Cardio vs. Strength Training: What Each Does for Your Body

What Cardio Does for Your Body

Cardiovascular exercise — commonly called cardio — refers to any sustained, rhythmic activity that raises your heart rate for an extended period. Running, cycling, swimming, brisk walking, and rowing are all examples. The defining characteristic is that your heart and lungs are doing most of the work to supply oxygen to active muscles.

The most direct benefit of regular cardio is a stronger, more efficient heart. Over time, aerobic training lowers resting heart rate, improves stroke volume (the amount of blood pumped per beat), and reduces blood pressure in many people. These adaptations are associated with meaningfully lower risk of heart disease, the leading cause of death in the United States.

Cardio also supports weight management by increasing caloric expenditure and improving how the body uses stored fat for energy. Importantly, it has well-documented effects on mood and stress — largely through changes in brain chemistry. For a closer look at those connections, see what the research says about exercise and mental health.

To get the most from your cardio sessions, understanding effort levels matters. Our guide to heart rate zones and exercise intensity explains how to gauge and structure your workouts.

What Strength Training Does for Your Body

Strength training — also called resistance training — involves working muscles against an external load. This includes free weights, resistance bands, weight machines, and bodyweight exercises like push-ups or squats. Unlike cardio, the goal is not sustained elevated heart rate but rather creating enough muscular stress to stimulate adaptation.

The most important adaptation is muscle hypertrophy: the growth and strengthening of muscle fibers. But the benefits extend well beyond appearance. Muscle tissue is metabolically active, meaning maintaining more of it raises your resting metabolic rate — the number of calories your body burns at rest. This becomes especially significant with age, as adults naturally lose muscle mass (a process called sarcopenia) beginning in their 30s if they don't actively counteract it.

Resistance training also strengthens connective tissue and bones. Weight-bearing resistance exercises are among the most effective non-pharmacological strategies for reducing bone density loss, which is particularly relevant for postmenopausal women and older adults. Anyone managing existing bone density concerns should consult a healthcare provider before beginning a new resistance training program.

Additionally, strength training improves insulin sensitivity — meaning muscles become more responsive to insulin and more efficient at absorbing glucose from the blood. This has clear implications for blood sugar management and type 2 diabetes risk reduction.

Do You Have to Choose?

The short answer is no — and most leading health organizations say you shouldn't. The U.S. Department of Health and Human Services Physical Activity Guidelines recommend that adults get at least 150 minutes of moderate-intensity aerobic activity per week and perform muscle-strengthening activities on at least two days per week. These are complementary recommendations, not competing ones.

Research consistently shows that people who do both forms of exercise tend to have better overall health outcomes than those who do only one. This includes lower rates of cardiovascular disease, type 2 diabetes, and all-cause mortality.

That said, getting the balance right matters. Pushing volume or intensity too hard in either modality — without allowing adequate recovery — can slow progress and increase injury risk. For more on why recovery is a non-negotiable part of any fitness plan, see why skipping rest days can stall your progress.

Before beginning any new exercise program — especially if you have a chronic condition, are pregnant, or have been sedentary for an extended period — consult a qualified healthcare professional to identify an approach appropriate for your individual health status.

This article is for general informational and educational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider before starting or significantly changing an exercise program.