Resistance training is the category of exercise that improves both muscular endurance and muscular strength. Also called strength training or weight training, it includes any exercise where your muscles work against an external force, whether that’s a barbell, a resistance band, a machine, or your own body weight. What changes between building strength and building endurance is how you structure the workout: the weight you use, how many repetitions you perform, and how long you rest between sets.
How Resistance Training Builds Strength and Endurance
Resistance training triggers two distinct sets of adaptations in your muscles depending on how you approach it. When you lift heavy loads for fewer repetitions, your muscle fibers grow larger by adding contractile proteins in parallel, increasing the cross-sectional area of individual fibers. Your nervous system also adapts, becoming more efficient at recruiting motor units to produce force. The result is greater maximal strength.
When you use lighter loads for higher repetitions, the adaptations shift. Your muscles develop more mitochondria (the structures inside cells that produce energy) and grow additional capillaries to deliver oxygen. These changes help your muscles resist fatigue over sustained or repeated efforts. That’s muscular endurance: the ability to keep producing force over time rather than in a single maximal effort.
The Repetition Continuum
Exercise scientists use a framework called the repetition continuum to guide how resistance training should be loaded for different goals. The general breakdown looks like this:
- Strength: 1 to 5 repetitions per set at 80% to 100% of your one-repetition maximum (the heaviest weight you can lift once)
- Muscle growth (hypertrophy): 8 to 12 repetitions per set at 60% to 80% of your max
- Muscular endurance: 15 or more repetitions per set at loads below 60% of your max
These ranges aren’t rigid walls. Training in the strength range still builds some endurance, and high-rep endurance work still produces modest strength gains, especially in beginners. But if you want to prioritize one quality, the load and rep scheme you choose matters significantly.
Rest Periods Make a Difference
How long you rest between sets is another variable that steers your results. For strength-focused training, rest periods of 3 to 5 minutes allow your muscles and nervous system to recover enough to handle heavy loads again. For muscular endurance, shorter rest periods of 30 to 60 seconds keep your muscles under sustained metabolic stress, which is the stimulus that drives endurance adaptations.
Cutting rest short during heavy lifting means you can’t maintain the loads needed for strength gains. Resting too long during endurance-focused sets removes the fatigue stimulus your muscles need to adapt. Matching your rest periods to your goal is just as important as choosing the right weight.
Types of Resistance Exercise
Resistance training is a broad category that includes several formats, all of which can be adjusted for strength or endurance goals.
Free weights like barbells and dumbbells are the most traditional approach. They allow you to load movements progressively and are effective for both heavy, low-rep strength work and lighter, high-rep endurance training. Machines offer similar versatility with more stability, which can be useful for isolating specific muscles or for people newer to training.
Bodyweight exercises (sometimes called calisthenics) are another effective form of resistance training. Push-ups, pull-ups, squats, and lunges use your own body as the load. Because that load is fixed, bodyweight training naturally lends itself to higher repetitions and endurance development, though you can increase difficulty through leverage changes, slower tempos, or progressing to harder variations like single-leg squats or muscle-ups.
Circuit training arranges resistance exercises back to back with minimal rest, typically 30 to 60 seconds between movements. This format elevates heart rate higher than traditional strength training while imposing similar strength demands on the muscles. It’s a practical option when your goal is developing both qualities in limited time, though some research suggests it may not produce strength gains beyond what traditional training achieves in already well-trained individuals.
Can You Build Both at the Same Time?
Training for strength and endurance simultaneously, sometimes called concurrent training, is common but involves a trade-off. Research dating back to a landmark 1980 study by Robert Hickson has consistently shown that combining strength and endurance work in the same program can blunt gains in muscle size and strength compared to doing resistance training alone. This is known as the interference effect.
The interference primarily runs in one direction. Endurance training can reduce strength and hypertrophy gains, but strength training does not appear to compromise aerobic capacity. In fact, adding heavy resistance work to an endurance athlete’s program has been shown to improve both short-duration performance (4 to 8 minutes) and longer-duration endurance capacity (around 80 minutes), even without changes in maximal oxygen uptake.
For most people who aren’t competitive athletes, this interference effect is modest enough that a well-designed program can still improve both qualities. The key is structuring your training so that high-rep endurance work and heavy strength work aren’t competing for the same recovery resources on the same days.
What About HIIT and Cardio?
High-intensity interval training, or HIIT, sometimes gets credit for building strength, but the evidence is lukewarm. A meta-analysis comparing HIIT to traditional resistance training found that resistance training is likely superior for building strength, with HIIT producing only modest improvements of roughly 3% to 5% in measures like leg press strength. HIIT is effective for cardiovascular fitness and can slightly increase lean mass compared to moderate-intensity cardio or no exercise, but it’s not a substitute for resistance training if strength is your goal.
Traditional endurance exercise like running, cycling, or swimming improves cardiovascular endurance and delays fatigue during prolonged aerobic activity. These adaptations happen primarily through increased oxygen delivery and energy production within muscle cells. But this is whole-body aerobic endurance, which is distinct from muscular endurance, the ability of a specific muscle group to perform repeated contractions against resistance. Running will make your cardiovascular system more efficient, but it won’t meaningfully improve how many times you can press a weight overhead.
Progressive Overload Drives Both Adaptations
Regardless of whether you’re training for strength or endurance, the underlying principle is progressive overload: gradually increasing the demands on your muscles over time. For strength, that means adding weight to the bar or progressing to more challenging exercises. For endurance, it means adding repetitions, adding sets, or reducing rest periods.
Without progressive overload, your muscles adapt to the current stimulus and stop improving. A practical approach is to increase one variable at a time. If you’re doing 3 sets of 15 repetitions at a given weight for endurance, try 3 sets of 18 before increasing the load. If you’re lifting 5 sets of 3 for strength, add a small amount of weight when all sets feel manageable. Consistency across 2 to 3 sessions per week, with rest days between, provides enough stimulus for measurable improvement in either quality within a few weeks.