You have probably experienced this. A training session feels solid, your main lifts go well, and then you step onto the field or court and something feels off. A step feels slow. A shoulder feels unstable under load. A landing feels wobbly in a way you cannot explain. Most athletes blame fitness, technique, or just a bad day. But often the real answer is simpler and more specific than that.
There are muscles in your body that almost nobody trains directly. Not because they are unimportant, but because they never show up in a standard program and they never get sore enough to demand attention. They just quietly fail you at the worst possible moments. These are seven of them, and training them properly changes things fast.
1. Serratus Anterior
Most athletes have never heard of this muscle. It sits on the side of your ribcage, underneath your armpit, and its job is to pull your shoulder blade forward and upward against your ribcage. When it works properly, your shoulder blade moves smoothly through every pressing, throwing, and overhead movement you make. When it stops working, your shoulder blade wings outward and your shoulder joint starts grinding through positions it was never designed to handle.
The moment this muscle fails you is during a hard overhead press, a volleyball spike, or a baseball pitch. Your shoulder feels impinged even though nothing is technically wrong. Physios call this “scapular dyskinesis,” which is a complicated way of saying your shoulder blade is not tracking properly. The serratus anterior is almost always part of the problem.
Train it with scapular push-ups. Get into a push-up position and, without bending your elbows, push your upper back toward the ceiling by spreading your shoulder blades apart. Hold for two seconds. Return. Do three sets of fifteen. Add wall slides as a companion exercise. Neither movement looks impressive, but both create shoulder stability that transfers to everything else you do with your upper body. Athletes who add this work to their routine regularly report that nagging shoulder discomfort disappears within a few weeks, without changing anything else.
2. Tibialis Anterior
This is the muscle that runs down the front of your shin. Its job is to dorsiflex your ankle, which means pulling your toes toward your shin as your foot swings forward during running. Every time your foot leaves the ground, this muscle fires to control where your foot lands next. Without enough strength here, your foot slaps the ground rather than landing with control, your shin absorbs more impact than it should, and the repetitive stress that causes shin splints builds up quickly.
Shin splints affect millions of athletes every year. Many coaches blame training load, footwear, or running surface. Those factors matter, but a weak tibialis anterior is one of the most common and most overlooked contributors to the problem.
Train it with tibialis raises. Stand with your back against a wall, heels about six inches from the baseboard. Lift your toes toward your shin as high as they go, hold briefly at the top, and lower slowly. Do three sets of twenty to twenty-five reps. Once that feels easy, do it single-leg or add a weight plate on your foot. Two weeks of consistent tibialis work genuinely reduces shin splint pain in athletes who have been struggling with it for months. That is not a claim. That is what athletes report when they actually do it.
3. Glute Medius
The gluteus maximus gets all the attention. It is the big mover, the sprint driver, the force producer. But the glute medius sits on the side of your hip and does something just as critical. It keeps your pelvis level when you stand on one leg. Every single stride during running is a single-leg stance. Every jump landing is a single-leg moment. Every cut, every lateral step, every deceleration asks this muscle to hold your hip from collapsing.
When the glute medius is weak, your hip drops with each stride. That hip drop creates a chain reaction. Your IT band tightens. Your knee tracks inward. Your lower back compensates with every step. Runners who experience recurring IT band syndrome, knee pain, or lower back tightness often trace the root cause to this exact muscle. The IT band syndrome breakdown makes this connection explicit, because the glute medius failure pattern sits right at the center of why that injury keeps coming back.
Train it with clamshells, lateral band walks, and single-leg glute bridges. The glute medius responds well to moderate rep ranges with controlled tempo. Three sets of fifteen to twenty reps on clamshells with a band, two sets of lateral walks for twenty steps each direction, and two sets of single-leg bridges. Do this three times a week and your hip stability transforms over six to eight weeks.
4. Deep Neck Flexors
Nobody in the gym trains their deep neck flexors. Almost nobody even knows they exist. These are the small muscles at the front of your cervical spine, and their job is to stabilize your head and upper neck during movement. When they are strong and active, your head sits centered over your spine and your neck moves safely through athletic ranges. When they are weak and inhibited, your superficial neck muscles compensate by overworking, your head drifts forward, and every contact sport you play becomes riskier.
Here is the connection that matters most for athletes. Research on concussion biomechanics consistently shows that athletes with stronger neck musculature experience less brain acceleration during impacts. Neck strength does not prevent collisions, but it does reduce the whiplash-like motion of the head during them. For any athlete in a contact sport, that is not a marginal benefit. It is a meaningful protective factor.
Train deep neck flexors with chin tucks. Lie on your back, gently flatten the curve of your neck against the floor, and hold for five to ten seconds. That movement activates the deep flexors directly. Progress to seated chin tucks against light resistance from a band. Add this to your warm-up routine three times per week. It takes three minutes and costs you nothing.
5. Soleus
Most athletes know the gastrocnemius, the prominent muscle at the back of the lower leg. The soleus sits underneath it, deeper and flatter, and it handles a completely different job. While the gastrocnemius produces power at the ankle during sprinting and jumping, the soleus acts as the primary load-bearing muscle of the calf during slower, sustained activities like jogging, walking, and prolonged standing. It absorbs an enormous amount of force and it rarely gets trained directly.
Achilles tendinopathy is one of the most common overuse injuries in running athletes. The soleus plays a central role in most cases. Because it attaches directly to the Achilles tendon, a weak or unconditioned soleus transfers excessive load to the tendon with every step. Athletes who never train the soleus specifically are slowly accumulating tendon stress without knowing it.
Train it with bent-knee calf raises. That is the key detail. A straight-leg calf raise primarily works the gastrocnemius. Bending your knees to about thirty degrees shifts the emphasis to the soleus. Do three sets of fifteen to twenty slow reps with added weight once bodyweight becomes easy. Single-leg bent-knee calf raises are the most effective version. Add them to the end of any lower body session and your Achilles tendon will thank you over a long career.
6. Brachialis
The bicep gets all the credit for arm flexion. But underneath the bicep sits the brachialis, a wider, flatter muscle that actually produces more force during elbow flexion than the bicep does when your grip is in a neutral position. For athletes who wrestle, climb, row, grapple, or do any sport involving pulling and gripping, the brachialis is the hidden engine behind upper body pulling strength.
More importantly, a well-developed brachialis pushes the bicep upward, which creates a fuller, more stable upper arm. But the athletic reason to train it goes beyond aesthetics. Grapplers and climbers who develop brachialis strength report better endurance during prolonged holding and pulling actions, because the brachialis can sustain effort longer than the bicep before fatiguing. The grip strength article covers the broader picture of arm and hand endurance for athletes, and brachialis development fits directly into that system.
Train it with hammer curls and neutral-grip chin-ups. Both movements place the wrist in a neutral position, which shifts emphasis from the bicep to the brachialis. Three sets of ten to twelve hammer curls and two sets of neutral-grip pulls will develop this muscle quickly because most athletes have never specifically loaded it before. Initial gains come fast.
7. VMO (Vastus Medialis Oblique)
The VMO is the teardrop-shaped section of the quadriceps that sits just above and to the inside of your kneecap. Its primary job is to pull the kneecap inward during the final degrees of knee extension, keeping it tracking in the right position throughout movement. When the VMO fires properly, the knee moves smoothly and safely. When it lags behind the rest of the quad, the kneecap drifts laterally, creating the friction and irritation that leads to patellar tracking problems and runner’s knee.
The challenge with the VMO is that it does not get recruited well by standard quad exercises like leg extensions or even regular squats. It requires specific loading in the last thirty degrees of knee extension to fire maximally. That is a range most athletes either skip or rush through.
The moment this muscle fails you is on your landing. A jump landing where your knee buckles slightly inward, or a deceleration where you feel your kneecap grinding, often traces back here. Athletes with chronic runner’s knee who start VMO-specific work frequently see rapid improvement, because the actual cause of their pain was never the kneecap itself but rather the muscle failing to keep it in line.
Train it with terminal knee extensions using a resistance band, Spanish squats, and step-down exercises with a deliberate pause in the last twenty degrees of flexion. These movements isolate the VMO effectively and create knee stability that transfers directly to sport. The connection between VMO weakness and knee injury is explained in detail in the runner’s knee guide, which covers the full picture of what drives that injury pattern.
How to Actually Add These to Your Training
You do not need a separate session for these muscles. That would be overkill and would create fatigue that interferes with your main training. Instead, attach them to existing sessions in small doses.
Add tibialis raises and deep neck flexors to your warm-up. They take four minutes combined. Add serratus work and glute medius activation to your upper and lower body sessions respectively as pre-activation before the main lifts. Add soleus raises and VMO-specific work as accessory movements at the end of lower body days. Add brachialis work as a finisher on any pulling day.
None of these additions takes more than ten minutes of total weekly training time. But the cumulative effect over three to six months changes how your body holds up under sport demands. The athletes who consistently train these muscles do not necessarily look different. They just keep performing when others start breaking down. That resilience is the real return on investment here.
The foundation of posterior chain work and the principles of posterior chain training connect directly to several of these muscles, particularly the glute medius and soleus. Building both the primary movers and the supporting cast is what separates durable athletes from fragile ones.
