates more fatigue than the goal requires.

Modality matters for the same reason. Walking and cycling generally create less impact and eccentric muscular stress than running. Running is not inherently bad for hypertrophy, but it tends to be more expensive from a recovery standpoint, particularly as volume and intensity rise. If someone is preparing for a race, that cost is necessary because running is the adaptation being pursued. If someone is simply trying to burn a few extra calories while maximizing lower-body hypertrophy, choosing a lower-cost modality is usually the more sensible option. The principle is simple: use the least costly tool that still accomplishes the job.

The Mechanism Is Probably Less Complicated Than It Sounds

A great deal of discussion around concurrent training has focused on molecular signaling. One of the better-known explanations was that endurance exercise activates AMPK and other signaling pathways associated with aerobic adaptation, which could suppress mTOR signaling and interfere with the muscle-building response to resistance training. That explanation is interesting, but the evidence has not supported such a clean relationship. Aerobic and resistance exercise can be performed in relatively close proximity without necessarily producing the kind of suppression of anabolic signaling that the original hypothesis predicted.

There are other molecular explanations that remain possible, but from a coaching standpoint there is a much simpler explanation that matters more: fatigue reduces what you are able to do in the gym. Resistance training needs to provide enough tension and effort to stimulate the muscle fibers you are trying to grow. If hard cardio leaves you fatigued before your next lifting session, you may use less weight, perform fewer reps, produce less force, or struggle to recruit the same high-threshold motor units you otherwise could. An isolated bad workout does not matter much, but if cardio repeatedly reduces the quality of the resistance-training stimulus, the accumulated result can be less hypertrophy than you would have achieved otherwise.

That is the useful way to think about the interference effect. Cardio does not have to directly destroy muscle to interfere with muscle growth. It simply has to make the training responsible for building that muscle consistently worse.

If Muscle Is the Goal, Protect the Lifting

Once the priority is clear, the order of training becomes fairly straightforward. If size and strength are the primary goals, lifting should receive the best of your energy and recovery. That generally means resistance training comes first when lifting and cardio need to happen on the same day. Low-intensity work can often be performed immediately afterward because it creates relatively little additional fatigue. If the cardio session is harder, separating the two sessions by several hours can be useful so there is time to eat, hydrate, and regain some performance capacity before training again.

The exact number of hours is not magical. Something around three to six hours is a reasonable practical guideline when the second session is more demanding, but the larger principle is simply to avoid asking the body to perform two difficult sessions back-to-back when there is no need to do so. If the goal is hypertrophy, the resistance-training session is the one you want to protect.

There is also a difference between separating training sessions and separating training days. Coaches sometimes alternate lifting and cardio throughout the week because it appears to create more recovery between each type of training. In reality, this can leave the same muscles working almost every day. A lower-body session on Monday, running on Tuesday, another leg workout Wednesday, and more conditioning Thursday technically separates the modalities while providing very little actual recovery for the legs.

In many cases, it makes more sense to consolidate the stressors. Place cardio on the same days as lifting when appropriate, perform the lifting first, and then leave complete recovery days afterward. This concentrates the workload into fewer days and gives the muscles and nervous system longer uninterrupted periods to recover. For someone whose main goal is hypertrophy, that can be a much cleaner way to organize concurrent training than spreading some form of lower-body stress across the entire week.

How Much Cardio Should You Actually Do?

There is no single cardio prescription because the amount should come from the goal rather than from the belief that more exercise is automatically better. If body composition is the priority, start with daily movement and use steps as the first lever. If additional expenditure is needed, add 20–30 minutes of low-intensity work after lifting sessions and assess what happens before doing more. If fat loss is already progressing at the desired rate, adding more cardio simply because it is available does not accomplish anything useful.

For general health, the goal is to establish a consistent aerobic base that complements resistance training. Moderate aerobic sessions a few times per week are enough to provide meaningful cardiovascular work for many people without turning the entire program into conditioning. Higher-intensity intervals can be added if there is a reason for them, but they should not automatically replace lower-intensity work simply because they feel more difficult.

For endurance performance, the required amount becomes much more specific to the event. More running, cycling, intervals, or longer sessions may be necessary, and eventually that increased workload has to be reflected elsewhere in the program. Resistance-training volume may need to come down, lower-body training may need to be reorganized, and expectations for hypertrophy may need to change during that phase. Training resources are finite, so increasing the priority of one quality inevitably changes how much can be invested in another.

You Can Improve Both, but One Has to Take Priority

This is ultimately the part of concurrent training that people tend to avoid. You can improve multiple qualities at the same time, but you cannot assume that every quality can be maximized simultaneously. If bodybuilding is the goal, lifting should drive the program and cardio should support body composition, health, or conditioning without consistently compromising resistance-training performance. If you decide to prepare for a marathon, endurance training becomes the primary focus and hypertrophy takes a secondary role for that period.

Neither choice is better. They simply require different programs. The problem begins when someone says muscle growth is the priority while training like an endurance athlete, or says endurance performance is the priority while refusing to give it enough training volume because they are afraid of sacrificing any hypertrophy. The goal has to determine what receives the majority of your time, effort, and recovery.

The simplest way to know whether you have found the right balance is to watch the thing you are trying to protect. If your loads, repetitions, execution, and recovery continue improving while cardio is in the program, there is little reason to assume the cardio is meaningfully interfering. If your legs are constantly fatigued, performance begins to fall, soreness never resolves, or progression stalls after cardio volume increases, the dose has probably exceeded what you can currently recover from. At that point, reduce the frequency, lower the intensity, choose a less demanding modality, reorganize the week, or improve the recovery supporting the training.

Cardio and lifting are not natural enemies. The problem is usually trying to do more work than the goal requires or more work than the athlete can recover from. Determine why the cardio is there, choose the modality that accomplishes that goal with the lowest necessary recovery cost, give the priority training the best of your performance, and adjust the total dose according to what your body is actually showing you. You can improve both cardiovascular fitness and muscle mass. You simply have to be clear about which one leads when the demands begin to compete.

For Fat Loss & Building Strength - Sprint Don't Walk!

#1: Burn More Belly Fat with Sprint Intervals
A large number of convincing studies show that high-intensity interval training is the best conditioning strategy for losing belly fat. In contrast, one research group that has conducted a number of experiments comparing aerobic and anaerobic training for belly fat loss write, “Disappointingly, aerobic exercise protocols have led to negligible fat loss.”

The reason anaerobic interval training works so much better is that it requires the body to adapt metabolically—your body is forced to burn fat to sustain the level of intensity being asked of it. It also elevates energy use for more than 24 hours post-workout, which has a dramatic effect on belly fat loss.

For example, a 2008 showed that a 6-week program increased the amount of fat burned during exercise by 12 percent and decreased the oxidation of carbohydrates—obviously, a favorable result for losing fat.  More impressive, a 2007 study showed that in as little as 2 weeks, active women who performed interval training experienced a 36 percent increase in the use of fat for fuel during exercise.

Interval training is so effective for fat loss because it taps into different energy pathways than aerobic exercise. Simply, aerobic exercise tends to burn carbohydrates first and activate pathways that are degrading to muscle, whereas high-intensity exercise such as weight lifting and sprinting will burn a greater percentage of fat, enhance the body’s production of enzymes involved in fat breakdown, and activate pathways that lead to muscle development.

The other reason anaerobic intervals are superior for belly fat loss is that they increase excess post-exercise oxygen consumption (EPOC) a huge amount. A 2006 review showed that protocols that are more anaerobic in nature produce higher EPOC values than steady-state aerobic training because the trained muscle cells must rest restore physiological factors in the cells, which translates to a lot of energy expenditure.

Additional research on high-intensity training (HIT) programs noted that “the effect of regular aerobic exercise on body fat is negligible” whereas research into high-intensity exercise “indicates that it may be more effective at reducing subcutaneous and abdominal (visceral) body fat than other types of exercise.”

One study that compared the effect of high-intensity exercise (60 sprints of 8 seconds each, 12 seconds rest) with aerobic exercise (60 percent of maximal oxygen uptake for 40 minutes) found thatHIT resulted in significant decreases in overall fat mass, while the aerobic exercise group had a fat gain of 0.44 kg on average. The HIT group also had a significant 9.5 percent decrease in visceral fat, whereas the aerobic group had a non-significant increase of 0.2 kg or 10.5 percent. Of related interest is that the HIT group decreased fasting insulin significantly more than the aerobic group (31 versus 9 percent).
 
A second study found that in men with type 2 diabetes, an eight-week program that mixed aerobic and anaerobic exercise (twice a week of 45 minutes of aerobic exercise at 75 percent of max, and once a week of 5 sprints for 2 minutes at 85 percent) had a significant 44 percent decrease in visceral fat, with a 58 percent improvement in insulin sensitivity. They had no change in bodyweight but did have a 24 percent increase in thigh muscle cross sectional area, indicating muscle development, which accounted for the fact that they didn’t decrease bodyweight.

A third study performed on obese women compared a 16-week low-intensity protocol with a high-intensity protocol, based on rating of perceived exertion—not a very scientific indicator, but I’ll mention it anyway. The protocols produced comparable volumes of work as well as almost equal calories burned and miles completed. Despite this, only the HIT protocol yielded significant changes in metabolic markers or visceral fat loss. They lost significantly more total and visceral fat than the low-intensity group. Interestingly, both groups had similar exercise adherence to the program with 80 percent of each group completing the study, indicating that the high-intensity protocol was not too demanding for an obese, previously untrained population.
 
High-intensity exercise is effective because it increases exercise and post-exercise fat burning and may yield decreased post-exercise appetite. During exercise and after HIT, fat burning increases to remove built up lactate and hydrogen ions. Elevated growth hormone also supports fat burning and is a result of HIT programs.

#2: Lose Belly Fat With Sprint Intervals: The Proof
The following are examples of the superiority of anaerobic interval training for belly fat loss from the research:

• A 12-week high-intensity interval training program produced a 17 percent decrease in belly fat in overweight young men. Subjects lost 1.5 kg of belly fat and 2 kg of total fat, while building 1 kg of muscle. Fat burning was increased by 13 percent due to the 3-day a week program of 20-minutes of cycling in which the subjects sprinted for 8 seconds and then did 12 seconds of recovery, repeating these intervals for a total of 60 sprints.
• The same 20-minute cycling interval program produced 2.5 kg of fat loss in young women in 15 weeks, and the majority of the fat loss come from the legs and abdominal area. The sprint intervals were compared to a steady-state aerobic program that produced no fat loss.
• A 16-week study had trained athletes perform either a sprint interval protocol or steady-state running four days a week. The sprint interval protocol varied each day, but an example of one of the workouts used was 10 intervals of 30-sec sprints with 90 seconds rest. The sprint interval group lost 16 percent or 1 kg of visceral fat as well as 2 kg of total fat, compared to the endurance group that lost no belly fat, but did lose 1.4 kg of lean mass. The belly fat loss appears to be small, but be aware that subjects were lean, trained athletes to begin with and had less belly fat to lose than overweight subjects.
• An 8-week interval program using both high- and moderate-intensity intervals decreased belly fat by 44 percent in middle-aged men with type 2 diabetes. Subjects increased quad muscle size by 24 percent and improved insulin sensitivity by 58 percent—a dramatic improvement that highlights the other mechanisms involved in belly fat loss (muscle building, insulin health & blood sugar management).

#3: Sprints Take Less Time than Aerobic Exercise
Not only do sprints help you lose MORE belly fat, they help you lose it FASTER and with LESS training time. Repeatedly, studies show that more fat loss is achieved in high-intensity programs that use 20 to 25 minutes of training time than those that use 45 or 50 minutes of aerobic training time.

Scientists write that anaerobic intervals are overwhelmingly preferable to aerobics for producing belly fat loss, and that the estimated optimal dose of aerobic exercise necessary to lose belly fat appears to be 3,780 calories expended per week. This is an enormous volume of exercise that would require 1 hour of moderate intensity aerobic cycling 7 days a week to burn 550 calories a day so that you could lose even a pound a week!

In less than half the time you can get better results with anaerobic training. A 1994 study is indicative of this: Participants did either 20 weeks of aerobic training or 15 weeks of intervals (15 sprints for 30 seconds each) and lost nine times more body fat and 12 percent more visceral belly fat than the aerobic group.

What is so interesting about this study is that the energy cost of the aerobic program over the whole study period was 28,661 calories, whereas for intervals it was less than half, at 13,614 calories. In less time, the interval group lost much more weight—nine times more weight. How do researchers explain it?

Aside from greater fat oxidation and higher EPOC, hormone response plays a major role…

#4: Sprints Improve Hormone Response for More Belly Fat Loss
Sprint intervals and anaerobic exercise in general improve your entire endocrine system. Both training modes enhance the cells’ sensitivity to insulin, making anaerobic training a successful treatment for diabetes.

Perhaps most important, anaerobic exercise also elevates growth hormone (GH) —a powerful fat burning hormone that helps restore tissue and build muscle—much more than aerobic training. GH is released by the body in greater quantities in response to physical stress above the lactate threshold, which is the reason heavy, sprints are so effective.

Another hormone called adiponectin that is released from fat tissue during exercise also helps burn fat. Emerging scientific evidence shows that any time you perform forceful muscle contractions, adiponectin is released, and then your body produces a substance called PGC1 that is like a “master switch” that enhances muscle and metabolic functions, thereby burning belly fat. Naturally, anaerobic training is most effective for increasing adiponectin and PGC1 to burn fat since sprints and especially weight lifting require extremely forceful muscle contractions.

#5: Anaerobic Training Produces Less Cortisol For More Belly Fat Loss
Cortisol is the stress hormone that is elevated when you are under both physical and psychological stress. Research shows cortisol is chronically higher in endurance athletes—one study found that aerobic athletes had significantly higher evidence of cumulative cortisol secretion in their hair than controls.

In addition, cortisol is generally elevated more following aerobic training than anaerobic training. Part of this has to do with the fact that strength training and intervals do elevate cortisol, but they also elevate anabolic hormones such as GH and testosterone that counter the negative effects of cortisol.

If GH and testosterone are not elevated, cortisol overwhelms tissue, having a catabolic effect that leads to gradual muscle loss and fat gain. By doing aerobic training without strength training, you will lose muscle, lower your metabolic, rate, and gain fat.  Worst of all, high cortisol causes chronic inflammation, which lead to belly fat gain over time—all-around bad news!

#6. The more aerobic volume, the more your brain ages. Therefore, senile dementia in Olympic athletes is proportionate to the annual volume of aerobic works.

#7. Slow long distance aerobic work is not a guarantee of cardiac health. Actually top cardiologist Dr. Bijan Pourat considers it “junk exercise”. He espouses resistance training for cardiac patient.

#8.  Aerobic training can help you lose fat if you are just starting to exercise. Although it is not the most effective type of exercise for fat loss, aerobic-style cardio can work if you are new to exercise.

The Duke study used sedentary, out of shape, overweight people. The aerobic training they did was fairly intense (80 percent of max heart rate), so it's no surprise that they lost body fat.  Being overweight and out of shape, and then exercising at that intensity for 40 minutes 3 times a week for 8 months can clearly lead to fat loss.

#9: In the long run, aerobic training is useless for fat loss. In a Duke study the aerobic group only lost an average of 1.6 kg of fat (not much!) and they didn't build any muscle, which is where we see the fault in the plan. By decreasing body weight, the aerobic group lowered metabolism, while improving aerobic conditioning.

They were “in shape” and thinner, but no stronger, and they had decreased their resting energy expenditure. In order to maintain that fat loss, they would need to eat less, change their macronutrient proportions, or exercise longer and more intensely.

For example, in the 2006 study of runners, only the runners who tripled their weekly mileage from 16 km/week to 64 km/week did not gain fat over the 9-year study. That's a huge increase that would naturally triple the amount of training time required to prevent fat gain.

#10: Doing smart anaerobic training, you can lose more fat quicker, while building muscle so that you raise your metabolism. For example, in a study of women that compared an anaerobic resistance training program with an aerobic protocol, the heavy load training group lost nearly 5 kg of body fat, gained about 3 kg of muscle, and had dramatic increases in strength. The women who did the high rep, aerobic-style lifting program had no change in body composition.

The benefit of building muscle is that your hard work lasts longer if you quit exercising: A study that tested what happens when subjects stopped exercising for 3 months after doing aerobic or resistance exercise found that a resistance training group maintained improvements in strength, muscle, and cardiovascular fitness longer than an endurance group.

The benefit of resistance training is even more pronounced for people who are in shape. In trained male athletes, a 6-week heavy load strength training program with multi-joint lifts (deadlift, squat, military press, chin-up, and bench press) allowed them to lose 1 percent body fat , while gaining 1.3 percent muscle mass for a dramatic improvement in body composition.

Compare that to the Duke study: The aerobic group also lost 1 percent body fat but gained no muscle, resulting in a less valuable body composition; the resistance group lost 0.65 percent body fat percent and gained 2 percent muscle; the concurrent group lost 2 percent body fat and gained 1.4 percent muscle mass.

The most favorable body composition was seen with the concurrent group, but it took double the time. When you consider the long-term effect of such a time-consuming, stressful program, it certainly is suboptimal.