The muscles around your ribs respond to targeted training just like any other muscle group, but “rib muscles” is an informal term that covers several distinct muscles with very different jobs. The two groups most people want to develop are the serratus anterior, the finger-like strips of muscle visible on lean physiques along the side of the ribcage, and the intercostals, the smaller muscles that sit between each rib and power your breathing. Each group requires a different training approach, and understanding which one you’re after shapes the exercises you choose.
Which Muscles Are We Actually Talking About
When people say they want to “build their rib muscles,” they usually mean one of two things. Some want the aesthetic look of a well-developed serratus anterior, the muscle that wraps from under the shoulder blade forward around the ribcage and creates that serrated, interlocking appearance just below the chest. Others want stronger breathing muscles, either for athletic performance or for recovery from an injury or illness. These are the intercostals, and there are two main layers of them.
The external intercostals run diagonally between each rib and assist with inhalation by helping lift the ribcage outward. The internal intercostals, a deeper layer, assist with forceful exhalation by pulling the ribs back down and inward. Their mechanical roles depend on where exactly they sit along the ribcage. The external intercostals toward the back and upper ribs have the strongest role in expanding the chest during a breath in, while the internal intercostals toward the lower ribs are most active when you’re forcing air out.1PubMed. Respiratory action of the intercostal muscles During quiet, relaxed breathing, many of these muscles barely fire at all. They ramp up when you need deeper breaths, when you’re exercising hard, or when something is making breathing mechanically harder.2PubMed. Respiratory function of the rib cage muscles
A few other muscles contribute to the area around the ribs as well. The pectoralis minor, a small muscle beneath the chest, attaches to the upper ribs and helps elevate the ribcage during deep breathing. The subclavius, a tiny muscle under the collarbone, assists in lifting the first rib. And deeper still, the levatores costarum and subcostales connect vertebrae to ribs, contributing to trunk rotation and breathing.3PubMed. Twente spine model: A complete and coherent dataset for musculo-skeletal modeling of the thoracic and cervical regions of the human spine These deeper muscles don’t respond well to isolation exercises in the gym, but they benefit from the same compound movements and breathing drills that target the larger rib-area muscles.
Training the Serratus Anterior for a Visible Ribcage
If your goal is that chiseled look along the side of your torso, the serratus anterior is the muscle to focus on. It originates on the upper eight or nine ribs and inserts along the inner border of the shoulder blade. Its main job is to protract the scapula, meaning it pulls the shoulder blade forward and around the ribcage. It also rotates the scapula upward when you reach overhead, and it pins the shoulder blade flat against the ribcage to prevent “winging.” Weakness or poor activation of the serratus anterior is linked to shoulder pain and dysfunction, so training it serves both appearance and joint health.4PubMed Central. Kinesiologic considerations for targeting activation of scapulothoracic muscles – part 1: serratus anterior
The good news is that the serratus anterior is a surprisingly responsive muscle once you know how to reach it. The bad news is that most standard chest and shoulder exercises don’t activate it enough on their own. Bench pressing and overhead pressing involve it, but the serratus fires most powerfully in the final few inches of a pushing motion, when your arms are fully extended and you push your shoulder blades apart. That last bit of “push” beyond lockout is where the magic happens.
Push-Up Variations That Fire the Serratus Hardest
The push-up plus is the single most studied exercise for serratus anterior activation. It’s a standard push-up with one extra step at the top: after you lock out your elbows, you keep pushing, rounding your upper back and spreading your shoulder blades as far apart as possible. That added protraction at the top is what maximally engages the serratus. A systematic review and meta-analysis found that the standard push-up plus on a stable surface, performed with full elbow extension and hands placed about shoulder-width apart, produced high electromyographic activity in the serratus anterior while keeping upper trapezius activity relatively low. Lifting one leg during the movement increased serratus activation even further.5PubMed Central. Serratus Anterior and Upper Trapezius Electromyographic Analysis of the Push-Up Plus Exercise: A Systematic Review and Meta-Analysis
That ratio matters. Many shoulder exercises activate the serratus anterior but also crank up the upper trapezius, which tends to dominate and take over the movement. The goal is to find exercises where serratus activity is high relative to trap activity, and the push-up plus on a stable surface hits that sweet spot. Shoulder-flexion angles of about 110 to 120 degrees, meaning your hands are positioned slightly ahead of your shoulders rather than directly beneath them, seem to optimize the ratio further.
Beyond the push-up plus, a critically appraised review of multiple studies identified several other push-up variations that produced strong serratus activation, reaching at least half of the muscle’s maximum voluntary contraction. These included standard push-ups on an unstable surface like a Swiss ball, elbow push-ups on both stable and unstable surfaces, wall push-ups against an unstable surface, and push-ups at various hand widths.6International Journal of Athletic Therapy and Training. Serratus Anterior Muscle Activation During Different Push-up Exercises: A Critically Appraised Topic The instability component forces your serratus to work harder to stabilize the shoulder blade against the ribcage, which is one of its primary functions in real-world movement.
Here are the most effective variations to rotate through:
- Push-up plus: Standard push-up with added scapular protraction at the top. The baseline exercise for serratus development.
- Swiss ball push-up: Hands on a stability ball, which adds an instability challenge that forces the serratus to stabilize the scapula throughout.
- Single-leg push-up plus: Lift the leg on the same side as the working serratus. This increases demand without adding external load.
- Wall push-up on unstable surface: Good entry point if full push-ups are too difficult. A foam pad or small ball against the wall creates enough instability to boost serratus activation.
Other gym exercises also target the serratus, though the research base is thinner. Dumbbell pullovers, landmine presses, and overhead reaches with scapular protraction at the top all involve the serratus through a significant range. Cable punches, where you press a cable handle forward and reach at the end, mimic the protraction pattern of the push-up plus with adjustable resistance.
Strengthening the Intercostals Through Breathing Training
The intercostal muscles sit between each pair of ribs and don’t respond to conventional weight training in any meaningful way. You can’t load them with a barbell. Instead, they strengthen through the same mechanism they naturally work by: breathing against resistance. This falls under the umbrella of respiratory muscle training, or RMT, and it involves using handheld devices that make inhalation, exhalation, or both harder than normal.
Inspiratory muscle training uses a device with an adjustable valve that restricts airflow when you breathe in, forcing the diaphragm and the external intercostals to contract harder to expand the ribcage. Expiratory muscle training does the opposite, resisting the outward flow of air so the internal intercostals and abdominal muscles have to generate more force to push air out. Most training protocols involve breathing through the device for a set number of breaths, usually around 30, twice a day, at a resistance set to a percentage of your maximum inspiratory or expiratory pressure.
The external intercostals function as a reserve system during quiet breathing, barely activating unless ventilatory demand rises. They kick in when you need bigger breaths, whether from exercise, respiratory loading, or elevated carbon dioxide levels.2PubMed. Respiratory function of the rib cage muscles Inspiratory muscle training deliberately creates that elevated demand, coaxing the intercostals into repeated, forceful contractions that stimulate adaptation over weeks.
An interesting feature of intercostal muscle behavior is how position-dependent the thickening response is. When researchers used ultrasound to measure intercostal muscle thickness during maximal breathing, they found that the muscles thickened significantly in the front of the chest, specifically in the first through fourth and sixth intercostal spaces, but showed no significant thickness change on the sides or back of the ribcage.7PubMed Central. Measurement of intercostal muscle thickness with ultrasound imaging during maximal breathing This suggests that the anterior intercostals, particularly the parasternal intercostals that assist with inhalation, are the most responsive to deep breathing efforts.
What Respiratory Muscle Training Does for Athletic Performance
Respiratory muscle training isn’t just for people with lung conditions. A growing body of research shows measurable benefits for healthy athletes. In a study of college-level 800-meter runners, four weeks of inspiratory muscle training improved maximum inspiratory pressure from roughly 113 to 131 cmHâ‚‚O, and the runners shaved about six seconds off their 800-meter times, going from an average of roughly 163 seconds down to 157. The control group, which did not receive the training, showed no change in either measure.8PubMed Central. Effects of 4-Week Inspiratory Muscle Training on Sport Performance in College 800-Meter Track Runners Six seconds in an 800-meter race is a substantial improvement, and the training only involved breathing through a device, not additional running volume.
A broader systematic review and meta-analysis looking at respiratory muscle training across multiple sports found that it improved several measures of lung function in athletes. Soccer players appeared to benefit particularly strongly, showing improvements in both respiratory capacity and physical performance on the field.9PubMed. The effectiveness of respiratory muscular training in athletes: A systematic review and meta-analysis The likely mechanism is that stronger respiratory muscles fatigue less during intense exercise, which means less blood is diverted away from the limbs to keep the breathing muscles going. In the 800-meter runner study, the trained group also showed reduced changes in limb blood flow, consistent with this theory.
For recreational athletes and gym-goers, this translates into a simple practical takeaway: if you run out of breath before your legs or arms give out, your respiratory muscles may be the weak link. A few weeks of focused inspiratory muscle training can shift that bottleneck. The devices themselves are inexpensive, portable, and require only a few minutes of daily use.
Nutrition and the Respiratory Muscles
You can’t grow any muscle without adequate nutrition, and the rib-area muscles are no exception. What’s less obvious is how specifically vulnerable the respiratory muscles are to underfeeding. Research on malnourished patients has shown that inadequate caloric and protein intake decreases both respiratory muscle strength and endurance. The damage includes loss of muscle mass, shrinkage of individual muscle fibers, and depletion of energy-rich compounds within the muscle cells. Malnutrition particularly impairs the glycolytic, or fast-energy, pathways that the respiratory muscles rely on for sudden forceful contractions.10European Respiratory Journal. Structure and function of the respiratory muscles in patients with COPD: impairment or adaptation?
While this research comes from studies of patients with chronic obstructive pulmonary disease, the underlying principle applies more broadly. If you’re training your intercostals through respiratory muscle training or hammering your serratus anterior with push-up variations, you need adequate protein to support muscle repair and growth, and sufficient overall calories to fuel the process. Aggressive dieting while trying to build any muscle group is counterproductive, and the respiratory muscles seem especially sensitive to energy deficits. A reasonable protein intake of at least 1.6 grams per kilogram of body weight per day, which is the general recommendation for people engaged in resistance training, applies here just as it does for any other muscle-building goal.
Programming It All Together
In practice, building your rib muscles means running two parallel tracks. For the serratus anterior, incorporate push-up plus variations into your regular upper-body training two to three times per week. Start with three sets of 10 to 15 reps, focusing on that extra protraction at the top of each rep. Once standard push-up plus variations become easy, progress to unstable surfaces or add the single-leg variation. These exercises double as shoulder-health work, so they slot in naturally alongside pressing movements.
For the intercostals, pick up an inspiratory muscle trainer and commit to daily use. Most validated protocols call for 30 breaths against resistance, twice a day, at roughly 50 to 60 percent of your maximum inspiratory pressure. You find your max by breathing as hard as you can through the device at its highest setting and noting the pressure reading. Then dial it back to about half. As your muscles adapt over weeks, you increase the resistance. The daily time investment is under five minutes per session.
These two tracks complement each other. The serratus anterior anchors the shoulder blade to the ribcage and assists with deep inhalation. The intercostals expand and compress the ribcage itself. Training both gives you a ribcage that looks more muscular from the outside and actually performs better during demanding physical activity.
Tracking Progress Without Guesswork
One challenge with rib-area muscles is that progress can be hard to see, especially for the intercostals. The serratus anterior becomes visible as body fat drops below a certain threshold, and you can feel it contracting by placing your hand on the side of your ribcage during a push-up plus. But the intercostals are hidden between the ribs, and you can’t exactly flex them in a mirror.
For the intercostals, the simplest metric is your maximum inspiratory pressure, which the training device itself measures. If that number is climbing week over week, your intercostals and diaphragm are getting stronger. Ultrasound imaging provides a more direct window. Researchers have demonstrated that ultrasound can reliably measure intercostal muscle thickness at rest and during contraction, and that tracking changes in thickness over time offers a useful estimate of how the muscles are adapting.11PubMed Central. Ultrasonographic assessment of parasternal intercostal muscles during mechanical ventilation This is primarily a clinical and research tool, but some sports physiotherapy clinics offer it if you want a precise baseline and follow-up measurement.
For the serratus anterior, the most practical indicators are performance-based. Can you hold a plank without your shoulder blades winging outward? Can you do more push-up plus reps before your form breaks down? Has the scalloped appearance along the side of your ribcage become more defined? Progress photos under consistent lighting are surprisingly useful here, because the serratus shows through the skin in a distinctive pattern that’s easy to compare over time, especially when viewed from the side or at a three-quarter angle with your arm raised overhead.
Common Mistakes That Slow You Down
The biggest error people make when trying to build the serratus anterior is skipping the protraction at the top of pressing movements. A standard push-up is fine for the chest and triceps, but without that extra push at the top where your shoulder blades spread apart, the serratus barely gets challenged. The muscle only works hard through its full range when the scapulae move around the ribcage, not just when the arms push a load. Every rep of every push-up variation should end with your upper back slightly rounded and your shoulder blades as far apart as you can spread them.
Another common mistake is over-relying on the upper trapezius during overhead work. When the traps dominate, the serratus doesn’t need to contribute much to scapular rotation. You can usually feel this happening: if your shoulders shrug up toward your ears during overhead presses or lateral raises, the traps are doing the heavy lifting. Cueing yourself to “pull your shoulder blades down and forward” before initiating overhead movements shifts some of the demand back to the serratus.
For respiratory muscle training, the most frequent error is setting the resistance too low. Breathing through a device at a resistance you can comfortably sustain for dozens of breaths without fatigue doesn’t generate enough stimulus for adaptation. The research showing meaningful gains in inspiratory pressure and athletic performance used loads in the range of 50 percent or more of maximum inspiratory pressure, which should feel genuinely difficult by the last few breaths of each set.8PubMed Central. Effects of 4-Week Inspiratory Muscle Training on Sport Performance in College 800-Meter Track Runners If you finish a session without any sense of respiratory fatigue, the resistance is too easy.
Finally, people sometimes expect quick visible results from serratus work and give up after a few weeks. The serratus anterior is a relatively thin muscle and sits under a layer of skin and fat on the side of the torso. Even with solid training, it won’t pop out visually until body fat is low enough to reveal it, typically in the range where abdominal definition is also visible. Strength and stability improvements happen faster than the cosmetic changes, so judge your progress by how your shoulders feel and function before you judge it in the mirror.