Running is not resistance training in the traditional sense. Health guidelines from the ACSM and CDC classify running as aerobic activity, not as a muscle-strengthening exercise. The two categories carry separate weekly recommendations: at least 150 minutes of moderate aerobic activity (or 75 minutes of vigorous activity like running) plus at least two days of muscle-strengthening work. Running doesn’t count toward that second number.
That said, running does place mechanical load on your muscles, bones, and connective tissue. Whether that load is enough to produce meaningful strength or size gains depends on the type of running, the terrain, and your current fitness level.
What Your Muscles Actually Do During a Run
Running requires your legs to absorb and produce force with every stride. During steady-state jogging, peak ground reaction forces reach about two to three times your body weight. During sprinting, those forces jump to roughly four to five times body weight. That’s a significant amount of force traveling through your ankles, knees, and hips, and your muscles have to manage all of it.
But force alone doesn’t make something resistance training. In a squat or deadlift, your muscles work under heavy load through a full range of motion, spending meaningful time under tension. During running, each ground contact lasts only a fraction of a second. Your muscles act more like springs, rapidly absorbing and releasing energy rather than slowly contracting against a heavy load. This distinction matters at the cellular level.
Why Running Builds Endurance, Not Size
Resistance training triggers a signaling pathway in muscle cells that drives protein synthesis and muscle growth. Growth factors and amino acids activate this pathway, telling cells to build new contractile proteins and get bigger. Running activates a different pathway. When your muscles burn through energy stores during sustained effort, cells flip a metabolic switch that prioritizes mitochondrial production, fat burning, and improved oxygen delivery over muscle building.
These two pathways actually oppose each other. The endurance signal actively suppresses the growth signal. This is why endurance training improves your muscles’ ability to use oxygen and resist fatigue but has limited impact on strength or mass. Resistance training does the opposite: it stimulates net muscle protein synthesis, producing hypertrophy and strength gains.
One study examined whether eccentric running (downhill) could increase muscle fiber size, since eccentric loading is a known hypertrophy stimulus. Researchers found that muscle fibers appeared roughly 30% larger a week after exhaustive downhill running, but this turned out to be localized swelling from tissue damage, not actual muscle growth. The researchers themselves noted that high-volume downhill running “has little resemblance to resistance exercise.”
Sprinting Is the Closest Running Gets
If any form of running blurs the line with resistance training, it’s sprinting. Ground reaction forces during maximal sprinting can reach 4.75 times body weight, and the explosive muscle contractions involved recruit fast-twitch fibers, the same fiber type targeted by heavy lifting. Sprinters develop noticeably more muscle mass in their glutes, hamstrings, and quads than distance runners, and their training produces high glycolytic demand and intense muscle activation.
Research on concurrent training supports this distinction. Sprint interval training and repeated sprint training produce both high muscle activation and metabolic stress, which means they don’t create the same interference with strength adaptations that steady-state running does. In practical terms, sprinting shares some physiological overlap with resistance work in a way that jogging simply doesn’t.
Still, sprinting alone won’t replace squats or lunges for building maximal strength. The loading pattern is ballistic and brief, not sustained and progressive in the way resistance training programs are designed to be.
Where Running Does Build Tissue
Running’s real structural benefit is to your bones. High-impact forces improve bone mineral density in the femoral neck and hip, the exact sites most vulnerable to fractures later in life. This is a meaningful form of skeletal loading that resistance training also provides, though the two modes target slightly different areas. Resistance training has stronger evidence for lumbar spine density (one study found a 1.82% increase in postmenopausal women over six months), while running’s impact forces are concentrated in the lower extremities.
Running also strengthens tendons and ligaments over time. These connective tissues adapt to repetitive loading by becoming stiffer and more resilient, which is why gradual mileage increases matter so much for injury prevention. This is a form of tissue strengthening, but it’s not what most people mean when they ask about resistance training.
Uphill Running and Added Resistance
Intuitively, running uphill feels like it should count as strength work. Your legs have to push harder against gravity, and the effort is unmistakable. Research on uphill walking confirms that inclines increase both the magnitude and duration of muscle activation in the glutes, hamstrings, calves, and the muscles along the front of the shin compared to walking on flat ground.
Interestingly, though, one study comparing high-incline walking to level-ground jogging at the same calorie burn found that jogging actually produced higher peak muscle activation in the quads, glutes, and calves. The impact forces of running, even on flat ground, demanded more from those muscles than the slower, grinding effort of steep incline walking. This suggests that the “resistance” feeling of hill work comes more from sustained metabolic effort than from the kind of peak mechanical loading that drives muscle adaptation.
Hill running can complement a strength program, particularly for sport-specific power in the glutes and calves. But it doesn’t replace progressive resistance training for building muscle.
How Running Interacts With Lifting
If you both run and lift weights, the interaction between the two matters. The interference effect describes how combining endurance and strength training in the same program can blunt muscle and strength gains compared to lifting alone. The magnitude of this effect depends on several variables: intensity, volume, exercise order, and recovery time between sessions.
Interference is greatest when high-intensity interval running (at 95 to 100% of your aerobic capacity) is paired with high-rep resistance training. In that scenario, both types of exercise send competing molecular signals to your muscles, and neither adaptation fully develops. Moderate-intensity continuous running, on the other hand, appears to minimize interference regardless of how heavy you lift. If you want to run and maintain your strength gains, keeping most of your running at a conversational pace is the simplest strategy.
When scheduling matters, performing aerobic work after strength training rather than before also reduces interference. Running before lifting can pre-fatigue muscles and compromise your ability to generate force during resistance exercises, which limits the growth stimulus.
The Bottom Line on Classification
Running loads your body, strengthens your bones, and builds muscular endurance. It does not, however, produce the mechanical stimulus your muscles need to grow larger or significantly stronger. The forces are too brief, the range of motion too limited, and the metabolic signals point your cells toward endurance adaptations rather than hypertrophy. Sprinting comes closest to resistance training in its demands, but even sprint programs aren’t a substitute for progressive overload with external weight. If your goal is muscle strength or size, running is a complement, not a replacement.